TRANSPORT and ROAD RESEARCH LABORATORY

Department of the Environment

TRRL REPORT LR 477

A REVIEW OF METHODS OF VENTILATING ROAD TUNNELS

by

H J Hignett, CEng, MIMechE, AMIED

and

L Hogbin

Environment, and, Tunnels; Divisions Transport System s,~ ~n- d st ru ctu res, Departments

Transport and, Road:ReSearch iLab~ratdry Cr-owthorne'~ B~'rE~h[re~

1972"

CONTENTS

Abstract

1. Introduction

2. The quantity and compostion of exhaust gases

3. The physiological effects of carbon monoxide

4. The type of ventilation system

4.1 Natural ventilation

4.2 Traffic induced ventilation

4.3 Mechanical ventilation

4.3.1 Longitudinal system

4.3.2 Upward semi-transverse system

4.3.3 Lateral semi-transverse system

4.3.4 Upward fully-transverse system

4.3.5 Lateral fully-transverse system

4.3.6 Unit blower system

4.4 Chemical air reconditioning

5. The design of ducts and vents

5.1 Quantity of air and pressure

5.2 Sectionalisinglong tunnels

6. Automatic controls

6.1 Carbon monoxide analysers

6.1.1 The Hopcalite analyser

6.1.2 The Infra-Red Gas Analyser

7. Conclusions

7.1 Tolerable concentration of carbon monoxide and other pollutants

7.2 Emission of carbon monoxide from motor vehicles

7.3 Choice of ventilation system

8. References

9. Appendix

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© CROWN COPYRIGHT 1972

Extracts from the text may be reproduced

provided the source is acknowledged

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on ! st April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

A REVIEW OF M E T H O D S OF V E N T I L A T I N G

ROAD T U N N E L S

ABSTRACT

This paper reviews ventilation requirements for road tunnels and describes the ventilation systems currently available. The areas where present knowledge is deficient are identified and recommendations are made for future research and the production of standards for road tunnel ventilation.

1. I N T R O D U C T I O N .

Artificial ventilationof road tunnels is required when the noxious and toxic gases and smoke emitted from

the exhausts of vehicles become either a danger or a nuisance.

Tunnels built before the Holland Tunnel, New York, which was planned in 1919 and opened in 1927,

were not ventilated mechanically, although ventilation systems were added to the Old Blackwall Tunnel and

the Rotherhithe Tunnel in 1922 and 1925 respectively as motor traffic increased. The Holland Tunnel is

2540 m between portals and its ventilation problems were without precedent. Little was known about the

ventilation of road tunnels except what could be applied from work in mines and in railway tunnels. It was,

therefore, imperative to establish fundamental data, and most ventilation systems in tunnels built subsequently

have been based at least in part on the results of the research carried out in the 1920's by the New York and

New Jersey Bridge and Tunnel Commission and the US Bureau of Mines under the direction of Singstad. 1

The following are the main considerations in the design of a tunnel ventilation system:-

a. The quantity and compositio n of exhaust gases.

b. The amount of fresh air required to be introduced into the tunnel to achieve adequate dilution

of the principal contaminants under knoWn traffic Conditions at all points in tile tunnel.

c. The type of ventilation system to provide the required quantity of fresh air to the tunnel most

economically.

d. The design of fans together with any ducts and vents required to achieve the air flow necessary.

e. Automatic controls to ensure economical operation.

1

Much of the information required to design a ventilation system for a road tunnel is still not known

precisely and consequently there are considerable variations in the practice and standards used by different

authorities. In a situation where life and health could be at risk it is not surprising that the tendency has

been towards caution and over-ventilation. The object of this report is to review and examine the existing

methods used to ventilate road tunnels and thereby indicate those areas where further development and research

would be worthwhile.

2. THE QUANTITY AND COMPOSITION OF EXHAUST GASES

!

(

Petrol and diesel engines emit the following from their exhausts: carbon monoxide, carbon dioxide, oxides

of sulphur, aldehydes, ketones, hydrogen, methane, oxides of nitrogen, water y~Cpour, and smoke which is

mainly free carbon and oil vapour. These are not equally important from thel~oint of view of ventilation.

Stahel et al 2 1960 has provided data on exhaust emissions from petrol and diesel engines shown in Table 1.

The values given in this table for maximum permissible concentration in a tunnel are to some extent arbitrary

because this quantity cannot be defined precisely. The relative values, however, are not in dispute and it is

generally agreed, that the greatest dilution is required to deal with the carbon monoxide from petrol vehicles;

a ventilation system which creates safe conditions in respect of this gas will adequately cater for other

contaminants.

Apart from noxious and lethal contaminats it is necessary to maintain good visibility in road tunnels.

When the Holland Tunnel was opened to traffic it was found that the ventilation needed to limit carbon

monoxide was also required to ensure good visibility. 1 In 1950 Gilbert 3 reported that the ventilation required

'to keep the atmosphere in the tunnels on the Pennsylvania turnpike clear and remove smoke generally limited

the carbon monoxide concentration to 100 parts per million (ppm). Griffieon in 19644 considered that the

capacity of the ventilation system was determined by smoke and visibility and not by carbon monoxide levels,

although carbon monoxide is still monitored for control purposes because visibility determinations are not

• standardised. Morgan et al (1965) 5 reinforce this view and state that although it is customary to design tunnel

ventilation systems to limit the carbon monoxide concentration to a maximum of 250 ppm in practice the

value is between 60 and 80 ppm because of the necessity to restrict haziness.

In the case of diesel engines Table 1 shows that oxides of nitrogen which have a corrosive effect on the

lungs requires the greatest dilution. A concentration of 100 ppm of these compounds has serious effects on

humans while 250 ppm is fatal after short periods. Diesel vehicles make up about 5 per cent of the vehicle

population in the United Kingdom, but their average annual mileage is about twice that of petrol vehicles.

Diesel vehicles would thus form about 10 per cent on average of the total traffic in a tunnel but the figure

could well be higher on routes carrying considerable commercial traffic. Exhaust emissions from diesel

powered vehicles vary considerably according to engine condition, but in view of existing legislation against

excessive smoke emission and the likelihood of its enforcement becoming stricter in the future, diesel traffic

need not be considered separately as far as tunnel ventilation is concerned.

The variation in volume of carbon monoxide emission from petrol engines is closely related to the work

being done by the vehicle. The data in Table 2 show the range of carbon monoxide emission from a variety

of vehicles under different conditions of use. Singstad 1 showed in 1929 that the carbon monoxide emission

increased by about 33 per cent when vehicles travelled up a 3½ per cent incline compared with travel on the

level. Since then gradients in tunnels have often been limited to about 4 per cent.

More recently Zulian and Bonforte 6, 1969, working on the design of the 2.7 km long Straight Creek

Tunnel at an elevation of 3,300 m above sea level in Colorado, showed that at high altitudes the effect of

slope on carbon monoxide emissions to be even more pronounced. For instance on a 3 per cent incline at

an elevation of 2,300 m the increase is about 150 per cent and at 3,000 m the increase was of the order of

400 per cent for the same gradient. At these altitudes the carbon monoxide emissions from vehicles travelling

on the level were some 100 to 300 per cent above those measured at sea level. This is due to lack of oxygen

at high altitudes leading to incomplete combustion in petrol engines and higher proportion of carbon monoxide

(CO) relative to carbon dioxide (CO2) in the exhaust gasses. While the increased carbon monoxide emissions

due to altitude are not very relevant in Great Britain the increases due to gradients could be very important

because of the more wide spread use of steep gradients particularly in urban situations.

Table 3 summarises measurements by Fussell 7 (1967) of the volume of carbon monoxide emitted from

25 British cars when tested on a Crypton-Heenan chassis dynamometer set up in accordance with the California

test procedure where the vehicles were put through the Californian driving cycle starting with their engines hot.

This driving cycle includes the gear changing and periods of idling considered typical of normal city driving

in that State. A driving cycle more appropriate to the smaller European engines is under consideration. The

values of emission given under conditions of the Californian driving cycle are thought to be slightly greater

than the values for cars travelling steadily at about 50 km/h as in a tunnel; in any case long tunnels may well

have traffic lights at intervals to regulate traffic flow, and the correspondence with the driving cycle could

then be even closer.

Hiruma 8 has stressed the need to take into account the distribution of vehicle types in traffic, when

assessing a value for the volume of carbon monoxide emitted per minute. The volume of carbon monoxide

emission from an idling engine is less than that from an engine travelling at normal speed and Morgan, et al 5

consider that conditions resulting from a traffic standstill would be no worse than normal traffic flow. This

would be true only intunnels ventilated mechanically by a system where the air flow is mainly indepedent

of the traffic flow, and where traffic signals prevent a great increase in the number of vehicles present in the

tunnel since the headway of vehicles reduces as they slow down and stop. A standstill of traffic would in

any case mean that drivers and passengers were exposed to fumes for a longer time.

Morgan, et al 5 assert that the carbon monoxide emission from an average vehicle fell by 50 per cent

between 1930 and 1940 because of improved engine design. It would therefore seem as well to disregard

earliest measurements in making an assumption for the average volume of carbon monoxide emitted per

vehicle per minute. Table 4 gives some of the more recent values of carbon monoxide emission which various

authorities have considered reasonable for designing tunnel ventilation systems in recent years. The wide

variation in the values adopted clearly reflects the paucity of data on emissions from road traffic.

Consideration has been given recently to the possibility of replacing the internal combustion engine

by other forms of power unit which produce little or no toxic fumes. The development of the zinc-air

battery makes electric traction feasible. There has also been renewed interest in the air cycle engine where

fuel oil is burnt in excess air, and in steam propulsion.

Emission of toxic gases is less from the gas turbine car than from conventional vehicles. These are

long-term developments and meanwhile effort has been directed by most vehicle manufacturers to the reduction

of the emission from the petrol engine. This may be achieved either by more efficient fuel injection to the

engine or by the use of an after burner.

3

Air pollution mainly due to car engines has become acute in regions of the USA, in particular in Los

Angeles, California where photo-chemical smog is now common. Regulations already apply in California to

limit the emission of toxic gases, 2.3 per cent for engines between 820 cc and 1640 cc capacity, to 2.0 per

cent for engines between 1640 cc and 2390 cc capacity, and to 1.5 per cent for engines over 2390 cc capacity.

Since the Muskie Bill in 1968 the Federal Government is applying similar regulations to the whole of the USA.

Present indications are that these will come into effect in 1975.

3. T H E P H Y S I O L O G I C A L EFFECTS OF C A R B O N iMIONOXIDI:. "

The poisonous effect of carbon monoxide was studied in 1856 by Claude Bernard, a French physiologist, who

showed that the gas replaced oxygen in the red corpuscles of the blood, and that it was held in a combined

state. A more precise account of the effect was given in 1895 by Haldane 9 who studied the physiological

effects of carbon monoxide quantitatively by noting the effects of concentration and time of exposure when

air containing the gas was inhaled by humans.

Carbon monoxide has an affinity for the haemoglobin of the blood, with which it combines to form

carboxyhaemoglobin (COHb), some 350 times that of oxygen. This means that a person inhaling air containing

the usual 21 per cent of oxygen but only 0.06 per cent (600 ppm) of carbon monoxide would, when equili-

brium was reached, have the haemoglobin of his blood shared equally between the two gases. The rate at

which this equilibrium is approached is governed by the respiration rate which determines the volume of CO

laden air passing through the lungs; thus the rate of build up of carboxyhaemoglobin in the ~o~od is con-

siderably slower in a man at rest than when he is working. The effects on the body are basically those ot a

shortage of oxygen but are not accompanied by an increased rate of breathing as would occur in the case of a

simple lack of oxygen. A person breathing carbon monoxide can therefore reach the fatal stage without being

aware of the danger.

Much experimental work has been carried out on the absorption of carbon monoxide by man. Recent

work by Lawther and Cumins (1970) 10 has shown that the relations for the rate of carbon monoxide absorp-

tion by normal men at sea level, presented in 1945 by Forbes and his colleagues 11 compares favourably with

observed blood levels in their measurements. Fig 1 shows the increase of COHb in the blood for a man engaged in

light activity (average respiration 9.5 litres air per minute and average pulse rate 80) provided that less than

10 per cent COHb was originally present in his blood; this is the most common condition of exposure to CO

in practice. Also included in Fig 1 are the COHb levels at which Spencer 12 indicates various symptoms

become apparent.

The complete average COHb uptake relations derived by Forbes et al 11 are presented in Fig 2. The

rate of CO uptake was found to vary considerably between individuals and diverged by as much as -+ 20 per

cent from the average relations shown. These uptake rates were in general lower than the average rates of

CO uptake reported previously. More accurate measurements of COHb content and making allowance for

the initial COHb in the blood of the subjects were considered to explain these discrepancies. There is general

agreement, however, on the equilibrium values reached at any CO concentration.

The permissible concentration of carbon monoxide in a tunnel clearly depends on the time for which

people are expected to be exposed and also on the energy they expend. In the case of the Holland tunnel

a maximum value of 400 ppm carbon monoxide was adopted which was then considered to allow for 45

minutes of exposure without physical effort. This provided a large margin of safety since no vehicle would

be expected to be in the tunnel for more than about 10 minutes. It made no allowance for situations where

tunnel operating staff would be permanefltly in the tunnel for an 8 hour shift.

4

Later tunnel designers have adopted lower maximum levels as in the case of the Clyde tunnel opened

in 1963 where it was decided that 250 ppm should not be exceeded at any time. Indeed, at the present time

100 ppm is used as a working maximum by the Clyde, Dartford, Mersey and Tyne operating authorities. At

this concentration it would appear from Fig 1 that staff are in no danger from CO poisoning when working

in the tunnel or dealing with traffic accidents. Indeed conditions are probably no worse than in London

streets in calm weather when maximum hourly average carbon monoxide concentrations can exceed 100 and

50 ppm respectively. 10

The older measurements of carbon monoxide in the blood were fairly coarse, and attention is being

paid increasingly to the effects of lower concentrations as improved methods of measurements allow greater

precision. Broadly, there are two effects to be considered one being the short term effect on mental alterness

and concentration and the other on the long-term effect on health. Considering the short-term, Cotes 13 in

1962 stated that blood in equilibrium with 100 ppm of carbon monoxide contains about 13 per cent carboxy O

haemoglobin. At this concentration a man is often incapable of taking correct decisions or performing skilled

tasks though superficially he may appear to be quite capable; 50 ppm will interfere with accurate visual

discrimination, and even 20 ppm, which can be the result of smoking one cigarette, causes greater impairment

than is accepted in aviation. There the deficiency of oxygen,,is"the volume of air breathed at altitudes above

1200 m has a similar physiological effect as low Concentration of CO and pilots are recommended to use

oxygen in unpressurised aircraft above this altitude.

More recently Lawther and Cuminins 10 state that the possible effects of the comparatively low degrees

of saturation with CO as a result of city traffic did not give cause for alarm as great as that caused by the

concentrations of COHb resulting from heavy smoking. In their future work attention will be given to the _

possible synergistic effects of CO, alcohol, hydrocarbons and drugs as well as the possibility of disproportionate

effects of CO on people with cardiac and respiratory disease.

The levels of carbon monoxide in city streets could be an important factor when considering vehicle

induced, portal to portal, ventilation for a road tunnel. Carbon monoxide levels of 30 to 50 ppm persisting

for periods of ½ to 1 hour are now common in American and British cities 10' 14 so that already fouled air

would be introduced into the tunnel and even fouler air would be expelled at the far end into what might

even be a busy intersection.

Although little is known of the long-term effects of low concentrations of the other pollutants emitted

by vehicles it is presently accepted that carbon monoxide is the dominant pollutant. Controlling its concen-

tration in.the tunnel atmosphere below an acceptable level by artificial or natural ventilation automatically

keeps the concentration of these other contaminants below currently acceptable levels.

4. THE TYPE OF VENTILATION SYSTEM

From the length of the tunnel the number of traffic lanes and the spacing of vehicles the maximum number

of vehicles in the tunnel can be found. Assuming an average value for emission of carbon monoxide per

vehicle and a value of dilution required, the total volume of air required to be introduced can be found.

Knowing the volume of air required ventilation systems can then be considered for that particular tunnel.

The possible types of system are :-

1. Natural ventilation

2. Traffic induced ventilation

3. A mechanical ventilation system which can be:

(a) A longitudinal system

(b) An upward semi-transverse system

(c) A lateral semi-transverse system

(d) An upward fully-transverse system

(e) A lateral fully-transverse system

(f) A unit blower system

4. Chemical air re-conditioning.

The principles of each method are described below giving the merits and dis-advantages of each with examples

where possible. The methods are not always distinct and combinations are possible and in some cases

inevitable.

4.1 Natural ventilation

A tunnel may be ventilated sufficiently by wind, a difference in air pressure between portal ends, and

possibly a slight convective or chimney effect. These natural conditions can seldom be relied upon except

for short tunnels or where the traffic is light. An unusual example is the 3140 m long Tenda Pass tunnel

between Turin and Nice in Italy which relies on the strong prevailing wind to provide ventilation; but here

traffic at about 600 vehicles per day is very light. Natural ventilation of tunnels with portals at different

elevations has been considered by Pellis 15 who examined theoretically the draught induced by air temperature

and pressure differences. This is basically a 'chimney' effect and although it is not usually possible to arrange

tunnel portals at different heights there may well be some situations in mountainous terrain where the effect

would be worth considering.

4.2 Traffic induced ventilation

Underground railways are ventilated mainly by the piston action of the trains in pushing air before

them along the tunnel. This 'piston effect ' can ventilate single direction road tunnels although the induced

air velocity is less with road vehicles which do not fit the tunnel as closely as trains. However, as the tunnel

diameter increases the rate of gain of air volume is marginally greater than the reduction of induced velocity

and results in the dilution of contaminants slightly increasing with tunnel size. Gurney and Butler 16, 17, 18

investigated the effect during the design stage of the 340 m long Crindau Tunnel to find out whether that

tunnel would be adequately ventilated by traffic induced airflow. The investigation consisted of model tests

using water in a 76 mrndiameter pipe, tests in air on models of the Crindau and Heathrow Airport passenger

tunnel and full-scale measurements on the Heathrow passenger tunnel. A formula was developed relating

the induced draught to vehicle speed and headway and to the dimensions and air flow characteristics of the

tunnel. From this a second formula was derived relating the carbon monoxide concentration to the previous

parameters and to the average exhaust emissions. Details of the formulae are given in the Appendix. The

conclusion was that the Crindau tunnel would be satisfactorily ventilated by traffic alone ie the carbon

monoxide concentration would not exceed 400 ppm and that tunnels up to about a kilometre long could be

expected to be adequately ventilated under all but the most arduous traffic conditions. It was found however

in the full-scale tests on the 630 m long Heathrow passenger tunnel that adverse winds could more than halve

the vehicle induced draught.

Fielder 19 working at the 1.9 km long Liberty tunnel, Pittsburgh, USA found that wind induced air

velocity and traffic induced air velocity can be added algebraically. Spencer 20 reports that in the 1.7 km long

Maas tunnel, Rotterdam traffic induced ventilation kept the carbon monoxide concentration below 50 ppm

when the traffic was 1,200 vehicles per hour. In the 1770 m long Velsen tunnel, also in the Netherlands, no

mechanical ventilation was required when the flow was 30,000 vehicles per day. When the traffic induced

ventilation is adequate for normal traffic conditions, fans are usually provided to cater for slow moving and

idling traffic and adverse wind conditions where the traffic flows are high.

A large proportion of road tunnels in the world rely on wind and traffic for ventilation. Generally,

they are not more than 1 km long and a high proportion that are over ½ km long are twin tube tunnels each

of which carries traffic in one direction only. Ventilation of this type is common in mountainous countries

like Japan, Norway and Italy, where, at the time of building the tunnels, traffic was very light. It will be

interesting to see if any of these tunnels are found to require the addition of artificial ventilation because

of increasing traffic. The 970 m long Del Pino and the 900 m long Dei Giovi tunnels in Italy carrying a

maximum of 26000 vehicles daily and 1600 vehicles per hour respectively 21 are situations well worth further

study.

4.3 Mechanical ventilation

4.3.1 Longitudinal system The simplest arrangement of this system is that installed in the Flughafen.

tunnel, Germany (Fig 3a) and is being considered for the proposed Thamesmead Tunnel in London. Small

reversible fans up to 1 m diameter are spaced throughout the length of the tunnel and fresh air is drawn in,

at one portal and expelled at the other. This system is relatively cheap and easy to install and is particularly

suitable for the shorter tunnels carrying traffic in one direction only where the 'piston effect' would assist

air flow.

A variant used in the Limfjord tunnel is shown in Fig 3b, where banks of reversible fans are mounted

centrally and can be used to move air in either direction thus taking advantage of traffic and wind induced

air flow.

The more common arrangement of the system is shown diagramatically in Fig 4(a). It has an exhaust

fan in a shaft at the centre of the tunnel and fresh air is drawn in along the traffic space from the portals.

This method is again relatively cheap, but the 'piston effect' in a one way tunnel may cancel the air flow in

one half of the tunnel. The modification in Fig 4(b) allows the shaft to be at the end of the tunnel if it

should not be convenient at the centre. Alternatively as shown in Fig 4(c) air is injected into the tunnel in the

same direction as the traffic flow. An arrangement which eliminates the cancelling of the 'piston effect'

resulting from the layouts in Fig 4 is illustrated in Fig 5(a). Here reversible air injectors have been fitted in

the shafts and are directed so that vehicle and wind induced air flow is enhanced. Fig 5(b) shows another

similar arrangement incorporating pairs of reversible fans in a single shaft.

7

Fig 6 shows an arrangement proposed for utilizing the principle of the Coanda effect to enable a single

shaft and blower to create air flow in either direction as required by traffic or external wind conditions. The

Coanda effect is the phenomenon in which the proximity of a surface to a jet stream will cause the jet to

attach to and follow the surface contour. The method is described by Nishimura 22 who carried out tests on

models. The system was said to be workable and attractive and was considered for a tunnel in Canada. The

jet stream would be directed by a nozzle that could swivel on to either Coanda surface so that air would flow

along the tunnel in the chosen direction. It was proposed that the jet would be directed automatically

according to the external wind and in a two-way tunnel according to the direction of the greater traffic flow.

Longitudinal ventilation systems are relatively cheap. However in long tunnels, particularly when traffic

is heavy, the quantity of fresh air required to dilute the noxious gases is so great that a high air velocity is

required; smoke spread in cases of fire in the down wind direction would be relatively greatest with this

system. At present one kilometre or so is considered the upper limit for the length of tunnels using longitudinal

ventilation. However, a long tunnel could be divided into sections each of which could be ventilated separately.

This approach was considered for the Holland tunnel but was rejected because of construction difficulties,

presumably in this case the installation of vertical shafts in the Hudson River; such problems arise only with

sub aqueous tunnels since access to the ground surface for fresh air would be much easier elsewhere. More

recently interest has been shown in Italy in longitudinal ventilation systems and such a system is to be installed

in the l0 Km long Gran Sasso d'Italia's tunnel on the L'Aquila-Adreatica motorway; 23 maximum average

longitudinal air velocities are about l0 m/sec.

4.3.2 Upward semi-transverse system. In this system fresh air is supplied to a duct under the road

deck and this air enters the tunnel through a series of slots located just above carriageway level. The vitiated

air is drawn longitudinally along the tunnel to exhaust shafts which extract air from the crown of the tunnel

(Fig 7). Up to the present maximum average air velocities in the unobstructed traffic space have ranged

upwards to about 8 m/sec. In the United Kingdom the amount of fresh air injected into recently constructed

tunnels has varied from about 6 to 12 m3/min/meter of lane. The higher value probably represents the uppet

requirements but values below 6 m3/min/meter of lane are encountered in tunnels in other countries under i

light traffic conditions.

The system is extensively used in circular tunnels and has been used for all the Mersey tunnels. Several

ventilation systems were compared by Haldane 24 (1936) by introducing a number of arrangement of ceiling

ducts and shafts into a 300 m long section of the first Mersey Tunnel; in the traffic space, petrol, bales of

straw and smoke candles were burned and steam was generated. It was found that smoke cleared more

quickly when the upward semi-transverse system was used and this was adopted.

Although most writers consider the fully-transverse system described later to be better, the upward semi-

transverse system makes maximum use of the traffic space in the tunnel for ventilation purposes and thus

economises on space, ducting and power. It is more expensive to install than the simpler longitudinal system

although the space below the carriageway can be used in a circular tunnel to provide the blowing duct. On

the other hand because the fresh air is introduced uniformly along the tunnel it is less affected by dense

traffic and adverse winds than the longitudinal system.

4.3.3 Lateral semi-transverse system In this system fresh air is fed into the traffic space through

slots in a blowing duct at one side of the tunnel (Fig 8). The vitiated air is pushed along the tunnel to the

portals. An example of the system is the 630 m long passenger tunnel at Heathrow Airport, London.

8

4.3.4 Upward fully-transverse system In this system fresh air is forced by blowing fans into a longi-

tudinal duct usually below the roadway. It passes into the traffic space through a series of slots just above

kerb level and is extracted through slots at ceiling level, into a second duct which conveys the vitiated air to

the exhaust shafts: The amount of fresh air introduced into the tunnels are similar to those in the semi-

transverse systems. The conventional form of this system is shown in Fig 9a where the tunnel has a circular

cross-section. Fig 9b shows the system as applied less usually to a tunnel of horse shoe cross section. Broer 25

who was concerned with the design of ventilation for the proposed Velsen tunnel, concluded on theoretical

grounds that the fully transverse system was more satisfactory than the semi-transverse.

By correct design and adjustment of the slots and ducts a regular flow of air across the tunnel can have

the same magnitude at all points along the tunnel, with only slight longitudinal flow induced by traffic. Ducts

are normally of constant area and tl~e size and/or spacing of the slots is varied to give a constant air velocity

through each and across the tunnel. An unusual method of achieving uniform ventilation was used in the

470 m long Durnstein tunnel in Austria. This tunnel, Fig 10, has a horse shoe section with three ducts at the

top; the adjustment for loss of pressure is made by varying the widths of the blowing and exhaust ducts.

4,3.5 Lateral fully-transverse system Here the fresh air is fed through slots from a duct at one side

of the traffic space and flows across the tunnel to be extracted through slots into an exhaust duct on the other

side of the roadway (Fig 12). The system is commonly used in rectangular shaped tunnels constructed by the

cut-and-cover and immersed tube methods; its use reduces the depth of the tunnel structure. An example of

the system is the North Sea Canal tunnel some 768 m long between portals at Velsen in the Netherlands.

There appears to be no great overall advantage or disadvantage compared with the upward transverse system

as, although the ducts in the lateral type are extra to the normal construction of the tunnel, they allow greater

freedom of design as regards shape.

4.3.6 Unit blower system A system in this category has a large number of separate small intake and:

possibly exhaust fans which are used to inject fresh air into and extract vitiated air from the traffic space:

Two examples are shown in Fig 12. .,

At the 640 m long tunnel under Battery Street, Seattle, which was opened in 1954, fresh air is drawn

into the traffic space through grilles in the footpath in Battery Street by 2.3 Kw (3 HP) helicoid fans of 1 m

diameter; each of the two tubes of the tunnel contains 36 such fans. Vitiated air flows out through grilles

set in the central reservation in Battery Street (Fig 12(a)). In a test with 200 cars stopped with engines

running in the tunnel the carbon monoxide concentration was kept at about 200 ppm while the level in the

street above was less than 100 ppm. There appears to be no trouble from recirculation of the fouled air.

Exhaust fans were considered instead of intake fans as these would clear smoke more quickly especially in

the case of fire,but mixing would be far less efficient. It was estimated before building that in this particular

site, this system would cost considerably less than a conventional transverse or longitudinal system.

Another variant of this arrangement is used on the central 200 m of the tunnel under the Avenue

Louise in Brussels (Fig 12(b)). Here fresh air enters a longitudinal trough measuring 2 m by 1.8 m through a

continuous grating 0.3 m wide at surface level. Seventeen 1.5 kw electric fans pump the air from this trough

into the tunnel through grilles above kerb level, while the vitiated air is extracted by seventeen similar fans

into a duct through grilles located just below ceiling level on the opposite side of the tunnel. The fouled

air passes to the atomosphere - through four 5 m by 3 m gratings situated at convenient locations at the

surface. The system was designed for a traffic flow of 8000 vehicles per hour including 20 per cent commercial

vehicles and a maximum carbon monoxide concentration of 400 ppm. In the event the capacity of the

ventilation system provided was about 11 times that required to maintain this CO concentration at the

designed traffic flow.

The large number of fan units in the system spreads the risk of breakdown and reduces standby require-

ments considerably. The fan units are simple and can be serviced and replaced from the street above. The

degree of ventilation can be finely controlled by switching individual fans on or off.

4.4 Chemical air reconditioning

Although chemical air reconditioning methods are available such systems have not so far been used in

road tunnels. An air regeneration unit capable of purifying some 5000 m 3 air per hour has been described

in outline by de Oran 26 who suggested using 1400 such units each controlled by a pollution detector in the

5,900 m long Great St Bernard tunnel linking France and Italy.

Capital and running costs were not given but it was stated that the use of such units instead of a trans-

verse ventilation system would reduce the cross-sectional area of the tunnel by 35 per cent. Examination of

the data shows the maximum power demand of the proposed system to be of the order of 1750 kw per 2-lane

kilometre some 10-15 times greater than conventional ventilation systems; at peak load the system would

also use "depurating liquid" at a rate of 1¼ million litres per hour. With the present value of the cost of

power consumption for ventilation and lighting over 50 years commonly representing some 2 - 5 per cent of the

construction costs it is clear that the cost of power alone for the chemical regeneration units could more

than offset any reductions in construction costs stemming from reducing the' tunnel cross-section.

5. THE DESIGN OF DUCTS AND VENTS

5.1. Quantity of air and pressure

Long, heavily trafficked tunnels have usually been ventilated by transverse systems, and for this reason

the design of these systems has been considered in greater detail than the design of other systems.

The quantity of fresh air to be introduced into the tunnel to maintain the carbon monoxide concentra-

tion below a chosen value is readily calculated, as described earlier, although the answer may be imprecise

because of the assumptions made on exhaust emissions and traffic density. It is tl~en necessary to calculate

the pressure at which the fans must deliver the air to the duct, taking tinto account that air should pass

through each slot in the duct at a uniform rate while the air velocity falls from a maximum at the fan to zero

at the far end of the duct. The pressure required at the fans is a function of the square of the air velocity,

the length and cross-section of the duct and a dimensionless friction factor related to the shape and dimensions

of the duct.

Singstad 1 gave formulae for the pressure drop in the case of a duct passing air at a uniform rate and

for the friction factor; thse relations were used to design the ventilation in the Holland tunnel.

More recently comprehensive measurements in the First Mersey Tunnel by Pursall 196427 have shown

that for ducts unobstructed by pillars, pipes, cables and their supports the actual friction factor was given by

the expression

f = 1 I___~_ 1 0"4

42r c 10

where r c is the radius of a circle of area equal to that of the duct = ~ / n and m is the hydraulic mean

radius = area/perimeter.

Where the duct is obstructed some allowance must be made for turbulence and shock losses which

effectively increase the friction losses. For example friction losses in the blowing duct in a Branch Tunnel

were almost 45 per cent higher than predicted by the above formula due to the presence of a line of pillars

down the centre of the duct. Pursal128 also derives formulae for calculating the slot areas required in a duct

to give uniform flow across the tunnel and gives worked examples of typical cases. Codegone 29, 30 has also

given formulae for duct pressures and slot areas.

The design of ducts and slots has been studied on a model scale by the British Hydromechanics Research

Association in connection with the proposed 2150 m long tunnel section of the Northumberland Strait crossing

in Canada. This tunnel is to be ventilated transversely using a central railway, tunnel as the exhaust duct for

the two roadway tubes.

5.2 Sectionalising long tunnels

There is an economic limit to the length of duct and tunnel which can be ventilated from one fan or

ventilation station. Ducts are expensive tO construct and in a circular tunnel the area of duct is normally

restricted to the segments cut off by the roadway and the ceiling. For a constant area of duct supplying a

constant volume of air per unit length of tunnel the power required at the fan increases as the fourth power

of the length of duct, thus imposing a limit on the length it is feasible to ventilate from one station with,

reasonable efficiency.

Kiavath 31 suggests an upper limit for air velocity of about 900 m per minute in ducts andconsiders

that a galvanised sheet iron lining to reduce friction is justified when the value exceeds 1200 m per minute.

The maximum distance between ventilation stations is therefore limited and controlled by a number

of factors. Atkinson et a132 suggested a maximum of about 900 roof duct on each side of a ventilation

station for a four lane tunnel using currently available equipment, that is about 1800 m between stationL

For two-lane roadways the practical maximum spacing of ventilation stations would at present be of the order

of 4 km; any reductions in the-level of toxic emissions from motor vehicles would, increase this value.

6. AUTOMATICCONTROLS

Many writers have stressed the importance of controls as the most important factor in reducing costs. Most

important is the measurement and recording of carbon monoxide concentration at various points in the tunnel,

and use of the measured signal to control the degree of ventilation by adjusting fan speeds or switching

individual fans on or off." The control of fan speed is recognised as an essential feature of a ventilation installa-

tion. The Queens Midtown 33 tunnel in New York was found to require only 0.111 kWhr per vehicle compared

with 0.529 kWhr per vehicle in the Holland tunnel. The difference was attributed to the fact that the fans

in the Queens Midtown tunnel could be regulated down to,20 per cent of their maximum speed, whereas

the fans in the Holland tunnel could be controlled only to 29.5 per cent.

Obscurity caused by the smoke or haze is measured with an optical system. The electrical output from

a photocell depends on the opacity of the air between it and a standard light source. The electrical signal

from the photocell may be fed to the same instrument as the carbon monoxide detector. Fog is not observed

in tunnels of any length but could be a problem at portals. 11

The traffic entering and leaving the tunnel is usually counted automatically. When the difference

between the two shows an excessive number of vehicles in the tunnel, traffic lights may be operated to stop

more vehicles entering the tunnel. When these traffic lights are installed they will also be arranged to be

operated by the carbon monoxide and visibility recorders when dangerous conditions arise in the tunnel, by

fire alarms, and manually in the case of accidents. The whole system is backed up by observation of the

tunnel traffic on closed circuit television.

6.1 Carbon monoxide analysers

There are many methods of measuring carbon monoxide, but only the Hopcalite and the Infra-Red

gas analysers are suitable for continuous measurements in tunnels. Both types are in use but preference is

now being given to the infra-red method as the Hopcalite analyser is bulky. Details of each are given below.

6.1.1 T h e Hopca l i t e ana lyse r The principle of this instrument was devised by Katz and is long

established. It consists of measuring the rise in temperature when a stream of air containing carbon monoxide

is passed through Hopcalite at 100°C. Hopcalite is a catalyst composed of a specially prepared mixture of

manganese dioxide and cupric oxide. At this temperature the Hopcalite promotes the Oxidation of the carbon

monoxide, giving a temperature rise directly proportional to the concentration of carbon monoxide in the

sample of air. The detector unit is shown in Fig 13. It consists of an enclosure, thermostatically controlled

at about 100°C, containing the detector cell and a heat exchanger. The heat exchanger raises the temperature

of the incoming air to that of the detector cell. This latter component contains the Hopcalite and a differential

resistance thermometer which measures the rise in gas temperature due to the heat evolved during the oxidation

of the carbon monoxide. The sample air is drawn from the tunnel by a diaphragm pump through a flow

gauge, and a series of filters which remove moisture, hydrocarbons and carbon dioxide. The Hopcalite needs

to be changed once a year.

6.1.2 The Infra-Red Gas Analyser This instrument is widely used and is shown schematically in Fig 14.

It depends on the selective absorption of infra-red radiation by a gas. An infra-red beam is split into two equal

beams which are then simultaneously chopped mechanically by a rotating vane at about 7 times per second.

One beam passes through a reference cell of non-absorbing gas and the other equal beam through the analysis

cell which contains the sample air. The radiation from each cell then passes through one of the absorption

chambers of the Luft detector. This consists of two sealed chambers filled with the gas of interest - in this

case carbon monoxide - and separated by a flexible diaphragm which forms one plate of a differential

capacitor. The other plates of the capacitor, one on each side of the separating plate, are perforated. If the

sample passing through the analysis cell contains carbon monoxide, energy is absorbed in the bands typical

of that gas. Hence less energy will be availabe to be absorbed in that half of the Luft detector and an imbalance

of temperature and therefore pressure will result. The central capacitor plate responds to 7 cycle/second varia-

tion on which is superimposed a variation of amplitude due to the concentration of carbon monoxide in the

analysis cell. The variation of capacity is used to give a waveform which can be amplified by a stable.AC

amplifier and used to operate a recorder.

7. CONCLUSIONS

This paper has outlined the ventilation systems and techniques that have developed up to the present for

use in road tunnels together with some of the more important research that has been carried out. In the

main the emphasis has been on the transverse and semi-transverse systems but in recent years increasing

interest has been shown in longitudinal and unit blower systems; this trend is likely to continue with the

increasing use of road tunnels in urban areas.

12

Much of the research and development on tunnel ventilation up to the present has to a large extent

been piecemeal and restricted. Even so experienced tunnels designers have been able to produce ventilation

systems which have coped adequately with vehicular pollutants and maintained safe conditions within the

tunnel. However there are questions to which the answers are still imprecise and where knowledge is deficient.

More information is required particularly on the following:-

7.1 Tolerable concentration of carbon monoxide and other pollutants

Although carbon monoxide is probably the chief hazard, it is possible that smoke and lack of visibility

are of comparable importance and the relative importance of these dangers should be established. There is

considerable variation in the maximum concentration of carbon monoxide, and the length of exposure, which

different designers have assumed to be safe when providing ventilation in tunnels; for tunnels built since

1945 maximum carbon monoxide concentration values have varied from 80 to 400 ppm.

7.2 Emission of carbon monoxide from motor vehicles

Various figures for exhaust emission from vehicles are quoted by different authorities. Further measure-

ments are required of exhaust emission from modern vehicles, taking into account trends in vehicle design,

and considering the effects of existing and possible future legislation in this country and abroad to limit these

emissions. The carbon monoxide emission, speed, gradient and vehicle headway relations need thorough

investigation.

7.3 Choice of ventilation system

It has hitehrto been accepted that long tunnels which are heavily trafficked are best ventilated by a

fully or semi-transverse systems. This may have arisen because most early tunnels were built under rivers,

estuaries or mountains where ventilation shafts at intervals along the tunnel were generally precluded by the

physical circumstances or their high cost. In urban areas where much of the future demand for road tunnels

in this country will lie the choice of ventilation system is not so constrained. In these situations access to the

ground~surface at intervals for supplies of fresh air would generally not present great problems. Unit blowers

or sectionalised longitudinal ventilation systems and developments of these simpler methods would merit

close study.

Finally there is a need also for all findings and standards on road tunnel ventilation to be collated by

a single body which would co-ordinate the research effort and ensure no significant factors were overlooked.

In the long term the objective would be to produce standards and a code of practice for the ventilation of road

tunnels.

8. REFERENCES

1.

2.

SINGSTAD, OLE. Ventilation of vehicular tunnels. Work Engineering Congress Paper 339 Tokyo

1929. L

STAHEL, M, ACKERET, J AND HAERTER, A. Die Luftung der Autotunnel. Mitteilung, Nr. 10

Institut for Strassenbau. Bidg. Techn. Mochschule, Zurich. 1960.

3. GILBERT, G B. Ventilation and control of carbon monoxide in Pennsylvania turnpike tunnels.

Highway Builder, October, 1950.

13

4.

5.

.

7.

.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

"i4

GRIFFIEON, A. Road structures. Wegen 1964 38 (1), (2).

MORGAN, H D, C K HASWELL, E S PIRIE. Clyde tunnel; design, construction and tunnel services.

Proc. 1.C.E. 1965 February.

ZULIAN, A and G A BONFORTE. High altitude multiple vehicle emission tests. Journal of the

Sanitary Engineering Division, Proc. Am. Soc. C.E. August 1967.

FUSSELL, D. R. (Esso Petroleum Co Ltd) Report on the measurement of exhaust volumes etc from

typical British cars tested by the Californian cycle. J. Inst. Pet. Vol. 53 p 251 July 1967.

HIRUMA, Y. New method of calculating required air volumes of vehicular tunnels. Annual report of

roads 1962. Japan Road Association. Tokyo 1962 (in English)

HALDANE, J S. The action of carbolic oxide on man. J Physiology 18:430-462, 1895.

LAWTHER, P J and B T COMMINS. Cigarette smoking and exposure to carbon monoxide. Annals of

the New York Academy of Sciences 174, (1), 135-147. October 1970.

FORBES, W H, F SARGENT and F J W ROUGHTON. The rate of carbon monoxide uptake by normal

men. American J Physiol. 143: 594-608, 1945.

SPENCER, T D. Effects of Carbon Monoxide on man and canaries. The Annals of Occupational Hygiene.

1962. Vol 5 Oct-Dec.

COTES, J E. Effects of carbon monoxide on man and canaries (discussion) The Annals of Occupational

Hygiene 1962 Vol 5. Oct-Dec.

LUDWIG, J N. Progress in control of vehicle emission. Journal of the Sanitary Engineering Division,

Proc. Am. Soc. Civil Engineers, August 1967.

PELLIS, P. Limits of the length of road tunnels in terms of the possibility of natural ventilation:

Anno XXIV - n.5 Luglio-Agosto 1959.

GURNEY, C and L H BUTLER. Self-induced ventilation of road tunnels. Engineer, London 1960

209 (5448).

BUTLER, L H. Laboratory air-model tests on road tunnel ventilation. Mechanical Engineering Research

Laboratory (National Engineering Laboratory) Fluids report No 64 January, 1958.

BUTLER, L H. Investigation of induced road-tunnel ventilation. Mechanical Engineering Research

Laboratory (National Engineering Laboratory) Fluids Report No 72 December 1958.

FIELDER, C. Natural ventilation of the Liberty tunnel. Engineering News Record, New York, Vol.

93, 1924.

SPENCER, E A. Visit to continental road tunnels. Mechanical Engineering Research Laboratory (N.E.L.)

Fluids Report No 20 1954 East Kilbride, Glasgow.

21. PERMANENT INTERNATIONAL ASSOCIATION OF ROAD CONGRESSES XIIIth World Congress

Tokyo 1967. Road Tunnels Committee Documentation and Studies.

22. NISHIMURA, Y. Application of a jet pump and Coanda surface to ventilation of a highway tunnel.

Institute for Aerospace Studies, University of Toronto. Technical Note No 82, February 1965.

23. SOCIETA' INIZIATIVE NAZIONALI AUTOSTRADALI SINA S.p.A - ROME - MILAN. Longitudinal

tunnel ventilation. Theoretical basis, studies and applications.

24. HALDANE, J S. The ventilation of tunnels. JIHVE 1936 4 (37). 18-41.

25. BROER, L J F. On the theory of the ventilation of ~ traffic tunnels. Applied Scientific Research,

Section A. The Hague 1956 6 (1).

26. DE ORAN, M A. Air regeneration for tunnels. Consulting Engineer, London 1965. 28 (2).

27. PURSALL, B R. The theoretical and practical determination of friction factors for vehicular ventilation

ducts. Journal of Heating and Ventilating Engineers, February 1964.

28. PURSALL, B R. Theoretical and practical aspects of slot ventilation in connection with vehicular

road tunnels. Journal of Heating and Ventilating Engineers, July 1963.

29. CODEGONE, C. Distribution of air in highway tunnels. Ingegneria Ferrovia 1952 6 (11).

30. CODEGONE, C. Flow in long ventilation ducts for road tunnels. Termotecnia 1961 15 (11).

31. KRAVATH, F F. Methods of ventilating vehicular tunnels. Heating and Ventilating 38 (9) (10) (11).

32. ATKINSON, F S, B R PURSALL and I C F STATAM. Ventilation of vehicular tunnels. Journal of'

Institute of Heating and Ventilating Engineers September 1962.

33. ANON. The Queens Midtown tunnel: discussion on ventilation. Proc. Am. Soc. Civil Engineers

1943 69 (7).

34. FIELDNER - YANDELL AND OTHERS. Ventilation of vehicular tunnels "Report of US Bureau of

Mines New York for the New York State Bridge and Tunnel Commission. 1927.

35. ANDREAE, C. Zur Frage der Luftung Langer Autotunnel "Schweiz Baustg" Bdll S 225-249.

36. PERMANENT INTERNATIONAL ASSOCIATION OF ROAD CONGRESSES XIIth World Congress

Rome 1964. Road Tunnels Committee Documentation and studies.

37. SALZWEDEL, W. Garage and Tunnel Ventilation. Gesundheitsingenieur 82 1961.

38. LANE, A F. Ventilation of road and street tunnels. JIHVE May 1957.

1 5

9. APPENDIX

Traffic induced ventilation in a one-way road tunnel.

The vehicle induced draught and the carbon monoxide concentration can be estimated using the two

formulae below obtained from MERL Report No 64.17

(a) Induced Air Draught:

u

v = - C 1 1 k A t +Ct Pt L

1 / "4 C v A v L

(b) Carbon Monoxide level: (parts in 1,000,000)

s A t C v A v L

k A t +Ct Pt L u - C 1 +

C v A v L

106

where:

At

Av

Cl

Ct

Cv

k

L

Pt

s

u

Cross-sectional area of tunnel - m 2

Vehicle frontal area - m 2

Velocity correction constant - small enough (6 to 12 m/min) to be usually ignored

Tunnel wall drag coefficient. (In the order of 0.0155)

Vehicle drag coefficient. (In the order of 0.5 fo r light vehicles and 1.0 for heavy vehicles.)

End loss coefficient - 1 for sharp entry and exit, but may be less with profiled entry and exit

Length of tunnel - m

Perimeter of tunnel - m

Vehicle spacing - tunnel length/number of vehicles in tunnel, as an approximation in the case

of a non-uniformly distributed traffic - m

Vehicle speed (average) - m/min

16

v Induced air draught - m/min

x Carbon monoxide level in parts per million

ec Carbon monoxide discharge factor.

The following variables compared favourably with experimental results.

for cars = 2-25 m 2, also one heavy vehicle is equa ! to 6 cars.

C t can be taken as 0.0155

C v for cars = 0.8

k = 1 (or less)

cc : light vehicles can be taken as .169 x 10 -4

medium vehicles can be taken as .258 x 10 --4

heavy vehicles can be taken as .43 x 10 ..4

m3/min

m3/min

m3/min

17

T A B L E 1

The dilution required for the various contaminants emitted from vehicle exhausts

(After Stahal et al 2)

Contaminant

PETROL ENGINES

Carbon Monoxide

Carbon Dioxide

Aldehydes

Formaldehyde

Oxides of Nitrogen

Sulphur Dioxide

DIESEL ENGINES

Carbon Monoxide (Normally)

Carbon Monoxide (Unfavourable conditions)

Carbon dioxide

Concentration in Undiluted Exhaust ppm

30,000

132,000

40

7

600

60

200

1 , 0 0 0

90,000

Acceptable concentration in Tunnel ppm

100

5,000

5

5

5

10

100

100

5,000

Aldehydes

Formaldehyde

Oxides of Nitrogen

Sulphur Dioxide

20

11

400

200

5

5

5

10

Dilution required

300

26

8

1.4

120

6

10

18

4

2.2

80

• 20

1 8

TABLE 2

Carbon monoxide emission per petrol driven vehicle according to vehicle type, engine condition and speed

Source of Information

Bureau of Mines USA 192734

Andreae, Switzerland 193835

NEL Fluids Report No 64 from MOT unpublished report 1947

French authorities based at Lyons 1961-221

Volume of CO emitted

m3/min

0.0405 0.0558

0.0062 0.0161 0.0258 0.0125 0.0323 0.0515 0.0207 0.0535 0.0838

0.0142 0.0283 0.0473 0.0615 0.O235 0.0473 0.0707 0.0943 0 . 0 3 7 6 0.0756 0.1133 0.1510

0.0178

Vehicles and conditions

Cars on level at 24 km/h Trucks 2 - 5 tons on level at 24 km/h

Cars 16 km/h 6.4 km/1 Good " " " Average . . . . . . Bad

Lorry 16 km/h 3.3 km/1 Good " " " Average . . . . . . Bad

Lorry 16 km/h 2.0 km/1 Good '~ . . . . Average . . . . . . . Bad

• Light vehicles 16 km/h . . . . . . 32 km/h . . . . . . 48 km/h . . . . . . 64 km/h

Medium vehicles 16 km/h . . . . 32 km/h . . . . 48 km/h . . . . 64 km/h

Heavy Vehicles 16 km/h . . . . 32 km/h . . . . 48 km/h . . . . 64 km/h

Mean value found in six tunnels by dividing total CO collected by

. No of vehicles at mean speed of 36 km/h

"19

TABLE 3

Carbon monoxide emission from vehicles operated on the Californian driving cycle with engines hot and in correct adjustment. (After Fussell 7)

Engine Capacity CC

88O

1060

1100

1150

1500

1500

1590

1660

1730

1730

1730

1800

Volume of CO Emitted

m3/min

Engine Capacity CC.

0.0138

0.00792

0.0079

0.0133

0.0029

0.020

0.0167

0.015

0.0113

0.0195

0.0065

0.013

1980

2000

2140

2490

2550

2910

2970

3000

3300

3910

4240

4240

6230

Volume of CO Emitted

m3/min

0.0118

0.0215

0.01415

0.026

0.020

0.034

0.0325

0.0150

0.00792

0.0164

0.032

0.0167

0.037

, Mean CO emission 0.0176 m3/min

20

TABLE 4

Values of average carbon monoxide emission per vehicle assumed by recent authorities

Authority

Morgan, Haswell and Pirie 5 1965

Atkinson 32 1962

Ramel quoting a Swiss Expert Committee 36 1959

Salzwede137 1957

Lane 38

quoting an American formula 1957

Lane 38

quoting a British formula 1957

Volume of Co emitted

M3/min

0.0353

0.0424.

0.0311

0.0167

0.0594

0.0504

21

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placed central ly

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(b) Example:- Limfjord tunnel Denmark 5 5 3 m

Fig. 3 LONGITUDINAL SYSTEMS USING FANS MOUNTED IN TUNNEL

~ Exhaust fans

/ / / / / 7 / \

/ /

/

/ / / / / Example :- St Cloud tunnel

Paris, France 819m

(o) C e n t r a l shaf t a r r a n g e m e n t

|

./-E/x ha ust fans

/ / - . .

/ / / / " / / Example :- S t rand underpass

London, England 5 3 4 m

(b) Shaf t at one end

/ /

Single d i rec t ion t r a f f i c (Bo th tunnels fed f r o m same v e n t i l a t i o n s t a t i o n )

Example :- Gt Char les S t ree t , (Twin tunne ls ) B i rmingham, England 5 5 0 m

(c) Air i n j ec ted into c e n t r e of tunnel

Fig. l.. BASIC LONGITUDINAL SYSTEMS

[~ ~ V e n

~ Rever

t i lotion shaf~t ~ ~ ~ ~ ~ ~ ~

s iblc oi r inJ'e

Direction of traff ic assisting air flow

Example Rendsburg tunnel, Germany twin one-way tunnels G40m

(a) Longitudinal system with reversible air injection

Reversible fans

t " Example: L iberty tunnel Pittsburgh, USA 1900m

(b) Longitudinal system using two fans in a single shaft

Fi9.5. LONGIIUOINAL SYSTEMS WITH REVERSIBLE AIR FLOW

~ Air supply duct

\ '~/I assisting flow Coanda s u r f a c e s ~ \ ~ S w i v e l nozzle: for reversing

, \ \ \ \ \

\ \ \ \ \ \ \ \ \ \~ ) Direction of induced vent i lat ion is dependent on traff ic and e x t e r n a l wind pressures, it can oppose traff ic

Proposal for tunnel at Ontar io, Canada-which was not built

Fig. 6. LONGITUDINAL SYSTEM USING COANOA SURFACES

p

Ventilation sh : ~

' I funnel I Section through ventilation building

Example-second Mersey tunnel, Liverpool, England 2 200m

Fresh air duct

Fresh a i r - - duct

Section through tunnel

County borough Ventilation Ventilation City of of Wa!lasey building building Liverpool

~ ~ R i v e r M e ~

1 ~ n 30

Longitudinal section of tunnel

Fig. 7. UPWARD SEMI TRANSVERSE SYSTEM

Cyclists and pedest r ians

tunnel

i

rash duct

7 . 9 0 m

E Main vehicle 0o

tunnel

T Services duct

f f '

Louvred g r i l l s Example:- Heathrow a i rpo r t passenger tunnel England 6 2 8 m

Fig. 8 LATERAL SEMI-TRANSVERSE SYSTEM

E x a m p l e : - Ho l land tunne l N.Y.U.S.A. 2 5 4 0 m

(a) In a c i rcu la r tunnel

E x a m p l e ' - Great St. Bernard S w i t z e r l a n d - I ta ly 5 6 9 0 m

( b ) In a ho rseshoe tunnel

Fig.9 UPWARD FULLY-TRANSVERSE SYSTEMS

Section A-A

Plan view of ducts

Section B-B

Axial fans.~

I

- - -B [ -~A

~ Inlet

Exhaust

Inlet

L~B

Example :-DLirnstein tunnel Austria 472m

Fig. 10. FULLY TRANSVERSE SYSTEM WITH VARYING OUCT AREAS

32.47m

E o

E x a m p l e :- Velsen tunne l N e t h e r l a n d s 7 G g m

Fig. 11. LATERAL FULLY-TRANSVERSE SYSTEM

Fa ns

Ro

[ In et

I49m II Ex,oos, gr,,, ° /

Building

level

7-5m

(a) Venti lat ion system in battery street tunnel Seattle USA G40m

Four occasional grilles

• ~ Stole t Fresh • \ air. t air

Duct

/ C o n t i n u o u s ~ 30cm grille

~_-~--- Trough

(b) Venti lat ion system in central section of tunnel under Avenue Louise,

Brussels Belgium 200m

Fig. 12. UNIT BLOWER SYSTEMS

Air outlet.

Air inlet

Temperoture sensing element

Differential resistance thermometers

Thermal i n s u l o t i o n ~

~-~lZlectrical connections to cell

Hdat exchanger

Analysing cell

Heating mat

Thermometer

Fig.13 HOPCALITE (KATZ) CARBON MONOXIDE ANALYSER

Analysis cell

L E

Infra-- red source

I

Z W i n d o w s ,

f

Rotating shutter

Reference cell

Luft d e t e c t o r

RF

unit

ndicator and

r e c o r d e r output

Signal ampl i f ier

Fig. l~. INFRA-REO GAS ANALYSER

(781) Dd891796 3,500 6/'/2 HPLtd., So'ton G1915 P R I N T E D IN E N G L A N D

ABSTRACT

A review of methods of ventilating road tunnels: H J HIGNETT, CEng, MIMechE, AMIED and L HOGBIN: Department of the Environment, TRRL Report LR 477: Crowthorne, 1972 (Transport and Road Research Laboratory). This paper reviews ventilation require- ments for road tunnels and describes the ventilation systems currently available. The areas where present knowledge is deficient are identified and recommendations are made for future research and the production of standards for road tunnel ventilation.

ABSTRACT

A review of methods of ventilating road tunnels: H J HIGNETT, CEng, MIMechE, AMIED and L HOGBIN: Department of the Environment, TRRL Report LR 477: Crowthorne, 1972 (Transport and Road Research Laboratory). This paper reviews ventilation require- ments for road tunnels and describes the ventilation systems currently available. The areas where present knowledge is deficient are identified and recommendations are made for future research and the production of standards for road tunnel ventilation.