cabin air quality in commercial aircraft - simple...
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Comprehensive Summaries of Uppsala Dissertationsfrom the Faculty of Medicine 1262
Cabin Air Quality inCommercial Aircraft
Exposure, Symptoms and Signs
BY
TORSTEN LINDGREN
ACTA UNIVERSITATIS UPSALIENSISUPPSALA 2003
Dissertation for the Degree of Doctor of Medical Science in Occupational and Environmental Medicine presented at Uppsala University 2003
Abstract Lindgren T. Cabin Air Quality in Commercial Aircraft - Exposure, Symptoms and Signs. Comprehensive Summaries of Dissertations from the Faculty of Medicine. MEDFARM 2003/564. Uppsala. ISBN 91-554-5631-6 The objective of the dissertation was to study the cabin environment, and identify personal and environmental risk factors, associated with symptoms, and perception of cabin air quality. Another objective was to study if ban of smoking, and increased relative air humidity on intercontinental flights, could have a beneficial health effect. The studies were performed among Scandinavian cabin crew in one Airline Company. Office workers from the same company served as controls. Exposure differed between cruise and non-cruise conditions. Air humidity was very low during intercontinental flights (3-8%). Concentration of moulds, bacteria, formaldehyde, and ozone was low. Tobacco smoking increased respirable particles in the cabin air, from 3 to 49 µg/m3, and increased cotinine in urine. The ETS-exposure was highest in the aft part of the cabin. Symptoms and environmental complaints were more common among flight crew than office workers. We could identify personal factors of importance, and certain conditions that could be improved, to achieve a better cabin environment. There was an association between symptoms and environmental perceptions and work stress, lack of influence on working condition, and a history of atopy. After ban on smoking in aircraft, there was a decrease of ocular and general symptoms, and increased tear-film stability in aircrew. Air humidification reduced headache and ocular, nasal, and dermal dryness symptoms, increased tear-film stability, and increased nasal patency. Our result indicates that ETS and low air humidity are important environmental factors in aircraft, and that atopy, and work stress could be significant risk factors for symptoms and environmental perceptions. Key words: airline crew, flight attendants, aircraft, cabin air quality, indoor air quality, questionnaire study, symptoms, work environment, environmental tobacco smoke, psychosocial work environment, personal factors. Torsten Lindgren. Department of Medical Sciences, Uppsala University, University Hospital, SE-751 85 Uppsala Sweden ©Torsten Lindgren 2003 ISSN 0282-7476 ISBN 91-554-5631-6
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LIST OF PAPERS
This thesis is based on following papers, which are referred to in the following by the numerals I-VI
I. Lindgren T, Norbäck D. Cabin air quality: Indoor pollutants and climate during intercontinental flights with and without tobacco smoking. Indoor air 2002;12:1-10.
II. Lindgren T, Willers S, Skarping G, Norbäck D. Urinary cotinine
concentration in flight attendants, in relation to exposure to environmental tobacco smoke during intercontinental flights. Int Arch Occup Environ Health 1999;72(7):475-9.
III. Lindgren T, Andersson K, Dammström B-G, Norbäck D. Ocular,
nasal, dermal and general symptoms among commercial airline crews. Int Arch Occup Environ Health 2002;75: 475-483.
IV. Lindgren T, Norbäck D, Andersson K, Dammström B G. Cabin
environment and perception of cabin air quality among commercial airline crew. Aviat Space Environ Med. 2000 Aug;71(8):774-82.
V. Wieslander G, Lindgren T, Norbäck D, Venge P. Changes in the
ocular and nasal signs and symptoms of airline crews in relation to the ban on smoking on intercontinental flights. Scand J Work Environ Health 2000 Dec:26(6):514-22.
VI. Norbäck D, Lindgren T, Wieslander G. Changes of ocular and nasal
signs and symptoms of airline crew, in relation to air humidification on intercontinental flights. Submitted 2003.
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CONTENTS
ABSTRACT ..........................................................................................1
LIST OF PAPERS ..........................................................................................2
CONTENTS ...................................................................................................3
ABBREVIATIONS ........................................................................................6
INTRODUCTION ..........................................................................................7 Background ................................................................................................7
ENVIRONMENTAL FACTORS IN AIRCRAFT.......................................10 The sequence of stages during a flight .....................................................10 Health implications of cabin pressure ......................................................11 Air distribution and ventilation ................................................................11 Transmission of infectious disease on board............................................12 Occupational exposure in airline crew .....................................................13 Exposure in aircraft ..................................................................................14
Physical factors....................................................................................14 CO2 levels ............................................................................................14 Chemical exposure ..............................................................................14 Environmental tobacco smoke (ETS)..................................................15 Bioareosols ..........................................................................................16
EPIDEMIOLOGICAL CABIN AIR STUDIES IN AIRCRAFT .................18 Questionnaire studies on symptoms in flight attendants ..........................18 Subjective Cabin Air Quality among flight attendants ............................19 Questionnaire studies on symptoms in passengers...................................20 Questionnare studies on symptoms and environmental perceptions in pilots.........................................................................................................20
AIMS OF THE INVESTIGATION..............................................................21
MATERIAL AND METHODS....................................................................22 Study design and study populations .........................................................22
Study I .................................................................................................22 Study II ................................................................................................22 Study III and IV...................................................................................23 Study V................................................................................................24
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Intervention study on health effects of ban of smoking..................24 Study VI...............................................................................................24
Intervention study on air humidification on board..........................24 Assessment of exposure ...........................................................................25 Biological monitoring ..............................................................................27 Assessment of personal factors, and psychosocial climate ......................27 Assessment of symptoms .........................................................................28 Assessment of perceived cabin air quality ...............................................29 Assessment of clinical signs from nose and eyes.....................................30
Acoustic rhinometry ............................................................................30 Nasal lavage.........................................................................................30 Tear film stability ................................................................................31
Statistical methods ...................................................................................31 Hypothesis tested .....................................................................................32
RESULT .......................................................................................................34 Study I- Cabin pollutants and climate on intercontinental flights with and without tobacco smoking. ........................................................................34 Study II- Urinary cotinine concentration in non-smoking flight attendants before and after work on intercontinental flights with environmental tobacco smoke (ETS). ..............................................................................37 Study III- Occupational and personal risk factors for medical symptoms among commercial airline crew ...............................................................38 Study IV- Occupational and personal risk factors for perception of cabin environment among commercial airline crew..........................................42 Study V- Health effects of ban on smoking on intercontinental flights. ..44 Study VI. Changes of ocular and nasal signs and symptoms in airline crew, related to air humidification on intercontinental flights. ................46
DISCUSSION...............................................................................................48 Comments on internal validity .................................................................48
Selection bias.......................................................................................48 Comments on external validity ................................................................50 Comments on the perception of the cabin environment in different occupational groups .................................................................................51 Comments on prevalence of symptoms ...................................................51 Comments on personal risk factors ..........................................................52 Comments on psychosocial environment.................................................53 Comments on health effects of ETS exposure .........................................54 Comments on health effects of low air humidity .....................................55 Comments on carbon dioxide (CO2) concentrations ................................56 Comments on other pollutants .................................................................57
SUMMARY AND CONCLUSION .............................................................58
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ACKNOWLEDGEMENTS..........................................................................60
REFERENCES .............................................................................................61
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ABBREVIATIONS
APU Auxiliary power unit BUT Tear film break up time CFU Colony Forming Units CI Chemical ionisation CI Confidence interval CO Carbon monoxide CO2 Carbon dioxide ECP Eosinophilic cationic protein, ETS Environmental tobacco smoke GPU Ground power unit H0 Null hypothesis H1 Alternative hypothesis HEPA High efficiency particle air filters MCA1 Anterior minimum cross-sectional area
in nasal cavity MCA2 Posterior minimum cross-sectional
area in nasal cavity MVOC VOC of possible microbiological
origin MPO Myeloperoxidase n/a Non-acceptance NO2 Nitrogen dioxide OR Odds ratio O3 Ozone PEF Maximum peak expiratory flow ppm Part per million RH Relative humidity SBS Sick building syndrome VOC Volatile organic compound VOL1 Anterior volume in nasal cavity VOL2 Posterior volume in nasal cavity WHO World Health Organisation
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INTRODUCTION
Background Since ancient time, mankind has wanted to fly like the birds (Ikaros, Mythology of ancient history), and in the 15th century the Italian genius Leonardo da Vinci drew the first construction maps for an aircraft that would have functioned, if the technology had been available. It is now 100 years since the first aircraft flight. Thursday, December 17, 1903, was the historic day when the brothers Wright decided that Wilbur would take the first turn as pilot. The final flight of the day carried Wilbur 852 feet during 59 seconds. In the early days of aviation, competitions on long distance flights were common. The Swedish Charles Lindbergh made remarkable first solo-flight between Europe and United States of America. On May 20-21 May, 1927, he made the solo-flight over the Atlantic Ocean, flying in 33 ½ hours from New York to Paris. This was the beginning of modern civil aviation. Eight years later, the first commercial aircraft, a Douglas DC3, flew the same trans-Atlantic route. The piston-drive combustion engines were replaced by jet motors in civil aviation during the 1950´s. Jet motors could increase speed up to 900 km/h, and flight height above 3000 meters, where a pressurized cabin is needed. To get more space available for flight corridors, maximum cruise altitude was increased to 10 000 meter after 1975. Today, aircraft are the most common vehicle for both long and medium distance transportation. According to statistics from the world's airlines, a total number of 1,647 million passengers were transported in 2000. The number of passengers on international flights fell by 2.2 % in 2001 as a result of the 11th September events. This represented the first annual decline in international passenger traffic since 1991 – the year of the Gulf War. The recovery is expected in 2003, with an increase of 7.4 % in scheduled international traffic1.
Flight speed, fuel cost per passenger and kilometer, and demands to reduce ambient air pollution from the jet engine are main factors
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influencing the technological development of modern civil aircraft. The change of aircraft technology has influenced the cabin environment in different ways, which may have implications for safety, comfort, and health of passengers, flight attendants, and pilots. Today aviation medicine is a well-recognized medical specialty, which combines aspects of preventive, occupational, environmental and clinical medicine with the physiology and psychology of man in flight2.
Possible health risks with air recirculation due to spread of pathogenic bacteria or virus through the recirculation system have frequently been a public issue3. Man-to-man transmission from fellow passengers is the most likely route of transmission of infection disease on aircraft4. Another concern has been deep vein thrombosis due to long term exposure to a sedentary position on intercontinental flights4,5. Sedentary positions for longer time, and spread of infectious diseases from man-to-man are not specific for aircraft transportation, since the similar conditions may occur in trains and long distance busses. Other current topics are cancer risks related to cosmic radiation, jet lag after intercontinental flights, as well as discomfort and symptoms related to cabin air quality. .
Two gentlemen playing chess on board an aircraft with cigarette and pipe smokers around. A delighted little girl takes a look about the result of the game of chess. .
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The cabin crew serving drinks and coffee to satisfied smoking passengers
Steward in first class cabin lights a lady’s cigarette.
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ENVIRONMENTAL FACTORS IN AIRCRAFT
The technological development of commercial aircraft has consequences for both aviation safety and the cabin environment. The new generation of aircraft is being built extensively with the use of lightweight composite materials, and equipped with state-of-the-art systems: “glass” cockpits, side-stick controllers, and new, fuel-efficient engines. Computers are being used extensively to control the aircraft, helping it to fly more safely and more comfortably, whatever the weather. Sometimes the technological development has created new environmental problems, which have been solved by new techniques. Pressurized cabins were introduced during the 50’s, enabling cruise levels up to the troposphere ozone layer which starts at about 10 000 meters6. Earlier studies measured average concentrations of 200 ppb ozone in the cabin, with peak concentrations up to 600 ppb7. Introducing ozone converters in the supply air system, converting ozone to oxygen eliminated this potential health hazard8. At higher flight altitudes, the exposure to cosmic radiation increases. There are international regulations limiting the exposure to cosmic radiation among flight personnel to 1 mSv /year9. The radiation dose depends on flight level, distance to the North Pole, solar cycle and flying time. There are computer programs available, which can be used by the airline companies to estimate the annual dose of each airline crew, depending on the flight schedule.
The sequence of stages during a flight The cabin environment is influenced by the flight sequence. During embarkation, the aircraft is supplied by electricity and conditioned air at the gate by an auxiliary power unit or ground power unit (APU/GPU). This system is disconnected when the airplane taxis out from the terminal to standstill at the centerline of the runway. The pilots apply full takeoff power and the aircraft starts to roll forward as
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the speed increases to takeoff. After takeoff, the aircraft continues to climb until the desired cruising altitude is established. From embarkation until reaching cruise level, the outdoor airflow can be decreased or shut off, resulting up to 100% air recirculation. This is crucial for security reasons. Supplying the aircraft with outdoor air during climb would reduce the power of the engine, which could seriously hamper flight security. When the aircraft is approaching the airport, it starts to descend at a desired rate. The touchdown is the actual point of wheels making contact with the landing surface. After the landing, the aircraft taxis to the terminal building. For similar security reasons, outdoor air supply is shut off during descent, resulting in 100% air recirculation. For intercontinental flights of 7-12 h, cruise conditions corresponds to approximately 80-90% of flight time. For shorter flights, with duration of 1 hour or less, the majority of the time may be spent under non-cruise conditions (embarkation, taxi out, stand still at runway, climb, descend, taxi out, disembarkation).
Health implications of cabin pressure Cabin pressure is a very important environmental factor in aircraft. There is an economical interest to increase the flight altitude, because reduced air resistance at high altitudes reduces fuel consumption. In a modern jet aircraft, the cabin is pressurized to a corresponding to that at 2500-3000 meters above sea level (cabin altitude), while the flight altitude is about 12 000 m. At this altitude, the partial pressure of oxygen is about 24% lower than at sea level. The reduced oxygen pressure may cause a reduced partial pressure in the lung, which may affect subjects with impaired lung function2. The low oxygen pressure may also influence color vision in normal subjects2. Pressure changes during the flight may affect middle-ear pressure in subjects with swollen mucous membranes due to common cold or allergy. Expansion of intestinal gases during pressure changes may cause severe stomach pain, especially among subjects with gastro-intestinal infections2.
Air distribution and ventilation Initially, commercial jet aircraft did not have cabin air circulation systems. Air recirculation systems were developed as a result of
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studies conducted by the National Aeronautics and Space Administration (NASA) and McDonnell Douglas Aircraft8. The studies indicated that in this way substantial fuel savings could be made without compromising cabin air quality8.
In a modern commercial aircraft, the bleed system is the heart of the environmental control system (ECS). It automatically provides air from the ambient air to the cabin, at the proper temperature and pressure. The outflow valve is operated to maintain constant cabin pressure, equivalent to 2,500-3,000 meters above sea level, at a cruise level of 12,000 meters. The outdoor air is supplied by the, and becomes sterile while passing through heated zones in the engine (400° C). The air then passes an ozone converter, converting ozone to oxygen by catalyzing action, and reaches the air-conditioning pack. An air-conditioning pack is an air cycle refrigeration system that uses the air passing through and into the aircraft as the refrigerant.
For most modern aircraft the air-conditioning pack provides approximately 10 cubic feet outdoor air per minute or about 25-30 air changes per hour. The modern generation of aircraft uses about 50% filtered recirculated air and 50% outside air. In some aircraft, the pilot can shut off the recirculation system for shorter moments, resulting in a 100% fresh air supply and a twofold supply of fresh air. The air recirculation system is equipped with pre-filters for larger particles, and fine particle filters, usually high efficiency particle air type filters136 (HEPA filters). The HEPA filter is specified to capture particles greater than 0.3 um with 99.99% efficiency9. In addition, some air recirculation systems are equipped with active charcoal filters, removing VOC but not CO2. Some aircraft use the same air recirculation system for the cabin and the flight deck (cockpit). Others use two separate ventilation systems. Since the air volume on flight deck is much smaller than the cabin volume, the air exchange rate can be higher on flight deck. As an example, Boeing 767 has an air exchange rate of about 25 turnovers per hour in the cabin, but about 60 turnovers per hour on flight deck.
Transmission of infectious disease on board. Passengers or crew boarding an aircraft may have an infection. Case studies indicate that in rare cases, transmission of potentially serious diseases may occur in aircraft. Such cases include virus infections10 and tuberculosis, following long haul flights11,12,13,14. It is not just in the cabin that infections can spread, but also in the terminal prior to
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boarding or in any other public areas. The increased overseas travel might increase the possibility of coming into contact with unfamiliar viruses and pathogens, which can result in illness shortly after returning home5. The Center for Disease Control in Atlanta has studied disease transmission on aircraft and has so far identified proximity, length of exposure and infectiveness of the patient as the important factors15. Available information suggests that the most likely transmission route is man-to-man, but it has been suspected that the air recirculation could facilitate spread of infectious disease. However, if HEPA filters are used, 99.99% of microorganisms down to 0.3 micrometers are removed from the recirculated air. This filtration should remove all bacteria, an possible also viruses. Viruses could theoretically pass through a HEPA-filter, but are likely to be attached to larger particles, which are deposited in the HEPA-filter. Modern intercontinental aircraft are all equipped with HEPA-filters. On shorter flight destinations, less efficient filters are used in some aircraft.
Occupational exposure in airline crew In a recent questionnaire survey, the airline crew was asked which occupational factors risks that were their main concerns. The answer fell into five main areas: deep vein thrombosis, air quality, infection, cosmic radiation, jet lag, and work patterns16. All these aspects are important issues for airline crew, but the main focus of this thesis have been air quality aspects of the cabin environment. Airline crew spend most of their working time in the aircraft, but it can be estimated that 10-20% of the time may spent in airport buildings or in the crew bus commuting to the hotel. There are few publications available on indoor air quality in airports17. During winter season, the airline crew may be exposured to mist from the deicing-procedure18,19, when walking on the ground to an aircraft. The de-icing fluid may contain ethylene glycol, or propyleneglycol in Scandinavian countries. Walking on the ground to an aircraft may also result in exposure to jet exhausts. Some investigators have concluded that the highest exposure to formaldehyde and nitrogen dioxide (NO2) occurs when the crew is walking to an aircraft, the source being exhaust from taxiing aircraft20,21,17,22 .
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Exposure in aircraft
Physical factors At cruise level, the ambient temperature is typically –50 to –70 C, particularly low on polar flights. The wall is typically a 10-20 cm thick construction, insulated with mineral fibers. Depending upon the seating zone cold radiation from badly isolated doors, warm radiation from ovens, and draught may cause thermal discomfort. Most available studies have measured cabin temperature, but not operational temperature, or wind velocity. There are relatively large variations of cabin temperature in aircraft23,24,25,26. Relative air humidity aboard is low, particularly at cruising altitudes27,28,25,23,29,30,31,26. Health implication of low air humidity has recently been revued by Nadga32 2003. Despite the low air humidity, the aircraft may gain hundreds of kilos of weight during an intercontinental flight, due to “cold wall” condensation of moisture in the wall construction. Noise is another environmental problem in aircraft. Sources include the air velocity outside the aircraft, and engine noise during takeoff when the throttle is at full setting16. Turbulence may occur during certain meteorological conditions, and the cabin crew could be even physically injured (CORS; Internal report system, SAS).
CO2 levels Carbon dioxide is often used as an indicator for ventilation flow, and a maximum level of 1000 ppm is commonly established as a comfort level in buildings33,34. In aircraft, mean levels ranging from 719-1500 ppm CO2 have been reported23,29,35,36,37,25,38. The highest concentration occurs on the ground, during take-off and during landing, when the ventilation flow is reduced. Use of dry-ice for chilling food, may also cause higher levels of sublimated CO2 in galley areas.
Chemical exposure Airline crews are exposed to ambient ozone in the upper troposphere and lower stratosphere39,23,40,41,42. Modern aircraft are equipped with ozone converters, which dissociate ozone to oxygen8.
On board the aircraft exposure to formaldehyde43,29,25,23 and NO2 could occur occasionally as a result of tobacco smoking on
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board29,25,23. Carbon monoxide (CO) concentrations are recorded in a few papers 23,29.
Table 1. Cabin air quality: Summary of air quality monitoring result
Studies
Number of flights
Aircraft type
Smoking flight
CO2 mean (Min-max)
Temperature mean (Min-max)
Humidity Mean (Min-max)
Respirabel particles level (Min-max)
Ozone NO2 VOC mean
ATA 1994 35 B 727, B757, DC 9, MD 80
no 1200 ppm 176 µg/m3 no
DOT 1989 92 yes 1500 ppm 40-175µg/m3 0.01-0.02 ppm
no
Pierce 1999 8 B 777 no 1469 ppm 19.5-30˚C 14% < 200 µg/m3 5 ppb 0.25 ppm
Lee 1999 16 Airbus 330/340, B 747-400
13 no 3 yes
629-1097 ppm
21.9˚C (19.3-27.1)
4.9-76.8% b7.6 µg/m3 (1-17) a138 µg/m3 (71-264)
10-90 ppb 3.9-13.8 ppb
O´Donnell 1991
45 Seven indentical aircraft
no 719 (330-2170)
23.4˚C (13.2-35.1)
18.5% (4.6-48.5)
105 µg/m3 (25-200)
5.3 µg/m3 <0.1 µg/m3
n.d
Malmfors 1989
48 DC 9, MD 80
No yes
990-1310 ppm
21-25% b60-160 µg/m3 a220-250 µg/m3
Haghighat 1999
43 Airbus 320/340, DC 9, B 767
no 386-1091 ppm (293-2013)
20.2-23.8˚C c1.8-23%
Some volatile organic compounds (VOC) may originate from tobacco smoking. Other sources of exposure to VOC are vapours from alcohol consumption, cabin materials, cleaning chemicals, disinfectants, and perfume among passengers44,23. Aircraft engines leaking jet oil to the cabin air, through the ventilation system, may lead to uncontrolled exposure 45,46,47. Such events are mainly expected to occur in smaller aircraft. Jet oils and in some hydraulic fluids are specialized synthetic oils, which may contain toxic ingredients like tricresyl phosphate (TCPs) and trimethyl propane phosphate 45,47 (TMPP).
Environmental tobacco smoke (ETS). The cabin in a commercial aircraft is densely populated, and considerable exposure to ETS may occur if smoking is allowed. Nowadays, tobacco smoking in aircraft is history, but as late as 1997, ETS exposure was still common on intercontinental flights. In aircraft, smoking and non-smoking passengers were usually separated into different sections. Air movements in the aircraft, in combination with recirculated air systems, could cause involuntary ETS exposure on
aSmoking bNon smoking cMin value
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board.27,48,49,43,51,24,52,53. Striking differences in the concentration of respirable particles, in relation to smoking on board, have been reported 48,43,24,23,,44,37.
Bioareosols Available information from measurements of viable moulds and viable bacteria in cabin air have reported low levels, as compared to other indoor environments, typically between 10 and 300 CFU/ m3, (table 2) 44,23,54,37,36,29.
Table 2. Detected Colony Forming Units in aircraft cabin
CFU = Colony Forming Units, MLD = Mold aWith HEPA filer bWihout HEPA filer Ccabin domestic flight dcabin intercontinental flight
Dechow (1997) concluded that microbial contamination in ventilation air was low due to the high efficiency of the circulation filters. The bacteria concentration was higher in economy class than in business or first class, and he concluded that the main source of bacteria was the passengers. Lee et al (1999) concluded that overall bacteria counts were below the Hong Kong proposed IAQ standard of 1,000 CFU/m3. Bacteria recovered were those typically shed from human skin and mucous membranes, and levels were within the normal range in public environments. Wick et al (1995) concluded that microbiological concentrations in cabin air were typically lower than those common to locations associated with ordinary daily activities. In some cases, they were an order of magnitude less. Beside microbial components, indoor particles may contain allergens, e.g. from furry pets. Significant indirect contamination of cat allergen (Fel d 1) has been demonstrated in dwellings55, and schools56 where cats have never been. Allergen has a tendency to adhere to clothing and will collect on aircraft seats,
Investigator Bacteria CFU/m3 Fungi CFU / m3 Lee 1999
33-93 17-107
Dechow 1997
28a 76b
Wick 1995 16-281c 3-282d 0-34c 3-72d DOT 1989 131 9 ATA 1994 0-360 0-110 Pierce 1999 336
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particularly if they are not adequately cleaned. To our knowledge, there is no information available on allergen contamination in aircraft.
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EPIDEMIOLOGICAL CABIN AIR STUDIES IN AIRCRAFT
Questionnaire studies on symptoms in flight attendants Some cross-sectional questionnaire studies on medical symptoms among flight attendants are available. A few have included measurements of environmental factors in the cabin 57,63,29,35, or measurements of air quality parameters 30,64,29,35. None of the published studies has attempted to study associations between individual symptoms during a specific flight, and exposure levels in the aircraft. The flight attendants have reported different types of symptoms, including respiratory symptoms57,58,59,60,39; dermal, ocular, or throat symptoms 61,59,62; stomach problems or nausea65,57; headache or earache57,60; dizziness 60; fatigue, and sleep disturbance due to jet-lag57,63,59,60,62,66,67. In some studies with control groups, flight attendants tended to report more symptoms than both pilots and passengers. One study reported that symptoms were exacerbated by longer flight duration, and was more common at early morning or late night flights32.
The influence of personal factors on symptoms has been handled in very few studies. Eng et al. (1979) found a higher frequency of gastrointestinal problems among females, both among flight attendants and in the control groups. Multiple logistic regression analysis was applied by Reed et al. (1980), to account for confounding by some of the personal factors. The main conclusion was that flight duration was a significant factor for all 14 examined symptoms. The prevalence of symptoms are often very high. Most studies were performed when smoking was allowed on board. There is little information on symptoms in flight attendants after the ban on smoking.
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Table 3. Cabin air quality: Symptoms
Subjective Cabin Air Quality among flight attendants Over the past decade, there have been some studies on perception of cabin air quality and other environmental factors. Most studies were performed when tobacco smoking on board was still allowed 58,61,57,63,59. Erneling 1988 and Haugli 1994 found that tobacco smoke and humidity are the primary concern on board. Two studies, performed after the ban on smoking, report perceptions of environmental factors and measurements on cabin air quality29,35. In a Pierce 1999 study, flight attendants had poor rating of cabin humidity, but none of the other air quality factors were rated particularly low or high.
Studies Number of participats
Aircraft type
Smoking flights
Symptoms
dee Ree 2000 et al.
409 B 747 yes 90% skin irritation. <90% nasal and throat symptoms.
Eng 1979a
774
yes
95% ocular irritation
Erneling 1988
Lee et al. 2000
185
yes
64% eye irritaiton, 74% nasal symptoms, 57% skin irritation, 59% throat symptoms.
Pierce 1999 ASHREA/CSS
27
B 777
yes
70% Skin irritation, 67 % nasal symptoms, 49% eye irritation
Reed et al 1980
1330
B 747, L1011, B 707
yes
51% eye irritation, 48% fatigue, 30% headache, 25% throat symptoms
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Questionnaire studies on symptoms in passengers. Flight attendants and passengers are sharing the same cabin environment, but flight attendants spend more time in the galley areas, where the environment can be somewhat different. There are some previous in-flight studies on passengers, all performed when smoking on board was still allowed50,24,42. In a study performed by Pierce 1999, it was found that the most likely symptoms were dry or stuffy nose, itchy or irritated eyes, and ear problems.
Questionnare studies on symptoms and environmental perceptions in pilots To our knowledge, there are no such studies available.
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AIMS OF THE INVESTIGATION
The principal aim was to study associations between perception of the cabin environment, medical symptoms among flight crew in relation to selected personal risk factors, perceived psychosocial work environment, occupation, and work on intercontinental flights with exposure to environmental tobacco smoke (ETS).
One further aim was to measure cabin climate and selected air pollutants in the cabin of an aircraft (Boeing 767) commonly used in intercontinental flights, both during smoke and non-smoke conditions.
Another aim was to evaluate study influence of environmental tobacco smoke and relative air humidity in the aircraft, with respect to cotinine in urine, perceived air quality, medical symptoms, and physiological signs from the ocular and nasal mucosa..
The questionnaire study and the medical investigations were approved by the Ethics Committee of the Medical Faculty of Uppsala University.
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MATERIAL AND METHODS
Study design and study populations
Study I Hygienic measurements were performed in 26 arbitrarily selected intercontinental flights between Scandinavia and Asia (Beijing, Osaka, Tokyo) or North America (New York, Seattle), during a three-year period (November 1995 to November 1998). They included temperature, relative air humidity, and concentration of respirable particles, CO2, NO2, O3, and formaldehyde. A major intercontinental aircraft (Boeing 767-300), with a total number of 190 seats, was used on all flights. Al together, nineteen measurements were performed before 1 August 1997, when smoking on board was still allowed. The smokers’ seats in Tourist class (row 21-39) were located near the AFT galley. Smokers in the Business class (rows 1-17) were located near the middle section. In total, seven measurements were performed after 1 August 1997, when smoking was not allowed.
Study II The investigations were made on 15 intercontinental flights with B 767 operated by the Scandinavian Airlines System (SAS). During the study period, smoking was allowed on all intercontinental flights and longer European flights, but prohibited on all flights within Scandinavia, and between Scandinavia and destinations north of the Alps. In order to study exposure to environmental tobacco smoke on flights with tobacco smoking, urine samples were collected from 24 flight attendants, and one pilot. Non-smoking flight attendants, living in dwellings without any active smoker, were invited to participate in the study. Nicotine from tobacco smoke is metabolized to cotinine, which can be detected in urine. Urine samples were collected before
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and after the flight. On each flight, there are always three pilots and seven flight attendants. Purser, stewards and one air hostess/host are working mostly with forward (fwd) passengers based in the fwd galley. The other three flight attendants are working with passengers based in the aft galley. Information was gathered on personal characteristics, including smoking habits, use of snuff or nicotine chewing gum, and possible exposure to ETS in different locations during a three days period prior to the investigation. Information on ETS exposure on earlier flight, during the previous five-day period, was gathered from current crew schedules.
Study III and IV The cross-sectional question study was performed in February-March 1997 when smoking still was allowed on intercontinental flights. The study population consisted of all Stockholm based airline crew at the SAS airline company, and an internal reference group of SAS employed office workers. The participation rate was 81% (N=1513) in the airline crew, and 77% (N=168) in the office group. In addition, the answers were compared with an external reference group for the questionnaire67,68 (MM 040 NA). A standardized questionnaire was mailed to all Stockholm airline crew on duty in a Scandinavian flight company (N=1857), and office workers from the same company (N=218). We selected all office workers from two arbitrary selected units at the Stockholm office of the same airline company, not working at the check in desks at the airport. None of the two office buildings had any known indoor air problem or complaint.
All flight attendants had a rotating work schedule, changing aircrafts from day to day, while the pilots were operating the same type of aircraft for a longer period. In SAS, the majority (about 90%) of all airline crew are flying within Europe and Sweden, with small risk for jet-lag (maximum 2 h time difference). About 10% are working on intercontinental flights between Scandinavia and America or Asia, with obvious risk for jet-lag (3-8 h time difference). In study III, associations between risk factors and symptoms such as ocular, nasal, throat and dermal symptoms, headache and tiredness were evaluated. In study IV, associations between risk factors and different perceptions of cabin environment was evaluated. In addition, noise measurements, and hygienic measurements were performed in study IV. These hygienic measurements are a sub-set of the measurements in study I.
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Study V
Intervention study on health effects of ban of smoking This is an intervention study, investigating possible health improvements among airline crew when smoking was prohibited on all flights from 1 September 1997. Since the airline crew is changed for each intercontinental flight, it was not possible to make paired comparisons. In-flight investigations were performed on board, during two flights from Scandinavia to Japan, and two flights in the opposite direction, with a participation rate of 98% (N=39). In addition, Scandinavian crew on six flights from Scandinavia to Japan participated in a post-flight investigation at the crew hotel after landing, with 85% participation rate (N=41). Half of the flights were performed when smoking was allowed on board (August 1997), the other half one month later, after ban of smoking. All flights were performed by the same aircraft type (Boeing 767) with 190 seats operated by SAS. Most flights were full. A physician performed a standardized medical investigation of pilots and flight attendants. It comprised of a self-administered symptom questionnaire, and physiological measurements. Nasal patency was measured by acoustic rhinometry, nasal lavage was performed to measure biomarkers of inflammation, and measurement of tear film break up time (BUT) was performed to study tear film stability. Eosinophilic cationic protein (ECP), myeloperoxidase (MPO), lysozyme and albumin were analysed in the nasal lavage fluid. Finally, hygienic measurements were performed during the in-flight investigations, and at the crew hotel in Tokyo.
Study VI
Intervention study on air humidification on board This is an experimental study on possible health effects of air humidification on airline crew. The study was a double-blinded intervention study, with a cross-over design. In-flight investigations were performed on board, during eight flights from Stockholm to Chicago, and eight flights in the opposite direction. The investigations were performed from December 2001 to October 2002, when smoking was not allowed. All flights were performed on one individual of Boeing 767 with 204 seats operated by SAS. The investigation team followed the airline crew, stayed one night in Chicago, and returned together with the same airline crew. The air humidification device was
25
activated on one of the flights, and deactivated on the other flight. The order of humidification was randomised. By this study design, each airline crew was investigated once with air humidification, and once without air humidification. A standardized medical investigation of pilots and flight attendants was performed by a physician or a nurse. It comprised of a self-administered symptom questionnaire, and physiological measurements. Nasal patency was measured by acoustic rhinometry, measurement of tear film break up time (BUT) was performed to study tear film stability, and peak expiratory flow (PEF) was performed in order to study airway obstruction. Finally, hygienic measurements were performed during the in-flight investigations, and at the crew hotel in Chicago.
Assessment of exposure The hygienic measurements included temperature, relative air humidity, and concentration of respirable particles, ultra fine particles, CO2, NO2, O3, and formaldehyde. Pumped air sampling was performed during 4 hours, diffusion sampling was performed during 8 hours. All direct reading instruments were calibrated at the factory, or at the department of Occupational and Environmental Medicine in Uppsala, prior to investigation. The temperature was measured with a thermistor sensor, air humidity was measured with a thin-film capacitive sensor, and CO2 was measured with two instruments equipped with non-dispersive infrared sensors. The CO2 instruments are based on mass detection, they are only independent of cabin pressure if they are calibrated in mg/m3. As they were calibrated in ppm, the ppm value must be corrected to the actual cabin altitude.
An occupational hygienist performed all the hygienic measurements. Most measurements were restricted to the cruising period, at a flight altitude of 11,000-12,000 meters, and with a specified cabin pressure similar to about 2500-3000 meters. Some measurements were performed during non-cruise conditions. Most measurements were performed in galley areas and some were performed on flight deck. In the aft galley all measuring equipment was located on the wall between the galley and the rear section of the passengers cabin, 160 cm above the floor. In the forward galley the equipments were located in the middle of the galley on a working table. In study VI, measurements were performed on the first row in Business class (row 1), and on the last row in Tourist class (row 39). Finally, measurements were performed in the crew hotel where
26
medical investigations were performed (study V), and in one room in the crew hotel in Chicago (study VI).
In studies I, IV and V, temperature and relative air humidity were measured with a SWEMA logger 15 (SWEMA AB, Sweden), sampling one-minute average intervals. In study V, additional short-term measurements of temperature and air humidity were done manually by an Assman psychrometer. In study VI, temperature, and relative air humidity were measured with a Q-TracktTM IAQ Monitor (TSI Incorporated, USA), sampling one minute average intervals.
In studies I, IV and V, CO2 concentrations were measured by a direct reading infrared spectrometer (Rieken RI-411A, Rieken Keini, Japan), calibrated by standard gases containing known concentrations of CO2. The signal was recorded with the SWEMA logger, sampling one-minute average intervals. In study VI, CO2 concentrations were measured with a Q-TracktTM.
In studies I, IV and V, respirable particles were measured by a direct reading instrument based on light scattering (Sibata P-5H2, Sibata Scientific Technology Ltd, Japan. The instrument gives a reading in µg/m3, calibrated by the manufacturer to 0.3 µm particles of stearic acid. The signal was recorded with the SWEMA logger, sampling 1-min average intervals. In addition, the respirable particles were measured manually, obtaining 15-minutes average values, in study V. In study VI, particles were measured with both P-Trak™ (Model 8525 Ultra fine Particle Counter) measuring particles in the size range 0.02 to 1 micrometer, and Dust- TracktTM (Model 8520) with a sensor type 90 degree light scattering laser photometer, measuring particles from approximately 1- 10 micrometer (TSI Incorporated, USA).
In study I, V and VI, formaldehyde was measured by sampling on glass fibre filters impregnated with 2,4-dinitro-phenylhydrazine (sampling flow 0.2 L/min during four hours). The filters were analysed by liquid chromatography69. Nitrogen dioxide and ozone were sampled with a diffusion sampler from IVL, Sweden 70,71. Nitrogen dioxide was measured in study I, and ozone in study I, V. The concentrations measured by the diffusion samplers were adjusted for cabin altitude pressure during cruise conditions.
In studies V and VI, airborne micro organisms were sampled on 25 mm nucleopore filters with a pore size of 0.4 µm and a sampling rate of 1.5 L/min for 4 hours. The total concentration of airborne moulds and bacteria, respectively, was determined by the CAMNEA method 72. Viable moulds and bacteria were determined by incubation on two
27
different media. The detection limit for viable organisms was 30 colony forming units (cfu) per m3 of air.
Finally, noise was measured in study IV, using a Norwegian Electronic 110 noise detector (class I), giving both equivalent noise levels in dB(A) and frequent analysis. The noise measurements were performed during cruising at flight deck, in forward galley, over wing, and in aft galley.
Biological monitoring In Study II, urinary samples were collected before departure and after landing, and were kept frozen (-20 °C) until analysis. Cotinine (CAS No 486-56-6) was analysed by a previously developed gas chromatographic (CG method, using mass spectrometry (MS) with selected-ion monitoring73 (SIM). The method is based on basic extraction of cotinine from 2 ml of urine into dichloromethane. After evaporation of the dichloromethane solution to dryness, 100 µl of toluene is added, prior to the GC-MS analysis. Trideuterated cotinine (CAS No 97664-65-8) was used as internal standard. Molecular ions (M) of cotinine and trideuterated cotinine (m/e= 176 and 179) were monitored in the electron impact (EI) mode and m/e= 177 (M+1) and m/e 180 (M+1) in the chemical ionisation (CI) mode with isobutane. The standard deviation of the method was 5%, and the minimum detectable concentration, using SIM, was 2 µg/l in the EI mode and 0.2 µg/l in the CI mode. Creatinine in the urine samples was analysed at the department of Clinical Chemistry, University Hospital in Lund, Sweden, and Creatinine adjusted concentrations of cotinine in urine was calculated and given as "µg/g crea". Unadjusted concentration of cotinine in urine was given as "µg/l".
Assessment of personal factors, and psychosocial climate Three different questionnaires were used in the studies. All questionnaires collected information about age, gender, smoking habits, asthma, and allergies. In study V and VI, this information was collected by an interview with the medical investigators (doctor or nurse). A history of atopy was defined as reporting allergy to tree or grass pollen (hay fever), allergy to furry animals, or a history of eczema in childhood. A current smoker was defined as a subject who
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reported current smoking (>1 cigarette/day) in the questionnaire, or who had stopped smoking less than 6 months ago. In study III and IV, a longer self-administered questionnaire was used (“flight crew questionnaire”). It contained questions from a standardized questionnaire (MM 040 NA) developed by the Department of Occupational and Environmental Medicine in Örebro67,68. The Örebro questionnaire has been validated previously, and has been used in the large Office Illness Study in northern Sweden74. In addition, the flight crew questionnaire contained questions used in previous epidemiological studies75,76, and questions about asthma and respiratory symptoms from the European Respiratory Health Survey77. Moreover, it contained specific questions for airline crew, about work tasks and work history.
Moreover, the cabin crew questionnaire contained four questions covering different aspects of the psychosocial work conditions, obtained from the MM040 NA questionnaire68. The aspect "interesting/stimulation work" measured work satisfaction. The aspect "Too much work to do" covered stress due to excess of work, "Opportunity to influence on working condition" measured the degree of influence on working conditions, and the aspect "Do you get help from your colleagues when you have a problem at work" measured the degree of social support. The questions on psychosocial conditions, had four possible answers; "yes, often", "yes sometimes", "no, seldom", and "no, never". Each of the variables was assigned an index value from 0-3; "yes, often" was assigned "3"; "yes sometimes" was assigned "2"; "no, seldom" was assigned "1"; and "no, never" were assigned a zero value. The values were then divided by three, in order to get psychosocial variables ranging from 0-1.
Assessment of symptoms The cabin crew questionnaire used in study III contained twelve symptom questions, obtained from the MM 040 NA questionnaire68. A recall period of three months was used for these questions. For each perceived climate variable, there were three alternatives to answer, "no, never", "yes, sometimes", and "yes, often". Often means every week. The prevalence of weekly complaints was calculated for each subjective climate variable. In the statistical analysis, weekly complaints was assigned value "1", and both "yes, sometimes", and "no, never" were assigned a zero value. There was one additional question asking whether the respondent attributed the symptoms to the
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indoor environment at their workplace. This information was used to calculate the proportion of symptoms being attributed to the work environment, among airline crew and office workers. Since it was found that the majority of the symptoms were reported as work-related, the statistical calculations were based on the total prevalence of symptoms, regardless of the subjects’ opinion on causes.
In study V, current symptoms were assessed by another questionnaire, used in previous studies on physiological effects of the indoor environment 76,78. The questionnaire contained 20 questions on nasal symptoms, ocular symptoms, throat symptoms, dermal symptoms, dyspnea, and general symptoms, requiring “yes”/”no” answers. The questionnaire asked about symptoms during the specific flight when the medical investigation was performed.
In study VI, current symptoms were assessed by a newly developed questionnaire, harmonized with an ongoing larger study on cabin environment, The CABIN AIR project, supported by the European Community (Fifth RTD Framework Programme, 1998-2003). The questionnaire contained 23 symptom questions, asking for the degree of symptoms, requiring answers on a 6-graded scale. In the statistical analysis, absence of a symptom was coded “0”, and maximum intensity of a particular symptom was coded “6”. The questions included nasal symptoms, ocular symptoms, throat symptoms, dermal symptoms, sinusitis, musculosceletal symptoms, dyspnea, nausea, headache, and tiredness. The questionnaire asked about symptoms during the specific flight when the medical investigation was performed. In addition, it collected information about amount of water and non-alcoholic beverages consumed by the cabin crew during the flight.
Assessment of perceived cabin air quality The cabin crew questionnaire contained twelve questions on subjective workplace air quality, used questions from a standardized questionnaire67,68 (MM 040 NA), in study IV. A recall period of three months was used for these questions. For each perceived climate variable, there were three alternatives to answer, "no, never", "yes, sometimes", and "yes, often". Often means every week. The prevalence of weekly complaints was calculated for each subjective climate variable. In the statistical analysis, weekly complaints was assigned value "1", and both "yes, sometimes", and "no, never" were assigned a zero value. The questionnaire used in study V, contained
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three analogue rating scales, asking about perception of general air quality, air humidity, and perception of particles in the air (dustiness). The rating scales were from 0-100 mm, and the answers were expressed as percent (0-100%). The questionnaire used in study VI contained 9 questions about perception of cabin environment, but these questions were not used in in study VI, because the aim was to study effects on medical symptoms and physiological signs.
Assessment of clinical signs from nose and eyes
Acoustic rhinometry Acoustic rhinometry (Rhin 2000, S.R. Electronics, Denmark; wideband noise; continuously transmitted) was performed in the end of the flight (study V and VI), and at the crew hotel (Study V). The measurements were made under standardized forms (sitting), after five minutes rest, and prior to the lavage78,79. By means of acoustic reflection the minimal cross-sectional areas (MCA) on each side of the nose were measured from 0 to 22 mm (MCA1) and from 23 to 54 mm (MCA2), from the nasal opening. Also the volumes of the nasal cavity on the right and left side were measured from 0 to 22 mm (VOL1) and from 23 to 54 mm (VOL2). The mean values were calculated from three subsequent measurements on each side of the nose, and data on nasal dimensions in the present study are presented as the sum of the values from the right and the left side76.
Nasal lavage Lavage of the nasal mucosa was made with a 20-ml plastic syringe attached to a nose olive, as a part of the post-flight investigation at the crew hotel (Study V). The subjects were standing, with their head flexed ca 30° forward78,79. The room tempered (20-22°C) sterile 0.9% saline solution was introduced into the nasal cavity. Each nostril was lavaged with five ml solution that was flushed back and forth five times via the syringe, at an interval of a few seconds. The fluid was transferred into a 10-ml polypropylene centrifuge tube. They were kept on ice and within 300 minutes, the solution was centrifuged at 800 g for five minutes. The supernatant was recentrifuged at 1400 g for five minutes, and immediately frozen76 to -20°C. Lysozyme was analyzed by means of radioimmunoassay80. The concentration of ECP
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and MPO were measured by means of a double antibody radioimmunoassay method81,50. The intra- and interassay variation coefficients for all three tests were less than 11%. Albumin was measured by rate nephelometry on an Array protein system (Beckman Instruments Inc).
Tear film stability In study V and VI, tear film break up time was estimated by a standardized method, self-reported BUT or BUT(s) measuring the time the subject could keep the eyes open without pain, when watching a fixed point at the wall78. The method has been used previously in field studies, and has been shown to correlate well with the fluoresceine method for detection of tear film break-up time82,83 (BUT). In study VI, tear film stability was also investigated directly, using a small eye microscope (Keeler Tearscope Plus. Keeler UK). The Tearscope projects a small net of lines on the ocular surface, and the breaking up time of the tear film can be observed directly, without adding fluoresceine. The Tearscope investigation was performed 1-2 minutes after the BUT(s) investigation.
In study VI, maximum peak expiratory flow was measured three times (Mini-Wright Peak Flow Meter. Clement Clarke International Ltd. UK). The highest value was used in the statistical calculations.
Statistical methods In study I, differences in average values from 1-minute measurements of cabin climate, and respirable dust concentrations, between smoking and non-smoking flight, were analyzed by Student's t-test. Influence of different factors on temperature, air humidity, and carbon dioxide (study I) were calculated by multiple linear regression, adjusting for the influence of different flight characteristics. Differences in exposure between non-cruising and cruising conditions were calculated by Students’ t-test
In study II, differences in adjusted U-cotinine concentration µg/g crea before and after flights were analyzed by Wilcoxon-matched paired singed rank test. Mann-Whitney U-test was used to analyze differences in age, and U-cotinine concentrations between groups. Differences in proportions were analyzed by Fishers's exact test for 2*2 contingency tables. The correlation between the number of
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smoking passengers on board, and increase of U-cotinine during the flight was analyzed by Spearman’s rank correlation test.
The influence of different factors on subjective indoor air quality and on different symptoms (Study III – VI) was analyzed by multiple logistic regressions, by Statistical Package for Social Sciences (SPSS). The collinearity diagnostics available in another statistical package (SPIDA) was applied on the data set84. For logistic regression, the program uses a method described by Belsley85 1991 in which a conditioning index exceeding 20 is used as an indicator of collinearity problems.
In study V, differences in dichotomous personal characteristics and symptoms between flight crew from smoke and non-smoking flights, were analyzed by Fishers’ exact test. Mann-Whitney U-test tested differences in age, total symptom index, and all types of clinical signs.
In study VI, Mann-Whitney U-test calculated the change of tear-film stability, nasal patency, peak expiratory flow, liquid intake, and symptom score in relation to humidification sequence.
Hypothesis tested Different hypotheses were tested in the different studies, and the null hypotheses, H0 can be formulated as follows:
There is no relationship between measured aspects of the cabin environment and air pollutants and environmental conditions such as smoking onboard, type of flight (polar vs. non-polar), measuring site in the cabin (forward vs. AFT galley), cruise altitude, number of passengers, and cruise vs. non-cruise conditions (study I).
There is no relationship between exposure to environment tobacco smoke (ETS) in forward and AFT galley, and urinary cotinine concentration among non-smoking flight attendants (study II).
There is no relationship between symptoms among flight crew, and selected personal risk factors, perceived psychosocial work environment, occupation, and work on intercontinental flights with exposure to environmental tobacco smoke (study III).
There is no relationship between the perception of cabin air quality (CAQ) among flight crew, and selected personal risk factors, perceived psychosocial work environment, occupation, and work on
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intercontinental flights with exposure to environmental tobacco smoke (study IV).
There is no relationship between exposure to environmental tobacco smoke in aircraft, and measured and perceived cabin air quality, symptoms, and clinical signs such as tear film stability, nasal patency, and biomarkers in nasal lavage fluid (study V).
There is no relationship between air humidification in aircraft, and measured and perceived cabin air quality, symptoms, and clinical signs such as tear film stability, nasal patency, and maximum peak expiratory flow (PEF) (study VI).
The research hypotheses H1 ≠ H0
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RESULT
Study I- Cabin pollutants and climate on intercontinental flights with and without tobacco smoking. Mean cabin concentration of measured chemical contaminants was low. The mean NO2 and ozone concentration in AFT galley were 14.1 µg/m3 and 13.7 µg/m3, respectively. In the flight deck, mean NO2 concentration was 7 µg/m3 and ozone concentration was 26.3 µg/m3. The concentration of formaldehyde was below the detection limit (<5 µg/m3) during 17 out of 22 measurements, and the maximum concentration (15 µg/m3) was measured in aft galley during a smoking-allowed flight with 190 passengers and a normal number of smokers (20-30 subjects).
Average temperature was 22.2 °C (range 17.4-26.8°C), and relative air humidity was low (3-8%) during cruise. The mean CO2 concentration was 709 ppm (adjusted value), well below the recommended limit of 1,000 ppm33. The average personal outdoor airflow rate in the galley areas during cruise was calculated to be 15 l/s. The temperature was somewhat lower, and CO2 level and relative air humidity was somewhat higher in the aft galley (table 4).
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Table 4. Continuous, one-minute in-flight measurements of cabin climate at cruise.
a) Adjusted to the pressure (804 hPa) at cruise condition
b) Correction factor from ppm to mg/m3 is 1.91 at 22 °C, and sea level pressure During eight flights, the measuring time with the direct reading instruments were extended to gate-to-gate conditions. Embarkation, taxi out, climb, and descent were classified as non-cruise conditions. Cabin temperature, relative air humidity, and carbon dioxide in AFT galley were significantly higher during non-cruise conditions. The mean CO2-value was 1545 ppm, corresponding to a personal airflow rate of 4.2 l/s (table 5).
Table 5. Continuous, one minute in-flight measurements in aft and fwd galley, during five flights, at non-cruising and cruising conditions.
Aft galley
Non-cruising conditions M(SD) min-max
Cruising conditions M(SD) min-max
2-tailed p-valuea
Temperature (°C)
23.2(1.7) 18.7-27.1
21.9 (1.9) 17.4-26.8
<0.001
Relative humidity (%) 29 (7.4) 6-47 7.6(3.7) 2-27 <0.001 Carbon dioxide (ppm)a, 1656 (877) 694-3686 734(151) 415-1488 <0.001 Forward galley
Temperature (°C)
22.2 (1.5) 17.8-24.9
22.8 (0.26) 17.6-24.7
<0.001
Relative humidity (%) 26.8 (8) 7.3-39 3.2 0.9-24.8 <0.001 Carbon dioxide (ppm)a 1232 (541) 417-2490 637 (183) 410-1406 <0.001 N= number of one minute measurements a) Calculated for individual 1-min values, by Students’ t-test b) Adjusted to the pressure (804 hPa) at cruise condition c) Correction factor from ppm to mg/m3 is 1.91 at 22 °C, and sea level pressure
Type of factor Aft galley M (SD)
Min-max
Fwd galley M (SD)
Min-max
Temperature (°C)
21.9 (1.9)
17.4-26.8
22.8 (0.9)
17.6-24.7
Relative humidity (%)
7.6 (3.7)
1.8-27.4
3.2 (2.5)
0.9-25
Carbon dioxide (ppm) a, b
734 (151)
415-1488
636 (183)
410-1406
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There were striking differences in the concentration of respirable particles in the rear part of the cabin, when comparing smoke and non-smoking flights. During smoke flights, the average concentration of respirable particles was 49 µg/m
3 in AFT galley, 8 µg/m3 in forward galley (table 6)
Table 6. Respirable particles concentrations µg/m3, before and after ban on smoking, during cruising.
N= number of one minute measurements aone minute data logging interval bfifteen minutes manual sampling interval Relationships between continuously measured data and flight conditions during cruise were investigated. Flights to Seattle, Tokyo and Osaka were classified as flights near the North Pole, and flights to Beijing, and New York were classified as non-polar flights. When comparing measurements near the pole with other flights, no significant differences were found. The influence of number of passengers, flight altitude, and location in the aircraft (aft/forward) on temperature, relative air humidity and CO2-concentration was evaluated, by keeping the three dependent variables simultaneously in linear multiple regression models. Relative air humidity and CO2 were positively related to the number of passengers. No significant relationship between the cabin temperature and the number of passengers was observed. Relative air humidity was negatively related to flight level. All of mean temperature, relative air humidity and CO2 were significantly related to the location in the aircraft. On the average, temperature was 0.8 °C lower, relative air humidity was 4% higher, and CO2 was 37 ppm higher in AFT galley as compared to forward galley (p<0.001).
N
M (SD)
min-max
Before ban on smoking, aft galleya,b After ban on smoking, aft galleya
1465 768
49(49) 3(0.9)
2-253 <1-7
Before ban on smoking, forward galleyb After ban on smoking, forward galleya
255 1442
8(4.2) 4(0.7)
3-20 <1-12
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Study II- Urinary cotinine concentration in non-smoking flight attendants before and after work on intercontinental flights with environmental tobacco smoke (ETS). All 25 flight attendants were non-smokers, living in dwellings without current smokers, and none used snuff or nicotine chewing gum. The median U-cotinine was 3.71 µg/g crea (2.4 µg/l) before departure, and 6.37 µg/g crea (7.1 µg/l) after landing, a significant difference (table 7). The 18 flight attendants in aft galley had a significantly higher concentration of U-cotinine after landing as compared to those seven subjects working in the forward part of the aircraft (table 4). In contrast, those seven subjects working in the forward part of the aircraft had no significant increase of U-cotinine concentration during the flight.
Table 7. Cotinine concentrations in urine (µg/g creatinin) before takeoff, and after landing among flight staff (N=25)
aSignificant difference in U-cotinine after landing, when comparing subjects working in forward and aft part of the aircraft (p=0.001 by Mann-Whitney U-test) bSignficantly higher U-cotinine concentration after landing than before take off (p=0.006 by Wilcoxon matched pair sign rank test) cSignficantly higher U-cotinine concentration after landing than before take off (p=0.01 by Wilcoxon matched pair sign rank test) Urinary cotinine before departure did not differ significantly between subjects exposed, or non-exposed, to ETS in previous flights during last three days. Moreover, U-cotinine before departure did not differ between those with and without possible exposure to ETS during leisure hours previous days.
Workplace U-cotinine before take off U-cotinine after landing location N Median(interquartile range) Median (interquartile range) Forward 7 2.74 (0.62-4.25) 3.54 (2.57-5.04)a Aft 18 4.69 (2.43-27)c 12.2 (5.51-36.4)a,c Totala 25 3.71 (2.08-8.67)b 6.37 (3.98-19)b
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Study III- Occupational and personal risk factors for medical symptoms among commercial airline crew The most common complaints among airline crew were fatigue (21%), irritated, stuffy or runny nose (15%). Complaints of dermal symptoms from face (12%), itching, burning or irritation of the eyes (11%), and dermal symptoms (12%) were also common. When comparing the airline crew with office workers from the same company, the airline crew more often had irritated, stuffy or runny nose, hoarse, dry throat, cough, dry or flushed facial skin, and dry, itching, red hand skin. Among airline crew, 70-90% of all symptoms were perceived as work-related. Among office workers 40-80% of all symptoms were perceived as work-related.
The main difference in the perceived psychosocial environment, when comparing airline crew with office workers, or external referents, was a difference in the perception of work control. In total, 92% of the office workers and 82% of the external referents reported that they could influence their working conditions (often or sometimes). The corresponding figures for work control were 50% for pilots, 48% for purser, 40% for steward, and 29% for air hosts/hostess. Work satisfaction and social support from colleagues were rated in a similar way in both airline crew, and office workers. Work stress (often or sometimes) was reported by only 42% of the pilots, but was more common among office workers (94%), purser (91%), steward (88%), and air hosts/esses (82%).
When applying multiple logistic regression analysis, adjusting for; age, gender, atopy, current smoking, and psychosocial work conditions, airline crew had significantly more frequent nasal symptoms, throat symptoms, dermal symptoms from the face, and hands as compared to office workers from the same company (table 5).
As a next step, the analysis was restricted to airline crew, excluding the office workers. Multiple logistic regression analysis was performed, adjusting for age, gender, atopy, current smoking, psychosocial work conditions, and type of occupation on board. A history of atopy (pollen allergy, allergy to furry animals, or childhood eczema) was associated with an increase of most symptoms (OR=1.5-3.8) (table 8). There were no significant differences between smokers and non-smokers, except that smokers reported less cough. The prevalence of ocular symptoms was not significantly higher in contact lens wearer (13%), as compared to airline crew not wearing contact
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lenses (11%). No differences between men and women were observed, and no effect was seen for age. Stress due to excess of work was a significant predictor of fatigue, of feeling heavy-headed, of difficulties on concentrating, of headache, and of facial dermal symptoms. Those reporting better work control reported significantly less fatigue and heavy-headedness, and those with better work satisfaction had less fatigue. No major differences between occupations on board were found, except for less ocular, nasal symptoms, and dermal symptoms from the hand in pilots.
Finally, the significance of working on an intercontinental flight with exposure to environmental tobacco smoke (ETS) was investigated. In the logistic regression analysis, airline crew that had been on an intercontinental flight last week, reported significantly more fatigue, heavy-headedness, difficulties concentrating, and throat irritation (table 9).
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Table 8. Adjusted odds ratios (OR)a with 95 % confidence interval (95% CI) for relationships between at least weekly complaints on symptoms, and atopy, perception of psychosocial work climate, in the total material of airline crew (n=1513).
* p<0.05; ** p<0.01; ***p<0.001 aOdds ratio was calculated for the extremes of this variable (0-1) bPrevalence of cough among office workers = 0
Variable
Atopya OR(95%CI)
Stress due to excess of worka OR(95%CI)
Work controla OR(95%CI)
Fatigue 1.52(1.16-2.00)**
7.33(3.59-15.0)***
0.45(0.25-0.82)*
Feeling heavy-headed
1.90(1.24-2.91)**
9.52(3.03-29.9)***
0.16(0.06-0.44)***
Headache
2.21(1.36-3.60)**
5.10(1.36-19.1)*
0.48(0.16-1.46)
Nausea/dizziness
1.87(0.39-8.95) 13.8(0.23-831) 0.21(0.01-8.91)
Difficulties concentrating
1.61(0.61-4.22) 278(18.0-4307)***
0.11(0.01-1.08)
Itching, burning or irritation of the eyes
1.43(1.00-2.04) 2.84(1.09-7.44)
0.56(0.25-1.26)
Irritated, stuffy or runny nose
2.31(1.69-3.15)***
2.65(1.18-5.98)
0.53(0.27-1.05)
Hoarse, dry throat
2.37(1.57-3.58)***
2.40(0.81-7.16)
0.52(0.21-1.29)
Cough
2.92(1.65-5.17)***
1.59(0.37-6.89)
0.90(0.27-2.97)
Dry or flushed facial skin
2.23(1.58-3.14)***
3.75(1.55-9.09)**
0.62(0.29-1.30)
Scaling/itching scalp or ears
3.13(2.10-4.68)***
2.66(0.98-7.23)
0.87(0.37-2.05)
Hands dry, itching, red skin
2.55(1.81-3.60)***
2.10(0.85-5.16)
0.58(0.27-1.25)
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Table 9 Adjusted odds ratios (OR)a with 95 % confidence interval (95% CI) for relationships between weekly complaints on symptoms, flight crew vs. office workers and work on intercontinental flights in the total material of airline crew (n=1513).
* p<0.05; ** p<0.01; ***p<0.001 aOdds ratio was calculated for the extremes of this variable (0-1)
Variable
Work on inter- continental flightsa OR(95%CI)
Airline crew vs. office workersa OR(95%CI)
Fatigue 1.70(1.42-2.03)*** 0.94(0.59-1.50)
Feeling heavy-headed 1.75(1.33-2.29)** 0.70(0.34-1.45)
Headache
1.22(0.86-1.74) 1.04(0.42-2.60)
Nausea/dizziness
1.82(0.60-5.55) 0.79(0.06-10.0)
Difficulties concentrating
2.91(01.39-6.13)** 0.49(0.13-1.84)
Itching, burning or irritation of the eyes
1.06(0.82-1.37) 1.08(0.55-2.13)
Irritated, stuffy or runny nose
1.11(0.90-1.38) 3.12(1.48-6.59)**
Hoarse, dry throat
1.24(0.95-1.62) 5.75(1.35-24.5)*
Cough
1.22(0.84-1.79) not applicable
Dry or flushed facial skin
1.24(0.96-1.56) 2.03(1.01-4.08)*
Scaling/itching scalp or ears
1.13(0.87-1.47) 1.92(0.92-4.00)
Hands dry, itching, red skin
1.26(0.78-1.26) 3.68(1.50-9.05)**
42
Study IV- Occupational and personal risk factors for perception of cabin environment among commercial airline crew The most common complaints among airline crew are concerning noise, dustiness, stuffy air, dry air and static electricity. Noise measurements on Boeing 767 showed that the average equivalent levels during cruising was 73 dB(A) at flight deck, and 76 dB (A) in forward galley, 74 dB (A) over wing, and 78 dB (A) in aft galley.
Further statistical analysis was performed, comparing cabin crew with office workers from the same company, applying multiple logistic regression analysis, adjusting for possible confounders like age, gender, atopy, current smoking, and psychosocial work conditions. The prevalence of most complaints, except those concerning too low temperature, unpleasant odour, and environmental tobacco smoke, was higher among airline crew members, as compared to office workers from the same company. The greatest differences were observed for complaints on noise, dust, draught, dry air, static electricity, inadequate illumination, and stuffy air (table 10).
43
Table 10. Adjusted odds ratios (OR)a with 95 % confidence interval (95% CI) for relationships between at least weekly complaints on cabin environment, and perception of psychosocial work climate, atopy, airline crew versus office workers and in the total material of airline crew (n=1513).
p<0.05; ** p<0.01; ***p<0.001 Calculated by multiple logistic regression analysis, including age, gender, atopy, current smoking, 4 psychosocial variables, and type of occupation on board aOdds ratio was calculated for the extremes of this variable (0-1) As a next step, the analysis was restricted to airline crew, excluding the office workers. Multiple logistic regression analysis was performed, adjusting for age, gender, atopy, current smoking, psychosocial work conditions, and type of occupation on board. Atopy was associated with many types of complaints on the cabin environment. No major differences between males and females were
Stress due excess of worka to OR(95%CI)
Work controla OR(95%CI)
Atopy OR(95%CI)
Airline crew versus office workers OR(95%CI)
Draught 4.12(2.09-8.11)*** 0.32(0.18-0.56)***
1.32(1.00-1.73)*
9.24(3.29-25.90)***
Temperature too high
7.99(3.45-18.53)***
1.79(0.90-3.56)
1.16(0.84-1.61)
2.23(1.19-4.18)*
Varying temperature
5.28(2.75-10.12)***
0.56(0.33-0.95)*
1.50(1.16-1.95)**
1.80(1.10-2.96)*
Temperature too low
3.67(1.76-7.67)** 0.46(0.25-0.86)*
1.00(0.74-1.35)
1.31(0.73-2.34)
Stuffy air 5.41(2.72-10.77)***
0.68(0.39-1.20)
1.04(0.79-1.37)
3.26(1.91-5.57)***
Dry air 4.60(2.54-8.34)*** 0.52(0.32-0.84)**
1.29(0.99-1.66)
5.68(3.66-8.81)***
Unplesant odor
13.18(4.35-39.93)***
0.21(0.08-0.53)**
1.69(1.14-2.52)**
1.54(0.64-3.74)
Static electricity
2.93(1.40-6.16)** 1.01(0.55-1.86)
1.30(0.98-1.73)
4.76(2.51-9.06)***
Passive smoking
2.35(1.02-5.40)* 0.56(0.28-1.11)
1.02(0.74-1.41)
1.81(0.92-3.55)
Noise 6.36(3.53-11.46)***
0.63(0.39-1.02)
1.38(1.08-1.77)*
30.23(13.57-67.26)***
Inadequate illumination
11.11(5.62-21.97)***
0.46(0.27-0.80)**
1.18(0.89-1.56)
4.10(2.18-7.73)***
Dust and dirt 5.62(3.16-9.98)*** 0.54(0.34-0.87)*
1.59(1.25-2.02)***
11.00(5.55-21.78)***
44
observed, but females more often complained about too low temperature, dry air, and dust. Younger subjects reported more complaints on too low temperature, dry air, unpleasant odour, static electricity, and noise. Older subjects complained more on environmental tobacco smoke. For most types of complaints, there were no differences between smokers and non-smokers, but smokers complained less on stuffy air, and ETS exposure. No major differences were observed between cabin crew of different occupation. In contrast, flight deck crew had significantly less complaint on many aspects of CAQ. Flight deck crew, however, reported more complaints on inadequate illumination and dust. Flight crew that had been on an intercontinental flight with smoking on board last week reported significantly more complaints on dry air and ETS.
Study V- Health effects of ban on smoking on intercontinental flights. The study was performed on totally 37 (93%) non-asthmatic airline crew (two asthmatic subjects were excluded). A numerical decrease of all types of individual symptoms, except facial dermal symptoms, was observed in non-asthmatic subjects after ban of smoking (table 11). When dichotomising the material, with respect to occurrence of more than one symptom in each symptom category, the occurrence of more than one ocular symptom was decreased from 55% to 11% (p=0.004) (table 11). In addition, the total symptom score was higher during smoking conditions (M=3.9; SD=4.0) than non-smoking conditions (M=1.4; SD=1.6) (p=0.05). The symptom improvement was most pronounced for general symptoms. Before ban on smoking, 35% of the crew reported at least one general symptom (headache, fatigue, nausea, sensation of catching a cold). After ban on smoking, none reported any of these symptoms (p=0.005 by Fisher's exact test). In addition, the perception of the cabin air quality was improved after ban of smoking (p=0.03), while the ratings for perceived air humidity and dustiness remained unchanged.
45
Table 11. Proportion of non-asthmatic airline crew with different symptoms during flight, before and after ban of smoking.
aProportion of subjects with more than one symptom in each category aDifference before and after ban of smoking, calculated by Fishers exact test cBurning, itching, dry, or soar eyes, eye redness, or swollen eyelids dRunny nose, nasal itching, sneezing, or nasal obstruction eThroat dryness, sore throat, or irritative cough fHeadache, tiredness, nausea, or sensation of getting a cold gFacial rash or facial itching Measurement of tear film stability (BUT) during flight showed an increased tear film stability after ban on smoking (p=0.01), with a mean of 25 seconds as compared to 10 seconds. There were also alterations of nasal patency, in relation to ban of smoking. Rhinometric measurements on-board showed a greater posterior nasal cross-sectional area (MCA2) during smoking-allowed flights, as compared to non-smoke conditions (p=0.05), but no significant differences for other nasal dimensions (MCA1, VOL1, VOL2) (table 12).
Post-flight measurements at the hotel room, showed a numerical but insignificant increase of tear film stability BUT (s) after ban of smoking (a mean of 42 seconds as compared to 25 seconds). Rhinometric measurements showed a numerically greater nasal patency for all four parameters after smoke-free flights, statistically significant for anterior nasal volume (VOL1) (p=0.03). Nasal lavage, performed at the crew hotel, showed no significant effects of smoking on board (table 12).
Before ban After ban (N=19) (N=19) Category of symptoms (%)a (%)a P-valueb Eye symptomsc 55 11 0.004 Nasal symptomsd 20 5 0.19 Throat symptomse 20 0 0.06 General symptomsf 15 0 0.13 Facial skin symptomsg 0 5 0.49
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Table12. Tear film stability and nasal patency in non-asthmatic airline crew before and after ban of smoking.
aDifference before and after the ban on smoking, calculated by the Mann-Whitney U-test. (BUT= break up time, MCA1 = minimal cross-sectional area 0-22, MCA2 = minimal cross-sectional area 23-54, Vol1 = volume of nasal cavity 0-22 mm, Vol2 = volume of nasal cavity 23-54 mm).
Study VI. Changes of ocular and nasal signs and symptoms in airline crew, related to air humidification on intercontinental flights. The humidification increased the relative air humidity by 10% on 1st row in business class, by 3% in the last row (39th row) in tourist class, and by 3% in the cockpit. During flights with air humidification, there was an increased tear film stability, increased nasal patency in the proximal part of the nose (table 13), and a decrease of ocular, nasal, dermal symptoms, and headache (table 14).
BUT (s) Mean SD
MCA1(cm2) Mean SD
MCA2(cm2) Mean SD
Vol1(cm3) Mean SD
Vol2(cm3) Mean SD
During flight in the aircraft
Before ban 10 8.7 1.33 0.19 1.52 0.45 3.88 3.56 8.98 2.56 After ban 25 31 1.35 0.37 1.22 0.37 4.13 0.83 8.81 2.59 P-valuea 0.01 0.45 0.05 0.33 0.49
After flight at the crew hotel
Before ban 25 26 1.30 0.21 1.35 0.41 3.86 0.51 8.90 2.26 After ban 42 50 1.32 0.36 1.39 0.37 4.41 0.84 10.02 3.07 P-valuea 0.26 0.46 0.49 0.03 0.23
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Table 13. Physiological in non-asthmatics (N=70), during humidified and non-humidified conditions
Humidification to Chicago No humidification to Chicago no humidification from humidification from Chicago Chicago (N=38)b (N=38)b (N=32)c (N=32)c 2-tailed Physiological parameters M (SD) M (SD) M (SD) M (SD) p-value
a
BUT (tearscope) 7.7(2.6) 5.0(2.2) 7.3(3.8) 9.2(10.0) <0.001 MCA1(cm2) 1.10(0.22) 1.05(0.27) 1.05(0.25) 1.12(0.30) 0.02 aCalculated by Mann-Whitney U-test b36 subjects participated in BUT(s), 24 in BUT (Tearscope), 16 in rhinometry, and 38 in PEF measurement c30 subjects participated in BUT(s), 29 in BUT (Tearscope), 27 in rhinometry, and 30 in PEF measurement
The mean concentration of viable bacteria (77-108 cfu/m3), viable moulds (74-84 cfu/m3), and respirable particles (1-8 µg/m3) was low, both during humidified and non-humidified flights. On flights with air humidification, there were less particles in the forward part of the aircraft, and 50-80% lower concentrations of moulds, bacteria, and volatile organic compounds of microbial origin (MVOC) in the cabin.
Table 14. Change of symptom score among non-asthmatics (N=70), in relation to humidification sequence.
Humidification No humidification to Chicago to Chicago No humidification Humidification from Chicago from Chicago two-tailed (N=38) (N=33) p-value
aCalculated by Mann-Whitney U-test
Dry eyes 0.82(1.11) -0.09(1.38) 0.006 Watery eyes 0.68(1.31) 0.03(1.02) 0.04 Eye irritation (itching, burning) 0.82(1.44) 0.16(1.57) 0.05 Sneezing 0.37(1.00) -0.41(1.16) 0.03 Nasal obstruction 0.68(1.38) -0.19(1.45) 0.02 Dry skin 0.50(1.47) -0.66(1.49) 0.002 Facial skin irritation (itch, rash) 0.38(1.34) -0.34(1.00) 0.03 Headache 0.26(1.03) -0.47(1.08) 0.01
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DISCUSSION
Airline crew had an increase of symptoms, and complaints on work environment, as compared to office workers. Hygienic measurements during cruise showed varying temperature (17-27 ˚C), dry air (1-27%), noise (73-78 dB(A)) and respirable particles (1-253 µg/m3) on board the aircraft type used during intercontinental flights (Boeing 767). The exposure to formaldehyde, ozone, nitrogen dioxide, moulds, and bacteria was low during cruise conditions. Flight attendants working in the tourist class section had a significant exposure to environmental tobacco smoke (ETS), verified by particle measurements and biological monitoring of cotinine in urine. Ban of smoking on board reduced particle concentration from 49 to 3 µg/m3 in aft galley, and was associated with increased tear film stability, less ocular symptoms, and less headache and tiredness in crew. Air humidification increased the relative air humidity by 10% in business class, by 3% in tourist class, and by 3% on flight deck. The air humidification was associated with a decrease of symptoms, increased tear film stability and increased nasal patency in airline crew.
Comments on internal validity
Selection bias In study I, measurements were performed on arbitrarily selected intercontinental flights operated by SAS, during a 3 year period. The measurements were restricted to Boeing 767, the only aircraft type used on SAS operated intercontinental flights during the study period. It is unlikely that these measurements were seriously biased by selection bias. One limitation is that there was no measurements on other types of SAS operated aircraft types used on domestic or European destinations.
In study II, the source population consisted of all flight attendants working on 15 arbitrary selected intercontinental flights operated by
49
SAS. During the study period (November 1995 to March 1997), smoking was allowed on all intercontinental flights. The study population was restricted to non-smokers living in non-smoking households, none of the participants used snuff or nicotine chewing gum, and none of the participants was used twice. Selection bias could be expected to be less problematic in an exposure study based on biological monitoring, as compared to a questionnaires study with self-reported information on symptoms or exposure. We could not record either the number of excluded subjects or the number of non-participants fulfilling the selection criteria. Information on work on earlier intercontinental flights, during the previous five-day period, was gathered from current crew schedules. Mean age and proportion of females among participants did not differ from SAS flight attendants in general, according to employment statistics. The proportion of participants working in the forward part of the galley was less than expected. This could lead to an overestimation of the average ETS exposure, but this problem was handled by dividing the material with respect to workplace location in the aircraft.
The study population in study III and IV consisted of all airline crew belonging to the crew base in Stockholm, as well as two representative departments of office workers in Stockholm from the same airline company. The office workers were working outside the airport, in buildings without any known indoor environmental problems or reports of complaints. The response rate was reasonably high both in airline crew and office workers (82% and 77% respectively). Information on both perceptions of cabin environment in study IV, symptoms in study III, and psychosocial work environment, was gathered by the same questionnaire. This could have resulted in recall bias, but since we found different relationships for specific aspects of psychosocial work conditions, it is less likely that observed relationships were due to recall bias. Moreover, control for influence of different risk factors was made by multiple logistic regression analysis. Since different aspects of cabin environment were studied, quite many statistical tests were made. In most cases, significance levels were below 0.01 or 0.001, suggesting that the results were not due to mass significance.
In study V, the participation rate was relatively high, 85% in the post-flight clinical investigation and 98% in the study on board. The study was interventional, but, since the airline crew changes from flight to flight, none of the participants appeared more than once in the investigation. Selection bias due to low response rate was less likely since the participation rate was relatively high. Moreover, the
50
participants on board under the smoking and non-smoking conditions respectively were comparable with respect to mean age, gender, tobacco smoking, atopy, occupation, and season. The aircraft were the same, the medical investigations were standardized, performed by the same physician, and all nasal lavage samples were run in the same batch. In order to make the two groups more comparable, the statistical analysis was restricted to non-asthmatic subjects. The study was not blinded, since both the participants and the investigation team was aware of the ban of all smoking on board on 1 September 1997. This could have influenced symptom reporting, but is unlikely to influence effects on physiological signs.
In study VI, the participation rate was relatively high (89%). The study was an interventional follow up study, where each participant was its control. The study was double blind, since either the medical investigation team or the airline crew knew when the air humidification was on or off.
In conclusion, it is less likely that the studies were seriously influenced by selection bias or information bias, or due to mass significance or selection of a particular statistical model.
Comments on external validity The technical measurements were performed on arbitrarity selected intercontinental flights with one particular aircraft type (Boeing 767), covering flights to both Asia and North America, during smoking and non-smoking conditions. The measurements should have reasonable external validity, but may not be representative if there are technical modifications of the aircraft, e.g. change of number of seats on board. Some of the measurements were only performed during cruise conditions, and cannot be extrapolated to non-cruise conditions. Moreover, data from the measurements cannot be extrapolated to other aircraft types.
The questionnaire study was not performed on selected individuals, but covered all Stockholm based employees from one Airline Company, and arbitrarily selected office workers. The study should have reasonable external validity for crew in airline companies organized and operated in similar ways as SAS, but the results may not be generalized to all types of airlines.
51
Comments on the perception of the cabin environment in different occupational groups Many types of complaints on the cabin environment were more common among airline crew, as compared to office workers, irrespectively of occupation on board. No simultaneous measurements and questionnaire examinations were done in study III and IV. There were, however, indications that noise, insufficient cleaning, low relative air humidity, and temperature variations could contribute to the complaints. The prevalence of many types of complaints was 30-75% for airline crew, much more than corresponding figures among office workers and external referents. Pilots were more satisfied with most aspects of the work environment, but were often complaining about inadequate illumination, dust, and dirt. No major differences were observed between flight attendants, sharing the same cabin environment. We found no information on perceived cockpit environment in literature. Other investigations have studied perceived air quality in the cabin. Earlier studies have shown a high prevalence of complaints on air dryness (range 60 - 73%). Pierce 1999, performed a questionnaire study in flight attendants on cabin air quality, cabin or lavatory air, odour, and air humidity. There was a high prevalence of complaints on air dryness (73%), while complaints on other air quality factors were low, including cabin or lavatory air odour and cabin air quality in general (62%).
Comments on prevalence of symptoms Nasal, throat, and facial dermal symptoms were more common among airline crew, as compared to office workers. The most common complaints among airline crew were fatigue (21%), nasal symptoms (15%), dermal symptoms (12%), and ocular symptoms (11%). The prevalence of symptoms were not related to the type of occupation in the cabin, but pilots had fewer ocular, nasal symptoms, and dermal symptoms from the hands as compared to flight attendants. This could be explained by different work tasks, or differences in the cabin air quality. The hygienic demands can be different, with more frequent hand washing in cabin crew. The cabin air quality can be expected to be better on the flight deck than in the cabin, since pilots are not exposed to pollutants related to passenger activity, or cabin-related emissions. Moreover, flight deck may have better ventilation. We found no previous data on similar types of symptoms among pilots,
52
but other questionnaire studies among flight attendants have reported higher prevalence in our study of ocular, nasal, dermal, throat, and general symptoms64,29,30,59. Since different symptom questionnaires have been used in different studies, these studies are not directly comparable to our study. We find less complaint on most symptoms. This can be explained by that there were only 10 % working on smoke flights.
Comments on personal risk factors Besides the study by Ross et al (2000), there is sparse information on the significance of personal risk factors among airline crew, with respect to symptoms and perception for the cabin or flight deck environment.
The most important risk factor for both symptoms and environmental complaints was a history of atopy, defined as having either pollen allergy (hay fever, pet allergy or childhood eczema). We did not perform any allergy testing, but previous studies have demonstrated a reasonable agreement between self-reported allergy and allergy testing 86,87. In one study in house painters, a high specificity (90%) but lower sensitivity (50 %) was obtained, using a positive skin prick test to tree or grass pollen as gold standard88. Atopy was a significant predictor of both respiratory symptoms, dermal symptoms, and general symptoms such as headache and fatigue. This is in agreement with previous studies on similar symptoms among office workers, hospital workers, and the general population 89,90,91,92,93,74. One study in office workers concluded that atopy was not associated with symptoms94.
Female gender was a significant risk factor for some environmental complaints, but not a risk factor for any type of symptoms. In one study, Haugli 1994 found that female among flight attendants report generally more health complains such as dry skin, fatigue, eye irritation, and colds than men. The same results were found from studies among office workers, where the majority of studies have shown a higher prevalence of symptoms in females95,89,91. One possible explanation to the lack of gender differences in airline crew is that we adjusted for the effect of other risk factors that could be linked to gender. Another explanation could be that among flight attendants, both males and females share the same indoor environment.
Low age was a predictor for some types of environmental complaints, but not a predictor of any type of medical symptoms. In
53
one study among office workers in Singapore, younger subjects reported more symptoms96, but there is no consistent relationship between age and symptoms compatible with the sick building syndrome89,91 (SBS). In one study, a negative association was found between age and SBS102, while another study reported a positive correlation103,104. In three studies, no relation between age and SBS could be demonstrated 93,92,105. Burge106 (1987) found that those between 21 and 40 years of age reported more symptoms than either younger or older individuals. Furthermore, there are results showing age differences, on one-hand very young subjects reports more symptoms96, but others shows that very old subjects report more symptoms107 (Engvall 2000). Brasche108 (2001) found that age is a significant risk factor for SBS but only for men. Tobacco smoking was not a risk factor for symptoms or environmental complaints.. Some studies found a relationship with smoking and SBS97,98,90, but there are other that did not find such a relationship99,100. This could be due to the fact that wheeze and other asthmatic symptoms are not included in the definition of sick building syndrome. In two studies, a positive relation between current tobacco smoking and symptoms was found 93,101.
Comments on psychosocial environment Perceived psychosocial work environment was associated with both symptoms and environmental complaints (MM040 NA questionnaire). Work stress due to excess of work was the most significant factors, associated with both dermal and general symptoms, and all types of environmental complaints. Lack of work control was associated with fatigue and some environmental complaints, while work dissatisfaction was a predictor for a few symptoms, but not associated with any type of environmental complaints. Lack of social support seemed to be of less significance in airline crew, and was not associated with any type of medical symptoms. Associations between perceived psychosocial work environment, and environmental complaints, have previously been demonstrated in offices, schools, and hospitals109,110,75,111,99. Moreover, a relationship between symptoms, stress and psychosocial work conditions have been reported in several previous studies112,113,93,74,92,110. The type of work organization may differ considerably between different occupations, and this may influence associations between psychosocial work conditions and health. Both pilots and flight
54
attendants, have a work strongly influenced by a fixed schedule, with little work control. Moreover, there is no fixed work group, since the airline crew are exchanged for each flight. This may create a psychosocial work condition different from other non-industrial work, e.g. office workers. This could explain why work stress were more important predictor of symptoms than lack of work control, or lack of social support, in airline crew.
Comments on health effects of ETS exposure Environmental tobacco smoke (ETS) was a significant source of air pollution in the cabin. The ban on smoking reduced the mean concentration of respirable particles to 3-4 µg/m3 , levels lower than in the crew hotel in Tokyo (12 µg/m3), and lower than the mean concentration (19 µg/m3) measured in dwellings in Uppsala, by the same instrumentation114. Earlier studies, mainly focusing on the passenger’s exposure to ETS, have found similar results as in our study. There has been measured a 5-20 fold increase of respirable particles at passengers seats during smoking-allowed flights, as compared to non-smoking flights48,50,24. In another ETS study115 in an new four-story office building with unrestricted smoking, the concentration of respirable particles was 59 µg/ m3; similar to what could be measured in aft galley during smoking-allowed flights (67 µg/m3 ).
Tobacco contains nicotine, which is metabolised to the main metabolite cotinine116. Nicotine has a short half-life in biological tissues, while the half-life of cotinine is longer117 (about 18 h). Cotinine is widely used as a specific biomarker of ETS exposure117. Dietary intake of some food (mainly from the Solanaceae family) may influence the measurements, but dietary sources of cotinine are neglectible118. Cotinine in urine is a reliable biomarker of recent ETS exposure117. It has been previously used to quantify ETS exposure among adult non-smokers53,119,120,118,121,122,123,124. We could quantify the exposure to ETS in flight attendants, by measuring cotinine in urine, using a specific and reliable method, using mass spectrometry with selective ion monitoring73. The cotinine levels measured in flight attendants after working on smoke flights were similar as in other Nordic studies on occupationally exposed groups118,73,122.
Exposure to ETS in aircraft was associated with an increase of irritative symptoms, particularly ocular and general symptoms impair the perception of cabin air quality, decrease the tear film stability, and
55
alterations of nasal patency in airline crew. There are few other intervention studies on health improvements after ban on smoking in work environments. In one study on bartenders´ respiratory health, the establishment of smoke free bars and taverns in California was associated with a reduction of respiratory and sensory irritation symptoms, and improved lung function125. Our results support the view that despite the high air exchange rate and efficient air filtration, smoking in commercial aircraft leads to a significant pollution in aircraft.
Comments on health effects of low air humidity The relative air humidity was very low in both aft and forward
galleys (2-10 %), much lower than the relative air humidity indoors (33-75%) in mid-Swedish dwellings during the heating season126. Other studies have also found low relative air humidity in aircraft, typically 5-49%27,28,25 , but not as low as our values measured during cruising at high altitude (10-12 000 meters), and near the North Pole with extremely low outdoor humidity. We could demonstrate that air humidification increased relative air humidity by 10% in business class, but only by 3% on flight deck and in tourist class. This can be explained by the fact that the air humidifier was placed in the front of the cabin, and cold wall condensation quickly reduces the effect of the humidifiers when the air is moving backwards in the cabin. The effect of air humidification of flight deck is also expected to be less, since the cockpit has a separate air supply, but with some support of humidified return air.
Despite the small increase of relative air humidity when the evaporation humidifier was operating, we could measure beneficial health effects from the air humidification, both with respect to symptoms and clinical signs from the ocular and nasal mucosa. Air humidification may, however, represent a potential health hazard, if there is a microbial growth in the humidifier 127,106,99. In our study, a ceramic evaporation humidifier was used. According to the manufacturer, it had a construction that should not represent any microbiological hazards. In order to verify this, we measured concentration of microbiological and MVOC. We could not detect any significant differences in concentration of moulds, bacteria or MVOC in cabin air, when comparing humidified and non-humidified flights.
Our data is in agreement with other experimental studies, showing a reduction of symptoms effects of air humidification in offices or
56
hospitals128,129,130,82,. In these studies, air humidification was increasing the relative air humidity with about 10% up to 30-40%, while the control unit without humidification had 20-30% R.H.. One recent exposure chamber study studied health effects of relative air humidity at lower levels (5-35%; 22 C), similar to the levels in aircraft. The study showed that lower humidity might reduce tear film stability, increase blink frequency, and cause skin dryness symptoms 132.
Comments on carbon dioxide (CO2) concentrations The CO2 concentration in the galley areas was mostly between 500-
700 ppm in the studies performed from 1995 to 2000. During this period, 4 % of the measured one minute values exceed the current Swedish ventilation standard for workplace buildings of 1000 ppm33. In the air humidification study for 2002-2003, the average CO2 concentration was higher (1100-1200 ppm). Dry ice was not used to chill the food in any of the B 767 in our study. Other investigators have reported higher values, with average concentrations of 629 -1756 ppm of CO2, and 25-87% of all measurements above 1000 ppm133,23,29,25,37,36,26.
These differences can be explained by differences in ventilation and proportion of recirculated air in different aircraft types, and different population density. In Boeing 767, operated by SAS, the number of seats was increased from 190 to 204 in 2001. The measuring equipment was placed the in fwd passengers cabin in the humidification study and in the fwd galley with less occupants in earlier studies. This could partly explain the higher levels measured in the last air humidification study.
Since humans are emitting CO2, this compound can be measured as a proxy variable for personal outdoor air supply flow. It can also be measured as a proxy variable for bio effluents from humans. Already in 1858, Pettenkoffer showed that at CO2 levels above 1000 ppm, the air is perceived as deteriorated. The deterioration of air quality was observed among non-adapted visitors. Adapted visitors can be exposed to CO2-levels above 1000 ppm without perceiving poor air quality. Direct health effects from CO2 are not expected until the levels are well above 5000 ppm, the actual Swedish threshold limit value being 5000 ppm134. The association between symptoms and ventilation has been reviewed. One review article concluded that there is limited evidence to suggest that ventilation rate increase up to 10 l/second and person can be effective in reducing symptom prevalence
57
and occupant dissatisfaction with air quality. Higher ventilation rates may not be effective. In another review article, it was found that about half of the ventilation studies suggest that the risk for symptoms is reduced down to 800 ppm of CO2 135. Modern aircraft use air recirculation systems with air filtration, and sometimes HEPA filters and active charcoal filters. Thus, the relationship between ventilation flow and symptoms may not be directly comparable with results from research in mechanically ventilated buildings. Since there are no interventional studies available from aircraft, no evaluation on health effects of different outdoor air flow, it is difficult to draw conclusion about which CO2 levels that are acceptable in aircraft.
Comments on other pollutants Our low levels of ozone are in agreement with other studies from the 90'ies, showing low levels (<2-20 ppb) of ozone 48,25. Earlier studies in aircraft have reported higher ozone concentrations in cabin air, typically 200-800 ppb41,42. However, Nagda 2000, suggests that the existing measurement techniques are not adequate, and development of a reliable and practical method of continuous measurement of O3 is necessary. High temperatures, pressures and air pollution in cabin have an influence on dissociation of O3 to O2. We found very low levels of formaldehyde in our measurements, both during smoking or non-smoking flights. O´Donnell et al. reported higher values of formaldehyde than our results (25 µg/m3, 17-82 µg/m3), These differences could be due to different formaldehyde emissions.
In our study, the concentration of moulds and bacteria was low both in the aircraft and at the hotel, less than 10% of average levels of moulds and bacteria measured in Swedish dwellings by the same method (Norbäck et al., 1993). Other investigators, using different methods to measure microbial contamination, have reported similar findings54. The low levels of micro organisms can be explained by the fact that the outdoor air is sterile, and that the return air in B 767 goes through a HEPA filter, which should keep levels of micro organisms at an acceptable level.
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SUMMARY AND CONCLUSION
Annoyance by factors in work environment were found to be more common among aircraft crew than office workers, particularly discomfort due to draught, thermal conditions, stuffy air, dry air, static electricity, noise, inadequate illumination, and dust. The variation of cabin temperature was relatively large, which shows a need for better temperature control, to achieve a more stable thermal climate. Important factors were work stress due to excess of work, lack of influence on the working conditions, and work on intercontinental flights. Similar risk factors were found for medical symptoms. Symptoms from the mucous membranes, and dermal symptoms were more common among aircraft crew than office workers, and many perceived the symptoms as being work-related. Important risk factors for symptoms were work stress due to excess of work, and work on intercontinental flights where smoking was allowed. The most consistent risk factor for both symptoms and annoyance was a history of atopy, suggesting that subjects with atopic sensitization are more prone to react to environmental factors in aircraft.
The hygienic measurements in aircraft, performed only on intercontinental flights, showed that the relative air humidity was very low onboard and that tobacco smoking leads to a significant pollution of respirable particles. The concentration of other air pollutants, such as moulds, bacteria, formaldehyde, nitrogen dioxide, and ozone was low onboard. The exposure to ETS was most pronounced in the aft galley. Besides particle measurements, the exposure to ETS on smoke flight was verified by biological monitoring of cotinine in urine. In the clinical study onboard the aircraft, it was found that the ban on smoking resulted in a reduction of ocular and general symptoms, improved perception of cabin air quality, and improved the tear film stability. Exposure to environmental tobacco smoke is now history in aircraft, but the experience from aircraft can encourage those fighting against involuntary exposure to tobacco smoke in other indoor environments, e.g. bars and restaurants. The experience from aircraft showed that a total ban of smoking is beneficial from a health point of
59
view, and that smoke free zones may not be an effective way to reduce the exposure.
The air humidification study showed that the low relative air humidity can be slightly increased by use of a ceramic evaporation humidifier, without any measurable increase of micro-organisms in cabin air. The medical evaluation in that study demonstrated that an slight increase of relative air humidity on intercontinental flights could be beneficial from a health point of view. An increase of relative air humidity by 3-10% increased tear film stability, increased nasal patency in the proximal art of the nose, and reduced headache and ocular, nasal, and dermal dryness symptoms.
Some environmental conditions that could be improved were identified. In the future, the technological development of aircraft will continue, and demands to reduce fuel costs per passenger and kilometres will continue to influence the cabin environment. Sometimes the technological development has created new environmental problems, which have been solved by new technique. The cabin environment affects a large number of subjects, on a global scale. As in many other areas of the modern society, there is an increased demand on safety, and comfort, which may result in a rise on the standards onboard the aircraft. In view of the worldwide increase of civil aviation, the working conditions for aircrew needs further attention Moreover, improved cabin air quality can become an important commercial factor in the future in the competition to attract customers.
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ACKNOWLEDGEMENTS
I wish to express my sincere gratitude to: Associate Professor Dan Norbäck, my tutor, for excellent guidance in my research and for his commitment, patience and confidence. Associate Professor Gunilla Wieslander, my co-tutor, for generous collaboration, advice and constructive discussions.
My superior, Professor Christer Edling, for providing time and facilities to perform this study. Jan Ivar Mattsson, for improving my English. The flight crew for their co-operation. The staff on the Department of Occupational and Environmental Medicine for having the patience to listen to my talking at the coffee table. My son Jonas, for accepting me not watching television.
My brother Sven for his always better knowledge. My fiancée Mary for her love, support and understanding.
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REFERENCES
001. World Air Transport Statistic 2002 ( IATA), www.iatagabi.com. 002. Rayman RB. Clinical Aviation Medicine 3rd ed: Published by Castle
Connoly Graduate Medical Publishing, LLC. 2000. New York. 003. Ekdahl K. Läkartidningen (In Swedish) 2003;16:1420-1425. 004. deHart RL Health Issues of Air Travel. . Annu Rev Public Health 2002
Nov 7. 005. Study on the Possible Effects on Health of Aircraft Cabin Environments
- Stage 1.Department for Transport, by MRC, Institute for Environment and Health, Jan 2001.
006. Swedish Meteorological and Hydrological Institute, SMHI.
www.smhi.se. 007. van Heusden S, Mans LG Alternating measurement of ambient and
cabin ozone concentrations in commercial jet aircraft Aviat Space Environ Med 1978;49:1056-61.
008. Elwood H. Hunt. Commercial Airliner Environmental Control System.
Engineering Aspects of Cabin Air Quality. Proceeding Aerospace Medical Association (ASMA), Anaheim California, 1995.
009. Joint Aviation Authorities/Joint Aviation Requirements. Cosmic
radiation JAR OPS 1.390. 2001. 010. Moser MR, Bender TR, Margolis HS, Noble GR, Kendal AP, Ritter DG.
“An outbreak of influenza aboard a commercial airliner.” Am J Epidemiol 1979; 110:1-6.
011. Al-Jahdali H, Memish ZA, Menzies D. Tuberculosis in association with
travel. Int J Antimicrob Agents 2003 Feb; 21(2): 125-30. 012. Whitlock G, Calder L, Perry H. A case of infectious tuberculosis on two
long-haul aircraft flights: contact investigation. N Z Med J 2001 Aug 10;114(1137):353-5.
62
013. WHO guidelines address risk of tuberculosis transmission during air travel. Cent Eur J Public Health 1999 Aug; 7(3): 144-154.
014. Miller MA, Valway S, Onorato IM. “Tuberculosis risk after exposure on
airplanes.” Tubercle and Lung Dis 1996; 77:414-9. 015. Kenyon TA, Valway SE, Ihle WW, Onorato IM, Castro KG.
“Transmission of multidrug-resistant Mycobacterium tuberculosis during a long airplane flight.” N Engl J Med 1996;334:933-8.
016. Brown TP, Shuker LK, Rushton L, Warren F, Stevens J. The possible
effects on health, comfort and safety of aircraft cabin environments. J R Soc Health 2001 Sep; 121(3): 177-84.
017. Swedish Civil Aviation Administration (LFV). Air Quality at
Stockholm-Arlanda Airport. Edt. Ernedal S. May 1995. 018. Gerin M, Patrice S, Begin D, Goldberg MS, Vyskocil A, Adib G, Drolet
D, Viau C. A study of ethylene glycol exposure and kidney function of aircraft de-icing workers. Int Arch Occup Environ Health 1997; 69(4): 255-65.
019. Switzenbaum MS, Veltman S, Mericas D, Wagoner B, Schoenberg T.
Best management practices for airport deicing stormwater. Chemosphere 2001 Jun; 43(8): 1051-62.
020. Miyamoto Y. Eye and respiratory irritants in jet exhaust. Aviat Space
Environ Med 1986 Nov; 57(11): 1104-8. 021. Tesseraux I, Mach B, Koss G. Aviation fuels and aircraft emissions. A
risk characterization for airport neighbors using Hamburg Airport as an example. Zentralbl Hyg Umweltmed 1998 Jun;201(2): 135-51.
022. IVL Svenska Miljöinstitutet AB, (In Swedish). Luftkvalitetundersökning
vid Arlanda Flygplats Oct. 1986-Feb. 1987, Stockholm 1997. 023. Lee SC, Poon CS, Li XD, Luk F. Indoor Air Quality Investigation on
Commercial Aircraft. Indoor Air1999; 9:180-187. 024. Nadga NL, Koontz MD, Konheim AG, Hammond SK. Measurement of
cabin air quality aboard commercial airliners. Atmospheric Environment. 1992; 26A: 2203-2210.
025. O'Donnell A, Donnini G, Nguyen VH.. Air quality, ventilation,
temperature and humidity in aircraft. ASHRAE Journal 1991, April 42-6. 026. Haghighat, F., Allard, F., Megri, A. C., Blondeau, P. and
Shimotakahara, R. () "Measurements of Thermal Comfort and Indoor Air Quality Aboard 43 flights on Commercial Airlines", Indoor Built Environment. 1999; 8:58-66.
63
027. Owe JO. Air transportation In: Brune D, Gerhardsson G, Crockford
GW, Norbäck D (eds). Major Industries and Occupations. Geneva: International Labour Office, 1997, pp.107-25.
028. Rayman RB. Passenger safety, health and comfort: A review. Aviation
Space and Environmental Medicine 1997; 68:432-40. 029. Pierce WM, Janczewski JN, Roethlisberger B, Janczewski MG. "Air
Quality On Commercial Aircraft", ASHRAE Journal 1999 Sep:26-34. 030. de Ree, H., Bagshaw, M., Simons, R. and Brown R.A. (2000) Ozone
and Relative Humidity in Airline Cabins on Polar Routes, Measurements and Physical Symptoms, Ed. Nagda, N.L., ASTM, STP 1393, Air Quality and Comfort in Airliner Cabins, American Society for Testing and Materials.
031. Backman, H, Haghighat F. Air quality and ocular discomfort aboard
commercial aircraft. Optometry 2000; 71(10): 653-656. 032. Nadga NL, Koontz MD. Review of Studies on Flight Attendant Health
and Comfort in Airliner Cabins. Aviation, Space, and Environmental Medicine 2003;74(2):101-109.
033. Anonymous. Ventilation and quality of air. National Swedish Board of
Occupational Safety and Health. AFS 2000:42 Stockholm, 2000 (in Swedish).
034. ASHRAE (1999) "Ventilation for Acceptable Indoor Air Quality".
American Society of Heating, Refrigerating and Air Conditions Engineers (ASHRAE Standard 62-1999, Supersedes 62-1989).
035. Ross D Hadi M, Palmer J, et al. Cabin air quality monitoring in Boeing
777s. United Kingdom: Centre for Safety, Health, and Environment; Dec. Report No 201543, 2000.
036. Air Transport Association of America (ATA). Airline cabin air quality
study. Washington DC: The Association. 1994. 037. U.S. Department of Transportation. Airliner Cabin Environment:
Contaminant Measurements, Health Risks, and Mitigation Options. 1989 Report No. (DOT-P-15-89-5).
038. Malmfors T, Thornburn D, Westlin A. Air quality in Passengers Cabin
of DC-9 and MD-80 Aircraft. Environmental Technology Letters, Vol. 10, pp. 613-628. Publications Division Selper Ltd., 1989.
039. Reed D, Claser S, Kaldor J. Ozone toxicity symptoms among flight
attendants. Am J Ind Med 1980; 1:43-54.
64
040. Tashkin DP, Coulson AH, Simmons MS, Spivey GH. Respiratory symptoms of flight attendants during high-altitude flight: Possible relation to cabin ozone exposure. Int Arch Occup Environ Health 1983; 52:117-37.
041. Bischof W. Ozone measurements in jet airliner cabin air. Water, Air,
and Soil Pollution 1973; 2:3-14. 042. Nastrom GD, Holdeman JD, Perkins PJ. Measurements of cabin and
ambient ozone on B747 airplanes. Journal of Aircraft 1980; 17:246-249. 043. Eatough DJ, Caka FM, Crawford J, Braithwaite S, Hansen LD, Lewis
EA. Environmental tobacco smoke in commercial aircraft. Atmospheric Environment 1992; 26A: 2211-18.
044. Dechow M, Sohn, J, Steinhanses, J. Concentrations of selected
contaminatants in cabin air of Airbus aircraft. Chemosphere 1997; 35: 21-31.
045. van Netten C. Analysis and implications of aircraft disinsectants. Sci
Total Environ 2002 Jul 3;293 (1-3):257-62. 046. Winder C, Balouet JC .The toxicity of commercial jet oils. Environ Res.
2002 Jun; 89(2): 146-64. Review. 047. van Netten C, Leung V. Hydraulic fluids and jet engine oil: pyrolysis
and aircraft air quality. Arch Environ Health. 2001 Mar-Apr; 56(2): 181-6.
048. Crawford WA and Holcomb LC. Environmental tobacco smoke (ETS)
in airliners- a health hazard evaluation. Aviation Space and Environmental Medicine 1991; 62:580-6.
049. Drake JW, Johnson DE. Measurements of certain environmental tobacco
smoke components on long-range flights. Aviation Space and Environmental Medicine 1990; 61: 531-42.
050. Schmekel B, Karlsson SE, Linden K, Sundström C, Tegner H, Venge P.
Myeloperoxidase in human lung lavage I. A marker of local neutrophil activity. Inflammation 1990;14:447-54.
051. Mattson ME et al. Passive smoking on commercial airline flights.
JAMA 1989; 261:867-72. 052. Oldaker III GB, Condrad FC. Estimation of effect of environmental
tobacco smoke on air quality within passenger cabins of commercial aircraft. Environmental Science and Technology 1987; 21:994-9.
65
053. Matsukura S, Taminato T, Kitano N, Seino Y, Hamada H, Uchihashi M et al. Effects of environmental tobacco smoke on urinary cotinine excretion in non smokers. New Engl J Med 1984; 311:828-832.
054. Wick RL and Irvine LA. The microbiological composition of airliner
cabin air. Aviation Space and Environmental Medicine 1995;66:220-4. 055. Martin IR, Wickens K, Patchett K, Kent R, Fitzharris P, Siebers R,
Lewis S, Crane J, Holbrook N, Town GI, Smith S. Cat allergen levels in public places in New Zealand. N Z Med J 1998 Sep 25;111(1074):356-8.
056. Almqvist C, Wickman M, Perfetti L, Berglind N, Renstrom A, Hedren
M, Larsson K, Hedlin G, Malmberg P. Worsening of asthma in children allergic to cats, after indirect exposure to cat at school. Am J Respir Crit Care Med 2001 Mar; 163(3 Pt 1): 694-8.
057. Erneling L, Orring R, Joachimsson A. Cabin attendants´working
environment study. Stockholm Occupational Health and Safety. Sept 1988.
058. Cone JE. Cabin air causalities: flight attendant health survey. San
Francisko CA: San Francisko General Hospital; 1984. 059. Haugli L, Skogstad A, Hellesøy OH. Health, sleep, and mood
perceptions reported by airline crews flying short and long hauls. Aviation, Space, and Environmental Medicine 1994; 65: 27-34.
060. Pelletier F. The perspective of canadian flight attendants on cabin air
issues. Toronto, Canada: Canadian Union of Public Employees, Airline Divison; 1998 Jun.
061. Eng WG. Survey on eye comfort in aircraft. I. Flight attendants.
Aviation, Space and Environmental Medicine 1979; 50: 401-404. 062. Smolensky MH, Lee E, Mott D, Colligan M. .A health profile of
American flight attendants (FA). J Hum Ergol (Tokyo). 1982;11 Suppl:103-19.
063. Galipault JB. A study of airline flight attendants sleepiness, fatigue and
stress. Worthington, OH: The Aviation Safety Institute; 1980 Sept. Report No: 80-2.
064. Lee SC, Poon CS, Li XD, Luk F, et al . Questionnaire survey to
evaluate the health and comfort of cabin crew. In: Nadga NL, ed. Air quality and comfort in airliner cabins: ASTM STP 1393. West Conshocken, PA: American Society for Testing and Materials; 2000:259-68.
66
065. Enck P, Muller-Sacks E, Holtmann G, Wegmann H. Enck 1995. Gastrointestinal problems in airline crew members. Z Gastroenterol. 1995 Sep;33(9):513-6.
066. Lowden A, Akerstedt T. Retaining home-base sleep hours to prevent jet
lag in connection with a westward flight across nine time zones. Chronobiol Int 1998 Jul;15(4):365-76.
067. Andersson K, Stridh G. The use of standardized questionnaires in
building-related illness (BRI) and sick building syndrome (SBS) surveys. In: Levy F. and Maroni M. (eds), NATO/CCMS pilot study on indoor air quality, National Institute of Occupational Health, Oslo. 1992 pp. 47-64.
068. Andersson K. Epidemical Approach to Indoor Air Problems. Indoor Air;
Suppl 1998; 4:32-39. 069. Andersson, K, Hallgren, C, Levin JO, Nilsson, CA. Chemisorptions
sampling and analysis of formaldehyde in air, influence on recovery during simultaneous sampling formaldehyde, phenol, and furfural alcohol. Scandinavian Journal of Work Environment & Health 1981; 7: 282-289.
070. Ferm, M. Functioning and use of passive samplers. In: Proceedings from
Fourth CAAP workshop, 9-12 November 1998, Chulalongkorn University, Bangkok, pp. 41-44.
071. Ferm, M. Svanberg, P-A. Cost-efficient techniques for urban and
background measurements of SO2 and NO2. Atmospheric Environment, 1998; 32: 1377-1381.
072. Palmgren U, Ström G, Blomqvist G, Malmberg P. Collection of airborne
micro-organisms on Nucleopore filters, estimation and analysis-CAMNEA method. J Appl Bacteriology 1986; 61: 401-6.
073. Skarping G, Willers S and Dalene M. Determination of cotinine in urine
using glass capillary gas chromatography and selective detection, with special reference to the biological monitoring of passive smoking. J Chromatogr 1988; 454:293-301.
074. Stenberg B, Hansson Mild K, Sandström M, Sundell J, Wall S. A
prevalence study of the sick building syndrome (SBS) and facial skin symptoms in office workers. Indoor Air 1993;3:71-81.
075. Smedje G, Norbäck D, Edling C. Subjective Indoor Air Quality in
Schools in Relation to Exposure. Indoor Air 1997; 7:143-150. 076. Wålinder R, Norbäck D et al. Nasal patency and biomarkers in nasal
lavage- the signifance of air exchange rate and type of ventilation in schools. Int Arch Occup Environ Health 1998; 71:479-486.
67
077. Burney P. Ten years of research on asthma in Europe. The European Community Respiratory Health Survey. Rev Epidemiol Sante Publique 1998 Dec; 46(6): 491-6.
078. Wieslander G, Norbäck D, Wålinder R , Erwall C, Venge P.
Inflammation markers in nasal lavage, and nasal symptoms in relation to relocation to a newly painted building: a longitudinal study. Int Arch Occup Environ Health 1999; 72:507-515.
079. Wålinder R, Norbäck D, Wieslander G, Smedje G., Erwall C, Venge P.
Nasal patency and lavage biomarkers in relation to settled dust and cleaning routines in schools. Scand J Work Environ Health 1999; 25:137-43.
080. Venge P, Hällgren R, Stålenheim G, Olsson I. Effects of serum and
cations on the selective release of granular proteins from human neutrophils during phagocytosis. Scand J Haematol 1979; 22:317-26.
081. Peterson CGB, Nystrand J, Andersson AS, Nilsson L, Venge P.
Radioimmunoassay of human eosinophil cationic protein by an improved method. Establishment of normal levels in serum turnover in vivo. Clin Exp Allergy 1991; 21:561-7.
082. Wyon D. Sick buildings and the experimental approach. Environment
Technology 1992; 13:313-22. 083. Wyon NM, Wyon DP. Measurement of acute response to draught in the
eye. Acta Ophtalmol 1987; 65:385-92. 084. Gebski V, Leung O, McNeil D, Lunn D. SPIDA users manual, version
6, 1992, Statistical Computing Laboratory, Eastwood, Australia. 085. Belsley D. Conditioning diagnostics collinearity and weak data in
regression. Wiley & Sons 1991. 086. Lakwijk N, Van Strien RT, Doekes G, Brunekreef B, Gerritsen J.
Validation of a screening questionnaire for atopy with serum IgE tests in a population of pregnant Dutch women. Clin Exp Allergy. 1998 Apr; 28(4): 454-8.
087. Bergmann RL, Forster J, Schulz J, Bergmann KE, Bauer CP, Wahn U.
Atopic family history. Validation of instruments in a multicenter cohort study. Pediatr Allergy Immunol 1993 Aug; 4(3): 130-5.
088. Wieslander G, Norback D, Edling C. Airway symptoms among house painters in relation to exposure to volatile organic compounds (VOCS)--a longitudinal study. Ann Occup Hyg. 1997 Apr; 41(2): 155-66.
089. Apter A, Bracker A, Hodgson M, Sidman J, Leung WY. Epidemiology
of the sick building syndrome. J Allergy Clin Immunol 1994; 94:277-88.
68
090. Björnsson E, Janson C, Norback D, Boman G. Symptoms related to the
sick building syndrome in a general population sample: associations with atopy, bronchial hyper-responsiveness and anxiety. Int J Tuberc Lung Dis 1998 Dec; 2(12): 1023-8.
091. Hodgson M. The sick building syndrome. Occup Med State of Art Rev
1995; 10:167-175. 092. Norbäck D, Edling C. Environmental, occupational, and personal factors
related to the prevalence of sick building syndrome in the general population. Br J Ind Med. 1991; 48: 451-62.
093. Skov P, Valbjorn O, Pedersen BV. Influence of personal characteristics,
job-related factors and psychosocial factors on the sick building syndrome. Scand J Work Environ Health 1989; 15:286-295.
094. Muzi G, dell'Omo M, Abbritti G, Accattoli P, Fiore MC, Gabrielli AR.
Objective assessment of ocular and respiratory alterations in employees in a sick building. Am J Ind Med 1998 Jul;34(1):79-88.
095. Stenberg B, Wall S. Why do women report 'sick building symptoms'
more often than men? Soc Sci Med. 1995 Feb;40(4):491-502. 096. Ooi PL, Goh KT, Phoon MH, Foo SC, Yap HM. Epidemiology of sick
building syndrome and its associated risk factors in Singapore. Occup Environ Med 1998 Mar; 55(3): 188-93.
097. Skov P, Valbjorn O, et al. The sick building syndrome in the office
environment: The Danish town hall study. Environment International 1987; 13: 339-34.
098. Norback D, Michel I, Widstrom J. Indoor air quality and personal
factors related to the sick building syndrome. Scand J Work Environ Health. 1990 Apr;16(2):121-8.
099. Zweers T., Preller l., Brunekreef B., Boleij J.S.M. Health and indoor
climate complaints of 7043 office workers in 61 buildings in the Netherlands. Indoor Air 1992; 2:127-136.
100. Lenvik K. Smoking habits, atopy, and prevalence of sick building
syndrome symptoms among office workers in Norway. Environment International 1993;19:333-340.
101. Rogier C, Dabis F, Teissier JF, Salamon R. What role do smoking and
air conditioning play in the occurrence of building sickness among hospital personell? Rev Epidemiol Sante Publique. 1989;37(3):255-62. (in French).
69
102. Taylor PR, DellÁcqua BJ,Baptiste, MS, Hwang H-L, Sovik RA. Illnes in office building with limited fresh air access. J Environ Health 1984;47:107-14.
103. Hedge A, Sterling TD, Sterling EM, Collett CW, Sterling DA, Nie V.
Indoor air quality and health in two office buildings with different ventilation systems. Environ Int 1989;15:115-28.
104. Hedge A, Burge PS, Robertson AS, Wilson S, Harris-Bas J.
Workrelated illness in offices: aproposed model of the “sick building syndrome”. Environment Int 1989;15:143-58.
105. Jaakkola jjk, heinonen op, seppänen o. sick building syndrome,
sensation of dryness and thermal comfort in relation to room temperature in an office building: need for individual control of temperature. Environment internationlal 1989;15:163-8.
106. Burge S, Hedge A, Wilson S, Bass JH, Robertson A. Sick building
syndrome: a study of 4373 office workers. Ann Occup Hyg 1987; 31(4A): 493-504.
107. Engvall K, Norrby C, Bandel J, Hult M, Norback D. Development of a
multiple regression model to identify multi-family residential buildings with a high prevalence of sick building syndrome (SBS).
108. Brasche S, Bullinger M, Morfeld M, Gebhardt HJ, Bischof W. Why do
women suffer from sick building syndrome more often than men?--subjective higher sensitivity versus objective causes. Indoor Air. 2001 Dec;11(4):217-22.
109. Norbäck D. Subjective indoor air quality in schools - the influence of
high room temperature, carpeting, fleecy wall materials and volatile organic compounds (VOC). Indoor Air 1995; 5:237-246.
110. Nordström K, Norbäck D, Akselsson R. Subjective indoor air quality in
hospitals - the influence of building age, ventilation flow, and personal factors. Indoor Environment 1995; 4:37-44.
111. Wallace L.A., Nelson C.J., Highsmith R., Dunteman G. Association of
personal and workplace characteristics with health, comfort and odor: A survey of 3948 office workers in three buildings. Indoor Air 1993; 3:193-205.
112. Boxer PA. Indoor air quality: a psychosocial perspective. J Occup Med
1990 May; 32(5): 425-8. 113. Crawford JO, Bolas SM.. Sick building syndrome, work factors and
occupational stress. Scand J Work Environ Health. 1996 Aug; 22(4): 243-50. Review.
70
114. Norbäck D, Björnsson E, Widström J, Ström G, Edling C, Palmgren U, Jansson C, Boman G. Asthma and the home environment. Sterling E, Bieva C, Collett C (eds) Building Design, Technology, and Occupant Well-being in Temperate Climates ASHRAE Special Publications 90353, Atlanta, USA, 1993, pp.329-333.
115. Jenkins RA, Maskarinec MP, Counts RW, Caton JE, Tomkins BA,
Ilgner RH. Environmental tobacco smoke in an unrestricted smoking workplace: area and personal exposure monitoring. J Expo Anal Environ Epidemiol. 2001 Sep-Oct; 11(5): 369-80.
116. Apseloff G, Ashton HM, Friedman H and Gerber N (1994) The
importance of measuring cotinine levels to identify smokers in clinical trials. Clinical Pharmacology & Therapeutics. 56:460-462.
117. Haufroid V, Lison D. Urinary cotinine as a tobacco-smoke exposure
index: a minireview. Int Arch Occup Environ Health. 1998 May; 71(3): 162-8. Review.
118. Willers S, Skarping G, Dalene M, Skerfving S. Urinary cotinine in
children and adults during and after semi-experimental exposure to environmental tobacco smoke. Arch Environ Health 1995; 50(2): 130-8.
119. Thompson SG, Stone R, Nanchahal K, Wald NJ () Relation of urinary
cotinine concentrations to cigarette smoking and to exposure to other people's smoke. Thorax 1990; 45(5): 356-361.
120. Trout D, Decker J, Mueller C, Bernert JT, Pirkle J (1998) Exposure of
casino employees to environmental tobacco smoke. Journal of Occupational & Environmental Medicine 40(3): 270-276.
121. Gaffuri E, Maranelli G, Romeo L. Durigato S. The exposure to tobacco
smoke of the employees of a telephone company. Medicina del Lavoro 1992; 83(6): 596-604.
122. Husgafvel-Pursiainen K, Sorsa M, Engström K, Einistö P. Passive
smoking at work: biochemical and biological measures of exposure to environmental tobacco smoke. Int Arch Occup Environ Health 1987; 59:337-345.
123. Jarvis MJ, Foulds J, Feyrabend C. Exposure to passive smoking among
bar staff. Br J Addict 1992:87:111-113. 124. Willers S, Bensryd I, Skarping G, Skerfving S. Urinary cotinine
excretion at work. In: Quality of The Indoor Environment, ed: Lester, Perry and Reynolds. Publications Division, Selper Ltd. London 1992; 347-351.
71
125. Eisner MD, Smith AK, Blanc PD Bartenders' respiratory health after establishment of smoke-free bars and taverns. JAMA. 1998 Dec 9; 280(22): 1909-14.
126. Björnsson E, Norbäck D, Janson C, Widström J, Palmgren U, Ström G,
Boman G. Asthmatic symptoms and indoor levels of microorganisms and house dust mites. Clin Exp Allergy 1995; 25:423-31.
127. Anderson K, Watt AD, Sinclair D, Lewis C, McSharry CP, Boyd G.
Climate, intermittent humidification, and humidifier fever. Br J Ind Med 1989 Sep;46(9):671-4.
128. Reinikainen LM, Jaakkola JJ, Seppanen O. The effect of air
humidification on symptoms and perception of indoor air quality in office workers: a six-period cross-over trial. Arch Environ Health. 1992 Jan-Feb;47(1):8-15.
129. Reinikainen LM, Jaakkola JJ. Effects of temperature and humidification
in the office environment. Arch Environ Health. 2001 Jul-Aug;56(4):365-8.
130. Nordström K, Norbäck D, Axelsson R. Effect of air humidification on
the sick building syndrome and perceived indoor air quality in hospitals: a four month longitudial study. Occupational and environmental Medicine 1994; 51:683-688.
131. Norbäck D, Wieslander G, Nordström K, Wålinder R, Venge P. The
effect of Air Humidification on Symptoms and Nasal Patency, Tear Film Stability, and Biomarkers in Nasal Lavage: A 6 Weeks`Longitudial Study. Indoor Built Environment 2000; 9:28-34.
132. Wyon DP. Pr. Proceedings: 9th International Conference on Indoor Air
Quality and Climate. Indoor Air 2002, Monterey California. 133. Hocking MB. Indoor air quality: Recommendations relevant to aircraft
passenger cabins. Am J Ind Hyg Assoc J 1998; 59:446-54. 134. Anonymous. Hygieniska gränsvärden. National Swedish Board of
Occupational Safety and Health. AFS 2000:3, Stockholm, 2000 (in Swedish).
135. Seppanen OA, Fisk WJ, Mendell MJ. Association of ventilation rates
and CO2 concentrations with health and other responses in commercial and institutional buildings. Indoor Air. 1999 Dec; 9(4): 226-52. Review.
136. High efficiency air filters (HEPA and ULPA)- Part 1: Classification,
performance testing, marking. European Committee for Standardization, EN 1822-1, Brussels 1998.