Three main factors that influence heat stress are clothing, work demands and environmental conditions. Gender may also influence the amount of heat stress an individual can tolerate. The purpose of this study was to examine the role of gender in heat stress limits (critical WBGT) and heat strain (heart rate and core temperature). The null hypothesis was that there was no gender difference among critical WBGT, heart rate and core temperature. Fifteen subjects (11 men and 4 women) wore five different clothing ensembles (cotton work clothes, cotton coveralls, particle barrier Tyvek, water-barrier/vapor permeable NexGen LS417, and vapor barrier Tychem QC made by Dupont) at three levels of metabolic rate (115, 175 and 250 W m-2). A treadmill was used to set the metabolic workload. A climatic chamber was used to control the environmental conditions. The participants continued to walk on the treadmill until their core temperature (Tre) reached a steady state. Then the air temperature and humidity were slowly increased. The point at which the core temperature increased steadily was defined as the inflection point. Environmental data as well as core temperature and heart rate were recorded at five minute intervals. The critical conditions were noted at five minutes before the inflection point. Metabolic rate, critical WBGT, core temperature and heart rate were analyzed by 3-way ANOVAs (participants nested by ensemble by metabolic rate) with all two way and three way interactions. Significant differences were observed between genders for metabolic rate and heart rate, but not for core temperature and critical WBGT across metabolic level and ensembles. While there were differences between genders in metabolic rate they did not affect the overall conclusions. The heart rate was significantly higher (12 bpm) for women than for men.

Heat stress is an environmental and occupational hazard exacerbated by climate change. Rural populations and sub-populations continue to experience disproportionate risks of heat-related impacts due to their low adaptive capacities in terms of infrastructure, information and other resources which are critical in dealing with heat. The study goals were to determine heat-related mortality risks in rural populations globally, explore the contribution of the outdoor work environment and other factors in association with occupational heat-related illnesses (HRI), and assess the risk of heat stress among crop workers using the Wet Bulb Globe Temperature (WBGT). Published peer-reviewed scientific literature on heat-related mortality in rural areas was used to assess heat-related risks among rural populations worldwide. Excess risks of both all-cause and cardiovascular mortalities were found although temperature had a stronger impact on cardiovascular deaths than for all-cause mortality. Also, using cross-sectional data from health screening clinics conducted during the summers of 2014, 2015, and 2016, a total of 425 patient encounters were analyzed using chi-square and logistic regression analyses to determine the role of the outdoor work environment and other factors associated with heat stress. As expected, the outdoor work environment was significantly associated with HRI. Out of the total of 67 HRI cases that were self-reported or diagnosed, 82% (55 cases) worked outdoors. There were nonsignificant elevations in HRI prevalence reported in males, workers below 40 years of age, individuals who have worked in agriculture for ten years or less, and those trained on heat safety. Further, a comprehensive evaluation of heat stress among crop workers was conducted using the four thermal climate factors-- air temperature, humidity, wind speed and solar radiation-- as well as work load and clothing factors. It found both acclimatized and non-acclimatized workers at risk of HRI. Regression analysis revealed that HRI prevalence was strongly correlated with the daily maximum WBGT (R2= 0.89; p= 0.03). Thus, effective heat safety precautions are needed, in addition to acclimatization, to protect vulnerable outdoor workers.

The Department of Defense (DoD) has acknowledged climate change as a risk national security. Ongoing impacts include the loss of training and operational sites to climate hazards. Operationally, conflict and natural disasters around the world have been exacerbated by increasing heat, desertification, and flooding. Increasing average temperatures, the flagship issue of climate change, is a significant contributor to heat-illness in military personnel. This project explores the relationship between climate change and the U.S. military, ongoing efforts to evaluate and address the risk, and the overall impacts on training readiness. Measuring climate related vulnerability is a complex process. For the DoD to apply a common framework across a vast network of fundamentally different sites is an especially wicked problem. I recommend a tiered approach to iteratively narrow the focus and resources allocated to the most mission critical and at-risk sites. The process begins with a screening survey, continues to in-depth site-specific impact assessments, and ends with implementation of technical and institutional adaptations. Recent efforts by the DoD have not fully executed this process and resulting reports are resultingly insufficient. I identify a lack of consideration for heat stress on servicemembers. Using historical site data and projections, I determine that the risk of heat-illness and lost training time will increase. Leaders can use this data to plan risk mitigation efforts through changing training locations, timing, or control measures. The military must continue to adapt and overcome challenges of the coming century by using available scientific information to reduce risk during the planning process.

The rate of heat-related fatalities in crop production workers is almost 20 times that of other industries. Heat stress was investigated in migrant tomato workers in July, 2012, using measurements of body temperature, heart rates, body weight loss, evaluation of the thermal environment, and survey data. Using occupational safety criteria, these workers were found to work in an environment that should require protective measures to prevent heat strain. Increases in body temperature, heart rate, and physiological strain correlated with heat exposure. One third of workers had body weight percentage losses that indicated dehydration. However, working in hot environments appears to elicit a low magnitude of strain in well acclimated workers who self-pace. Key findings suggest the need for worker and employer safety training regarding acclimation and hydration. Survey data showed that less than 30% have had any heat-related safety training.

Heat stress is a recognized occupational hazard present in many work environments. Its effects increase with increasing environmental heat loads. There is good evidence that exertional heat illness is associated with ambient thermal conditions in outdoor environments. Further, there is reason to believe that risk of acute injury may also increase with the ambient environment. For these reasons, the assessment of heat stress, which can be done through the characterization of the wet bulb globe temperature (WBGT), is designed to limit exposures to those that could be sustained for an 8-h day. The ACGIH Threshold Limit Value (TLV) for heat stress was based on limited data from Lind in the 1960s. Because there are practical limitations of using thermal indices, measurement of physiological parameters, such as body temperature and heart rate are used with environmental indices or as their alternative. The illness and injury records from the Deepwater Horizon cleanup effort provided an opportunity to examine the effects of ambient thermal conditions on exertional heat illness and acute injury, and also the cumulative effect of the previous day’s environmental conditions. The ability of the current WBGT-based occupational exposure limits to discriminate unsustainable heat exposures, and the proposal of alternative occupational limits was performed on data from two progressive heat stress protocol trials performed at USF. The USF studies also provided the opportunity to explore physiological strain indicators (rectal temperature, heart rate, skin temperature and the Physiological Strain Index) to determine the threshold between unsustainable and sustainable heat exposures. Analysis were performed using Poisson models, conditional logistic regressions, logistic regressions, and receiver operator curves (ROC curves). It was found that the odds to present an acute event, either exertional heat illness or acute injuries increased significantly with rising environmental conditions above 20 °C (RR 1.40 and RR 1.06, respectively). There was evidence of the cumulative effect from the prior day’s temperature and increased risk of exertional heat illness (RRs from 1.0–10.4). Regarding the accuracy of the current TLV, the results of the present investigation showed that this occupational exposure limit is extremely sensitive to predict cases associated with unsustainable heat exposures, its area under the curve (AUC) was 0.85; however its specificity was very low (specificity=0.05), with a huge percentage of false positives (95%). The suggested alternative models improved the specificity of the occupational exposure limits (specificities from 0.36 to 0.50), maintaining large AUCs (between 0.84 and 0.89). Nevertheless, any decision in trading sensitivity for specificity must be taken with extreme caution because of the steeped increment risk of heat related illness associated with small increments in environmental heat found also in the present study. Physiologic heat strain indices were found as accurate predictors for unsustainable heat stress exposures (AUCs from 0.74 to 0.89), especially when measurements of heart rate and skin temperature are combined (AUC=0.89 with a specificity of 0.56 at a sensitivity=0.95). Their implementation in industrial settings seems to be practical to prevent unsustainable heat stress conditions.

Heat stress occurs when the body cannot adequately cool itself due to the combined contributions of metabolic heat, environmental factors and clothing. Heat stress found in the workplace puts employees at risk of developing heat-related illnesses, disorders and could be fatal. The wet bulb globe temperature (WBGT) index is the current method used to assess environmental contributions to heat stress in an occupational setting. The purpose of this thesis was to explore whether the National Weather Service's Heat Index (HI) could substitute for the WBGT Index during occupational heat stress exposure assessment. The possibility of using the HI for heat stress exposure assessments was explored by first developing an occupational exposure limit based on the HI and then by comparing the HI to WBGT Index over a range of environments. Data from 10 selected studies were reviewed and categorized into two groups (Classic Data and Progressive Data) based on the method used to determine the upper limit of the prescriptive zone. WBGT and HI values were estimated from the environmental data provided in the 10 studies and the metabolic demands were also noted. These data were used to illustrate the relationship between environment (WBGT and HI) and metabolic rate. Next the relationship between HI and WBGT was compared over a range of environments consisting of combinations of air temperature and percent relative humidity as defined by the NWS's Heat Index Chart. Finally the effects of adding a high radiant heat load (Tg = Tdb+10 °C) to the relationship between WBGT and HI was explored. The HI occupational exposure limits were protective of the upper limit threshold points in a manner similar to WBGT. A greater spread in the Classic and Progressive upper limit data was observed above the occupational exposure limit when expressed as HI. High correlation was observed (R2 = 0.95) between the WBGT Index and HI over a range of environments, assuming no radiant heat. The incremental increase in HI due to high radiant heat indicated a strong dependency on the absolute value of HI, which makes using HI to predict WBGT in radiant heat environments problematic. Findings suggest the Heat Index could be used to assess heat stress exposures and to set occupational exposure limits for hot environments in the absence of high radiant heat.

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.

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.