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Human responses to intermittent work while wearing encapsulating chemical-biological protective clothing with personal HVAC.

ABSTRACT

Human responses and safe work time limits for persons wearing the US Army's Self-Contained Toxic Environment Protective Outfit (STEPO) with personal C[O.sub.2] scrubber, [O.sub.2] supply, and upper body cooling system were determined from human tests and human simulation modeling. STEPO is the Army's highest-level protective system. A rational thermal physiological model was assembled to simulate the responses and extend the human test results to other conditions. Comparisons between human and simulated responses include core and skin temperature, heart rate, thermal sensation, and water loss. Safe work time limits were until core temperature and heart rate exceeded 38.3[degrees]C (101[degrees]F) and 150 bpm.

INTRODUCTION

Chemical-biological protective clothing and equipment has become an increasingly important necessity for first responders to situations where the presence of hazardous materials in the environment are known or suspected. Such situations result from industrial process failures, transportation and storage accidents, medical contamination incidents, terrorist activities, and many others. To investigate and/or repair such situations, the responders wear an encapsulating life-support suit that isolates and separates them from the environmental hazard (Figure 1).

This paper is about the US Army's Self-Contained Toxic Environment Protective Outfit (STEPO) used by specially trained soldiers and civilians stationed around the nation to respond to the highest-level hazard situations. Under the encapsulating one-piece impermeable STEPO suit, an [O.sub.2] supply on the thigh and a C[O.sub.2] scrubber carried on a backpack are capable of sustaining the wearer inside for four hours. The scrubbed air passes through a small cold gel pack that can cool the air some for about 45 minutes. But in isolating and protecting the person from the outside environment the suit adds clothing insulation that reduces heat loss, particularly that from the evaporation of sweat. As a result, when working in warm environments, excessive body temperature and cardiovascular strain often limits the duration of work to less than four hours. To assist body heat loss, the person wears a hydronic long-sleeved shirt through which recirculating cool water flows. The water is cooled by passing though an ice container with battery-powered pump worn on the thigh. The ice in this container is external to the suit, can provide up to 150 W of cooling, and can be replaced when needed, i.e., about every 30 minutes when working in a 35[degrees]C (95[degrees]F) environment.

[FIGURE 1 OMITTED]

The protection and life-support system is heavy. The encapsulating suit weighs 12 kg, the backpack with C[O.sub.2] scrubber and [O.sub.2] supply is 15 kg, and the pump water and ice storage adds another 5 kg for a total of 32 kg (70.4 lb). The weight burden of the protective equipment significantly increases the effort, metabolism, and heat loss requirements for almost all activities. The STEPO wearer is often sweating and overheated, but the encapsulation prevents access to drinking water, increasing the risk of dehydration and its effect on performance.

To investigate and quantify the human physiological and subjective responses and safety issues of persons working in STEPO suits, laboratory experiments were conducted. These were done in climate chamber environments of 15.6[degrees]C, 24[degrees]C, and 32[degrees]C (60[degrees]F, 74[degrees]F, and 90[degrees]F) with heat-acclimated male subjects (average age: 26; height: 69.3 in. [1.7 6m]; weight: 173 lb [78.6 kg]) engaged in intermittent treadmill walking of 10/20-minute rest/walk cycles (Levine et al. 2003). The subjects wore shorts and socks under the protective suit. The metabolism during walking and sitting measured 4.05 met and 1.43 met, respectively. Without the extra weight of the protective and life-support equipment, these would have been about 3 and 1 met, respectively. A met is a relative unit of metabolism that equals actual metabolism/resting metabolism, or 58.1 W/[m.sup.2].

To extend safety guidance to conditions not tested, a simulation model was assembled to predict the workers' responses. This paper describes the simulation model and compares simulated with measured experimental results. The model predicts body core temperature ([T.sub.c]), heart rate (HR), skin temperature ([T.sub.sk]), sweat rate (SR), thermal sensation (TS), total water loss, and water accumulation in the suit.

MODEL DEVELOPMENT

The model, devised to simulate and predict responses to work in warm environments while wearing STEPO, started with an updated version of the popular rational Gagge model (Gagge et al. 1986) with added cardiovascular modeling features from Kraning and Gonzalez (1997). The Gagge model consists of two active physiological compartments representing the body core and skin surrounded by a passive clothing compartment. This is a reasonable approach for warm exercise conditions, as blood flow promotes uniform compartment temperatures even when they are large, as in this model. However, because of the cooling shirt, the skin compartment could not be assumed to be uniform in temperature and it was divided into two compartments representing noncooled or normal skin and cooled skin (Figure 2) (Berglund 2002). The clothing was similarly divided into two compartments. The model was configured to function in the Simulink modeling system architecture (Dabney and Harman 2001).

The cooling shirt was modeled as 6 mm (0.24 in.) diameter parallel tubes on 13 mm (0.51 in.) centers attached to a fabric (Figure 3). Heat was modeled as flowing into the tube water from the skin at tube locations and flowing from skin to environment in spaces between tubes. For the comparisons, the water flow rate was 0.473 L/min (7.5 gal/h), the same as in the human experiments, and the entering water temperatures were determined by regression from values measured in the human experiments.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

All of the metabolic energy (M) is assumed to be generated in the core. An energy balance on the core results in the equation,

M/Adu = qres + qkc + qknc + qskbfc + qskbfnc + Wc/Adu cbt dTc/dt, (1)

where Adu is the body surface area, qres is respiratory heat loss, qkc and qknc are passive heat conduction from the core to the cooled and to the noncooled skin, and qskbfc and qskbfnc represent heat transported by blood from the core to the cooled and to the noncooled skin compartments. The last term on the right in Equation 1 represents the rate of increase in internal energy of the core compartment, where Wc is the weight of the core ([approximately equal to] 0.95 of total body weight in this case), and specific heat of body tissue (cbt) is 0.97 Wh/([degrees]C x kg)(0.836Btu/[lb x [degrees]F]).

The passive heat conduction terms were calculated as qkc = k(Tc - Tskc)Ac/Adu and qknc = k(Tc - Tsknc)(1 - Ac/Adu), where Tskc and Tsknc are temperatures of cooled and noncooled skin, Ac is the area under the cooling shirt (Ac/Adu = 0.4), and the conductance (k) of the tissue between core and skin was 5.28 W/([degrees]C x [m.sup.2])(0.93 Btu/[h x [ft.sup.2] x [degrees]F]).

Similarly, the heat transported by blood flow to the cooled and noncooled skin was quantified from: qskbc = Skbfc x cpb(Tc - Tskc)Ac/Adu and qskbfnc = Skbfnc x cpb(Tc - Tsknc)(1 - Ac/Adu), where skin blood (Skbf) is modeled as proportional to deviations in core and skin temperatures from setpoint temperatures (Tcset, Tskset): Skbf = (Skbfn + Cdil[Tc - Tcset])/(1 + Cstr[Tskset - Tsk]) for conditions where Tc > Tcset and Tskset > Tsk. In the expressions, Cdil is 50 L/ (h x [m.sup.2] x [degrees]C)(0.68 gph/([ft.sup.2] x [degrees]F),neutral Skbfn is 6.3 L(h x [m.sup.2]) (0.1546 gph/[ft.sup.2]), Cstr is 0.5[degrees][C.sup.-1](0.28[degrees][F.sup.-1]), Tcset is 36.8[degrees]C (98.24[degrees]F), Tskset is 33.7[degrees]C (92.7[degrees]F), and specific heat of blood (cpb) is 1.163 W x h/(L[degrees]C)(8.34Btu/[g x [degrees]F]).

The rate of change of core temperature (Tc/dt), found by rearranging Equation 1:

dTc/dt = (M/Adu - qres - qkc - qknc - qskbfc - qskbfnc)/(WcCc/Adu) (2)

can be step-wise integrated to find the next core temperature (T[c.sub.2]) after time step ([DELTA]t),

T[c.sub.2] = T[c.sub.1] + [dTc/dt][.sub.1][DELTA]t. (3)

In like fashion, energy balances on cooled and noncooled skin compartments result in

qskbfnc + qknc = qdrync + qevapnc + Wsk cbt(1 - [Ac/Adu])dTsknc/dt, (4)

qskbfc + qkc = qdryc + qevapc + Wsk cbt(Ac/Adu)dTskc/dt, (5)

where qskbfc and qkc and qskbfnc and qknc are the heat flows from the core to cooled and noncooled skin, as discussed previously. Similarly qdryc and qdrync are the dry heat flows from the cooled and noncooled skin through their respective clothing compartments, and qevapc and qevapnc are the evaporative heat losses from the cooled and noncooled skin. The right-most terms in Equations 4 and 5 represent the rate of heat storage in the respective skin compartments. Wsk is the weight of all the skin.

Dry heat loss from noncooled skin was calculated by

qdrync = (Tsknc - To)/[R.sub.clt], (6)

where [R.sub.clt] is the total dry thermal resistance between skin and the environment and To is the operative temperature of the environment. The [R.sub.clt] values were measured for a range of air speeds on an articulated thermal manikin at USARIEM. To is defined as To = (hcTa + hrTr)/(hc + hr), where Ta and Tr are the air and meant radiant temperatures. The hr and hc terms are the coefficients of radiant and convective heat transfer evaluated at the person's outer surface (ASHRAE 2005).

The dry heat loss from the cooled skin (qdryc) was calculated as the sum of heat loss to the water tubes and to the environment between the tubes, with each loss weighted by the appropriate contact area. The thermal resistance to the environment between the tubes was higher than [R.sub.clt] by the resistance of a still air layer of tube OD thickness. Heat flow to the water tube was calculated for fully developed flow and to a mean water temperature.

The latent heat loss from the skin is from water diffusion (Ediff) through the dry skin and from the evaporation in areas covered with sweat. It is quantified as

qevap = (1 - w)Ediff + w[E.sub.max], (7)

where Emax is the maximum evaporation rate (W/[m.sup.2][Btu/h x [ft.sup.2]]), Ediff = 0.06[E.sub.max], and w, called skin wettedness, is the fraction of skin covered with water. Skin wettedness was determined in this case as w = sweat rate x hfg/[E.sub.max], where hfg is latent heat of evaporation (0.68 W x h/g [1050 Btu/lb]) and SR is the sweat rate. The sweat rate (SR) is driven by deviations in core and local skin temperatures from their setpoints, SR = Csw(Tmb - Tmbset)exp([Tsk - Tskset]/src), where Csw is 170 g/(h x [degrees]C x [m.sup.2])(0.0193 lb/(h x [degrees]F x [ft.sup.2]),src is 10.7[degrees]C (19.26[degrees]F), Tmb is mean body temperature, and Tmbset is 36.49[degrees]C(97.7[degrees]F).For the validation modeling, the maximum sweat rate was limited to 667 g/(h x [m.sup.2])(0.137 lb/[[ft.sup.2] x h]).

The maximum rate of evaporative heat loss ([E.sub.max]) from the skin surface is

[E.sub.max] = (psk - pa)/[R.sub.pclt], (8)

where psk is saturated vapor pressure (mmHg) of water at skin temperature, pa is ambient vapor pressure, and [R.sub.pclt] is total vapor resistance of the clothing from skin to the ambient. The [R.sub.pclt] values were measured on an articulated sweating thermal manikin at USARIEM. The vapor resistance from the cooled skin was the sum of [R.sub.pclt] and the area-weighted vapor resistance of the still air layer between the tubes. The skin under the tubes was assumed to be blocked for evaporation.

As with the core compartment, the rate of change of temperature in the skin compartments is determined from the energy balances and then stepwise integrated to find the skin temperatures at time t + [DELTA]t.

The model's heart rate estimates were determined from the body's total blood flow. The total blood flow is the sum of skin blood flows plus the blood flows for oxygen transport to the working and resting muscles, fat, and other tissues. This total, divided by the stroke volume of the left ventricle using methods of Kraning and Gonzalez (1997), was used to estimate HR. As this model is always aerobic and does not consider oxygen debt, the predicted HR tends to overestimate HR when exercise starts to increase and to underestimates HR when activity starts to decrease.

A useful indicator of how workers are doing during a project is how comfortable they feel. The five test subjects of this study indicated their comfort assessments during the rest-walk routines using the nine-point thermal sensation scale of Figure 4. The TS responses were modeled as being dependent on the core (Tc) and area-weighted average skin (Tsk) temperature. The dependency was determined by multiple regression of the responses during the walk-rest treadmill experiments in 32[degrees]C, 24[degrees]C, and 15.6[degrees]C (90[degrees]F,74[degrees]F, and 60[degrees]F) environments. The resulting TS prediction equation (multiple R = 0.83) is

[FIGURE 5 OMITTED]

TS = Kc(Tc + 0.00884 Tsk) - A, (9)

where Kc is 1.967[degrees][C.sup.-1] (1.093[degrees][F.sup.-1]) and A is 74.84 (112.9).

RESULTS

Rectal temperatures (Tr) (mean of five subjects) measured at the end of the rest and walk activities during the test at 32.2[degrees]C (90[degrees]F) are compared to simulated core temperatures (Tc) in Figure 5. The walk-rest effects on the simulated core temperature are clearly evident. The heart rate responses to this condition are displayed in Figure 6. Figures 5 and 6 also show the recommended safe upper limits of core temperature and heart rate of 38.3[degrees]C (101[degrees]F) and 150 bpm. The limits are based on laboratory experience with encapsulated subjects at USARIEM. Measured and simulated skin temperatures are compared to measured values as available in Figure 7.

In all the responses (Figures 5-7) the agreement between simulated and measured values was generally good for quasi-steady physiological conditions, but during the initial exposure the simulated responses were usually higher than the measured values. Part of this difference is because the model's skin blood flow and sweat rate control equations were developed using core temperature measured in the esophagus that corresponds to arterial blood temperature rather than the more slowly responding rectal temperature. This, together with the model's aerobic metabolism and reliance on only proportional control schemes, may account for the early response differences seen in the figures.

Simulated core temperature responses for the 15.6[degrees]C, 23.9[degrees]C, 32.2[degrees]C, and 38[degrees]C (60[degrees]F, 74[degrees]F, 90[degrees]F, and 100[degrees]F) environments are plotted in Figure 8 along with measured rectal temperatures as they were available. Subjects were not tested in the 38[degrees]C (100[degrees]F) environment.

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

The subject's thermal sensation responses and the model predictions are displayed in Figure 9. The model overpredicted thermal sensation during initial periods of activity, particularly for cool environments. After each of the tests, the subjects typically reported feeling very tired and weighed down by the STEPO system.

Statistical Agreement

Agreement between simulated and measured responses shown in Figures 5-9 were analyzed over the 240-minute test duration (120 minutes for Tsk) for significant differences (Stata 2003). The results are listed in Table 1. The TS responses at the cooler test conditions (Tc at 24[degrees]C and Tskc at 32[degrees]C) were significantly different primarily due to differences prior to reaching a quasi-steady physiological state. Inspection of Figures 5-9 show generally good agreement for all parameters at quasi-steady physiological states or in the region preceding thermal exhaustion (32[degrees]C [90[degrees]F] condition) making the simulation model useful for anticipating and judging performance and health risks of STEPO applications.

Sweat Rate and Water Accumulation in Suit

The sweat rates predicted by the simulation model for the intermittent activities over the range of environmental temperatures are shown in Figure 10. At temperatures of 24[degrees]C (74[degrees]F) and cooler, sweat rates are modest and stable, but at warmer conditions they increase with temperature and duration.

The sweat rates predicted by the model are essentially unevaporated from the skin of a person in the STEPO suit because of the nearly perfect vapor impermeability of the suit. The sweat does no cooling but instead just drips off and accumulates in boots and gloves and other low parts of the suit (Figure 11). The experimental accumulations were difficult to measure. The result is that, except for low activities in cool environments, the skin becomes saturated with water, or nearly so, making it soft. This decreases the protective properties of the skin so that it is more susceptible to abrasion, tears, blisters, and other injuries.

[FIGURE 9 OMITTED]

Safe Work Time Limits

Test results from the soldier volunteers, together with the simulated results for other temperatures, enabled development of safe work time limits for a range of warm environments (Figure 12). The environmental temperature is the operative temperature, which can include radiant and solar effects (ASHRAE 2005). Environmental humidity outside the encapsulating suit has no or little effect on the work time limits. At conditions of 24[degrees]C (74[degrees]F) and cooler, activities in the STEPO suit can proceed for the four-hour limit of the air supply, but at warmer conditions, the safe working time decreases steadily with increasing temperature. In a 38[degrees]C (100[degrees]F) environment, the recommended work limit is 70 minutes. Such guidance is helpful in developing schedules for planning and re-supplying investigative and repair activities in warm hazardous environments.

[FIGURE 10 OMITTED]

[FIGURE 11 OMITTED]

[FIGURE 12 OMITTED]

CONCLUSION

Human responses and safe work time limits for intermittent work in warm environments for persons wearing the STEPO suit with personal cooling and life-support systems were determined from human tests and human simulation modeling. The response information is helpful for planning and organizing activities and support for work dealing with hazardous situations. Further, the simulation model enables human responses to be rationally predicted for conditions not tested and, thus, reduces the cost and health risks of such human testing.

NOMENCLATURE

A = thermal sensation coefficient

Ac = area of cooled skin, [ft.sup.2]([m.sup.2])

Adu = body surface area, [ft.sup.2]([m.sup.2])

Cdil = coefficient of vasodilation, g/(h/[ft.sup.2] x [degrees]F)(L/[h x [m.sup.2] x [degrees]C])

Cstr = coefficient of vasoconstriction, g/(h/[ft.sup.2] x [degrees]F) (L/[h x [m.sup.2] x [degrees]C])

Csw = coefficient of sweating, lb/(h x [ft.sup.2] x [degrees]F)(g/[h x [m.sup.2] x [degrees]C])

cbt = specific heat of body tissue, Btu/(lb x [degrees]F) (W x h/[kg x [degrees]C])

cpb = specific heat of blood, Btu/(lb x [degrees]F)(W x h/[kg x [degrees]C])

Ediff = latent heat loss by diffusion through dry skin, Btu/(h x [ft.sup.2])(W/[m.sup.2])

Emax = maximum evaporation rate, Btu/(h x [ft.sup.2])(W/[m.sup.2])

hc = convective heat transfer coefficient, Btu/(h x [ft.sup.2] x [degrees]F) (W/([m.sup.2] x [degrees]C)

hr = radiant heat transfer coefficient, Btu/(h x [ft.sup.2] x [degrees]F)(W/([m.sup.2] x [degrees]C)

HR = hear rate, bpm

hfg = latent heat of evaporation, Btu/lb (W x h/g)

Kc = thermal sensation temperature coefficient, [degrees][F.sup.-1] ([degrees][C.sup.-1])

k = thermal conductance between core and skin, Btu/(h x [ft.sup.2] x [degrees]F)(W/[[degrees]C x [m.sup.2]])

M = metabolism, Btu/h (W)

pa = ambient water vapor pressure of air, psi (kPa)

psk = vapor pressure of water on skin, psi (kPa)

qdryc = dry heat loss from cooled skin, Btu/(h x [ft.sup.2])(W/[m.sup.2])

qdrync = dry heat loss from noncooled skin, Btu/(h x [ft.sup.2]) (W/[m.sup.2])

qevap = skin heat loss by evaporation, Btu/(h x [ft.sup.2])(W/[m.sup.2])

qevapc = heat loss by evaporation from cooled skin, Btu/(h x [ft.sup.2]) (W/[m.sup.2])

qevapnc= heat loss by evaporation from noncooled skin, Btu/(h x [ft.sup.2]) (W/[m.sup.2])

qkc = conductive heat loss from core to cooled skin, Btu/(h x [ft.sup.2])(W/[m.sup.2])

qknc = conductive heat loss from core to noncooled skin, Btu/(h x [ft.sup.2])(W/[m.sup.2])

qres = respiratory heat loss, Btu/(h x [ft.sup.2])(W/[m.sup.2])

qskbfc = convective heat loss from core by skin blood flow to cooled skin, Btu/(h x [ft.sup.2])(W/[m.sup.2])

qskbfnc = convective heat loss from core by skin blood flow to noncooled skin, Btu/(h x [ft.sup.2])(W/[m.sup.2])

Skbfc = blood flow to cooled skin, g/(h/[ft.sup.2])(L/[h x [m.sup.2]])

Skbfnc = blood flow to noncooled skin, g/(h/[ft.sup.2])(L/[h x [m.sup.2]])

Skbfn = blood flow to skin at neutral thermoregulatory conditions, g/(h/[ft.sup.2])(L/[h x [m.sup.2]])

SR = sweat rate, lb/([ft.sup.2] x h)(g/[h x [m.sup.2]])

src = sweat rate constant, 19.26[degrees]F(10.7[degrees]C)

Ta = air temperature, [degrees]F([degrees]C)

Tc = core temperature, [degrees]F([degrees]C)

Tcset = core setpoint temperature, [degrees]F([degrees]C)

Tmb = mean body temperature, [degrees]F([degrees]C)

Tmbset = mean body setpoint temperature, [degrees]F([degrees]C)

To = operative temperature, [degrees]F([degrees]C)

Tr = mean radiant temperature, [degrees]F([degrees]C)

Trem = measured rectal temperature, [degrees]F([degrees]C)

TS = thermal sensation

Tsk = skin temperature, [degrees]F([degrees]C)

Tskc = temperature of cooled skin, [degrees]F([degrees]C)

Tsknc = temperature of noncooled skin, [degrees]F([degrees]C)

Tskset = skin setpoint temperature, [degrees]F([degrees]C)

t = time, h

[DELTA]t = time step, h

Wc = weight of core compartment, lb(kg)

Wsk = weight of skin compartment, lb(kg)

w = skin wettedness, fraction of skin covered with sweat, decimal fraction

ACKNOWLEDGMENT

The authors appreciate and acknowledge the excellent guidance and assistance with statistics and graphics from Dr. Miyo Yokota of USARIEM.

DISCLAIMER

The views, opinions, and/or findings in this paper are those of the authors and should not be construed as an official Department of the Army position, policy, or decision unless so designated by other official documentation.

REFERENCES

ASHRAE. 2005. 2005 ASHRAE Handbook--Fundamentals, Thermal comfort, p. 8.3. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.

Berglund, L.G. 2002. Simulation of human thermoregulatory responses to micro-cooling in hot environments. SAE 2002 Transactions Journal of Aerospace, Section 1. 111:269-73.

Dabney, J.B., and T.L. Harman. 2001. Mastering SIMULINK 4. Upper Saddle River, NJ: Prentice Hall.

Gagge, A.P., A. Fobelets, and L.G. Berglund. 1986. A standard predictive index of human response to the thermal environment. ASHRAE Transactions 92(2B):709-31.

Kraning, K.K., and R.R. Gonzalez. 1997. A mechanistic computer simulation of human work in heat that accounts for physical and physiological effects of clothing, aerobic fitness, and progressive dehydration. Journal of Thermal Biology 22:331-42.

Levine, L., B.S. Cadarette, and M.A. Kolka. 2003. Endurance time in the self-contained toxic environment protective outfit (STEPO) with personal ice-cooled microclimate cooling system (PICS) in three environments. USARIEM Technical Report T03-13. US Army Research Institute of Environmental Medicine, Natick, MA.

Stata. 2003. Stat Base Reference Manual, vol. 1, Release 8. Stata Corporation, College Station, TX.

DISCUSSION

H.F. Khalifa, Professor of Mechanical and Aerospace Engineering, Syracuse University, Syracuse, NY: (1) What is the basis for the MET rate used in the simulation? (2) Would the model be applicable to soldiers wearing protective clothing in the field?

Larry G. Berglund: (1) The MET unit of metabolism is a dimensionless relative value that equals actual metabolism/ resting metabolism. In terms of energy per unit area of skin, 1 met equals 58.1 W/[m.sup.2]. With this unit, a resting person has a metabolism of 1 met and a maximum aerobic metabolism of about 12 met. Table 4 in chapter 8 of the ASHRAE Handbook--Fundamentals lists met levels for various activities.

(2) The model described is applicable for neutral to hot environments. It should yield fairly accurate predictions of responses for reasonably fit and heat-acclimated people wearing this protective suit. A soldier's normal field protective clothing may be different and is dependent on the situation. Jim Hill, NIST, Gaithersburg, MD: (1) Are these military suits or ones worn in the private sector? (2) What is being done to address the poor performance at high environmental temperatures and the accumulation of water inside the suit? Larry G. Berglund: The army's Self-Contained Toxic Environment Protective Outfit (STEPO) is used by specially trained soldiers and civilians stationed around the nation to respond to the highest-level hazard situations. It is recommended that for work in warm or hot conditions (>24[degrees]C) the rest period be increased and/or water-cooled shorts or leggings be worn in addition to the water-cooled shirt described in the paper. With more cooling, sweating and the accumulation of water would be reduced.

Larry G. Berglund, PhD, PE

Fellow ASHRAE

Bruce S. Cadarette

Leslie Levine

Margaret A. Kolka, PhD

Larry G. Berglund is a research biomedical engineer and Margaret A. Kolka is chief in the Biophysics and Biomedical Modeling Division and Leslie Levine and Bruce S. Cadarette are research physiologists in the Thermal Mountain Division, Institute of Environmental Medicine, US Army, Natick, Massachusetts.
TS

0.0 Unbearably cold
1.0 Very cold
2.0 Cold
3.0 Cool
4.0 Comfortable
5.0 Warm
6.0 Hot
7.0 Very hot
8.0 Unbearably hot

Figure 4 Thermal sensation ballot.

Table 1. ANOVA for Repeated Measures of the Difference Between Predicted
and Available Measured Responses Over the Test Duration for the
Different Environmental Conditions

 Response Significant
Environment Parameter Difference

32[degrees]C (90[degrees]F) Tc
 HR
 Tsknc
 Tskc *
 TS
24[degrees]C (74[degrees]F) Tc *
 TS *
15.6[degrees]C (60[degrees]F) Tc
 TS *

Note: * Indicates a significant difference at p
[greater than or equal to] 0.05.
COPYRIGHT 2006 American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2006 Gale, Cengage Learning. All rights reserved.

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Author:Berglund, Larry G.; Cadarette, Bruce S.; Levine, Leslie; Kolka, Margaret A.
Publication:ASHRAE Transactions
Geographic Code:1USA
Date:Jul 1, 2006
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