Laboratory Simulation of a Hot Industrial Job to Find Effective Heat Stress and Resulting Physiologic Strain

7/29/2019 Laboratory Simulation of a Hot Industrial Job to Find Effective Heat Stress and Resulting Physiologic Strain

1/7

Belding, Hari^iood S., Bruce A. Hertig and Marvln L. RiedeseLaboratory simul-ation of a hot industrial job to findheat stress and resulting physiologic strain. Ary:r". Hy.giene Assoc, J. 21: 25-31.1. 1960.effectiveIndustrial

plrrints i1.*srilrti til ltclrt cxpo$ure. '1.'lrc tr:tttilgr'-rlenl, rr,lnt*d to knol' u.hethcr this l'orlt shouldl.le re,gartlerl ls rhngi:rouslI, hot.The {irst r:tt:p in o}rl,tilirrg llr illls\\1)t \rii-{ to;rssess i.hc hc;1.{: klltl gtrrcultcrl }l' f lrt l}ro(josscquipnrmt, the rvelrtlrer lrnr{ t}rc rctir.itiris of thcrr'orkcr. This inr.olvr:rI coller:tir:n o{ irrfonnlrl.iolon glohc tempemturc, liir tcntpern,ttrre, lir r.tloc-itv, level o{ rr:tivitv lntl tiunri.ion of i:x1xr'lurc lielr.eh rrork site. From ilti-,r infornrrrtion nct ht:tl,glin to tlic bodr. by rlriiltiol {ll,) rnd colrvc{r-tiou {C} rvlrs ccnrrllrrtcrl, usirrg l,hc eocfficicntsgir.on bv HitI{, ;rncl tht: nrctnbolic rontributiotrf,o the Jr:nd (LI) wrrs cstirnntcd. Tho srrnr ofthrsc rvus t*kcrr ns tlic hcirt loud g'hich lir,rrl tolie dissipllteel b-v srre*ting (Ii""") lf ii rvorkct'nere to rcmiiin in hetl l:lluncc.

.Secondl-v, thc pottntinl ior cr.rporltivc r:ool-iug (11,,,--) u.:rs crrlrrrlnterl to lintl out rvlx,tlrcrlJre reqtrircd lcr.tl oi']oss corrki bc nriiirrtlinetl.l)openrlent prinurill' orr rvrtrir vlpor prrrssuroof lhe ntnrosplxrr: {hrrmirliir-) lnil ern irir lr;}oc-ity, it rv;rs ctxnputml rrsing ii i:ocllicient rrlso pro-r"idccl bv H&l-I.The t,hir:rl stcp in the lrplllorch rrri.s to prerlicttlrt ,rkgroe of phvsiologic s1 rrrin, rrsing thr ron-ccpts given lry It&H.Frotn infortnirtion srr]l1tlir:rl l:J' sirpttvisors lrrtrliroui clircct nlxctvrrtious, it n'rrs li':rrrrlrl 1hrr1 thrln-ork ol this qlrrlir:trlrrr itilr is t,rlirrrill'rlivirl,:rlhctu'ectt the Jirst ltnt.l socottrl Itrrlvcs of r,rrr'ltshift. Each h:rlf+hift; intolvt:s: (l) rborri. rrrlxlur of light prcprrltorl lr'ork, rr1 1.urn1x.'rrrturoslul:orrt 5'F ahot-c otit-oi-rlorlr shlr'lc irinrprltlr-lrrres: (b) the hot prirl; of 1|r1r job, r:onsisting o1'1fi u'ork-rest c'r,.eks, elreli ltrst.ing nlroul r^ix nrirr-r.rtos; ul.rr[ (ci rrst, rr.pproxinurtcll- liO rninrrtes olcreh hrll'-shiff spent in nn rrir-corrditiorrcrl lunclrtot)t1LOl"i;crvirtions ol' t.hr: condil:ioris |rcr.liling lol(lr.i, tlrc hol p*rt o{ tlrt jol:, tttrt'c ututlc lit, rl'r'-ol'ill iocnt.ion.{ olr t\1:o chvs rvhtn rir ri'l.rs enit'rirrg

Laboratory Simulation of a Hot Industrial .fohto Find Effective Heat Stress andResulting Physiologic Strain*HARWOOD S. BBLDII\G, Ph.D.o BRUCE A. HERTIG? M.P.H,9antl II{ARVIN L. RIEDESEL, Ph.D. lqGO,

tr)rpartrntnt o! Otrupot;i.onal lIealtJt. Gradu,ate Sch.oal $ Putclil: I'fccllth,U n.i.z, ersitlJ o f Pi.ttsbu'11 lt, Pittsbtt rEl h, 1 3, P erutsll Lu ania,

fYf llLN -{ ,lolt inr.olvr,s e\iro:uro ro ir po-lY rer,ti,,lh' noriorr-* ;rqclrt the rlireet lnrl oftenLh,: lrcst, r\':rv tu:lssr.js its t,ilt,,.l.s is iu olrsene1rli1'.*iologic chrngr:s rr.liich occur lrnong thosetr4to rrrc cx1-roscrl- Envircnnrrntll heal is such rnirgcnl rld il' orrc is in tloubt regarding strainsprorlrrrierl Lx' l prrrticrrlrir hot job the hcst lp-proitch is 1() nxrili:ul'o (:irfilli1tor'll rersixlnses,sn'clrting :rnrl l:oti-v 1.crn1x:lttrrre cf the rvorkers.\\rherr ciircct urcrlsrut,rrxtl, is uot fctsibie, ont:nlilJ' tr]- to llrcdict tkrgrce o1' luret strrin frourilru rxieusir,e ph.r'siological litcrrLture ou cilecl.qof ctpo-*rrrt' rtrttlcr vttions nonditiols. 'l'ltr-q is anrrccoullt ol'srrr:h itn ntttnrpt to prcclir:i,, in whicbthc svsturr ol asscssing he;r.t stlcss clescribcd l;r,Hlincs nnc[ H:rtch' *nr1 ihe s-r.steul of grld-ing .strrrin there{rorn, suggestetl b}' Bat.,tn* otrr,Hltch" (lurreintfter refenetl to as H&f{ anclIlttII, reslrcclitclv) *'cre rrtilizecl {or etalua-f.ir:u o[' :rr itirin..triili jolr irrr,o]r.irrg cslro*ure torrrlilnl hol1,. .4pplieltiou of tirc, sr'.-tons i'ieldedrr, llrrge or.ert-.stim*le of ]re*t. stress rrnd conse-cgurttlr, of rcsulting phl'siological strain.Thc fllst l)urposc oi this rrlxrrl is to lrccountIol tlris ovcrestinratc, lrorrunso others l,ho usetlur ,r1'rtorns rre lilrblc to the sulic error. Thesccontl objectir.e is to ilhrstrrLte ihe u,qe{ulnessol l:ri:rorlton' -*inurhtion lor ;rssossirrg the sevcrr-it'r' o1' l hot intlustrirl job l-he* cirr,umstnncesl)l'0\'()rlt tlilorrt s1.udv of thc *r:trrrI torkcn" Thellrirrl ol:ljcciivc is to rk'nrou-"lrric ccrtlriu friclrrsri'irich rrlc operutivc in tkrtcrmining thc rrsefrrl-ncss ol rur'llllic-cou1r'rl rcflct:tirrr rlothirtg lorI)ro1r(:{,ion rgiiiusl, r';rrliurri }rorrl.lndustriol Field Srudy

Thc job lvitir *'Irich rve llecilrrle concernecl isirr r. nol' plrrnl rrnrl r:rrnrc to otr nttontion be-r:rrusc llur first hot, rue:rllurr hlrd l-rought, corrr-u Prrl ill srrpport lor tliese sludies rvls providerl l:y Grurri,

Nr,. ltc-43{? irrrrl fltc Nrt'itrnal hrstilute$ oi llctltl). U. S.[)rrlrlic llellth Servire


2/7

g6 -. February,lg60Ta.rr,s I T.rnr,r IIAverlge Conditiorrs l)ruing tiix-minute C.vcles llstimade of Hourll' Heat Load of Hot ptr{; ofof Hot Job Job* in g0oF Wenther0utsi


3/7

Indu,strial Hy giene J ournalrvind tr.rnnel through rvhich air t'as being movedat approximatell' 250 feet per minute.Thc rvork, which rvas repeated at 10 secondintervals, involved standardized arm and backmovemcnts in pulling and releasing a 30 poundrveight. It n,as performed from a fixed stance,u'1iile facing a batterl' of Calrod heaters im-beddecl in the tunnel llnll. Heat intensity I'asadjusted so that the average temperature ofthree blackened Vernon globes mounted verti-calll in the position occupied by the subjectrvas 142'F: at the air temperature (97') and air."peecl (250 ft/rnin) in tliis position, the meanracliant temperature rvas calculated to be 205'F.During the trvo-minr-rte rest of each cyclesubjects sat in a corridor outside the u'indtunnel. Herc, both air and rvall temperaturess'ere 95"F, and air speed was 400 ft/min. Acomparison betwccn the situation predicted forthe industrial job on a 90'F day and the situ-ation created in the laboratory appears in TableIII. Note that the predicted total heat loadat rvork and at rest in the laboratory (derivedusing the H&H sl.stem) coircsponded well rvithtlie prototype field situation. In the laboratorymodel, this was accomplished *'ith a somervhat-qmaller fraction of metabolic and convectiveheat and somervhat larger of radiant.The subjects rvere three ]'Ioung men, aged 20,20, and 28. The-,v lere acclimatized for t'orkin the heat.Initially, effects of three levels of ambientvapor pressure and three types of clothingassemblies rvere sought, using the three subjects.Accordingly, a Latin Square design calling fornine exposures rvas u-sed. The three vapor pres-sures originallr. spec fied rvere intended to in-clude one situation in rvhich evaporation rvaspredictcd to be adequate for maintaining heatbalance (17 mm Hg) and another in which it*,as not (22 mm Hg), in addition to the levelof critical interest in the actual industrial situ-ation (19 mm Hg) . Failure to find that limiton evaporation \\:as critlctl) elren at 22 mm Hg,led to trial of 25 and 27 mm Hg levels. This in-volr.ed a seconcl Latin Square arrangement usingthe data alread5- collected at 22 mm Hg.The three clothing assemblies rvere specified inorder to obtain comparative data on ordinaryas well as metallic-coated clothing, and on me-tallic-coated clothing rrhich permitted trvo de-grees of ventilation of the skin. Seminude stattiswas specified in a collateral series to achieve adirect demonstration of blocking effect of ordi-nar-v clothing against radiation. The four as-semblies are described belorv:(a) ordi,narll work clothing, . consisting ofcotton khaki shirt and trousers, Iong

ory

Te.nr,n IIIEstimate of Average Heat Load on the ActualJob on a 90'F Day and in theLaboratorv Studv

Actual job LaboratorystudyDuratiou (hours).....Cycle tine (minutes)

Body heat production(BTU/hour)

Radiation(BTU/hour)

Conrection(BTU/hour)

Total ]reat load(BTU/hour)

workrest. .both.workrest. -bothworkrest.bothworkrest.both

1.8*4.02.06.0760160

106060

1120530

-605702450

1602610

2.04.02.06.0540130670

17300

1730110

0110

2410130

2510

rvorkrest. .both

* This is {or each half-s}rift and neglects prior one hour of lightwork v'ith heat load equivalent to about 500 BTU.cotton underdrawers, tee shirt, cottoncap, cotton Nork gioves' cotton socksand leather shoes, and dark glasses;(b) reflectiue apron assemblg, rvith kneelength metallic-coated asbestos apron andknce-length leggings (the latter opendorvn the backs of the legs to favor venti-lation), over items of outfit (a), exceptthat cotton shorts were substituted forlong underdrat'ers;(c) reflectiue coat assemblg, rl-ith knee-lengthmetaliic-coated :lsbestos coat, knee-length leggings rvrapped completelyaround legs and hard hat, over itemsof outflt (a), except that cotton shortsrvere substituted for Iong underdrarvers;(d') seminude assemblg, rvith. socks, shoes,-qh6fi.s, gloves and dark glasses only.Results of the physiological study u'ere usedto furnish a chcck on predicted heat stress that'r,r'as ca,lculatcd from environmental conditionsand measurement of the heat produced in per-forming the rvork. The result of each exposure

rvas production of srveat, with or rvithout heatingup of the body tissue. Whcn the sweat wasevaporated from the skin we knew that about2.3 BTU of heat rvas removed from the skinper gram because this is the heat of Yaporiza-tion of rvater at 95"F. The amor-rnt of srveatevaporated was considered to be represented by


4/7

OQ

thc gross loss in clothecl rveight cluring cxposure.Suitable correction rvas nade for u'eight of rvaterimbibed. This method r.ielded overestimate ofevaporative cooling to the extent that sweatdripped off or lr,as evaporatcd fron the clothesinstead of the skin. Obviousl)., anv part of thes*.eat *.hich st:r1.ed in the clothes rv:rs ineffectivefor cooling. In case-s rvhcre there l'as storage ofheat in the bodr. tissues, inclic:rtecl b1 rise inbodl- temperature, tlie amount hacl to be esti-nated and aclcled to the evaporative heat lossto obtain actual heat load. Storage was calcu-lated from ayerage ri.qe in body temperature(skin temperature l-eightecl 1/5, rectal a/il Xbodr. u'eight X specific heat of bod-v tissue. Inthese stuclies, storage r.as negligible except underthe most dilficult combinations of conditions.Recovcr.r. pulse rate, the average of 30-secondcounts taken one mimrte after each four-mimrtcrvork period, rl as used &rq :t rrruSllr of circula-torl: s1."in. The rates obtained rvere acljustedto compcnsate for individual differences betweensubjects. Nude rveight lo.qs * ri.eight of r.aterimbibed rv:rs the measLue of srveat. Fatignc lvasindicated on a point scale, r-it1i fir'e points in-clicating inabilitv to continue.Protection, with Ordinary Il:orl; Clotlti,ng

Hea,t stresses ancl strains of exposure rt\.ilriou-q vapor prcssures in ordinrrv l'ork cloth-Tenr,n IVHeat Stress and Strains of Performing a Hot Jobin Ordinar-v Worl< Clothirrg

lleat stresspredicted heatIoad..........

February, 1960ing are given in Trble II. E""' of this rvork waspredicted to be 2540 BTU/hour. The actualheat loacl i.illpears to havc becn about 1740BTU/hour, onl-v 6g pcr cent of the prediction,suggesting error in estimate of X,I, R or C inm&king the prcdiction. II, determincd b1,' sam-pling of ox-vgen consumptiou, :rnd C) negligibleunder these conclitions becar-rse skin terlpera-ture anfl air tcmperaturc \\-ere both :Lbout 95'F,r.ere not subject to important error. Therefore.Il corrlrl hrrr o been no n'or" rlrrn rborrt lU70BTII/hour, 62 per cent of its predicted vahie(cf Tablc III). It appear.i that thi-s ordinarywork clotiring blockecl nearlr' 40 per cent ofimpinging radiation.\\ritli the :rctual hert lo:rd at 1740 BTU/hourcvaporate c:r1racit1' should become a critical fac-tor at vapor pre-qsures above 22 mm Hg. Thephr,siological data indicatc that -strain \va-s Lln-affected at vapor pres-sLtres from 17 through22 mm Hg. At 25 mm Hg rcctal tempcratnrerise ancl reco\rer). pul-se r:lte l-ere significantlr.higher as t':Ls fatigtre. Sl-eating and t-astecl st'ertrvcre not increasecl until the next higher levcl,27 mm Hg, r.:Ls rcached.In a, collateral stndl', rn tLttempt rr.as madc todernonstratc the protectir.e cffect agninst radi-ation more clirectl1., br. exposing the .subjects tothe same ra.di:rtion source l-hile scminucle anclclothed lnd comparing thc rctual helt loaclin the tu'o cuses. The ler-el of recliant hcat useclin thc previoLls exposrlrcs l-ls founcl to be in-tolerable rvhen seminrrde, (furnishing qualitativecvidencc of blocking effect agrrinst the raclilntload). Ilesults obtained after rirdiltion had beenrednccil to :l tolerable ler-el ure -summerizcd inTnblc. \,-. Hcre, blocking of abotrt 30 per ccntof impinging energv resulted from the \rcaringof orclin:trr. clothes. The resultinq clecrclse instrain n'a-s signilicant.Heat Reflectiue ClLotling

Effects of wc:Lring metallic-co:Ltecl clothing onthis iob t-ere studied because of interest in thcirpractic:rl nscfulncss for clecreising strain. Thcreflcctir.e llpron outfit sccnred sensible becauseit coverecl most of the arer directll- cxposed toratliation, rncl nppeared to provide minimnminterfercncc u,ith evrporrtion. Thc outfit rvithrcflcctive coat and itcces,cories promised sorne-r-hlt rnore lrrotcction, but rt thc cost of nnurlknoryn lmount of interference tr,ith cvapora-tion.Rcsults are summarized in Table VI. Thepreclicted heat load of 25.10 BJlTlh6ur againr.as the rcsult of 680 BTU contributed br- X,Iancl a snperimposed 1760 BTU b1. R. The a\.erageprotection against radiltion of ordinarl' r.ork

predicted uaxi-Ilum evapori!tion..... .. ... 21701880

22{0520

19901680

21r'0480

actuzrl heat loadIIeat strainssrveatina......rvasted s*.eat(in clothing).lectal terrpera-ture rise.....sliin ternpera'ture.... .....recovery pulser&te.......-..metabolic ]ieat

production ..fatigue after 2horrrs

2170180

3040920

+0.795.4

280

-0.295. 197

660+

0.094.592

680

+0.295.591

l*.,95.0

]',,jzoo

'F7'2 hrs.F

++* Overestinate of load due to drip off of sweat.


5/7

Inclustrial Hy 91iene J oulnalclothing, in this c:Lse rrvcraging 39 pcr cent, I'asririsecl to 52 per cent b1. use of the rcfiectiveapron lnd to 66 per cent b1'use of tlie reflectivecoa t.That the urlvant,age of such clothing is r.rotnecessarill. proportional to the protection rvhichit provides rgairist ntdiation is indicrted b1' theobscrvetion.q on strlin. Sl.eating, recover-v pulserate ancl fatigue r.ere somctr,hrt le-ss in thereflcctive :llrron than in the orclinur\'["ork cloth-ing. In the lor.er rirnge of r'-apor prcssures,strain in the reflectir.e cort rvas abor,rt equal tothat in the ordinarl-*,ork clotiring, but at higheryapor pre-ssllres the reflective coat caused signifi-cutl1' gre:lter strain.Discussion

Hacl sole reliance becn placed on results ofthe plarrt stttdv ancl predictions of heat strainby thc ncthod of I3&H, this job would havebeen classecl :rs overlv .stressful in hot, humiciweather. In f:rct, at 90'F and 19 mm Hg theHeat Stres-" Index (HSI) r'ahre for thc hot partof thc job u'a,q 155 (100 is supposedlv the maxi-num regularll' tolerable for a full -shift), andthe preclictcd tolcrance timc for the rr'ork wasa maximttm of 16 niinutcs at a timc. Industrialcxpcriencc belied the prediction and the labo-ratorv studv indicated the source of the crror.In terns of HSI thc real stress u'as ubout 85.In vier.v of the fact that ordinarl' clothing, re-g:rrdless of its color, has a verl' high absorptiveefficiencl. for long-rvave radiation of the typeu-sed in t1'ris stud--v, erplanation of the observationthrt such clothing actualll' blocked 30 to 40 percent of impinging racliation is in orcler. Theprinciple involved x-a.r originlllv establishedin stuclies of thc efficieno' of electrical heatsr.rpplied to flving clotliing, and lias been citedbv Bnrton" as applicable for determining effi-ciencl' of cvnporation of moisture from clothing.\Yhen heat is rclcased or taken r.rp in clot,hing theefficicncv for ri arming or cooling the skin isindiclre,l bv the r:rtio:

insulation outside locus ofrelease or uptake of heattotal insulatiori over skinThe total insulation of orclin:rr.v l'ork clothingwill be provided b:. (a) air trapped in thc fabricancl between the fabric and skin, and (b) ihefilm of air overll.ing the fabric. Thus, to ac-count for a 60 per cent transmission for imping-ing radiation, as in tr'igurc 1, it is on11'necessaryto assume :rbsorption near the surface of thefrbric, end to iissumc that 0.4 of the insulationlies under the locus of absorption and 0.6 over,thc lrrtter bcing attributecl largell' to air fi1m.

T.q.sr,p \rEffcct of OrdinarS'Work Clothing onRadiant Heat Load

29

Seminude Clothed

Predicted Radiant Load.Apparent -{ctua1 Radiant

Load(evaporation -| storage.- metabolisrn)........total....Load Blocked by Cloth-ing......./6 blocked.Er.idence of Strainsweating.rvork and tecoverybeart rates.. .. -......rectal telrperature rise.mean skin ternperatureskin circulation re-quired to renovernetabolic heat... .. ..

1210 BTL:/irr

1480 + 10-680810 BTU/hr

.100 BTU/br

1760 B.l.LT/hr96 - 86 per rnin-0.2 "F/hr95.2

1 .2 liters/min

1210

t800 + 80-680

1200

4{t3

1810105 * 91-0.196.2

1.7

T,lsr,n VIHeat Stress and Strain of Tu'o-Hour Exposuresin Three Clothing Assemblies(Heat in BTU/hr)

Predicted RadiantLoad..........Actual Radiant Load(eveporation +storage - rue'tabolism)Protection againstRadiation.......per cent protectionS{'eating. .efficiency for cool-ing:

load-x100weat

Recorery Pulse Rate(per rnin)

Fatigue after TrvoHours...-.......

HzO Vupor 17-22 HrO Vrpor 22 27mm Hg mm Hgrllitl:F == ir =Fl ==:o Lz .:.e o: oot> E< =uJ =-t ?< i-atratzl-rllr;nu r760 1760 1760 1760 1760liloo ;oo I o+o I 160 lro I sio

I

l760 1000 1 120 0u0 820 I 180137o Sira 6tra Slab .ir, 67i2()oo l;80 2roo 2 t8o 12260 2.roo L'ltL

8yt srz] o:", tlaa n";J 5'tne2 87 ,, | ,oo s7 roo F

ltl++ - Fr-1*-1-rL ,l*1*'I* Exposure at' 27 mm IIg \vas terminated after onecause of oversirain. hour be


6/7

30 Febru,ary, 1960strain of the real job must be hedged. Thc lab-oratorl' studl. involved abont half as nuch ex-posure time :Lnd less than half as much u-ork perda1'as was per{ormcd on thc reai job. Further-more, the laborator-v situation did not simulatethe extreme air temperatures possible for a ferv

IOO units of Rodiotion NUDE

4O Unirs Convctionond Rerodioiion

Locus of Absorptionin Fobric

lnsuloling

Frcunn 1. Diagrammatic cross-"section throughshin and clothing to shol' factors affecting effi-cicncl' 6f protection against long-rvave radiantenergy.Then, 0.6/1.0 X 100 : 60 per cent. (In thissituation the absorption level probabl-v rvascloser to 95% than 100% because the Calrodheating elements rvere radiating partly in thevi.qible spectrum, in that they a,ppeared dullred.) Other studies indicate that this model isentireil. reasonable. Since :rir speed affects boththe insulation of the clothing itself and of theoverlying air film lve may assume that the block-ing efficienc-v of about 40 per ccnt seen underthe condition of this stud,v ma1. have a rangeof 30 to 50 per cent lor most rvork clothing usedat most air speeds. Clothing also blocks transferof heat b1' convection, not considered here be-cause there w&s no temperature gradient be-trveen skin and air. Inward convection undoubt-edly 6s.,,..a.1 during performance of ."ubtasks(a) and (b) of this industriel job. Evidcncefrom other sources indicates that the ratio ofblocking of convective transfer rvith this amonntof clothing may be about the samc as for radi-ation. On this basis it is provisionall"v recom-mended that value-q for R ancl C computed b1'the sr.stem of H&H be muitiplied b1. 0.60 rvhen\yorkers are covered lith light clothing. Thi-q isIogical bccause the coefficients of H&H n'creadopted from studies on nude men.'The accumulated evidence from other physio-iogical studies (cf. references given by B&H)indicates that the peak requirement of this jobfor energv expenditure, for circulation of bloodto the skin, and for sweating rvill not be ex-ces-si'n.e as long as the heat loacl does not exceedthe capacity for evaporatiye cooling. Hot'ever,conclusions from the re-creation as reEa.rds

hours at a time somctime during the summer,cLorHED the conditions in an emergenc)' rvhich requireclextra, rvork, or the cumulative effects of a pro-longcd halt ii'ave.The margin of safetl- in the lnboratorl' s1l',6oapears to have been about 250 RliU7t o.,r,basecl on the difference bett-een the actr.ral heatIoad of about 1740 BTII/hour and the E-"- of1990 IITLT/hour predicted at 19 mm Hg. Thismargin I'ould allolv anJ. onc of the follorving: anincrease in air and r,r'all temperatures of at least5"F; a rise in ambient vapor pressure of B mmHg; an increase in l'ork ler.el of 50 per cent; oran rrnderesiinrrte oi tho actu:lI l)orl lold or over-estimate of E-," :rmounting to 12 per cent. Them:lrgin of safetl, is further augmented b1. thefact that 250 BTLT of unbalance rvill be toleratedfrom time to time.r*evertheless, the strrin of this job is largerel:rtive to the margin of safetl'. Tlie complexitiesancl uncert:rintics of prediction of strain frominformation limited to environmental measrrre-ments and observation of the activitr. serve toemphasize the real neecl for measuremcnts ofstrain directl)r on the workers, on the hottestdavs, before making confident statements re-garding risk to health.The stucll' of effe cts of metallic reflectiveclothing in some respects is not an adequatebasis for gencralization. Under the circumstancesof use, greatcr protective effect against racliantlieat r.vas the prediction." That the protectionr,as at the 65 per cent ratlier than the 80 to 90per cent level mir1. be s1rpri..ing. Burtono hasreported linding that belorv a critical size me-tallic particles do not reflect long-r,ave energy(e.g., flnel)' divided platinum is "black"). in.some application.s the binder u.qed to assure ad-herence of the metal to the fabric, or a cover-ing lacquer has itself been a poor reflcctor forlong r.vaveJength radiation. ft has also beendemonstrated that the presence of even a thinfilm of oil or dirt (not pre-"ent in these tests)cl n de.r rov r he reffeel ir i tr-.For protection against verr. high levels ofradirnt herf ovor pcriojs of minutns, design oimetrllic rellerlive ovot"gtrnrents so t hrt tlte\.will permit ventilation and consequent evapo-ration of su'eat is not critical, and in fact suchdcsign ma1. be contraindicated if air tempera-tures are expected to be r.'erv high. Horvever,ior cxp6.ulps mcasured in hours, design to per-


7/7

Industrial H y giene J oumalmit evaporation of sweat is all-important. Inthe preseut studies a net decrease in strainrvith reflective clothing was noted only with therefleetive apron assembly, and this decrease wasscarcely enough to justify provision of apronsfor this job because experienee has sholvn thatsxtra items of protective clothing fall into di!-uso unless the advantage which lhey give iselearly felt by the users.Summory ond Conclusions

Laboratory simulation of environmestai andwork conclitions of a hot industrial job revealedthat resulting heat strain was substautially lessthan had been predicted by the iudex of Beldingand Hatch. This was attributed to blocking ofabout 40 per cent of impinging radiation bythe ordinary *e1ft slslhing that was worn- Thisblocking effect should be taken into aceount infirture use of the lleat Siress Iudex.The laboratory analysis indicated the proba-bility that this partieular industrial job is physi-ologically safe, but that the margin of safetyis too narrow for full reliance on this estimate'Confidence in this prediction would best be in-

@7tr I

creased by making simple physiologic obser*vations on actual workers under the hottest'weather conditions.Metallic reflective clothibg provided someaclditional protection againsii beat lead. Whensuch clothing is to be worn for periods of hours,itlvas shorrn that the design must permit goodventilation 4s a means for achieving evapora,-tion of sweat; othenvise such clothing may giverise to more strain than ordinary work clothing.References1. garN$s, G. I., Jn., exo T, I" Illrcn: fndushial l{entSxposuree-Evaluation md Control. .Eleor" and' Vent' 49:03 (Nov. 1952).9. BBr.nnrc, H. S,,,rxD T. F. Ifarcn: Index lor EvaluotingEmt Strcss in Terms o{ Beultine Physiological $trains.Ileat. Pip. md Air Cond.9/: 120 (Aug. 1956).3, BnBToli, A, C,, eul O. G, Eosor,u: Mm i* a Cokl En'uilonnent, p, ?0, Eclward Araold Ltd', London (1955)'4, NELsoN, N., L. W. ErcuNa, S' M. f,onvats, aND T. tr'.H,rrss: Tbermsl Exohange of Mon at figh Environ-menia.l Tesper&turea' An. tr. Phusi'ol. 151: 02S (19{7) .5. FooBr, L., Art'D M. Ilrnrus: Phgsiologu ol Hmt Regula'tion and the Stiet ce al Clothiw, Ed' L. E. l'Ien'burgh' p.

301, W. A. Sauaders Co. (1949).0. Bunro:v, A, C.: ?rivato Commuicslion.

Documents

Laboratory Simulation of a Hot Industrial Job to Find Effective Heat Stress and Resulting Physiologic Strain