On the Transition Thermal Discomfort to Heat Stress as a ... · On the Transition Thermal...

On the Transition Thermal Discomfort to Heat Stress as a Function of the PMV Value

Francesca Romana d’AMBROSIO ALFANO1, Boris Igor PALELLA2* and Giuseppe RICCIO2

1 Dipartimento di Ingegneria Industriale, Università di Salerno, Italy2DipartimentodiEnergetica,TermofluidodinamicaApplicata eCondizionamentiAmbientali,Università degli

Studi di Napoli Federico II, Italy

Received September 26, 2012 and accepted January 9, 2013 Published online in J-STAGE February 4, 2013

Abstract: ISO 15265 Standard − Ergonomics of the thermal environment − Risk assessment strat-egy for the prevention of stress or discomfort in thermal working conditions − can be considered as a key document for helping responsible for the health protection and prevention of working situ-ations. According to the SOBANE strategy, this standard provides a three-step protocol aimed to the prevention, elimination or reduction of risks affecting the workplaces. Although both methods and procedures suggested by ISO 15265 appear very clear, this standard could bring in confusion both beginners and not specialists in occupational health concerning Predicted Mean Vote (PMV) threshold values consistent with comfort − hot discomfort and the discomfort − hot stress transi-tions. In this work such matter has been extensively discussed showing a certain difficulty in the definition of an unambiguous PMV threshold value for each working situation in any microclimate.

Key words: Hot working environments, Physiological heat stress, Predicted heat strain model, PHS, Physical agents risk assessment

Introduction

TheEuropeanDirective89/391/EECdevotedtothein-troduction of measures to encourage improvements in the safety and health of workers at work1) moved the interest of the occupational hygiene to the risk prevention rather the risk assessment, leading to an Industrial Health for all as stressedbyParsons2). This policy resulted in the for-mulationofaspecialstrategycalledSOBANE,developedbyMalchaireatthebeginningof21stCentury3, 4) actually validated in 14 fields (social facilities, safety, machines and hand tools, electricity, fire and explosion, lighting, work on VDUs, noise, thermal environment, chemical

agents,biologicalagents,musculoskeletaldisorders,WBV,HAV).SOBANEstrategyisdevelopedinfourphases:1)screening;2)Observation;3)Analysis;4). In thefieldofthermalenvironments,thisstrategyisthebaseoftheInter-national Standard ISO 152655) devoted to the evaluation of the risk for the prevention of constraints or discomfort under thermal working conditions. The Standard provides foraprotocolofinvestigationcharacterizedbyathoroughanalysis of the working conditions aimed to identify quick solutions foreasyproblemsor special investigations incomplex situations. Therefore the main goal is not the quantificationof the risksbut theirprevention,elimina-tionorreduction.InISO15265thegoaloftheSOBANEphasesare:a)Observation. ISO15265Standard5) requires only a

preliminarycollectionofinformationabouttheworksitu-ation, in general, concerning the working conditions, the

*Towhomcorrespondenceshouldbeaddressed.E-mail:[email protected]

©2013 National Institute of Occupational Safety and Health

Industrial Health 2013, 51, 285–296 Original Article

FRd’AMBROSIOALFANO et al.286

Industrial Health 2013, 51, 285–296

climatic conditions and the heat or cold sources. The air temperaturecanbemeasuredwhile theothersvariablesresponsible for thephysiological responseof thehumanbody6) to the microclimate (mean radiant temperature, airvelocity, relativehumidity,metabolic rateandcloth-ingproperties)have tobeonlyestimated.Moreover itprescribes to take intoaccount theworkers’ judgementattributedonmono-orbi-polar scales,where thezeroscorecharacterizes theoptimal situation.Thenumberofpreventiveandcontrollingactions tobe implemented(e.g. a changing of the clothing, a shielding of the radiant surfaces and so on) is strictly related to the deviation with respecttozero(inprincipletherangeofacceptabilityisintherangefrom−1to+1onabi-polarscale).Inanycase,if the actions of control were not enough or their imple-mentationdidnotleadtoforeseeableresults,afurtherstepof analysis is needed.b)Analysis.This phase is basedon a three-steps

investigation. The analysis on the sequence of activities carried out in the workplace and some thermal comfort facets isprimarilyrequired. Inparticularshouldbe takenintoaccountpossiblerisesorfallsof theair temperature,differences of the relative humidity indoor-outdoor, the solar direct radiation, hot and cold surfaces, draughts and, finally, theworkloadandtheclothingcharacteristicespe-cially if protective clothing is required. The second level deals with the assessment of the working situation and the calculation of the main indices. The third level requires theriskassessmentbasedonthevaluesoftheindicespre-viously calculated. Finally, after the identification of the preventive and the short-term controlling actions, the real situationhastobecomparedwiththepredictedoneaimingtoassesstheresidualriskandtodefinetheprotectiveandmedicalsurveyactionstobeimplemented.Inthiscasethesixvariablesresponsibleforthephysiologicalresponseofthehumanbodyhavetobeestimated(incaseofpersonalparametersbymeansoftablesreportedinStandards)onlybycommontechnicians.

c) Expertise. This further step is required if the analysis stage does not lead to the solution. In particular it is aimed to quantify, analyse and assess the risks trying to solve all thoseunsolvedsituations recognized in theprevioussteps. To this aim special skilled personnel and the use of sophisticated measurement techniques are required. The implementation of this step requires a preliminary selec-tionof the situations tobedeepened, thedatacollectionunder average and extreme conditions and the calculation of the indices.Moreover, it requires thedefinitionof thepreventive and controlling actions, the selection of the

modifications tobe implemented (e.g.microclimaticparameters,workorganizationandsoon),theassessmentof the residual risks and, eventually, the choice of the measuresofpersonalprotectionandmedicalsurveytobeadopted.

The assessment of the class of risk in the analysis step isbasedonthecalculationofthePMVindex(andtheap-plication of PHS7–11) and IREQ12–14) models depending on the situation) which plays only a role of indicator in long termexpositionsasshowedinTable1. In particular, ISO 15265requiresforhotdiscomfortsituationsaPMVvalueintherange0.5–2.0,therebythetransitionvaluebetweendiscomfortandstress is justatPMV=2.0.Underhotsevereconditions,whenPMVexceeds2,theimplementa-tion of PHS (Predicted Heat Strain) model is required8–11); bythiswaythemaximumallowableexpositiontime,Dlim, shouldbecalculatedaccordingtoISO7933Standard7). In thisway, theclassof riskseemsveryeasy toassign,buttwoaspectsappearnotclearenough:i)ISO15265placestheonsetofdiscomfortatPMV=±0.5 indisagreementwith ISO 7730 Standard15) where the comfort-discomfort transitionissettledatPMV=±0.7(lowendandhighendofthecomfortrangeoftheclassC);ii)workingsituationsin thePMVrange0.5–2.0have tobeconsideredasonlyuncomfortableor in this range is itpossible to reach thelimit situation Dlim=480minwith theconsequentneedtomodulate theworking turn? InotherwordsPMV=2.0hasreallytobeconsideredasathresholdvalueofthehotstress for any microclimate and working activity?Thesefacetscannotbeignoredbybothpractitionersand

experts of Occupational Health since a wrong assignation of theclassof riskof theenvironmentcouldbring toan

Table 1. Classes of risk reported in ISO 15265 standard5)

Class Criteria

Immediate constraint Dlim < 30 minConstraintintheshortterm Iclr< IREQmin

DLE<120minConstraintinthelongterm PMV<–2

IREQmin≤Iclr ≤IREQneutral

Colddiscomfort –2≤PMV<–0.5Comfort –0.5≤PMV≤+0.5Warmdiscomfort +0.5<PMV≤+2Constraintinthelongterm* Dlim < 480 minConstraintintheshortterm* Dlim < 120 minImmediate constraint* Dlim < 30 min

*in these situations the water loss for 8-h of continuous work and the predicted risk of increase of the internal temperature of thebodyaccordingtoISO7933standardarerequired7).

DISCOMFORT-HEATSTRESSTRANSITIONASAFUNCTIONOFPMV 287

ineffective strategyofpreventionandprotection.More-over thisuncertaintycouldbe further increasedby thehighsensitivityofPMVindexandPHSmodel to theer-rors of measurement of personal and physical parameters, as showed in several papers16–20).Asamatterof fact, apoor measurement accuracy on one or more parameters (in particular the mean radiant temperature) although within theaccuracy requirements suggestedby ISO7726Stan-dard21),orunforeseeablenumericalmatters22), can lead in hot environments to a wrong assessment of maximum allowableexposure timeswhichundercertainconditionscanbeunderestimatedupto5h16).Aimingtoleadtoaclearandunmistakableclassification

of the risk of working situations in the presence of heat strain, this paper will deal with the identification of the PMVthresholdvalueforwhichthetransitiondiscomfort-hot stress can occur.

Methods

In order to evaluate, in case of long term exposition (Dlim =480min),theminimumPMVvalueatwhichthework-ingactivity shouldbe interrupted,numericalanalyses inthreesequentialstepshavebeencarriedout:a)inthefirstphasebothpersonalparameters(metabolic

rate and clothing insulation) the mean radiant temperature andtheairvelocityvalueshavebeensettledin therangeofvalidityofbothPMVandPHSmodel (Table2). It is noteworthytoobservethatISO7730Standard15), devoted only to moderate indoor environments, suggests the use of PMVindexonlyintherangefrom−2to+2;anyway,sincethe goal of EN ISO 152655) is the protection of workers bytheonsetofsuchconditionsrecognizeddangerousforworkerswehavetakenintoaccountPMVvaluesupto+3consistently with the original Fanger’s approach23);b)on thebasisofabovementionedvalues, theair tem-

perature and the humidity ratio values consistent with 8 h ofcontinuousworkaccording toPHSmodelhavebeencalculated(thesevalues,havebeendepictedonapsycho-

metricchart todefine inagraphicalway the limit curves of the working situation under examination11, 16));c)Finally,thePMVindexhasbeencalculatedfromthe

valuesobtainedasinb).Asthemathematicalfunctionbindingpersonalandmi-

croclimaticvariables to thephysiological responseof thesubject to the thermalenvironmentaccording to thePHSmodel is not handy to treat8–11), a special package devel-opedinDelphilanguagehasbeendesigned24).Accordingtothecaseunderinvestigationitisabletoreturn:•thefinalvaluesof the rectal temperatureand thewaterlosspredictedbyPHSmodel8) after eight hours of con-tinuous work;

•limitcurves for8hofworkingduration in termsoftemperature-humidity pairs;

•PMVvalueasafunctionoftheairtemperatureandthehumidity on a limit curve.ThecalculationofthePMVindexhasbeencarriedout

bytakingintoaccountthecorrectionoftheintrinsiccloth-ing insulationvalues related to theeffectofbodymove-ments25–28).Numericalcalculationshavebeencarriedout in the

ranges of personal and physical parameters consistent with thevalidationofbothPMVindexandPHS(Table2)andherereportedinTable3. In particular, concerning the met-abolicrate,theaveragereferencevaluesforlow(1.7met,class 1), moderate (2.8 met, class 2) and high (4.0 met, class3)activitiesproposedby the ISO8996Standard29) havebeenstudied.Due to theobviousnarrowrangeofapplicationofPMVindex (Table1)with respect toPHSmodel,underenvironmental situationscharacterisedbytemperature-humidity values over the application range of PMV(orsuchasPMVvalue isgreater than3),Fanger’sindexcanonly tobeconsideredas indicatorofextremeconditions.OtherpersonalorbehaviouralparametersrequiredbyPHSmodelhavebeenfinallyreportedinTable3;inparticularasPHSmodelhasbeenvalidatedforcloth-ingprovidedwithavapourpermeability similar to thoseexhibitedbycotton fabrics8, 10, 30), a reference value of

Table 2. Ranges of validation for PMV index15) and PHS model7)

Parameter PMV PHS Unit

Airtemperature 10–30 10–50 °CMeanradianttemperature 10–40 – °CDifferencebetweenmeanradiantandairtemperature – 0–60 °CWatervapourpartialpressure 0–2,700 0–4,500 PaAirvelocity 0–1.0 0–3.0 m·s–1

Metabolicrate 0.8–4.0 1.0–4.0 metClothingthermalinsulation 0–2.0 0–1.0 clo



0.38hasbeenadoptedforthestaticmoisturepermeabilityindex imst.

Results and Discussion

Inorder tomakeeasierboth the readingand the inter-pretation of the results here discussed, a typical limit curve of 8-h of continuous work in Fig. 1hasbeendepicted.Accordingtopreviousresults11, 16, 17), such a kind of curve

usuallyexhibitstwodiscontinuitiesinthesloperelatedtoadifferentkindofphysiologicalstraininducedbyheatinthehumanbody:•Area1. In the low temperature−highhumidityarea

of the psychometric chart, the physiological response of thehumanbody to theheat ismainly related to theattainmentof themaximumvalueof38.0°Cadmittedfor the rectal temperature31). Under these microclimatic conditions, sweating isunable togetover theheatac-cumulationfromthebody.Inparticular,thepoordrivingforceavailablefortheevaporationofsweatfavourstheincreasingoftheskinwettedness−withtheconsequentsweat trickling− leading toa supplementarydumpingof the evaporation due to a high skin wettedness and/or apoor sweatingefficiency8, 9, 32, 33).Asaconsequenceeven slightly changes of the air humidity result in strong variation of the air temperature values consistent with a 8 h-work shift;

•Area2. In thehigh temperature− lowhumidityzone,the thermoregulatory system tries to remove the heat accumulatedby thebodybymeansofahighsweatingrate. Under these conditions the rectal temperature pre-dictedbyPHSmodel isalwaysbelow38.0°C,but thestress inducedby thehotmicroclimates is leading thebody to the incipientdehydration (according toprotec-tioncriteriaonwhich ISO7933Standard isbasedon,the maximum admitted water loss is from 5% to 7.5% inweightof thewholebodymassdependingby theacclimatationstatusofthesubject).Inthisareathehighslopeexhibitedbythelimitcurveistheconsequenceof

Table 3. Physical and personal variables values investigated and non-measurable pa-rameters values required by PHS model7)

Parameter Values

MeasurableAirtemperature 15–50°CMeanradianttemperature 20–60°CDifferencebetweenmeanradianttemperatureandairtemperature 5÷10°CAirvelocity 0.10, 0.50, 1.0 m·s–1

Watervapourpartialpressure 0–4,500 PaMetabolicrates 1.7, 2.8, 4.0 metClothingthermalinsulation 0.20–1.0 clo

Non-measurableWeight 75 kg Height 1.70 m Posture StandingStaticmoisturepermeabilityindex 0.38Acclimatizationstatus Yes/NotFreelydrinkingpossibility Yes

Fig. 1. Microclimatic conditions expressed in terms of tempera-ture−humidity pairs consistent with 8 hours of continuous exposition predicted by PHS model.M=1.7met,Icl=0.2clo,va=0.1m/s,acclimatizedsubject.


the poor sensitivity of PHS model to the relative humid-ityduetothehighsweatingrateandefficiencyfavouredbythelowRH values.

•Area3.This isa transitionzonewherebodyheat re-moval is simultaneously related to the reaching of the maximum heat accumulation and the maximum water loss.

Discomfort-stress transition under uniform conditions (ta=tr)

The discomfort-stress transition under uniform condi-tionsasafunctionofthevalueofthePMVindexhasbeenhighlightenedbymeansofthespecialplotsshowedintheFigs. 2 and 3where theeffectsof themetabolic rate, theclothing insulationand theairvelocityhavebeen takeninto account. Before starting the discussion, a preliminary introductionforhelpthereadingofthefiguresisanywaynecessary.Fromageneralperspective, todescribe thechangingofthePMVindexona8-hlimitcurveconsistentwithPHSmodel, a special3-Dplot shouldbenecessarywithaconsequentpoor readabilityandahard interpreta-tionofobtainedresults.Toavoidasocomplexrepresenta-tion,twostack-plotshavebeenused:intheupperboxforthedesiredmetabolicrateandthespecificclothinginsula-tion values, the nominal microclimatic conditions consis-tentwith8hofcontinuousworkarehavebeendepicted;followingthearrow,thecorrespondingPMVvaluecanbereadontheplotbelow.AccordingtothecurvesdepictedinFig.2,theincrease

of the air temperature on a 8-h limit curve consistent with PHSmodel,generallyresults in the increaseof thePMVindexwitha sensitivity softenedby the increaseofbothmetabolicrateandclothinginsulation.Inparticular,astheslopeof the8-h limitcurves increaseswithbothMandIclup tobecomequitevertical, theconsequentvariationof thePMVissoftened,obviouslydue to itswell-knownpoor sensitivity to the humidity23). Due to the promoting effectoftheairvelocityontheheattransferbyconvectionand evaporation, the 8-h limit curves shift towards higher valuesof theair temperature(Fig.2onthebottom):asaconsequence thePMVvalue increases inall investigatedsituations and systematically exceeds the threshold value ofPMV=2suggestedby ISO15265Standard forva=1.0m·s−1.OnthebasisoftheresultssummarizedinTable4, it is

possibletorecognizethattheminimumvalueofthePMVindex PMV8h,minatwhichtheworkingconditionshouldbeinterruptedseems tobe stronglyaffectedby theclothinginsulation, themetabolic rateand theairvelocityvalues.

The general trend appears decreasing with the increasing ofboththemetabolicrateandtheclothinginsulationval-ues. In particular, under almost still air conditions (va=0.1m·s−1), PMV8h,min varies from 2.32 to 1.65 when the Icl value increases from 0.2 to 1.0 clo, whereas a variation of themetabolicratefrom1.7to4.0metresults inareduc-tion of PMV8h,min from 1.65 to 1.03 at Icl=1.0clo.Anyway,themainpatencyhighlightenedbyoursimula-

tions is that it seemsquite impossible to findanuniqueminimumPMVvalue forwhich theworkshifthas tobestopped due to the overcoming of the maximum rectal temperatureorwater losspredictedbyPHS. In fact, atlow air velocity the discomfort-stress transition occurs for M=1.7met in the range1.5–2.3whereasatM=4.0metthis phenomenon appears anticipated in the range 1.0–1.5 as a function of the clothing insulation value. From this perspective it is very important to highlight that so low valuesofPMVoccurforIcl values typical for work cloth-ingensembles(alwaysover0.6–0.8clo,accordingtoISO9920 Standard28)).

The acclimatation status of the worker does not affect thelimitvalueofPMVespeciallyatmeanandhighmeta-bolic rates.Onlyat lowmetabolic rateandunderquitestill air condition (va=0.1m·s−1)thePMVlimitvalueforanon-acclimatizedsubjectwasabout2decimalslowerthanthatexhibitedbyacclimatized.

Finally, it is very important to highlight that, especially at lowmetabolic rate (M=1.7met), the limit curvesobtainedaccording toPHSmodel fall ina rangemicro-climaticconditions inconsistentwithPMV15, 23) (e.g. ta>30°Cand/orpa>2,700 Pa corresponding to a humidity ratiogreaterthan17g/kg).Suchoccurrencehasnottobeinterpreted as a weakness of the discussion since the goal ofthisworkisnotusingPMVasaprimaryindexforthehot stress assessment, forcing its application in a range of bothmicroclimaticandpersonalparameters, ratherusingPMVonlyasindicatorofthetransitiondiscomfort-stress.

Discomfort-stress transition under non-uniform conditions (tr>ta)Thediscomfort-stress transition in termsofPMVhas

beenalso investigatedundernon-uniformenvironmentsfordifferentvaluesof thedifferencebetween themeanradiant temperatureandtheair temperature(upto10°C).Thesevalueshave tobeconsideredvery likely in thepresence of direct solar load34)asinbuildingconstructionactivities35, 36), in mines37), in the presence of hot surfaces or high-temperature ovens38) and in industrial sheds during the summer.



Fig. 2. Changing of the PMV index for microclimatic conditions consistent with 8 hours of work shift (acclimatized subjects) as a function of the metabolic rate, the air velocity and the clothing insulation. On each psychrometric chart the air temperature-humidity values consistent with 8 h of continuous work predicted by PHS.tr=ta;staticclothinginsulationvalue:0.20clo(a),0.40clo(b),0.60clo(c),0.80clo(d),1.0clo(e).ThegrayareahighlightsconditionsoutofthevalidationrangeofthePMVindex23)(Table2).


The main results are showed in Fig. 3andsummarizedinTable5.OnthebasisofthePMV8h, lim values reported inTable5itisalmosttrivialtorecognizethatinthepres-ence of high air velocity values the long-term criterion proposedby ISO152655) Standard is always satisfied since in all the investigated conditions PMV8h,min is always greaterthan2for8hofworkshiftpredictedbyPHS.Onthecontrary,averydifferentbehaviourhasbeenfoundatlow air velocity values where the clothing insulation, the metabolicrate,and,thevalueofthedifferencetr-ta play a crucial role.

In particular, under almost still air conditions (va=0.1m·s−1)and lowmetabolic rate, the rangeofPMV8h,min value slightly moves to higher values with the increas-ing of the difference tr-ta (from 1.65–2.32 under uniform conditions to 1.88–2.80 at tr-ta=10°Cforacclimatizedsub-jects).Formoderatemetabolicratevalues,PMV8h,min does notchangesignificantlybeingalwaysintherangeofabout1.5–2.0,whereasathighmetabolic rateacertain shiftofthe PMV8h,minrangetolowervalues,hasbeenfound(from1.03–1.47 under uniform conditions to 0.88–1.26 at a val-ue of the difference tr-ta=10°Cforacclimatizedsubjects).ThePMVtransitionvaluesup tonowdiscussedhave

tobeconsideredasabsolutelyprecautionarysince theyhavebeencalculatedonthePHSlimitcurveinthearea1

(Fig.1)simultaneouslycharacterizedbyveryhighrelativehumidityvalues.Toprovideapictureaswideaspossibleof the situation under less precautionary and more realistic conditions with respect to those exposed till to now, in Table6havebeensummarizedthePMVvaluescalculatedon the PHS limit curves for a settled relative humidity value of 50% PMV8h,50 for the two investigated values of the difference tr-ta.ObtainedresultsclearlyprovethatthePMVthresholdvalueofthediscomfort-stresstransitionissubstantially related to themetabolic rateand theairve-locity with a mild of effect of the difference tr-ta. In fact, at lowmetabolicratemostofinvestigatedconditionsrevealaPMVoftenexceeding3.Formoderatemetabolicrateonlyat low air velocity and high tr-ta values the protection cri-teriaatthebaseofthePHSmodelareexceededforPMVvalues lower than 2 (for Icl=1.0cloatPMV=1.52forannon-acclimatizedsubject).Finallyathighmetabolic rate(4.0 met) the discomfort-stress transition can occur also at PMVvaluesnearto1underquitestillairconditions.

Conclusions

The main goal of this paper devoted to the risk assess-mentofhotenvironmentshasbeentheidentificationofaPMVlimitvalueforwhichthetransitiondiscomfortstress

Table 4. Minimum PMV values PMV8h,lim consistent with 480 min of exposure times according to PHS model for acclimatized (A) and non-acclimatized (NA) subjects as a function of the metabolic rate, the static clothing insulation and the air velocity under uniform conditions (tr=ta)

Icl (clo)M=1.7met M=2.8met M=4.0met

A NA A NA A NA

va =0.1m·s-1 0.2 2.32 2.07 1.93 1.93 1.19 1.190.4 1.98 1.77 1.74 1.74 1.20 1.200.6 1.84 1.65 1.76 1.78 1.47 1.470.8 1.74 1.53 1.6 1.64 1.24 1.241.0 1.65 1.46 1.47 1.47 1.03 1.03

va =0.5m·s-1 0.2 2.66 2.61 2.68 2.68 2.20 2.200.4 2.35 2.19 2.47 2.37 2.03 2.030.6 2.22 2.04 2.29 2.29 2.13 2.130.8 2.12 1.93 2.11 2.11 1.87 1.871.0 2.01 1.82 1.97 1.97 1.66 1.66

va =1.0m·s-1 0.2 >30.4 2.65 2.61 2.93 2.93 2.86 2.860.6 2.46 2.36 2.72 2.72 2.77 2.770.8 2.37 2.25 2.55 2.55 2.53 2.531.0 2.29 2.32 2.41 2.41 2.31 2.31

InitalicshavebeenreportedPMVvaluesobtainedunderconditionsovertherangesofvalidationshowedinTable2.



Fig. 3. Changing of the PMV index for microclimatic conditions consistent with 8 hours of work shift (acclimatized subjects) as a function of the metabolic rate, the air velocity and the clothing insulation. On each psychrometric chart the air temperature-humidity values consistent with 8 h of continuous work predicted by PHS.Airvelocityva=0.1m·s−1;staticclothinginsulationvalue:0.20clo(a),0.40clo(b),0.60clo(c),0.80clo(d),1.0clo(e).ThegrayareahighlightsconditionsoutofthevalidationrangeofthePMVindex23)(Table2).


shouldbeidentifiedinanunmistakablewaybymeansofthePHSapproach.Obtained results stressed thecrucialroleplayedbythemetabolicrateoftheworkingsituation;particularly,forlowmetabolicrate,PMVtransitionvaluecan takeplaceataPMVvalueof1.5–1.9dependingonthe clothing insulation, the mean radiant temperature and thehumidity.Forhighermetabolicrates(upto4met)suchstress thresholddramaticallydecreasesup toPMV=1.0–1.4 depending the air velocity and the radiant asymmetry withanegligibleeffectof the relativehumidity.On thecontrary hand, the effect of the clothing insulation on the PMVtransitionvalueappearedsignificantonly in thepresenceofhighmetabolic rates.Concerningmicrocli-maticparameters, theeffectof theairvelocityobviouslyresulted inaverystrongpromotionof thePMVtransi-tion value to highest values often more than 3 (due to an enhancementofbothconvectiveandevaporative thermalflowswhichfavourtheheatremovalbythebody).Finally,

as themean radiant temperature isconcerned,obtainedresultshighlight−especiallyat low Icl values and high metabolicrate−thedifferentsensitivitytoPHSandPMVmodeltotheheattransferbyradiationwhichcanresultinaPMVthresholdvaluevery far to thevalue requiredbyISO 15265 Standard.Firstofall, itwouldbenecessaryanewdefinitionof

both lowerandupper limitsof thermaldiscomfort re-quiredbyISO15265Standard.Precisely, the lower limitshouldbeincreaseduptoPMV=0.7inordertoharmonizeit with ISO 7730 Standard which requires, for the worst discomfortclass(C),aPMVvaluesuchas0.5≤PMV≤0.7.Moreover,basedon thenumericalassessmenthere re-ported,upperlimitshouldbedecreasedinaprecautionarywayat least toPMV=1.5especiallyathighdifferencesbetween thevaluesof themean radiant temperatureandthe air temperature (working outdoor or in the presence of hot surfaces and high-temperature ovens), low clothing

Table 5. Minimum PMV values PMV8h,lim consistent with 480 min of exposure times according to PHS model for acclimatized (A) and non-acclimatized (NA) subjects as a function of the metabolic rate, the static clothing insulation and the air velocity at tr = ta + 5.0°C and tr = ta + 10°C


A NA A NA A NA

tr=ta+5°C

va =0.1m·s-1 0.2 2.53 2.49 1.97 1.97 1.05 1.050.4 2.2 2.06 1.75 1.75 1.08 1.080.6 2.04 1.82 1.76 1.76 1.34 1.340.8 1.91 1.68 1.61 1.61 1.16 1.161 1.79 1.56 1.46 1.46 0.95 0.95

va =1.0m·s-1 0.2 >3

0.4 2.89 3.03 2.93 >3 2.76 2.760.6 2.62 2.62 2.8 2.8 2.68 2.680.8 2.5 2.47 2.61 2.62 2.45 2.451 2.41 2.36 2.46 2.47 2.26 2.26

tr=ta+10°Cva =0.1m·s-1 0.2 2.8 2.93 1.95 1.95 0.84 0.84

0.4 2.37 2.33 1.75 1.75 0.93 0.930.6 2.12 2.01 1.75 1.75 1.26 1.260.8 2 1.83 1.59 1.59 1.06 1.061 1.88 1.69 1.45 1.45 0.88 0.88

va =1.0m·s-1 0.2 >3 2.29 2.29

0.4 2.71 2.89 2.7 2.7 2.21 2.210.6 2.45 2.49 2.54 2.54 2.3 2.30.8 2.36 2.36 2.41 2.41 2.14 2.141 2.25 2.25 2.28 2.28 1.98 1.98




insulation and high relative humidity values. In the future we will aim to extend this kind of investigations to the transition discomfort-cold stress.

Acknowledgement

WeoweaspecialthankstoMr.RaffaeleIovine(BSBE)forhisvaluablecooperation.

References

1) Councilof theEuropeanCommunity (1989)CouncilDirective89/391/EECof12June1989ontheintroductionof measures to encourage improvements in the safety andhealthofworkersatwork.http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31989L0391:EN:HTML.AccessedSeptember25,2012.

2) ParsonsKC(2008) Industrialhealth forall: appropriate

Table 6. PMV values at RH = 50% PMV8h,50 consistent with 480 min of exposure times according to PHS model for acclimatized (A) and non-acclimatized (NA) sub-jects as a function of the metabolic rate, the static clothing insulation and the air velocity at tr = ta + 5.0°C and tr = ta + 10°C


A NA A NA A NA

tr=tava =0.1m·s-1 0.2

>3>3 1.58 1.58

0.4 2.76 2.75 1.50 1.500.6 3.00 3.00 2.42 2.42 1.69 1.690.8 2.73 2.73 2.16 2.16 1.40 1.401.0 2.49 2.49 1.93 1.93 1.18 1.18

va =1.0m·s-1 0.2

>3

3.00 3.000.4 2.96 2.960.6 2.82 2.820.8 2.61 2.611.0 2.38 2.38

tr=ta+5.0°Cva =0.1m·s-1 0.2

>32.98 3.00 1.29 1.29

0.4 2.55 2.55 1.30 1.300.6 2.29 2.29 1.49 1.490.8 2.78 2.85 2.06 2.06 1.27 1.271.0 2.54 2.49 1.86 1.86 1.08 1.08

va =1.0m·s-1 0.2

>3

>32.85 2.85

0.4 2.7 2.70.6

>32.67 2.67

0.8 2.47 2.471.0 2.96 2.96 2.28 2.28

tr=ta+10°Cva =0.1m·s-1 0.2

>32.63 2.03 0.99 0.99

0.4 2.32 1.86 1.08 1.080.6 2.16 1.82 1.34 1.340.8 2.80 2.8 1.97 1.67 1.16 1.161.0 2.56 2.56 1.78 1.52 0.97 0.97

va =1.0m·s-1 0.2

>3

>32.10 2.10

0.4 2.20 2.200.6 2.93 2.93 2.26 2.260.8 2.79 2.79 2.09 2.091.0 2.66 2.66 1.96 1.96



physical environments, inclusive design, and standards that are truly international. Ind Health 46, 195–7.

3) Malchaire J,GebhardtHJ,PietteA (1999)Strategy forevaluation and prevention of risk due to work in thermal environment.AnnOccupHyg43, 367–76.

4) MalchaireJ,PietteA(2006)TheSOBANEStrategyfortheManagementofRisk,asapplied towholebodyorHand-Armvibration.AnnOccupHyg50, 411–6.

5) ISO 15265 (2004) Ergonomics of thermal environments −Strategyofevaluationof the risk for thepreventionofconstraints or discomfort under thermal working conditions. InternationalOrganisationforStandardization,Geneva.

6) ParsonsK (2003)HumanThermalEnvironments:TheEffectsofHot,Moderate, andColdEnvironmentsonHumanHealth,ComfortandPerformance,2ndEd.,Taylor&Francis,London.

7) ISO 7933 (2004) Ergonomics of the thermal environment −Analyticaldeterminationandinterpretationofheatstressusing calculation of the predicted heat strain. International OrganizationforStandardization,Geneva.

8) MalchaireJ,PietteA,KampmannB,MenhertP,GebhardtHJ,HavenithG,denHartogE,HolmerI,ParsonsK,AlfanoG,GriefahnB (2001)Developmentandvalidationof thepredictedheatstrainmodel.AnnOccupHyg45, 123–35.

9) MalchaireJ,KampmannB,MehnertP,GebhardtH,PietteA,HavenithG,HolmérI,ParsonsK,AlfanoG,GriefahnB(2002)Assessmentoftheriskofheatdisordersencounteredduringwork inhotconditions. IntArchOccupEnvironHealth 75, 153–62.

10) MalchaireJBM(2006)Occupationalheatstressassessmentbythepredictedheatstrainmodel.IndHealth44, 380–7.

11) d’AmbrosioFR,PalellaBI,RiccioG,AlfanoG (2004)Criteriaforassessmentofhotenvironments:WBGTindexandPHS(predictedheatstrain).MedLav95, 255–74.

12) HolmérI(1984)Requiredclothinginsulation(IREQ)asananalytical indexof thecold stress.ASHRAETRANS90, 1116–28.

13) Holmér I (2009)Evaluation of coldworkplaces: anoverview of standards for assessment of cold stress. Ind Health 47, 228–34.

14) d’AmbrosioAlfanoFR,PalellaBI,RiccioG (2013)Notes on the Implementation of the IREQ-model for the assessment of extreme cold environments. Ergonomics 56, 707–24.

15) ISO 7730 (2005) Ergonomics of the thermal environment −Analyticaldeterminationand interpretationof thermalcomfortusingcalculationofthePMVandPPDindicesandlocal thermalcomfortcriteria. InternationalOrganizationforStandardization,Geneva.

16) d’AmbrosioAlfanoFR,PalellaBI,RiccioG (2007)Therole of measurement accuracy on the heat stress assessment according to ISO7933:2004.WITTransBiomedHealth11, 115–24.

17) d’AmbrosioAlfanoFR,PalellaBI,RiccioG (2011)TheRoleofMeasurementAccuracyon theThermal

EnvironmentAssessmentbymeansofPMVIndex.BuildEnviron 46, 1361–9.

18) Dell’IsolaM,FrattolilloA,PalellaBI,RiccioG (2012)Measurementuncertainties influenceon the thermalenvironmentassessment.IntJThermophys33, 1616–32.

19) HavenithG,HolmérI,ParsonsK(2002)Personalsfactorsin thermalcomfortassessment:clothingpropertiesandmetabolicheatproduction.EnergyBuild34, 581–91.

20) CordeiroSousaOliveiraAR(2008)AvaliaçãodaIncertezanaDeterminaçãodosÍndicesdeConfortoTérmicoPMVePPD.MSCdegreethesis,CoimbraUniversity,Portugal(inPortuguese).

21) ISO7726(1998)Ergonomicsofthethermalenvironment−Instruments for measuring physical quantities. International OrganizationforStandardization,Geneva.

22) d’AmbrosioAlfanoFR,PalellaBI,RiccioG(2012)Ontheproblems related tonaturalwetbulb temperature indirectevaluation for the assessment of hot thermal environments bymeansofWBGT.AnnOccupHyg56, 1063–79.

23) FangerPO(1970)ThermalComfort.McGraw-Hill,NewYork.

24) d’AmbrosioAlfanoFR,PalellaBI,RiccioG (2005)TEE(ThermalEnvironmentAssessment): a friendly tool forthermalenvironmentevaluation. In:Proceedingsof11thInternationalConferencesonEnvironmentalErgonomics,May22–26,503–6,Ystad,Sweden.

25) ParsonsKC,HavenithG,Holmér I,NilssonH,MalchaireJB(1999)Theeffectsofwindandhumanmovementontheheatandvapourtransferpropertiesofclothing.AnnOccupHyg 43, 347–52.

26) Holmér I,NilssonH,HavenithG,ParsonsK (1999)Clothing convective heat exchange—proposal forimproved inStandarsandmodels.AnnOccupHyg43, 329–37.

27) HavenithG,NilssonH (2004)Correctionofclothinginsulation for movement and wind effects, a meta-analysis. EurJApplPhysiol92, 636–40.

28) ISO 9920 (2007) Ergonomics of the thermal environment —Estimationof thermal insulationandwatervapourres is tance of a c lo th ing ensemble . In ternat ionalOrganizationforStandardization,Geneva.

29) ISO 8996 (2004) Ergonomics of the thermal environment —Determinat ion ofmetabolic rate . Internat ionalOrganizationforStandardization,Geneva.

30) WangF,KuklaneK,GaoC,HolmérH(2011)CanthePHSmodel (ISO7933)predict reasonable thermophysiologicalresponses while wearing protective clothing in hot environments?PhysiolMeas32, 239–49.

31) WHO(1969)Health factors involved inworkingunderconditionsofheat stress.Technical report412.WHOScientificGrouponHealthFactors Involved inWorkingunderConditionsofHeatStress,Geneva.

32) CandasV,LibertJP,VogtJJ(1979)Humanskinwettednessandevaporativeefficiencyofsweating.JApplPhysiol46, 522–8.



33) CandasV,LibertJP,VogtJJ(1979)Influenceofairvelocityand heat acclimation on human skin wettedness and sweatingefficiency.JApplPhysiol47, 1194–200.

34) GasparAR,QuintelaDA (2009)Physicalmodellingofglobeandnaturalwetbulb temperatures topredictWBGTheat stress index inoutdoorenvironments. Int JBiometeorol 53, 221–30.

35) Mait i R (2008)Workload assessment in bui ldingconstruction relatedactivities in India.ApplErgon39, 754–65.

36) Pérez-AlonsoJ,Callejón-FerreAJ,Carreño-OrtegaA,Sánchez-Hermosilla J (2011)Approach to theevaluationof the thermal work environment in the greenhouse-

construction industry of SE Spain. Build Environ 46, 1725–34.

37) BrakeDJ (2001)Calculationof thenatural (unventilated)wetbulb temperature,psychrometricdrybulb temperatureand we t bu lb g lobe t empe ra tu r e f r om s t anda rdpsychrometricmeasurements. JMineVentSocSAfr54, 108–12.

38) d’AmbrosioAlfanoFR,PalellaBI,RiccioG (2010)RisultatidiunaIndaginesulleCondizionidiStressTermicoall’InternodiCristallerie.In:Proceedingsof65°CongressoNazionaleATI,September13–17,503–6,DomusDeMaria(CA),Italy.OnCDROM:ISBN8890411635(inItaly).

On the Transition Thermal Discomfort to Heat Stress as a ... · On the Transition Thermal...

Documents

Transcript of On the Transition Thermal Discomfort to Heat Stress as a ... · On the Transition Thermal...