USAFSAM..TR-887 \D

THERMAL STRESS IMPOSED BY PROTOTYPEU*' BILAYER AND CURRENT GROUND CREW00 CHEMICAL DEFENSE ENSEMBLES

A Umited Laboratory ComparisonOt)I"-

I

0Larry P. Krock, Ph.D.Ruflno Navalta, Technical Sergeant, USAFLoren G. Myhre, Ph.D.

SODTIC

SELE'CTEOCT 2 5 1W8•1

Interim Report for Period June 19S - January 1987

Approved for public r'elease; distributiorn Is unlimited.

USAF SCHOOL OF AEROSPACE MEDICINE We.Humen Systems Division (AFSC)Brouks Air Force Base, TX 78235-5301

sit 4 '17

,;

NOTICES

This final report wan submitted by personnel of the ChemicalDefense Br , Crew Techrzology Division, USM School of AerospaceMedicine, Human Systems -Division, ASSC,SroBxoas Air Force Base,Texas, under job order 2729-04-04. .

When Government drauings, specifications, other data areused for any purpose other than in connection with a definitelyGovernment-related procurement, the United: States GQvernmentincurs no responsibility or ary obligatioa VWhsoever. The factthat the Government may have formulated or ia any way supplied thesaid drawings, specifications, or other d*ta, is, not to beregarded by implication, or otherwise in any hanner construed, aslicensing the holder or any other person or corporation; or asconveying any rights or permission to manufacture, use, or sellany patented invention that may in any way be ielated thereto.

The voluntary fully Jnformed consent of the subjects used. inthis research was obtained in accordance with, Ar_ 169-3.

The Office of Public Affairs has reviewed this report, and itis releasable to the National Technical Inforsation Service, whereit will be available to the general public, including foreignnationals.

This report has been reviewed and is apprw4d for publication.

LAlRRYP KRP=, Ph.D. F. NKSLE? ~U NCRDN , Ph.D.Project Scientist Supervis"f

o " D A I S

.. ..

V W M C

VIS Colo

*.-UNCLASSIFIED

SEC?ITTY CLASSIFICATION OF THS AG

REPORT DOCUMENTATION PAGE FOms O A 70-0 In

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4. PERFORMING ORGAJ4IZATION REPOFR NUMBER(S S. MONITORING ORGANIZATION REPORT NUMBER(S)

uSAPSAM-TR-88-7

Ga. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL, 7a. NAMES Of MONITORING ORGANIZATION

USA.F School of Aerospace j N appkbi)Medicine IUSAPSAMIVNC6c AOORESS (City, State. AMd ZIP Cod.) M ADDRESS (COty. State, a&d ZIP Code)

Human Systems Division (AFSC)Brooks AFB, TX 78235-5301

Ba& NAME OF FUNDING/ SPONSORING 8b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION 14UNMSER

CAI0ofAerospace ~ a~

5L AOC'ESS (City, State. and Z'P Code) W. SOURCE OF FUNOIN4,v NUMBERS

H- ysem Dviio (FSC POGAM I R~EC 0TASK WORK UNIT

Bumno SstesAB Diiso 7823-530 ELEMIENT NO0 NO0 NO ACCESSION NO

Brok AETX 7835531622021 2729 04 0

11. TITLE (Incluft Secunt Clawfic~auonI -Therma~l Stress Imposed By Prototype Bil1ayer and (Aurreat Ground Crew Chemical Def ense

Ensembles: A, Limited Laboratory ComparisonQ2. PERSONAL. AUTH40R(S)Myrli____________K~rock, Larry P. ; Navalta, Ruf ino; and Myr, G._________13a. TYPIE OF REPORT 13b. TIME COVERED / 114. DATt OF REPORT (Yoiw. ~~th, 04y) S GE COUNT

Interim FROam86/06/30 T08710 1M 1988, July, 2110. SUPPLEMENTARY NOTAtION

FILD COSATI COOES Ia. SUBjEC %'RMS (ConIfqie on .evetm If nftena" and denntY by 6iock %mbv"f)

FED GROUP SUB.GROUP Chemical Defense; Thermal. Stress; Ground Crew Chemical0607Defense Ensemble; Open Bilayer)Chemical Defense Ensemble.

15 4 603 /-.

'9AS CT (Cofltulv on r*V"rt it fwqnary #ew 'dentflf# by bwOck ,MIftme__

An CMnbilaYer gurM~n c26w d~chuA4 defenin ersaid14 (CM) hads ban prnlosed to rew the thmira burdendaring vmor-'xly alposure perioft. This studly cayprind the thewmi stress profile of the pzVo~sedamoosirle to that prodke by the cwrrunt.y eyp1oy~I closed =. Four sub-4ats, alterncating ensabigs ongeprata days, ws..Lk ani a treaJ..ll in an eyvircrvert~a2 chuibar at 5. 3 )cm h"4ý (3.3 ii~i) wid 2's gxw* (an

eramr epairxturt of3YWi./~'- for a.Ltun~airq w.zk/rest Cycle, Of 3a andI 10 in.n, xzecw_±valjy.oft~ cciito i ýre: T .~ 7 At (8 0. 6 'tb T - 19 At (6 6.2 d r) ~5and~ e aproxinutely' 2 M I3t

Aork seqgmxt anal~ysis indicated a significart (p( .05) stxwA-4'-_ima% diLffet~nce between the 2 a'.seztlesfor parstreters of rw-tal tinrpratuzw, skinr tzrpraturs, and heart: rate. 7he rest intervals o~rsirIsufficieant to ach~ieve sig~i~ficam r ecovery. Mmw total sweet produlction wae lower (1.38 vs. 2 50Liters) and re-rcarit sweat evaporatici greater (65.7% vs. 30.0%) in the prototype ea~r~sorle than in the =E.77hu protottype enswtent rrovided greater heat dissipation~ and allowed nmrs efficient swostt evaporation-wruich had tre double ef it of zraducirxq hoat storag and 1.init~ii c~hydration .

20 :5!TR~IBUTION / AVAILA8'u'TY OF %aS-QACT 121 ABSTRACT SECURITy'CLAS$:FiCAT;ON

K3UNCL.ASSIPFIEO/UNLI MITE D 0 SAME AS QPT D TIC USERS Unclassified2. AMAE OF P.ESPfNSi8LF NOIVIOL.AL 22b TELEPwONE (Inoclude At*& Code) 2cc. OFF4CE SYMOOL

Larr'l P. Krock, Ph.D. (512) 536-3814 USAFSAM/VNC

00 Form 1473, JUN 86 Propvtus eiT.Qdmoba54t. -JCý..RITY CLAS:)FICATIQN OF THI4S OAGE

i UNCLASSIFLEZ

CONTENTS

Page

INTRODUCTION.. . ... . .. . . .. . ... .

EQUIPMENT AND PROCEDURES ........................... 2

Equipment .......... .................... . . . . . . . . 2

Current Chemical. Defenae,Ensemble ............... . . . 2Bilayer Chemical Defence Ensemble. .. ............... 2

Procedures .......................... # . . . . . .. .. 5

Experimental Protocol .......................... . . 5Data Analysis .............................. 6

RESULTS . ..................... . . . . .. . 7

Work Cycles . ................................... . . . .. 7Core (Rectal) Temperatures ..................... 7Skin Temperatures .............................. 7HHeart Rates ................. .......................... 10

Rest Cycles .............. .......................... 10Poistwork RecoveryI . ....................... ......... . .10

Thermal Sweating ...................................... 13

DISCUSSION ..................... ............................. .. 13

CONCLUSIONS .............. ............................. ..... 14

REFERENCES ............................ ........................... 15

List of Figures

Fig.No.

1. Current Ground Crew Chemizal Defense Ensemble ........ ......... 3

2. Prototype Biliyer Ground Crew Chemical Del.ense Ensemble. . .. 4

3. "tline of Experimental Protocol .............. ............... 6

4. Physiological Profile for One Subject .... ..............

M¶ean Temperatures and Heart Rates During Work Periodz o 9

6. Mean Temperatures and Heart Rates During Rest Cycles ..... 11

Fig.No. Pg

7. Mean Temperatureas and Heart Rates DuringRecovery Periods . . . . ......... .............. 12

8. Mean Sweat, Production and Percentage Evaporation ....... .. 14

List of TablesTable

No.

1. Physical Characteristics of Subjects . . .. ................... 5

2. Mean Sweat and Evaporation Values .............. . . . . . 13

. L

:t. jbu t CZ_/

Li'v

THERMAL STRESS IMPOSED BY PROTOTYPE BILAYER ANDCURRENT GROUND CREW CHEMICAL DEFENSE ENSEMBLES

A Limited Laboratory Comparison

INTRODUCTION

The problems involved with task performance while wearing the chemicaldefense ensemble (CDE) have received increased attention during recent basereadiness exercises. Physiological monitoring of volunteer subjects duringthese exercises has raised concerns about the physical ability of ground crewRto perform some operational tasks, especially in waer environments. The prin-cipal physiologic concern is the excessive thermal stress that is incurred byindividuals wearing the present CDE.

Ground crew personnel performing rapid runway repair--perhaps the mostphysically demanding of U.S. Air Force (USAF) operational tasks--while wearingthe CDE, demonstrated very rapid increases in core temperature under moderateenvironmental conditions. This rapid storage of body heat would, have limitedtheir ability to complete more than 1 h of work had, they not succumbed to fa-tigue before becoming a thermal casualty (1).

Yousef et al. (5) found similar heat stress problems in individuals per-forming integrated combat turnarounds while wearing the CDE under summer des-ert conditions. The investigators also concluded at temperatures above 30 °C(86 0 P) the tolerance time for a loader is 40-50% less than that of the crewchief ane that the loader would be limited to only 2 turnaround exercises. Ifthe ordnance loader was not replaced at that time, the entire crew would be-come nonoperational. In cool weather (below 20 °C (68 0F) noticeable heatstress was not a problem through 4 consecutive turnarounds.

Finally, Whinnery (4)--observing ground crew under simulated chemical war-fare conditions--noted significant thermal stress including symptoms of hoatexhaustion, cramos, synuope, and cardiac arrhytlmias. Recovery from heatstress was not easily achieved in a 12- to 16-h rest period. He also notedthat many of the Individuals treated eor heat-related problems on a gil'en daywere prone to repeat opisodes on following days, and these repeat episodeswere often more severe than the first.

Because of the severe negative impact that the q.ound crew CDE has on jobperformance, several methods for reducing the thermal burden have been tried-(1) chanqes in the proportional times of work and rest cycles, (2) microenvi-ronment conditioning, and (3) mechanization or "workarounds" of the task.

A concept has recently been proposed for modification of the CDE, separat-ing the outer liquid-protective layer from the inner charcoal vapur-protectivelayer. During a cobined liquid and vapor threat--which is cxpected to existfor only a short period--the wearer could be fully protected with the outerhood on and tho chest area of the outer garment fully secured. During vaporhazard conditions that followed and persisted for an extended pe-iod, thewearer could doff the over-mask zovering and unzip the outer garmer.t jacket to

the waist, thus decreasing the insulative quality of the ensemble and hope-fully reducing the thermal burden to the individual. This unziipped configu-ration is termed "open bilayer."

The purpose of this laboratory investigation was to compare the thermalstress profile of the proposed open bilayer ensemble, configured to impart thelowest thermal burden, to that of the present-ly employed CDE. This limitedlaboratory investigation sought only to evaluate a conceptual, prototype bi-layer chemical protective ensemble configured to impart the least thermal en-cumberance. Several critical factors will determine whether or not the ther-mal profile generated by this ensemble will be better than that of the presentCDE at the time of actual deployment. These factors include: (1) materia'.used in the final construction of the ensemble;, (2) chemical threat profile atthe time of deployment--since this will dictate whether the suit is worn openor closed; (3) weather conditions; (4) work requirements; and (5) the physicalwork capacity (1O2 max) of the individual ground crew member.

EQUIPMENT AND PROCEDURES

Equipment

Current Chemical Defense Ensemble

The current CDE was donned in the prescribed manner. the subject worecotton/polyester briefs and T-shirt, fatigue pants and jacket, and the CDEwhich was secured at ankles, waist, and wrists. The CDE jacket was zipped tothe neck and the M17AI mask with M6A2 butyl hood was put on and fastened down(Fig. 1). The average weight of the ensemble was 7.7 kg (16.9 lb).

Bilayer Chemical Defense Ensemble

The prototype open bilayer ensemble was assembled from available componentparts of existing ensembles. The von Bldcher material indergarment was wornover cotton/polyester briefs and T-shirt. This inner layer fit much like coldweather lonq Johns, conforming closely to the body surface. The outer layerconsisted of the current CDC jacket and pants with the foam charcoal liner re-moved. The A17AI mask was worn ovo~r a Balaclava head covering also made ofthe von Blucher material. The butyl hood (M6A2) was not worn as part of themask. The pants were worn secured at the waist and ankles. The jacket wassecured at the waist although it was um ipped to the waist and allowed to liefreely open at the chest (Fig. 2). The average weight of this prototype en-semble was 5.9 kg (13.1 lb).

The subjects were permitted to wear their own comfortable walking shoeswhich were covered by the current chemical defense overboots. The M-17AIprotective masks were modified by removing the inner filtar layer. Duringextended work the filters become iaturated with water condensation and sweat,leading to Increased inspiratory resistance; this increased resistance becomesa -onfounding ertect. Chemical defense gloves (14 mil) were wotn over cottoninserts v'ith both ensembles.

2

Figure 1. Curren~t grounid crew chanicaldefense ensemble.

3

Figure 2. Prototyp4 bilayer 7round crewcki.'mical defenas e ns emble.

4

Procedures

Experimental Protocol

Four healthy male volunteer subjects were obtained from the existing ther-mal subject pool at the USAF School of Aerospace Medicine, Brooks Air ForceBase, Texas. Some relevant physical characteristics of the subjects are des-cribed in Table 1. The participants were briefed on the objectives and natureof the experiment and each gave his voluntary, informed wzi•tten consent toparticipate in this study.

TABLE 1. PHYSICAl. CHARACTERISTCS OF SUBJECTS

Subject Sex Age Heigt Weight(y) an (in.) kg (Ib)

1 M 40 173 68.1 80.7 177.52 M 39 173 68.1 66.4 146.13 M 41 173 68.1 80.2 176.44 M 32 178 70.0 72.0 158.4

Mean: 38 174.3 68.6 74.8 164.6

Subjects reported to the laboratory on the morning of the scheduled testand were weighed nude and instrumented. They donned the designated ensembleand were weighed again fully clothed. Instrumentation consisted of: aCM 5-configured ECG lead connected to a Hewlett Packard telemetry system formonitoring heart rats (0R); rectal tharmistor inserted 10 cm (4 in.) formonitoring core temperature (T ), and 6 skin thermistors located on the chest(T ), mid-thigh (T ), laterai calf (T ), '.pper back (T_ ), upper arm (T ),n5n head (T. ). tean skin temperature (T ) was calculated followfng

Ramanathan's method (3). Temperature and hear krate data were collected on aDigital Equipment Corporation model 11/23 computer.

Following the final dressed weigh-in, the subject move6 to a pl&ce imme-diately outside the chamber (21 0C (69.8 OF)) ard sat quietly for 15 min.After this baseline period, the subject enterod the chamber where the follow-ing conditions existed: dry-bulb temperature (T ) 27 0C (80.6 OF), wet-bujbtemiperature (T ) 19 ~C (66.2 F), and air movement approximately 2 m sThe subject steppes onto a Quinton research treadmill and began to walk at aspeed of 5.3 km h (3.2 mph) and 2% grade, approximating an energy expendi-ture of 350 kcal h

The protocol 8pecified that the subject complete 4 consecutive cycles o"30-min work and 10-mmn rest periods. Following the final work cycle, the

5

Al .. " .-

subject remained fully dressed and rested within the chamber for 30 min whilehis recovery profile was monitored (Fig. 3).

Ctwrbw awon~mwtT~b 27 Or,(W0.6 OR

*T~Iý9 OC(66.2OF).Wxdfspeed: -2mr t *

5.3 km Irl (3.3 mO). 2.% Ogsd

I I I I 1 ' I

0 15 45 55 05 95 125 135 165 195

TIME (sirmn)

Figure 3. Outline of experimertal protocol.

The subjects understood that the work :equirement would be terminated forany of the following reasons: the subject's desire to stop (they were briefedon heat-stress symptoms); the medical monitor or inside observer requested thesession to be termina ted; orcpredetermined physiological endpoints werereached (T . 39.0 C (102.2 F) and/or HR > 180 beats min ). Immediately

refollcving the experimental session, the subject repeated the fully c.othed andnude weigh-ins. Total sweat loss (SLT), sweat rate (SR), sweat evaporatedfEVAP), and percentagc of SLT that evaporated (% EVAP) were calculated usingthe pro- and post-seesion weights.

Both experimental conditions (CDE and open bilayer) were experienced oyall subjects. A minimim rest of I day was given between repeat exposures. Arandomized counterbalanced design was used to a&sign the order for each sub-ject to don a given ensemble, thus reducing the possible bias due to learning.

Data Analyais

A repeated measures three-way mixed-model analysis of variance waseirploymd in the analysis of the heart rate and temperature data. Standard

6

covariance techniques were used to estimate missing data. If global analysisindicated significance, paired t-tests wete employed to determine where,within the given segmental analysis, differences occurred. Tha probabilitylevel for all tests was set at .05.

Paired t-test analysis was performed on the thermal sweat rate and evapo-ration data. The .05 probability level was also selected for thesecnmparisons.

RESULTS

Figure 4 illustrates a single subject's dependent variable responses dur-ing the 2 experimental conditions. ' Uuit analysis of a protocol as complex asthis would not provide the clearest understanding of how a given ensemble per-formed during a distinct phase of the task. Therafore, the 3 distinctlydifferent segments of the present protocol (work, rest, and recovery) wereanalyzed--and are reported here--separately.

Work Cycles

Core (Rectal) Temperatures

Mean core temperatures (T r) for both ensembles during work periods arepresented in Figure 5. The rectal temperature did not differ between theensembles prior to work and remeined statistically similar through the first Iwork intervals. From this point to the end of the experimental session, T•.remained significantly lower In the open bilayer ensemble than in the curreA2closed ensemble. ,This session represented a 1.05 CC (1.9 OF) difference inTre by the endof the fourth work cycle (Fig. 5).

Two subjects were unable to complete the fourth workbout while wearing thecurrent closed ensemble. Subject I did not attempt the fourth work intervaldue to a muscle cramp in the lower leg. The Tre at that time was 38.8 °C(101.8 OF) and rising. It was unlikely that he would have completed the finalinterval before ittaining the maximum allowable temperature. Subject 3 wasstopped after zeaching a Tre of 39.0 0C (102.2 OF) at a point 25 min into thefinal work interval.

Subiect I was also unable to complete the fourth workbout while wearingthe open bilayer ensemble. A lower back spasm forced him to qurit 15 min into

that work interval. The Tre at the time of this request to stop was 37.8 C(100 OF) and stable. He most likely would h1ve completed the work task had henot been forced to stop.

The Tre data suggests that under the present experimental conditions, bodyheAt 3torage is more rapid for a ground crew member wearing the closed,current CDE than for one wearing the bilayer ensemble, and that--even forthese rather moderate conditions--t!he time on task would be limited.

Skin Temperatures

Mean skin temperature for each work interval is also shown in Figure 5.Initial skin temperatures were statistically similar; however, significant

7

'17" 777

40 - -180

39- CURRENT CDEC _

38- 38-A _140ME

37-

36- 120

35-10

34-33 HEART 80

S~~RATE-o 32 60

-0=I- m4 40- 180

S39- BILAYER CDE0. 392• -160 •

- 38-

37- -4

36- -120

35- M O

34-

3332- 60

S~RATE19 t •t t

.4?

Figure 4. Physiological profile for -)ne subject's performances under bothexperimental conditions (CrE And open bilayer ensembles) . Arrowsinaicate initiation ofý rest (open) or work (closed).

8

o 40.0 40.03.5" 2uret 35.

0 38.5- , 85 - X

38.0- -3103&- "X$.=0M

S37.0

o 38.5""..

BASE '1 '2 3 6.0

Work Period

' Cr~nI

37 -37

36' -360, !.35I• 35 " 33

C:2J .' 3y4-, 34S33 33

(n1

0 2 32BASE 2 3 4

Work Period

• 180 , Curret 1.8

160" 160

- 140 -140S120 ,120

100 10

m .... GO..

BASE FWork Period

Fgure 3. Mean ( j-.0.) temperatures and heart rates during work periods forN - 4 subjects. Statistical significance (p<.0 5 ) indicated bya-uble asterisks.

9

differences betweena ensembles yere identified for all intervals of work. Amaximum difference between ensembles of 2 °C (3.6 Ot) was observed during thefinal workbout.

Significant ensemble-by-work-interval differences were noted in some ofthe individual skin temperatures as well. Differences in chest (Tch) and arm(Tar ) temperatures were highly siqnifiant. Beginning with dimilar values,the.e temperatures became increasingly different with successive work stress--demonstrating their largest difference during the fourth work interval.

Read waperature (Thd) demonstrated that no thermal advantaqe was gainedby removing the M6A2 hood from the mask and replacing it with the von BlUcherBalaclava. A significant difference occurred only during the final workinterval, and at this advanced point the influence of this body regional dif-terence on core temperatvre would appear to be minimal.

Heart Rates

Figure 5 also shows the mean HR for each of the work intervals. Ensemble-by-interval differences in mean HR were not significant at baseline (4 bettsmin" 1 ) but became significant during the first interval (14 beats min- ),peaked during the third interval (37 beats min ), and remained at this peaklevel for the final work interval.

The results of the work segment imply that although the absolute work re-quirement did not change over time, the ability of the ground crew member toperform a specific task was compromised more while wearing the current closedensemble than while wearing the open bilayer enseuble.

Rest Cycles

The moean Tre, Tk and HR during rest cycles are given in Figure 6. Themean values observes while wearing the bilayer ensemble were lower than thoseobserved for the current ensemble, and the differences between the 2 ensemblesincreased with time. The rest intervals were clearly insufficient to achievea significant recovery between workbouts. At best, the rest periods momentar-ily delayed the increase in # given varxable. This plateauing is most likelydue to a: temporary -eduction in generated heat resulting from a reduction inwork.

Post-Work Recovery

The recovery period following the last york interval--shown in Figure 7--began with elevated values carried over from the work ceqnent. The value fora given variable of interest was significantly higher throughout the recoveryperiod for subjects wearing the closed current CDE than fcr those wearing theopen bilayer assembly. The rate of decrease in a given variable was roughlythe same for both ensembles during the 30-min recovery period. Neither ensem-ble allowed a given variable to return to baseline by the end of the recoveryperiod (Fig. 7).. The implication from these results is that personnel in theopen bilayered COE would probably return to baseline sooner than personnelwearing the closed current CDE, primarily because they begin the recoveryperiod at a lower temperature and HR. There is no evidence from these datathat the Dilayered CDE expedites the heat dissipation duriiig recovery.

1C

40.0,- 40.0*0 39. 39A

39.0-CnvM 3.2 38.5 -38.5

'- 37.0 38.0

1! 37.0 7

X 65 -36.5

Q 3_______.0-______ 36.0

BASE 12 3

Rest Period

38- -38~ Current

348 36

(J34- 34

33-ea 33

BASE 1 2 3Rest Period

E 130716

140 140

~ 120 Current12100- 10080- so8

40 400BASE 12 3,

Rest Period

Figure 6. mean (tl. temperatures and heart rate~j during rest cyclesfo N- 5ujct. Statistical significance (p<.05) indicated

by doubi asterisks.

40.0 40.0

o 39.5 - 3I.5

39.0 current 39.0* L T T _ T_ ,.CL 65 Fmmmm.....L 37.5E

3V.0 V.j[3.0

30.5 SlayerI 37.5S, 27.0 -37.0

i,_l

36.0 3..0

0 5 1o0 15 2 25 30 35

Recovery Time (min)

38. 38.) Current°i1 37 T T 37

C.E 36- 36

I,,-

J9r

S32 .32

I0 10 15 20 2. 30 35

Recovery Time (min)

180 190

160- IS0

S140- 140

M, 120 120

100 " 1o(D 80 E

i0 4 Ii.jjh1:la:yer 2 C 60

-1L: 1 0 1o s 20 2 S 30 35

Recovery Time (mi v)Figure 7. mean (±S.D.)te temperatures and heart rates during recovery

after completion of final work p.eriod for N - 4 subjects.

Thermal Sweating

Group mean values and paired t-scores for the thermal sweat parametersare given in Table 2. Total sweat production was significantly less whilewearing the bilayer ensemble compared to the current ensemble and, althoughthe evaporation rates were slightly more in the current CDE, the bilayerassembly allowed a significantly greater percentage of tt. total sweat toevaporate. This finding indicates that individuals wearing the current CDEsecrete a far greater amount of sweat, but that much of it penetrates throughand evaporates from the outer surface of the ensemble. The body receiveslittle cooling effect from this remote surface evaporation. In contrast, theopen bilayer ensemble is associated with lower sweat production and a greaterpercentage of evaporation. Presumably, this enhanced heat dissipating effectis due to better air circulation close to the surface of the body which allowsfor better evaporation, thus better heat dissipation. The comparative sweatproduction and evaporation data are uuzmarized in Figure 8.

TABLE 2. MEAN (±SD) SWEAT AND EVAPORATION VALUES

Ensemble Sweat lost Sweat rate Evaporation Percent(itefs) (liters h- 1) (lers) evap.a

CDo, 2.50 (C.84) 0.90 (0.28) 0.35 (0.17) 39.0 (11.3)

Bilayer 1.38 (0.31) 0.47 (0.08) 0.30 (0.C4) 65.7 (11.1)

t-value 3.287 b 3.8 71 b 0.638 -4.42 b

a Percent nude body weight lost by evaporationb p <.05

DISCUSSION

Thermal stre6s resulting from moderate work while wearing the current CDEhas compelled thki research community to identify means to reduce this burdenand by doing so, to increase the ground crew work tolerance times. The pur-pose of this limited evaluation was to compare the thermal stress profile ofan open bilayer ensemble to that produced by the currently employed closedCDE.

The results clearly demonstrate that even under mild environmental condi-tions (T - 27 OC (80.6 F T, - 19 'C (66.2 (F)) and light-to-.oderatework requirements (1.2 L min Tke current CD0 imposes a work-uimiting ther-

ial burden. These results concur with those reported for other ground crewpersonnel (2, 4), although they are leas dramatic.

13

4.0-

3.5- Secretrod

q Evaporated3.0"

Z5

,..2.0

0 1.5

1.0-

0ý0Cunent CDE Bilayer CDE

Figure 8. Mean (±S.D.) sweat production and percentageevaporation during experiments (N - 4 subjects).

Apparently, the prototype bilayer CLE worn open allows better heat dissi-pation through evaporation of sweat than does the current MDE worn closed.This ensemble has the double advantage of reducing heat storage and limitingdehydration.

The results of this limited laboratory comparison must be kept in perspec-tive. Changes in any of the parameters defining the limits of this studywould likely diminish the apparent advantage noted by the wearing of the pro-totype ensemble.

CONCLUSIONS

Wearing the prototype open bil-yer ensemble--with the liquid-protectivelayer unzipped co the waist--resulted in lees body heat storage and less asso-ciated cardiovascular demand than did wearing of the current ensemble closed.Total sweat secretion was significantly lower, and the percentage of thatamount contributing to heat dissipation was significantly greater, while wear-ing the bilayer ensemble compared with the CDE.

14

The concept of a bilayer chemical defense ensemble, which would permit theground crew .ember to unzip the outer liquid-protective layer during a vapor-only threat scenario, has merit. Several key parameters (environmental con-ditions, persistent agent threat, work requirement, and maximum work capacityof the crew member) at the time of actual deployment would determine whetheror not this ensemble would be any better, thermally, than the current chemicaldefense ena•-ble.

The success of the bilayer concept will depend upon the refinement ofmaterial design and the understanding of the limitations of its use.

REFERENCES

1. Myhre, L. G. Field study observations of physiological responses of USA?groundcrew performing rapid runway repair activities. Aerospace MedicalAssociation Scientific Meeting, Bal Harbour, FL, 10-13 May 1982.Aerospace Medical Association Preprints, pp. 45-46.

2. Myhre, L. G. Conversation concerning research on the metabolic cost ofperforming rapid runway repair by USAF ground crew in chemical defenseclothing, Research Physiologist, Chemical Defense Branch, School ofAerospace Medicine, Brooks Air Force Base, Tex.

3. R•manathan, N. L. A new weighting system for mean surface temperature ofthe human body. J Appl Physiol 19:531-533 (1964).

4. Whinnary, J. E. Conversation concerning aeromodical aspects if wearingchemical defense personal equipment in hot weataer, Clinic Commander,Kelly AFS, TX, No, 1986.

5. Yousef, M. K., q. T. Rasmussen, and L. G. Myhre. Physiological stressesassociated with U.S. Air Force groundcrew activities. USAFSAM-TR-85-61,May 1988.

15