fluctuating atmospheric pressures · fluctuating atmospheric pressures a novel environmental...

FLUCTUATING ATMOSPHERIC PRESSURESA NOVEL ENVIRONMENTAL VARIANT

OBSERVED IN SUBMARINESBY

F. P. ELLISFrom the Royal Navy

(RECEIVED FOR PUBLICATION, JUNE, 1948)

The need has been stressed in recent years forrelating the design- of fighting equipment to thephysiological characteristics of the men who mustbe responsible eventually for its operation, as wellas to its mechanical efficiency. Changes in environ-ment may also affect mental or physical performanceof a given task or interfere in other ways withphysical well-being. The most widely knownexample is probably that of the airman, who hasto contend with rarefied atmospheres, high accelera-tions, and sudden fluctuations in atmosphericpressure or in the thermal conditions to which heis exposed. The study of aviation medicine andphysiology has arisen from the dual needs fordesigning aviation equipment and aircraft to meetthe physical and physiological requirements andlimitations of the air crew, and for selecting andtraining air crew to combat effectively the environ-mental stresses to which they are exposed.The changes in environment encountered in

submarines are of less violent degree, but in thepast, nevertheless, certain avoidable hardships havebeen accepted as part of the day's work by thesubmarine sailor, and the need for providing himwith an optimal environment is still less generallyappreciated than in the case of air crew. Theintroduction of the "',snort" or "schnorkel" toBritish submarines, to which references were madein both Houses on March 8, 1948, and in the pressfollowing the tropical and arctic cruises of H.M.Submarines Alliance and Ambutsh, led to a reviewby the Adrmiiralty of the human factors which arerelated to the design and operation of modemsubmarines.

Continuous underwater activity was limited untilcomparatively recently by the capacity of thebatteries to drive the motors which propelled thesubmarine underwater, and by the ability of thecrew to remain efficient in an atmosphere whichwas steadily depleted of oxygen and to which carbondioxide was constantly added by the respiratory

processes of the crew. -The batteries were chargedat intervals by running the diesel engines with thesubmarine proceeding on the surface, an unhealthyprocedure in close proximity to the enemy. Thecontrol of the latter factor was achieved duringlong dives by releasing oxygen when necessary fromcylinders or generators, and by removing carbondioxide with chemical absorbents.The Netherlands Navy made a considerable

advance just before the 1939-45 war when theyfitted to their submarines a hollow extensible mastwhich enabled air for the engines to be conveyedto the submarine whilst it lay submerged, so thatthe batteries could be charged without obviouslydisclosing the whereabouts of the submarine. Thisidea was further developed by the Germans afterthey captured Dutch submarines in the invasion ofHolland, and during the last two years of the warit was incorporated in U-boat design in the formof the " schnorkel," to enable operations to becontinued in the face of steadily increasing opposi-tion from Allied air and surface craft equipped withradar. The device proved successful; not onlycould the batteries be charged in greater safety thanpreviously, but useful underwater speeds were

achieved as well. The use of the "schnorkel " inBritish submarines was investigated in the earlyyears of the war, but the idea was temporarilyshelved, and then tried again in 1944.The German " schnorkel " or British " snort"

consists of a hollow mast which can be raised orlowered and connects the interior of a submergedsubmarine with the ambient air above the surfaceof the sea. Flooding of the submarine is preventedby a float-operated valve at the upper end of themast. The mast contains an induction pipe throughwhich air is drawn into the submarine, -and an

exhaust pipe through which the exhaust gases passto an outlet a few feet below the inlet to theschnorkel induction, where the gases bubble outbelow the surface of the sea.

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ATMOSPHERIC PRESSURES IN SUBMARINES 2

The resistance offered by the long narrow induc-tion pipe to the heavy fresh air requirements of theengines causes a depression of the pressure withinthe submarine to varying degrees below one atmo-sphere when the engines are running. The extentof this depression varies in relation to the totalrevolutions registered by the two main engines,irrespective of whether the engines are being usedto charge the batteries, to propel the submarine, orfor both purposes. Fluctuations in the internalpressure are related to the state of the sea and swell,which in choppy or rough weather may occlude theair inlet temporarily with water shipped in-boardor may close the float valve for short periods duringwhich the engines draw upon the air in the submarinefor their requirements; and tQ the skill of the menand the efficiency of the equipment which maintainthe submarine at a constant depth beneath thesurface when snorting and so keep the snort inletabove water.An opportunity for examining the nature of the

pressure variations and certain related chemicalchanges in the atmosphere arose during an early" snorting " cruise in temperate waters in a Britishsubmarine, which proceeded on the main enginesand the snort by day, and at greater depths on themotors with the snort lowered in the hours ofdarkness.

Pressure MeasurementsThe tracings shown in fig. 1 were selected from records

made during approximately 400 hours snorting withthree barographs which furnished 9-inch horizontaltracings of the pressure variations over 7-day, 10-hour,and 2-hour periods respectively. On each " 7-daytracing " the corresponding total engine revolutions areindicated, and the average state of the sea and swell forthe period under review is shown by the Douglas Scaleas estimated through the periscope by the officer of thewatch. (See footnote to fig. 1.)

In fig. 3 pressure fluctuations of unusual severityrecorded early on in the trial are shown on a tracingfrom the "2-hour" barograph, and by two tracingsfrom a large barograph which recorded pressure changesover a" 10-minute " period.In order to avoid confusion which might arise from

the various terms in use for describing pressures, suchas millibars, millimetres of mercury, inches of mercury,or pounds per square inch, the pressure changes areshown here as percentages of one atmosphere, and theaircraft heights at which reduced pressures of similardegree would be experienced are given to facilitatecomparison between the two situations.

Chemical MeasurementsThe partial pressure of oxygen in the air of the

.submarine was indicated continuously on a PaulingMeter, a direct reading instrument designed in theUnited States, which depends on the paramagnetic

properties of oxygen as opposed to the diamagneticproperties of most other gases.When the snort mast was lowered and fresh air

ventilation was impractical the percentage of carbondioxide in the air was measured with an indicator of newdesign, which depends on the differing thermal1 con-ductivities of air samples of different chemical composi-tion. The percentage of carbon dioxide in the air isshown on a galvanometer which indicates the differencein heat loss from two hot wires, one of which is exposedto compartment air saturated with water vapour fromwhich carbon dioxide has been removed by a chemicalabsorbent, whilst the other is exposed to saturatedcompartment air from which carbon dioxide has notbeen removed. The accuracies of these instrumentsunder laboratory conditions correspond reasonablyclosely with measurements obtained with the HaldaneGas Analysis Apparatus. Each time the ipstrumentswere read the atmospheric pressure was noted on a largeaneroid barometer which had been calibrated against a.mercury column before sailing.

Typical changes in the chemical composition of the airduring a 24-hour period on Day 20 are shown in fig. 2.Horizontal lines indicate the partial pressures whichcorrespond to 18 per cent. oxygen and 3 per cent.carbon dioxide at a pressure of one atmosphere, whichhave been suggested as permissible lower and upperlimiting levels for these gases in compartments whichmust be occupied for prolonged periods.

Traces of carbon monoxide, occasionally caused byback pressure on the underwater exhaust during un-expected submergence with the engines running, or witha following wind from exhaust gases drawn in through thesnort induction, were estimated with the Chemical CarbonMonoxide Indicator Mk. IIf developed at the RoyalAircraft Establishment, Farnborough.

Pressure ChangesThe range of the pressure changes experienced

on this trial is shown in figures IA to 1D by recordsselected from tracings on the " 7-day" barograph.Varying degrees of pressure depression below one-atmosphere were the main feature when snorting,and when submerged with the snort mast lowered,mild degrees of pressure elevation above oneatmosphere were observed due to high pressureair leakages within the submarine.

The marked fluctuations in figs. IA and IE weredue to slow speeds and low engine revolutions in achoppy sea before the crew were fully accustomedto the controls.

In fig. lB the relationship between the pressurevariations and the total engine revolutions may beobserved, and an increase in the amplitude of thefluctuations may be seen when the sea and swellincreased on Day 13.

In fig. Ic higher total engine revolutions andfaster speeds are related to further depressionof the atmospheric pressure to between 85 and 75

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ATMOSPHERIC PRESSURES IN SUBMARINES 27-

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BAITISH JO-URNAL OF INDUSTRIAL MEDICINE

per cent. of one atmosphere, but theamplitude of the fluctuations is of moremoderate degree. 80

On Day 23 (ID) in a very calm sea 85the effect of a sudden reduction in total 90

engine revolutions on the pressuredepression is shown clearly, and it isseen that in a calm sea pressure fluctua- '°°tions are observed rarely when the crew,are fully accustomed to the controls. 80

T'he pattern of the pressure variations 85

is shown in greater detail by enlarge- dment of the time scale in a horizontal ldirection in figs. IE to 1L. The vertical iscale is much the same, differing only ;with the calibrations of the three 95instruments used. Maintained reductionof the atmospheric pressure is observed /00

to be mainly a function of the totalengine revolutions, and fluctuations in 80

pressure vary in degree in relation toa

the state of the sea and the length andheight of the swell, the speed of thesubmarine, and- the efficiency of thedepth-keeping. Sudden severe pressurefluctuations due to errors of judgment 95

or mechanical faults may occuroccasionally, and an example of what {may happen is given in fig. 3, to whichreference will be made later. FIG.

Chemical Changes terbel

In fig. 2 are shown the partial press-ures of oxygen and carbon dioxide observed iair of the submarine during a typical 24period, submerged at a depth of 80 feet by.and proceeding at periscope depth on theengines using the snort by day.The partial pressure of oxygen va-ries wit.

total atmospheric pressure when the snort is iand when communication with the opendiscontinued it may rise with increases in pr

due to such factors as high pressure air leawithin the submarine, or it may fall grabecause of the respiratory requirements of theThe latter will be considerably increased ifphysical exertion is necessary at any time.. Phactivity is therefore kept to a minimum w]submnarine is submerged for long periods at cgreater than snorting depth in order to co

the supply of oxygen. The high engine revoliwhen snorting on Day 20 were associatedbetween 20 and 25 per cent. reduction in the Ipressure of oxygen in the air within the submDuring the periods submerged with the

lotwered the partial pressure of, carbon di

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3.-Unusually severe pressure fluctuations which gave rise tomporary discomfort in the ears or accessory nasal sinuses at theginning of the trial.

in the steadily increased until the fresh air supply through-hour the snort was re-established (chemical absorptionnight of CO2 carbon dioxide was not carried out). Amain' temporary submergence during the forenoon of

this day (see also figs. Ic and G) was associated withth the a slight further rise of carbon dioxide, and increasein use, of the partial pressure of oxygen to the normal level.air is Periods without fresh air ventilation are rarely*essure sufficiently prolonged under peacetime operatingikages conditions to allow the accumulation of harmful,dually amounts of carbon dioxide; and the periodic or

crew. continued use of the snort will greatly reduce theheavy probability of undesirably high accumulationshysical occurring in war time.Fhen adepths The Effect on the Crewnserve In the past the main environmental factors whichlutions required control in submerged submarines, whichi with had no air supply from the surface, were progressivepartial depletion of atmospheric oxygen associated withiarine. accumulation of carbon dioxide which were thesnort direct results of the respiratory processes of theirioxide crews.

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ATMOSPHERIC PRESS[

Oxygen lack, even when it is mild, is known to beassociated at night with diminished visual acuityand an increase in the time required for darkadaptation; and with more severe degrees of anoxialowered powers of judgment and discrimination,possibly associated with confident unawareness,occur in some people. Thus in the recent warRoyal Air Force pilots used oxygen continuouslywhen flying by night, and at altitudes above 10,000feet by day. The effects of oxygen lack are aggra-vated by physical exertion, or by any factor whichinterferes with oxygenation of the tissues such as

mild carbon monoxide intoxication.Carbon dioxide accumulation in the atmosphere

will cause headaches, nausea, malaise, and fatiguein some individuals towards the end of long dives(12 to 20 hours) if the facilities for air purificationare not available; and these symptoms may berenewed or intensified, or may even occur for thefirst time after restoration of fresh air supplies on

surfacing or on conimencing to snort.No ill effects result from the moderate increases

of pressure sustained during submerged periods,provided caution is exercised at the time of openingup to fresh air.The introduction of the snort has enabled fresh

air to be supplied and carbon dioxide to be eliminatedwhilst submarines are still submerged. This greatlysimplifies the problem of air purification under theseoperating conditions, but it also introduces the newproblems of reduced pressures and fluctuatingpressures. The effects of these may be subdividedinto those due to (1) reduced pressure, (2) sustainedpressure fluctuations, and (3) sudden pressurefluctuations.

Reduced Pressures.-The effects of pressure reduc-tions such as those shown in figs. IF to 1L are simplythose of the associated degree of oxygen lack. Infig. 2 it is observed that this would correspond tobreathing 16 per cent. oxygen at atmospheric pressurewhen snorting with high-engine revolutions (640 revs.)or even lower percentages under certain conditionsdescribed here. Thus, by night the visual efficiencyof men using the periscope whilst snorting might beimpaired; and, if careful control was not ensured ofthe pressures to which the crew were exposed, cs,)eciallyin rough weather, prolonged exposure to an atmospherepoor in oxygen might increase fatigue and impair judg-ment and general efficiency to an unacceptable degree.

Continuous Pressure Fluctuations.-The pressurefluctuations recorded on Day 7 represent unusuallysevere conditions which would probably be ex-perienced only if it was necessary to proceed with fairlyhigh engine revolutions at slow speeds in a rough orchoppy sea and if the depth-keeping was poor. Theseconditions did not cause a crew who had grownaccustomed to the usual range of pressure changes tocomplain ofimmediate discomfort, but the accumulated

URES IN SUBMARINES 29

effects of exposure throughout the day were thoughtto induce greater general fatigue than would otherwisehave been experienced, and mild anoxia may well havecontributed to this. About one third of the crew alsocomplained of headaches, which were generallyrelieved after snorting finished for the day. It isobserved that the pressures were equivalent to spendingthe day in an aircraft continuously ascending anddescending to and from varying heights between 1,000and 8,000 feet at intervals of a few minutes.Sudden Pressure Fluctuations.-Pressure fluctuations

such as those indicated in figs. 1E to IL did not causediscomfort or arouse complaints from the crew. Moresudden changes, however, such as are depicted infig. 3, which resulted from temporary loss of controlof the depth of the submarine,at the beginning of thecruise, added to the general picture given above byinducing temporary symptoms of acute sinus or otiticbarotrauma in those individuals who were unable toequalize, with the pressures in the submarine, thepressures within their accessory nasal sinuses or middleear cavities. This was generally due to temporaryblockage of the sinus foramina or eustachian tubes bysuch factors as mild congestion or catarrhal exudatedue to chronic catarrh or acute coryza. Difficulty inclearing the eustachian tubes was generally overcomeby men with temporary blockages or unaccustomed topressure fluctuations, by swallowing, by opening themouth and retracting the jaw, or by pinching the noseand puffing out the cheeks. Equalizing the pressureswas performed automatically by the great majority ofindividuals after a few days snorting.Acute dental pain was caused on one occasion when

the pulp cavity of a rating's tooth was exposed byextensive caries to sudden pressure changes of fairlysevere degree.

The pressure changes shown in fig 3 were ex-perienced before the crew had grown accustomed tofluctuating pressures, and mild symptoms of sinus orotitic barotrauma were experienced by a number ofmen. The rise of pressure following a sudden reduc-tion was the feature which generally caused discomfort,and with sudden fluctuations of this type it appearedthat the rate of change of pressure was of greaterimportance than the amplitude of the change. Thusthe rise of pressure graphically illustrated by tracing" A " caused ratings to complain of unpleasant symp-toms, but the mqre gradual rise shown in tracing " B"did not.The threshold rate of pressure change at which

discomfort was experienced by certain individualsduring more severe pressure fluctuations was observedto be of the order of 0 04 to 0-06 inches of mercury persecond, although the great majority of healthy menwere unatfected once they had become attuned to the

* more usual type of pressure variation. The changesof pressure related to normal starting or stopping ofthe engines did not cause discomfort.

In practice - pressure changes causing symptomsare experienced infrequently with a trained crew anda carefully handled submarine. Before and after



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this cruise the men were examined medically, andalso by an ear, nose, and throat specialist whomeasured their hearing acuity with an audiometer,and from the detailed observations made there is noevidence that such ill effects as may be experiencedamount to more than those which persons travellingin aircraft must endure at times. It is necessary toadd, however, that after exposure to the unusuallysevere pressure fluctuations shown in fig. 3 nearlyhalf the crew showed abnormal congestion of theirear drums. These appearances lasted only for aperiod of hours, or in a few cases for a few days,despite the fact that the men were exposed to pressurefluctuations of considerable, though less severedegree, for most of this time.One further factor should be mentioned in

discussing these pressure changes and the phenomenarelated to the use of the snort. In certain circum-stances-if the engine should be stopped followingsudden submergence with the engines running, orwhen snorting with a following wind-traces ofcarbon monoxide may be detected in the'submarineair. Whilst the degree of this hazard as'it has beenobserved so far would not be harmful alone, theadditional anoxia which might result at times inpersons already experiencing mild oxygen lack dueto low atmospheric pressure would be unacceptablefor a prolonged period under operational conditions.Measures for identifying and controlling carbonmonoxide are therefore of practical importance.

Conclusion

The environmental factors described here wereobserved under trial conditions 'with prototypeequipment, and some of the crew were unaccustomedat first to the novel operating conditions. Thepossible environmental stresses which might affectthe efficiency of the crew have been discussed in somedetail, but it is emphasized that these are all readily

-controllable, and the likelihood of undesirablestrain being placed on members of a crew will beprogressively reduced in future operations by modifi-cation of the design of the equipment and controlsystems, and as a result of operational experience.

In the same way as the aircraft pilot may imposestresses or discomfort on himself Qr his passengersby steep turns, power dives or other erobatics, somay the mishandling ofa submarine inflict unfavour-able environmental conditions on the crew. In warthe operational situation will demand at times thatunfavourable conditions of varying degree shall beaccepted, when the alternative course will involvegreater hazards at the hands of the enemy, or whenan important attack must be pressed home in specialcircumstances. The submarine captain, in assessing

the tactical situation, can take full account of anyunusual environmental stresses which may beimposed on his crew at these times only if he is wellinformed of the basic physiological facts and theirpractical implications, and has at his disposalaccurate direct reading instruments for indicatingthe conditions prevailing within the submarine.There is no evidence so far to suggest that special

conditions will occur in snort-fitted submarines toinfluence adversely the health or efficiency of thecrews, provided that the provision of an optimalenvironment for the men is borne in mind at alltimes by those responsible for designing the sub-marines and for handling them after they are built.On the contrary it is thought that the domesticcomfort of the crews will be considerably increasedby the reduced motion of the submarine whensubmerged, by the abolition of the wet and draughtyconditions which formerly resulted when a sub-marine was on the surface in rough weather, andalso by the concession allowed the crew of beingable to smoke when submerged. It is equallycertain that neglect to consider human factorsadequately will result in loss of efficiency.

In the Royal Navy when submarines are designedor operations are planned the application ofadvancesin physiology or psychology is ensured by the'closeco-operation of physiologists, psychologists, andsubmarine medical officers with the designers ofsubmarine equipment and the operationalcommands.The future development of submarines requires

that knowledge shall be as complete as possible onthe effect of the different environmental variationswhich may. be encountered on judgment an'ddiscrimination, visual or auditory functions, effi-ciency in the performance of psychomotor tasks,or in aggravating fatigue. The effects of prolongedor repeated exposure, or of different combinationsof factors, merit special attention. A fascinatingfield for further practical observations and forfundamental research is thus opened up, and theapplication of basic knowledge acquired in this waymay be expected to extend beyond the particularnaval requirement considered here.

This account summarizes the main physiologicalfindings of a preliminary investigation of the effects oft'snorting" carried out for the Royal Naval PersonnelResearch Committee of the Medical Research Council.

I am indebted for invaluable advice to the membersand scientific associates of that Committee; and particu-larly to the Staff of the Royal Naval PhysiologicalLaboratory for advice and assistance before the cruise,and to Mr' F, E. E. Smith of the Medical ResearchCouncil's Group for Research in Industrial Physiologyfor preparing Illustrations 1 to 3.

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