DEC

-HEAT STRESS CAUSED BY WEARING DIFFERENT'TYPES OF CW PROTECTIVE GARMENT (U)

by

S.D. Livingstone and RW. Nolan

DEFENCE RESEARCH ESTABLISHMENT OTTAWATECHNICAL NOTE 91-14

August 1991.ao .Ottawa

10) 4

*~4*Natonl ManseDfne national. . -

HEAT STRESS CAUSED BY WEARING DIFFERENTTYPES OF CW PROTECTiVE GARMENT (U)

by

S.D. Livingstone and L.W. NolanEnvironmental Protection Section

Protective Sciences Division

DEFENCE RESEARCH ESTABLISHMENT OTTAWATECHNICAL NOTE 91-14

PON August 1991051LCll Ottawa

ABSTRACT

.One means of reducing the heat stress caused by wearingprotective clothing is to eliminate the air layers between the skinand layers of the ensemble. In order to evaluate the effectivenessof this concept, four unacclimated males wearing either the currentCanadian Forces (CF) chemical protective overgarment, anindividually-tailored skintight protective garment or CF combatuniform participated in a series of experiments conducted at 40'Cand low relative humnidity. Each was instrumented with a rectalthermistor, donned the clothing and walked on a treadmill at 5 kmhr- and 2% grade for 90 min, until his rectal temperature reached39'C or he requested to withdraw from the experiment. The resultsof this preliminary investigation indicate that there appears to besome advantage to wearing the skintight clothing under theseconditions.

RESUME

Une des fagons de reduire le stress thermique cause par leport d'habillement de protection est d'dliminer les couches d'airentre la peau et les couches d'habillement. Pour Cvaluerl'efficacit6 de ce concept, quatre m&les non acclimatises portantsoit l'habillement de protection chimique des Forces Canadiennesactuel, un habit de protection moulant ajuste individuellement oul'uniforme de combat des Forces Canadiennes ont participes dans uneserie d'expdriences a 40°C et humidite relative basse. Chacun futinstrumente d'un thermistor rectal, et a marche habille sur untapis roulant a 5 km hr-' avec une pente de 2% pendant 90 minutes,ou jusqu'a ce que sa temperature rectale atteigne 39°C ou qu'ildemande d'arr~ter l'experience. Les resultats de cetteinvestigation preldminaire indiquent qu'il semble y avoir unavantage a porter un v~tement moulant sous ces conditions.

(iii)

EXECUTIVE BUMMXRY

A major problem associated with wearing chemical warfare (CW)protective clothing is the increased susceptibility to heat stressof the wearer. It has been suggested that skintight clothing wouldprovide less resistance to heat loss and thus reduce this problem.Since the Canadian Forces became involved in the Middle East inlate 1990 it was decided to examine this concept.

Subjects were exposed to an environment of 40°C and 25%relative humidity while walking on a treadmill at 5 km hr" whiledressed in one of the following ensembles:

1. undershorts, CF combat shirt, trousers,wool socks andcombat boots

2. undershorts, CF CW protective overgarment, C-4 gas mask,CW gloves, socks and combat boots

3. undershorts, C-4 mask, CW gloves, socks, combat boots,solarmax long underwear and a two piece tight fittingcharcoal impregnated lycra suit. The head was covered witha hood made from the lycra material.

Each subject wore each of the ensembles twice.

A second series of experiments, using the same protocol butwith an additional clothing configuration (ensemble 2 plus combatclothing) in place of ensemble 1, were performed. After completingthe protocol the subjects entered the laboratory at 24°C and theircore temperatures were measured as they cooled without removingtheir protective clothing.

The results indicate that there appears to be an advantage towearing the skintight clothing while working under the givenambient conditions since the body temperatures of the subjects rosemore slowly in this clothing than in the current CW clothing.These results are not surprising since the thermal insulation ofthe close-fitting material itself is less than that of the CWcoverall material, without considering the reduction caused byeliminating the air layers. Some of the subjects dressed in theovergarment dropped out of the experiment for reasons other thanthe rise in core temperature. Also, the subjects cooled faster inthe skintight clothing than in the other ensembles.

Further work should be done to determine if it is feasible toreplace the current overgarment with a closely fitting one to beworn at high ambient temperatures.

v

INTRODUCTION

Wearing chemical warfare (CW) protective clothing undrr mostconditions imposes restrictions and reduces the efficienc .* thewearer. One of the major problems associated with the wearing ofthe Canadian Forces (CF) CW protective overgarment is the increasedsusceptibility to heat stress since the coveralls increase theamount of thermal insulation and prevent the evaporation ofperspiration, inhibiting body heat loss to the environment.

Farnworth and Crow (1) have suggested that one of the factorscontributing to the heat stress caused by wearing CW clothing isthe fact that the garment is loose-fitting and that the air layersbetween the skin, underwear and CW suit all contribute to the totalthermal insulation of the ensemble. Theory indicates that if theair layers were removed, the thermal insulation would be reducedsignificantly. Farnworth and Livingstone (2) have shown thatclose-fitting garments do not provide as much insulation as loose-fitting garments when worn in cold conditions. As the CanadianForces became involved in the Middle East in late 1990, it wasdecided to perform a series of experiments to determine the effectsof wearing close-fitting clothing on the onset of heat stress whileworking in hot conditions.

METHODS

Three different clothing ensembles were examined. The firstconsisted simply of undershorts, CF combat shirt, trousers, woolsocks and combat boots. In the second, shorts, CF CW protectiveovergarment, C-4 gas mask, CW gloves, socks and combat boots wereworn. For the third ensemble, a two-piece close-fitting suitmanufactured using lightweight charcoal-impregnated lycra materialwas individually tailored to fit each participant. It was worn witha hood made of the same material, top and bottom long underwear(Solarmax), C-4 mask, CW gloves, socks and combat boots.

Three members of the DREO test team and one DREO civilian gavetheir informed consent to participate in the experiments. All werein reasonably fit physical condition and were unacclimated to theenvironmental conditions of the experiment. Their anthropometriccharacteristics are given in Table 1.

Table 1. Anthropometric characteristics of volunteers

Subject Age Height Weight(years) (cm) (kg)

1 30 183 772 26 185 743 24 182 894 26 170 70

1

Each subject first sat quietly for one hour in anenvironmental chamber at 40°C and 25% relative humidity after whichhe left the chamber and inserted a rectal thermistor 15 cm into theanus. He then dressed in one of the three different clothingensembles (chosen at random) and re-entered the environmentalchamber. He then walked on a treadmill at 5 km hr"' and 2% grade for90 min, until his rectal temperature reached 39°C or he requestedto withdraw from the experiment. The experiment was repeated oncewith each clothing configuration, making a total of six exposuresfor each participant. At least 48 hours elapsed between repeats, inan attempt to prevent the volunteers from becoming acclimatized.

During the experiment the subject's rectal temperature wasmeasured and recorded every minute using an automated dataacquisition system (Hewlett-Packard 3497A) and HP 85 computer. Alldata were stored for subsequent analysis. Each subject was allowedwater ad libitum.

A second series of experiments repeated the protocol of thefirst series using different clothing configurations. In thisseries, combat clothing worn under the CW ensemble was added andcombat clothing worn alone was not tested. After completing theprotocol at 40* C, the subjects left the chamber and sat in thelaboratory at 24° C without removing their protective clothing ormask. Rectal temperature continued to be measured and recorded forseveral minutes, until it had dropped approximately 1° C. Onlythree subjects participated in this series.

RESULTS

Because of the limited number of subjects tested and becauseof the known variability of physiological responses among subjects(Armstrong et al (3)), individual responses are shown -ather thanstatistical means of the results.

Changes in rectal temperature as a function of time whenwearing the different types of clothing are shown in Figure 1,where CW, CO and SK indicate chemical protective, combat andskintight clothing, respectively. The cooling curves of the secondseries of experiments are shown in Figure 2 where CWC indicatescombat clothing worn under the CW garment. Subject 3 did notperform the experiment when wearing only CW clothing.

A summary of individual results is given in Table 2, whichlists maximum rectal temperature observed (Tmax), the change inrectal temperature (AT), the duration of each experiment (time) andrate of temperature rise (AT/time).

2

With the exception of subject 1, who warmed fastest whenwearing the CW ensemble and slowest when wearing the combatclothing, it is apparent that consistent results were not obtainedwith the other subjects. However, an analysis of rate oftemperature rise (AT/time) indicates that there were significantdifferences between the clothing ensembles i.e. rectal temperatureincreased most rapidly when CW protective clothing was worn andleast rapidly with the combat clothing alone. As shown in Table 2,the reason for terminating the experiment was not always becausemaximum time or temperature limits were reached. This indicatesthat wearing the CW clothing created additional problems, causingthe subjects to abort the experiments earlier than when wearing theother ensembles.

The rectal temperatures measured during cooling (Fig. 2)indicate that the subjects cooled most rapidly in the close fittingclothing and least when wearing the CW clothing plus combatclothing. These results also indicate that wearing the skintightclothing is beneficial.

DISCUSSION

The results indicate that there appears to be an advantage towearing the skintight clothing while working under the givenambient conditions. Subjects' rectal temperatures increased bysimilar amounts but at different rates when wearing the differentensembles. When resting at a lower ambient temperature, thesubjects cooled faster when wearing the close-fitting clothing.These results are not surprising since the thermal insulation ofthe close-fitting material itself is less than that of the CWcoverall material, without considering the reduction caused byeliminating the air layers.

Results also indicate that change in rectal temperature wasnot the only parameter which caused subjects to withdraw from theexperiment. Several times subjects complained of feeling too hotand having trouble breathing. Similar observations have beenreported by Armstrong et al (3). As seen in Table 2, with oneexception, these complaints occurred only when the CW coverallswere worn. A more detailed study should be done to determine thereason.

Our experiments did not attempt to simulate the effects of theradiative heat input from the sun, a very real factor in the desertwhich would increase the severity of the conditions under which theprotective clothing would have to be worn. It may also bedifficult in the desert to find cool areas in which to rest. Thus,the cooling effect of resting for the times indicated in Figure 2would not necessarily alleviate the heat stress as shown. However,resting might possibly reduce the rate of increase of body heat.

3

CONCLUSIONS

The results of this preliminary investigation indicate thatthere appears to be some advantage to wearing the skintightclothing under these conditions. They also indicate thatadditional work is required to determine why some subjects abortedthe experiment before their rectal temperature reached 39* C whenwearing the CW overgarment. Further investigation is alsonecessary to determine if it is feasible to replace the current CWprotective overgarment with a more closely fitting one, resultingin less heat stress when worn at high ambient temperatures.

REFERENCES

1. B. Farnworth and R. Crow. "Heat stress in chemical clothing."Technical Note 83-28, Defence Research Establishment Ottawa,Ottawa, Ontario, 1983.

2. B. Farnworth and S.D. Livingstone. "The thermal resistance ofthe CF CW suit." Technical Note 85-22, Defence ResearchEstablishment Ottawa, Ottawa, Ontario, 1985.

3. L.E. Armstrong et al. "Prediction of the exercise-heattolerance of soldiers wearing protective overgarments."Aviat. Space Environ. Med. 1991; 62:673-7.

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Heat Stress Caused by Wearing Different lypes of CW Protective Garment(U)

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Livingstone, S.D. and Nolan, R.W.

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13. ABSTRACT ( a brief and factual summary of the document It may also appea elsewhere in the body of the document itself. It is highlydesirable that the abstract of classified documents be unclassified. Each paragraph of the abstract shall begin with an indication of thesecurity classification of the information in the paragraph (unless the document itself is unclassified) represented as S). (C), or (U).It is not necessary to include here abstracts in both offical languages unless the text is bilingual).

One means of reducing the heat stress caused by wearing protective clothing is toeliminate the air layers between the skin and layers of the ensemble. In orderto evaluate the effectiveness of this concept, four unacclimated males wearing eitherthe current Canadian Forces chemical protective overgarment, an individually-tailoredskintight protective garment or CF combat uniform participated in a series ofexperiments conducted at 40 C and low relative humidity. Each was instrumented with b

a rectal thermistor, donned the clothing and walked on a treadmill at 5 km hr- I and 2%grade for 90 min, until his rectal temperature reached 396C or he requested towithdraw from the experiment. The results of this preliminary investigation indicate

that there appears to be some advantage to wearing the skintight clothing underthese conditions.

4 KEvW RDS. DESCRIPTORS or IDENTIFIERS (technically meaningful terms or short Dhrases tiat characterize a document and could beretafui in :ataloguing tne document They shoulo be selected so that no security classification -s reouired. identifiers. such as equiomei""onoe' designation trade name military prolect code name. geograotic iocation may also be rnicuced. If possible keywords $nouti oe seiected110'T a ouolished thesaurus e.g. Thesaurus of Engineering and Scientific Terms (TEST! and that tnesaurus-ientified. if it s not DOoss'e toselect noexing terms wnicn are Jnciassified. the classification of eacr. Should be indicated as witn tine title.)

Skintight Clothing

Body TemperatureHot Ambient Temperature

Chemical Protective Overgarment

I

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