Protective clothing ensembles are worn by workers as a barrier to chemical and physical hazards, but can restrict heat loss and increase worker heat stress. The question of whether a respirator adds to heat stress or strain burden is a continuing concern among occupational health professionals. The purpose of this study was to determine if there are differences in heat stress or strain among the current Toxicological Agent Protective (TAP) ensemble and two ensemble variations used in demilitarization of chemical weapons. Four acclimatized adult males wore five ensembles in a balanced design while walking in a climatic chamber at a metabolic rate of about 170 W m-2. Heat stress (critical wet bulb globe temperature-WBGTcrit, evaporative resistance-Re,T,a, Clothing Adjustment Factor [CAF]) and heat strain (physiological strain index [PSI]) were compared against work clothes (WC) without respirator (a baseline ensemble); the current TAP apron over cloth coveralls with respirator (TAP+CA); the current TAP apron over cloth coveralls with respirator plus Tychem F® chemical barrier pants (TAP+CA+P); and Tychem F® Coveralls over cloth coveralls with respirator (VB+CA). A no-respirator comparison with the Tychem F coveralls (VB+CA-noR) was added to evaluate the contribution of a full-face negative pressure air-purifying respirator to heat stress. A progressive heat stress protocol was used to determine WBGTcrit, Re,T,a, CAF, and PSI. The results (WBGTcrit [°C-WBGT], Re,T,a [kPa m2 W-1], and PSI) were WC (35.5, 0.0112, 2.0), TAP (31.6, 0.0175, 1.8), TAP+P (27.7, 0.0240, 1.9), VB+CA (25.9, 0.0287, 1.8), and VB+CA-noR (26.2, 0.0293, 1.8). Mixed effects ANOVA was used to assess ensemble effects. Tukey's test was used to determine where significant differences occurred. WBGTcrit was the WBGT at the upper limit of thermal balance. Re,T,a increased while WBGTcrit progressively decreased going from WC to TAP+CA to TAP+CA+P to VB+CA. WBGTcrit was different between Work Clothes and TAP+CA and between WC and TAP+CA and the other ensembles. Re,T,a was different among all ensembles, except no differences in WBGTcrit and Re,T,a were observed between the presence and absence of a respirator with VB+CA. There were no differences among all ensembles for rectal temperature, heart rate, and PSI. Based on both WBGTcrit and Re,T,a, there were significant increases in heat stress going from WC to TAP+CA to TAP+CA+P to VB+CA. No differences in WBGTcrit, Re,T,a, and PSI were found for the presence or absence of a respirator, indicating no additional heat stress or strain burden. CAF is the WC WBGTcrit minus the ensemble WBGTcrit.. The recommended clothing adjustment factors (CAFs) are 0°C-WBGT for WC, 4 °C-WBGT for TAP+CA, 8 °C-WBGT for TAP+CA+P and 10 °C-WBGT for VB+CA. As vapor-barrier ensembles are sensitive to humidity, adding 2 °C-WBGT to VA+CA for a CAF of 12 °C-WBGT is recommended. This implicates the type of protective clothing ensemble worn will play a much bigger role in workplace heat stress effects and risk than the wear of a respirator.

Clothing can influence heat stress depending on the design and its ability to act as a barrier. The progressive heat stress protocol permitted the collection of data to empirically estimate the apparent total evaporative resistance (Re,T,a). Five different clothing ensembles were evaluated, which included work clothes, cotton coveralls, and three limited-use protective clothing ensembles including a pthesis-barrier ensemble, (Tyvek® 1424), water-barrier, vapor-permeable ensemble (NexGen® LS 417), and a vapor-barrier ensemble (Tychem QC®). The study design called for three metabolic level's: low, moderate, and high (L, M, & H) and three heat stages: compensable, transitional, uncompensable (C, T, U). The purpose of this study was to determine if Re,T,a values remained constant over a range of metabolic and heat stage levels. Calculated Re,T,a values were compared using a four-way mixed model analysis of variance. Significant differences for Re,T,a were found among ensembles, metabolic levels, heat stress stages, as well as interactions among ensembles and metabolic levels along with ensembles and heat stress stages (p < 0.0001). A Tukey's Honestly Significant Difference multiple comparison test identified where significant differences occurred (p < 0.05). Results show Re,T,a values differ over a range of metabolic levels and stages of heat stress. Additionally, convection is more supportive of evaporative cooling than diffusion.

Ebola, a type of filovirus that causes hemorrhagic fevers, dominated global headlines in 2014 when the largest Ebola epidemic in history took place in West Africa. Healthcare practitioners were at particular risk of contracting Ebola while taking care of patients with the disease because they were easily exposed to bodily fluids such as blood, urine, saliva, and feces, quite often in the intensive care unit (ICU). While personal protective equipment (PPE) protects the healthcare practitioner by providing an effective barrier against the virus, users were also at risk for heat stress because of the type of protective clothing. In this study, coveralls made of monolithic barriers, which prevent water vapor from escaping the suit, were compared to coveralls made of micro- porous material, which allows evaporated sweat to escape the suit. The Microgard® 2000 TS Plus, made of micro-porous barrier material and the monolithic barrier Microgard® 2300 Plus were compared against a control ensemble of work clothes consisting of a long-sleeve shirt and trouser. A progressive heat stress protocol was used to determine the critical environment at the upper limit of compensable heat stress. The critical condition was the point at which the heat gain caused by wearing the protective ensemble as well as dry heat exchange was balanced by the maximum heat loss due to evaporative cooling. Wet bulb globe temperature at the critical condition (WBGTcrit ) ,total evaporative resistance (Re,T,a), and clothing adjustable factor (CAF) were calculated for each ensemble based on data at the critical point. Also at the critical condition, participant rectal temperature vi (Tre) , heart rate (HR), skin temperature (Tsk), and physiological strain index (PSI) were noted and compared for each ensemble. A two-way ANOVA (ensemble x participant) for WBGTcrit and Re,T,a as dependent variables was used to determine whether or not there were differences among ensembles. Tukey’s honest significance test was used to determine where significant differences occurred. WBGTcrit was 33.8, 26.3, and 22.9 °C-WBGT for Work Clothes, M2000, and M2300 respectively. Re,T,a was 0.012, 0.031, and 0.054 kPa m2 W-1 for WC, M2000, and M2300 respectively. The higher the WBGTcrit for an ensemble, the more it can support evaporative cooling and hence the better it is at ameliorating heat stress. Based on this trial, the micro-porous ensemble Microgard® 2000 TS Plus has better heat stress performance than vapor-barrier Microgard® 2300 Plus. As expected, there were no differences for any of the physiological metrics at the critical conditions.