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This study aimed to assess current perceptions of heat stress, heat strain, acclimatisation and recovery practices in wildland fire suppression. A total of 1459 wildfire and structural firefighters, all involved in wildland fire suppression, completed an 18-question survey. Most participants (81.3%) reported heat strain as one of the main risks faced during wildland firefighting. Thermal strain is considered an important risk for health and safety in wildland firefighting. The best-valued heat strain mitigation strategies were those traditionally recommended in wildland fire suppression: (i) an adequate work/rest ratio (79.0%), (ii) acclimatisation (71.6%), (iii) enhancing body ventilation by opening protective clothing or removing helmets or gloves (63.5%), and (iv) drinking water and food supplementation (52.1%). Despite these results, only 22% of the participants reported carrying out acclimatisation in the workplace. The vast majority of the respondents (87.4%) consider active cooling strategies (i.e., ice slurry ingestion, ice vests, etc.) impractical in combating heat strain during wildfire suppression. We identified a gap between knowledge about heat strain, its mitigation strategies and the level of actual implementation of these practices in the workplace. Our results highlight the need to improve heat strain management and implement operational directives for acclimatisation and active cooling interventions.

Heat strain may cause heat-related illness and reduce work efficiency as well as represent individual differences. To simulate individualized physiological responses of the human body to various conditions, an individualized predicted heat strain (IPHS) model accounting for individual difference factors including height, weight, gender, and age was proposed based on the widely used predicted heat strain (PHS) model. Subsequently, the IPHS model was validated against the PHS model and human trials (total, 3 cases, 9 conditions, and 51 subjects) from the literature. The results indicated that the maximal difference between simulations and measurements in terms of the core temperature, mean skin temperature, and sweating loss was no more than 1.0 °C, 1.6 °C, and 10 g respectively, for all cases. Specifically, an excellent prediction performance of the IPHS model was found, with a lower maximal difference for the core temperature (PHS: 0.98 °C vs. IPHS: 0.55 °C) and sweating loss (PHS: 335.7 g vs. IPHS: 8.9 g) in Case 1. The maximal difference for core temperature was only 0.59 °C under high metabolism (320 W/m2) conditions in Case 2. Furthermore, the prediction performance of the IPHS model varied with the environment and gender. The proposed model performed better on steady-state skin temperature simulations for women than for men in Case 3. It was concluded that the proposed model can predict individualized core temperature, mean skin temperature, and sweating loss with acceptable accuracy for the studied cases. The proposed model can provide insights into personalized heat management and occupational safety protection. • An individualized predicted heat strain model (IPHS) was proposed. • The IPHS model can predict core temperature, skin temperature, and sweating loss. • The IPHS model improved prediction performance than the PHS model. • The prediction accuracy of the IPHS model varied with environments and gender. [ABSTRACT FROM AUTHOR]

Purpose: This paper investigates the relationship between core temperature ( T), skin temperature ( T) and heat flux (HF) during exercise in hot conditions. Method: Nine test volunteers, wearing an Army Combat Uniform and body armor, participated in three sessions at 25 °C/50 % relative humidity (RH); 35 °C/70 % RH; and 42 °C/20 % RH. Each session consisted of two 1-h treadmill walks at ~350 W and ~540 W intensity. T and HF from six sites on the forehead, sternum, pectoralis, left rib cage, left scapula, and left thigh, and T (i.e., core temperature pill used as a suppository) were measured. Multiple linear regressions were conducted to derive algorithms that estimate T from T and HF at each site. A simple model was developed to simulate influences of thermal conductivity and thickness of the local body tissues on the relationship between T, T, and HF. Results: Coefficient of determination ( R) ranged from 0.30 to 0.88, varying with locations and conditions. Good sites for T measurement at surface were the sternum, and a combination of the sternum, scapula, and rib sites. The combination of T and HF measured at the sternum explained ~75 % or more of variance in observed T in hot environments. The forehead was found unsuitable for exercise in heat due to sweating and evaporative heat loss. The derived algorithms are likely applicable only for the same ensemble or ensembles with similar thermal and vapor resistances. Conclusion: Algorithms for T measurement are location-specific and their accuracy is dependent, to a large degree, on sensor placement. [ABSTRACT FROM AUTHOR]

Objectives: The high values of thermal resistance (Rct) and/or vapor resistance (Ret) of chemical protective clothing (CPC) induce a considerable thermal stress. The present study compared the physiological strain induced by CPCs and evaluates the relative importance of the fabrics’ Rct, Ret, and air permeability in determining heat strain. Methods: Twelve young (20–30 years) healthy, heat-acclimated male subjects were exposed fully encapsulated for 3h daily to an exercise-heat stress (35°C and 30% relative humidity, walking on a motor-driven treadmill at a pace of 5 km h1 and a 4% inclination, in a work–rest cycle of 45min work and 15min rest). Two bipack CPCs (PC1 and PC2) were tested and the results were compared with those attained by two control suits—a standard cotton military BDU (CO1) and an impermeable material suit (CO2). Results: The physiological burden imposed by the two bilayer garments was within the boundaries set by the control conditions. Overall, PC2 induced a lower strain, which was closer to CO1, whereas PC1 was closer to CO2. Air permeability of the PC2 cloth was almost three times higher than that of PC1, enabling a better heat dissipation and consequently a lower physiological strain. Furthermore, air permeability characteristic of the fabrics, which is associated with its construction and weave, significantly correlated with the physiological strain, whereas the correlation with Rct, Ret, and weight was poor. Conclusions: The results emphasize the importance of air permeability in reducing the physiological strain induced by CPCs. [ABSTRACT FROM AUTHOR]

The article discusses the impact of climate change to the productivity of the workers in harvesting rice in India. It highlights the effect of heat exposure to the workers including high risk of heat stroke and limit work productivity. It notes that heat exposure contributes to the impairment of human physiological function and health.

Introduction: Physiological, anthropometrical and thermal perceptual are the most important factors affecting thermoregulation of men and women in workplaces. The purpose of this study was determining the validity of a questionnaire method for assessing women's heat strain in workplaces. Methods: This cross sectional study was carried out on 96 healthy women. Data were continuously collected over a period of 3 months (July-September) in 2012. Mean ± (SD) of age was found to be 31.5 ± 7.48 years, of height 1.61 ± 0.05 m, of weight 61.55 ± 10.35 kg, and of body mass index 23.52 ± 3.75 kg/m2 in different workplaces. Heart rate and oral temperature were measured by heart rate monitoring and a medical digital thermometer, respectively. Subjects completed a draft questionnaire about the effective factors in the onset of heat strain. After collecting the questionnaires, the data were analyzed by applying Cronbach'sa calculation, factor analysis method, Pearson correlation and receiver operator characteristic curves using the SPSS 18 software. Results: The value for Cronbach's a was found to be 0.68. The factor analysis method on items of draft questionnaire extracted three subscale (16 variables) which they explained 63.6% of the variance. According to the results of receiver operator characteristic curve analysis, the cut off questionnaire score for separating people with heat strain from people with no heat strain was obtained to be 17. Conclusions: The results of this research indicated that this quantitative questionnaire has an acceptable reliability and validity, and a cut off point. Therefore it could be used in the preliminary screening of heat strain in women in warm workplaces, when other heat stress evaluation methods are not available. [ABSTRACT FROM AUTHOR]

Cooling vests (CV) are often used to reduce heat strain. CVs have traditionally used ice as the coolant, although other phase-change materials (PCM) that melt at warmer temperatures have been used in an attempt to enhance cooling by avoiding vasoconstriction, which supposedly occurs when ice CVs are used. This study assessed the effectiveness of four CVs that melted at 0, 10, 20 and 30 °C (CV, CV, CV, and CV) when worn by 10 male volunteers exercising and then recovering in 40 °C air whilst wearing fire-fighting clothing. When compared with a non-cooling control condition (CON), only the CV and CV vests provided cooling during exercise (40 and 29 W, respectively), whereas all CVs provided cooling during resting recovery (CV 69 W, CV 66 W, CV 55 W and CV 29 W) ( P < 0.05). In all conditions, skin blood flow increased when exercising and reduced during recovery, but was lower in the CV and CV conditions compared with control during exercise (observed power 0.709) ( P < 0.05), but not during resting recovery (observed power only 0.55). The participants preferred the CV to the CV, which caused temporary erythema to underlying skin, although this resolved overnight after each occurrence. Consequently, a cooling vest melting at 10 °C would seem to be the most appropriate choice for cooling during combined work and rest periods, although possibly an ice-vest (CV) may also be appropriate if more insulation was worn between the cooling packs and the skin than used in this study. [ABSTRACT FROM AUTHOR]

Heat stress is well recognized among the hazardous physical agents that might be present during work. This study aims to compare WBGT index at acclimated and unacclimated people to permissible threshold limit value and study the differences between physiological parameters at them. Twenty one healthy men were participated in the study. All of the subjects were monitored in two different weather and working conditions: the Kar site (the work site) and the Paziresh site (the office site). A set of physiological and environmental parameters, namely heart rate, blood pressure, skin temperature and deep body temperature, dry temperature, wet natural temperatures, radiant temperature and relative humidity were measured and monitored simultaneously. The acclimated subjects were all of the ammonia-phase workers working in the hot-humid worksite. Other participants were selected from the work sites without risk of heat stress. Mean value of WBGT/TLV was less than one for the both acclimated and unacclimated groups at Paziresh site, while this value was more than one at Kar site and also mean of WBGT. For two groups, TWA / TLV were less than one during the working day. Mean physiological parameters were not significantly different between the acclimated and unacclimated subjects at both sites. However, physiological parameters such as heart rate and core body temperature showed statistically significant difference between two groups at Kar. Both groups of Paziresh were not exposed to heat stress, but Kar's operators continued work under conditions of heat stress. [ABSTRACT FROM AUTHOR]

Purpose: The limitations of conventional goggles have caused immense inconvenience, and even damage, to the physical and mental health of healthcare workers. Hence, this study aimed to build a modified goggle (MG) with better physical performance. The temperature-humidity index (THI) was used as an indicator to investigate the impact of goggle-related heat strain on the ocular surface., Methods: The basic functions of antifog, anti-ultraviolet (UV), and anti-blue-light radiation capabilities were evaluated. Furthermore, the clinical impact on noninvasive keratography tear film break-up time (NIKBUT), intraocular pressure, central corneal thickness, Schirmer test I, and the Dry Eye-related Quality of life Score (DEQS) were assessed in 40 healthcare workers by comparing MG with standard goggles (SG). The relationships between THI and the above parameters were explored., Results: MG had a significantly longer antifog time than SG (212.75 ± 23.95 vs. 138.35 ± 5.54 min, p < 0.05), stronger antiultraviolet ability at 400 nm (99.99 vs. 45.55%), and optimal anti-blue-light performance at 440 nm (33.32 vs. 13.31%). Tear film stability after wearing the goggle was significantly worse than that before wearing them ( p < 0.05). Both goggles achieved moderate to strong heat strain, with a THI of >80 at all timepoints. The MG group showed lower THI and DEQS and higher NIKBUT than the SG group ( p < 0.05). THI was significantly correlated with DEQS, NIKBUT, and real fogging time ( r = 0.876, -0.532, -0.406; all p < 0.05)., Conclusion: Wearing goggles for a long time may cause heat strain to the eyes, thereby leading to eye discomfort and changes in the microenvironment of the ocular surface. Our MG exhibited better antifog, antiultraviolet, and optimal anti-blue-light performance and lower heat strain than SG, thus making it ideally suited for healthcare workers., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Shao, Wu, Wu, Liu, Shen, Zhang and Bi.)

Recent studies have characterized individually experienced temperatures or individually experienced heat indices, including new exposure metrics that capture dimensions of exposure intensity, frequency, and duration. Yet, few studies have examined the personal thermal exposure in underrepresented groups, like outdoor workers, and even fewer have assessed corresponding changes in physiologic heat strain. The objective of this paper is to examine a cohort of occupationally exposed grounds and public safety workers (n = 25) to characterize their heat exposure and resulting heat strain. In addition, a secondary aim of this work is to compare individually heat index exposure (IHIE) across exposure metrics, fixed-site in situ weather stations, and raster-derived urban heat island (UHI) measurements in Charleston, SC, a humid coastal climate in the Southeastern USA. A Bland-Altman (BA) analysis was used to assess the level of agreement between the personal IHIE measurements and weather-station heat index (HI) and Urban Heat Island (UHI) measurements. Linear mixed-effect models were used to determine the association between individual risk factors and in situ weather station measurements significantly associated with IHIE measurements. Multivariable stepwise Cox proportional hazard modeling was used to identify the individual and workplace factors associated with time to heat strain in workers. We also examined the non-linear association between heat strain and exposure metrics using generalized additive models. We found significant heterogeneity in IHIE measurements across participants. We observed that time to heat strain was positively associated with a higher IHIE, older age, being male, and among Caucasian workers. Important nonlinear associations between heat strain occurrence and the intensity, frequency, and duration of personal heat metrics were observed. Lastly, our analysis found that IHIE measures were significantly similar for weather station HI, although differences were more pronounced for temperature and relative humidity measurements. Conversely, our IHIE findings were much lower than raster-derived UHI measurements. Real-time monitoring can offer important insights about unfolding temperature-health trends and emerging behaviors during thermal extreme events, which have significant potential to provide situational awareness., (© 2022. The Author(s) under exclusive licence to International Society of Biometeorology.)

In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this first paper of the series, we conducted a systematic review (registration: INPLASY202090088) to identify all TSIs and provide reliable information regarding their use (funded by EU Horizon 2020; HEAT-SHIELD). Eight databases (PubMed, Agricultural and Environmental Science Collection, Web of Science, Scopus, Embase, Russian Science Citation Index, MEDLINE, and Google Scholar) were searched from database inception to 15 April 2020. No restrictions on language or study design were applied. Of the 879 publications identified, 232 records were considered for further analysis. This search identified 340 instruments and indicators developed between 200 BC and 2019 AD. Of these, 153 are nomograms, instruments, and/or require detailed non-meteorological information, while 187 can be mathematically calculated utilizing only meteorological data. Of these meteorology-based TSIs, 127 were developed for people who are physically active, and 61 of those are eligible for use in occupational settings. Information regarding the equation, operating range, interpretation categories, required input data, as well as a free software to calculate all 187 meteorology-based TSIs is provided. The information presented in this systematic review should be adopted by those interested in performing on-site monitoring and/or big data analytics for climate services to ensure appropriate use of the meteorology-based TSIs. Studies two and three in this series of companion papers present guidance on the application and validation of these TSIs, to guide end users of these indicators for more effective use., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Government entities issue recommendations that aim to maintain core temperature below 38.0°C and prevent dehydration [>2% body mass loss] in unacclimated workers exposed to heat. Hydration recommendations suggest drinking 237 mL of a cool sport drink every 15-20 min. This is based on the premise that ad libitum drinking results in dehydration due to inadequate fluid replacement, but this has never been examined in the background of recommendation compliant work in the heat. Therefore, we tested the hypothesis that ad libitum drinking results in >2% body mass loss during heat stress recommendation compliant work. Ten subjects completed four trials consisting of 4 hours of exposure to wet bulb globe temperatures (WBGT) of 24.1 ± 0.3°C (A), 26.6 ± 0.2°C (B), 28.5 ± 0.2°C (C), 29.3 ± 0.6°C (D). Subjects walked on a treadmill and work-rest ratios were prescribed as a function of WBGT [work:rest per hour - A: 60:0, B: 45:15, C: 30:30, D: 15:45] and were provided 237 mL of a cool sport drink every 15 min to drink ad libitum . Mean core temperature was higher in Trial A (37.8 ± 0.4°C; p = 0.03) and Trial B (37.6 ± 0.3°C; p = 0.01) versus Trial D (37.3 ± 0.3°C) but did not differ between the other trials (p ≥ 0.20). Body mass loss (A: -0.9 ± 0.7%, B: -0.7 ± 0.5%, C: -0.3 ± 0.5%, D: -0.4 ± 0.6%) was greater in Trial A compared to Trial D (p = 0.04) and was different from 2% body mass loss in all trials (p ≤ 0.01). Ad libitum drinking during recommendation compliant work in the heat rarely resulted in dehydration. Registered Clinical Trial (NCT04767347)., Competing Interests: This article’s contents are solely the responsibility of the authors and do not necessarily represent the official views of the National Institute of Occupational Safety and Health. ZJS has received consultant fees from Otsuka Holdings Co., Ltd. No other conflicts of interest, financial or otherwise, are declared by the authors., (© 2022 Informa UK Limited, trading as Taylor & Francis Group.)

Power grid outdoor workers are usually exposed to hot environments and could suffer the threats to occupational health and safety like heat strain and injury. In order to predict and assess the thermophysiological responses of grid workers in the heat, the clothing thermal insulation of grid worker ensembles was measured by a thermal manikin and a multi-segment human bioheat model was employed to evaluate the thermophysiological response parameters of grid workers such as core temperature, skin temperature and sweat loss. The results show that working in a hot environment can cause a obvious increase in core temperature and skin temperature of grid workers, and the acceptable maximum working time of grid workers varies greatly in different hot environments. A reasonable work organization strategy can effectively decrease the core temperature and sweat loss, increasing the duration of acceptable maximum working time for grid workers. This study is helpful to assess heat-related risks of grid workers and support power grid companies to rationalize work organization strategies and personal protection guidelines.

This study aimed to better understand environmental heat stress and physiological heat strain indicators in lactating dairy cows. Sixteen heat stress indicators were derived using microenvironmental parameters that were measured at the surrounding of cows and at usual fixed locations in the barn by using handheld and fixed subarea sensors, respectively. Twenty high-producing Holstein-Friesian dairy cows (> 30.0 kg/day) from an intensive dairy farm were chosen to measure respiration rate (RR), vaginal temperature (VT), and body surface temperature of forehead (FT), eye (ET), and muzzle (MT). Our results show that microenvironments measured by the handheld sensor were slightly warmer and drier than those measured by the fixed subarea sensor; however, their derived heat stress indicators correlated equally well with physiological indicators. Interestingly, ambient temperature (T a ) had the highest correlations with physiological indicators and the best classification performance in recognizing actual heat strain state. Using segmented mixed models, the determined T a thresholds for maximum FT, mean FT, RR, maximum ET, mean ET, VT, mean MT, and maximum MT were 24.1 °C, 24.2 °C, 24.4 °C, 24.6 °C, 24.6 °C, 25.3 °C, 25.4 °C, and 25.4 °C, respectively. Thus, we concluded that the fixed subarea sensor is a reliable tool for measuring cows' microenvironments; T a is an appropriate heat stress indicator; FT, RR, and ET are good early heat strain indicators. The results of this study could be helpful for dairy practitioners in a similar intensive setting to detect and respond to heat strain with more appropriate indicators., (© 2022. The Author(s) under exclusive licence to International Society of Biometeorology.)

Background: Heat exposure among construction workers in the Persian Gulf region is a serious hazard for health. The aim of this study was to evaluate the performance of wet bulb globe temperature (WBGT) Index for estimation of heat strain in hot/humid conditions by the use of Physiological Strain Index (PSI) as the gold standard. Material and Methods: This cross‑sectional study was carried out on 71 workers of two Petrochemical Companies in South of Iran in 2010 summer. The WBGT index, heart rate, and aural temperature were measured by Heat Stress Monitor (Casella Microtherm WBGT), Heart Rate Monitor (Polar RS100), and Personal Heat Strain Monitor (Questemp II), respectively. The obtained data were analyzed with descriptive statistics and Pearson correlation analysis. Results: The mean (SD) of WBGT values was 33.1 (2.7). The WBGT values exceed from American Conference of Governmental Industrial Hygienists (ACGIH) standard (30°C) in 96% work stations, whereas the PSI values were more than 5.0 (moderate strain) in 11% of workstations. The correlation between WBGT and PSI values was 0.61 (P = 0.001). When WBGT values were less and more than 34°C, the mean of PSI was 2.6 (low strain) and 5.2 (moderate strain), respectively. Conclusion: In the Persian Gulf weather, especially hot and humid in the summer months, due to the WBGT values exceeding 30°C (in 96% of cases) and weak correlation between WBGT and PSI, the work/rest cycles of WBGT Index is not suitable for heat stress management. Therefore, in Persian Gulf weather, heat stress evaluation based on physiologic variables may have higher validity than WBGT index. [ABSTRACT FROM AUTHOR]

This investigation examined physiological and performance effects of cooling on recovery of medium-fast bowlers in the heat. Eight, medium-fast bowlers completed two randomised trials, involving two sessions completed on consecutive days (Session 1: 10-overs and Session 2: 4-overs) in 31 ± 3°C and 55 ± 17% relative humidity. Recovery interventions were administered for 20 min (mixed-method cooling vs. control) after Session 1. Measures included bowling performance (ball speed, accuracy, run-up speeds), physical demands (global positioning system, counter-movement jump), physiological (heart rate, core temperature, skin temperature, sweat loss), biochemical (creatine kinase, C-reactive protein) and perceptual variables (perceived exertion, thermal sensation, muscle soreness). Mean ball speed was higher after cooling in Session 2 (118.9 ± 8.1 vs. 115.5 ± 8.6 km · h−1; P = 0.001; d = 0.67), reducing declines in ball speed between sessions (0.24 vs. −3.18 km · h−1; P = 0.03; d = 1.80). Large effects indicated higher accuracy in Session 2 after cooling (46.0 ± 11.2 vs. 39.4 ± 8.6 arbitrary units [AU]; P = 0.13; d = 0.93) without affecting total run-up speed (19.0 ± 3.1 vs. 19.0 ± 2.5 km · h−1; P = 0.97; d = 0.01). Cooling reduced core temperature, skin temperature and thermal sensation throughout the intervention (P = 0.001-0.05; d = 1.31-5.78) and attenuated creatine kinase (P = 0.04; d = 0.56) and muscle soreness at 24-h (P = 0.03; d = 2.05). Accordingly, mixed-method cooling can reduce thermal strain after a 10-over spell and improve markers of muscular damage and discomfort alongside maintained medium-fast bowling performance on consecutive days in hot conditions. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the influences of menthol application according to the amount of surface area on physiological and psychological heat strains, along with body regional influences. Male students underwent two stages of experiments: [Experiment 1] Cutaneous thermal threshold test at rest on eight body regions with/without a 0.8% menthol application at T 28°C and 50% RH; [Experiment 2] Six exercise tests with/without a 0.8% menthol spray at T 28°C and 40% RH, while wearing firefighter's protective clothing (No menthol, PC; Face and neck menthol, PC; Upper body menthol, PC; Whole body menthol application, PC) or wearing normal clothing (No menthol, NC; Upper body menthol, NC). Experiment 1 showed that menthol caused no significant influence on cutaneous warm thresholds, while menthol applications evoked earlier detection of cool sensations, especially on the chest ( P = 0.043). Experiment 2 revealed that NC, PC and PC caused lower mean skin temperature, especially with higher peripheral vasoconstrictions on the extremities at rest. During exercise, NC, PC and PC induced greater and earlier increases in rectal temperatures ( T) and a delayed sweat response, but lessened psychological burdens ( P < 0.05). Both physiological and psychological effects of PC were insignificant. For a composite analysis, individual Menthol Sensitivity Index at cooling in Experiment 1 had significant relationships with the threshold for T increase and changes in heart rate in NC of Experiment 2 ( P < 0.05). Our results indicate that menthol's topical influence is body region-dependent, as well as depending on the exposed body surface area. [ABSTRACT FROM AUTHOR]

Background: Working under hot climatic conditions, especially in summer, has a high potential for inducing heat strain in workers. The wet-bulb globe temperature (WBGT) index has an inherent limitation to estimate the heat strain due to not taking into account the nonenvironmental factors. The aim of this study was to evaluate the combined application of WBGT index and a physiological strain index (PSIHR) based on heart rate in the estimation of the heat strain under hot climatic conditions. Materials and Methods: This cross-sectional study was conducted on 122 men in the center and south of Iran (51 and 71 workers from Isfahan steel company and Assaluyeh national petrochemical company, respectively) between July and September 2010. The WBGT index, heart rate and the auditory canal temperature were measured at rest and during the work. Data were analyzed using descriptive statistics and logistic regression. Results: Results of the logistic regression analysis revealed that the WBGT index is a poor predictor for heat strain with a sensitivity and specificity of 53% and 65%, respectively. However, the combined application of the WBGT and PSIHR indexes was a better predictor for heat strain and its sensitivity and specificity were 75% and 69%, respectively. Conclusion: A combined application of the WBGT and PSIHR indexes can be a valid estimator of heat strain for hot climatic conditions in the center and south of Iran. [ABSTRACT FROM AUTHOR]

This study examined heat stress, heart rate (HR), fluid balance, micro-environment temperature and humidity with Islamic athletic clothing (IC) compared to traditional soccer uniform (SC). Ratings of perceived exertion (RPE), session RPE (S-RPE), comfort, and cooling response were also examined. Female volunteers ( N = 8) completed a treadmill $$ \dot{V}{\text{O}}_{{2{\text{peak}}}} $$ test and then, in a randomized, counter-balanced order, two intermittent running bouts (45 min total) in a hot environment (30.0°C WBGT) in IC and SC. Thereafter, participants sat for 40 min in the hot ambient environment. Repeated measures ANOVA revealed significantly greater micro-environment temperature ( p = 0.02) (IC 33.3 ± 3.2°C, SC 32.0 ± 2.8°C) and humidity ( p = 0.04) (IC 48.4 ± 8.1%, SC 42.9 ± 7.9%) in IC during the exercise trial but no difference in the 40-min recovery period for micro-environment temperature ( p = 0.25) or humidity ( p = 0.18). No significant difference ( p > 0.05) was shown for core temperature ( T) (IC 38.3 ± 0.4°C, SC 38.2 ± 0.4°C), HR (IC l54 ± 28 beats min, SC 151 ± 26 beats min) or RPE (IC 4.7 ± 2.1, SC 3.8 ± 1.7) during the exercise trial or recovery period. Results from a paired t test revealed a significantly greater ( p < 0.05) S-RPE (IC 5.8 ± 1.2, SC 4.3 ± 1.9), sweat loss (IC 1.4 ± 0.4 L h, SC 1.2 ± 0.4 L h) and greater discomfort during the exercise and recovery period for the IC. IC clothing appears to have no detrimental effects on heat storage or heat strain during exercise or recovery. [ABSTRACT FROM AUTHOR]

Heat stroke is defined as a condition in which body temperature is elevated to such a level that it becomes a noxious agent causing body tissue dysfunction and damage with a characteristic multi-organ clinical and pathological syndrome. Marked hyperthermia, usually above 40.5 °C and associated encephalopathy, occurs after thermoregulation is subordinated to circulatory and metabolic demands and to the associated systemic inflammatory reaction. Exertional heat stroke is a function of both intrinsic and extrinsic modulators. Intrinsic modulators like genetics, fitness, acclimatization, illness, medications, and sleep quality can alter individual risk and outcomes, while extrinsic modulators like exercise intensity and duration, clothing and equipment, ambient temperature, relative humidity, and solar radiation can affect the group risk and outcomes. This review integrates the current theoretical and accepted knowledge of physiological alterations into one model that depicts a common pathway from heat stress to heat stroke. [ABSTRACT FROM AUTHOR]

Body ventilation systems (BVS) are effective in reducing heat strain, but the amount of heat that a BVS removes from a human body is unclear. The purpose of this study was to propose a method for quantifying BVS cooling capacity using manikin evaluation and modeling. Cooling capacity was calculated as the product of maximum cooling potential and cooling efficiency. The maximum cooling potential is calculated as the difference in enthalpy between the air entering and exiting the BVS where the outlet air temperature is equal to skin temperature with a relative humidity of 100%. The cooling efficiency, defined as a ratio of the cooling capacity to the maximum cooling potential, can be determined through measurements on sweating thermal manikins. A BVS system was evaluated on a manikin with the ventilation fan ON (flow rate 4.7 L/s) or OFF under eleven ambient conditions. The measured cooling efficiencies were 0.31 ± 0.02 and almost constant. Using this cooling efficiency, the BVS cooling capacities at various skin temperature and ambient conditions were estimated. This two-step approach can be used to quantify BVS cooling effectiveness during physiology studies. First, the cooling efficiency is determined on sweating thermal manikins. Second, the cooling capacity is calculated from the skin temperature, ambient temperature and relative humidity. However, various factors may reduce the actual cooling provided by the BVS, and the calculated cooling capacity should be considered the upper limit for cooling. [ABSTRACT FROM AUTHOR]

Heat acclimation (HA) often starts in a moderately hot environment to prevent thermal overload and stops immediately prior to athletic activities. The aims of this study were 1) to establish whether acclimation to a moderately hot climate is sufficient to provide full acclimation for extreme heat and 2) to investigate the physiological responses to heat stress during the HA decay period. 15 male subjects exercised for 9 consecutive days at 26°C Wet Bulb Globe Temperature (WBGT) and 3 days at 32°C WBGT on a cycle ergometer for up to 2 h per day and repeated the exercise 3, 7 and 18 days later in 26°C WBGT. Rectal temperature (Tre) and heart rate (HR) were measured during 60 min of steady state exercise (~45% of maximum oxygen uptake). During days 1-9, end-exercise Tre was reduced from 38.7 ± 0.1 to a plateau of 38.2 ± 0.1°C (p < 0.05), HR was reduced from 156 ± 10 to 131 ± 11 bpm (p < 0.05). No changes in HR and Tre occurred during the 3 days in the very hot environment. However, Tre during rest and exercise were significantly lower by 0.4 - 0.5°C after HA compared with day 9, suggesting that heat acclimation did not decay but resulted in further favourable adaptations. [ABSTRACT FROM AUTHOR]

The article provides information on a study to determine the validity of infrared tympanic membrane temperature for the assessment of heat strain of workers in hot environments. In the study the thermodynamics of infrared tympanic temperature was compared with rectal temperature under the various environmental conditions. The study concludes that using infrared tympanic temperature is valid as a thermal index in evaluating the heat strain of workers wearing impermeable protective coveralls.

The purpose of this study was to investigate the validity of a newly developed method for quantifying perceived skin wettedness (W (p)) as an index to evaluate heat strain. Eight male subjects underwent 12 experimental conditions: activities (rest and exercise) × clothing (Control, Tyvek and Vinyl condition) × air temperatures (25 and 32°C). To quantify the W (p), a full body map with 21 demarcated regions was presented to the subject. The results showed that (1) at rest in 25°C, W (p) finally reached 4.4, 8.3 and 51.6% of the whole body surface area for Control, Tyvek, and Vinyl conditions, respectively, while W (p) at rest in 32°C rose to 35.8, 61.4 and 89.8%; (2) W (p) has a distinguishable power to detect the most wetted and the first wetted regions. The most wetted body regions were the upper back, followed by the chest, front neck, and forehead. The first perceived regions in the skin wetted map were the chest, forehead, and upper back; (3) W (p) at rest showed a significant relationship with the calculated skin wettedness (w) (r = 0.645, p < 0.01) and (4) W (p) had a significant relationship with core temperature, skin temperature, heart rate, total sweat rate, thermal comfort, and humidity sensation (p < 0.05), but these relationships were dependent on the level of activities and clothing insulation. W (p) in hot environments was more valid as a heat strain index of workers wearing normal clothing in light works, rather than wearing impermeable protective clothing in strenuous works. [ABSTRACT FROM AUTHOR]

A previous study by the authors using a heated thermal manikin showed that the cooling rates of phase change material (PCM) are dependent on temperature gradient, mass, and covering area. The objective of this study was to investigate if the cooling effects of the temperature gradient observed on a thermal manikin could be validated on human subjects in extreme heat. The subjects wore cooling vests with PCMs at two melting temperatures (24 and 28°C) and fire-fighting clothing and equipment, thus forming three test groups (vest24, vest28 and control group without the vest). They walked on a treadmill at a speed of 5 km/h in a climatic chamber (air temperature = 55°C, relative humidity = 30%, vapour pressure = 4,725 Pa, and air velocity = 0.4 m/s). The results showed that the PCM vest with a lower melting temperature (24°C) has a stronger cooling effect on the torso and mean skin temperatures than that with a higher melting temperature (28°C). Both PCM vests mitigate peak core temperature increase during the resting recovery period. The two PCM vests tested, however, had no significant effect on the alleviation of core temperature increase during exercise in the heat. To study the possibility of effective cooling of core temperature, cooling garments with PCMs at even lower melting temperatures (e.g. 15°C) and a larger covering area should be investigated. [ABSTRACT FROM AUTHOR]

Heat strain in chemical protective clothing is an important factor in industrial and military practice. Various improvements to the clothing to alleviate strain while maintaining protection have been attempted. More recently, selectively permeable membranes have been introduced to improve protection, but questions are raised regarding their effect on heat strain. In this paper the use of selectively permeable membranes with low vapour resistance was compared to textile-based outer layers with similar ensemble vapour resistance. For textile-based outer layers, the effect of increasing air permeability was investigated. When comparing ensembles with a textile vs. a membrane outer layer that have similar heat and vapour resistances measured for the sum of fabric samples, a higher heat strain is observed in the membrane ensemble, as in actual wear, and the air permeability of the textile version improves ventilation and allows better cooling by sweat evaporation. For garments with identical thickness and static dry heat resistance, but differing levels of air permeability, a strong correlation of microclimate ventilation due to wind and movement with air permeability was observed. This was reflected in lower values of core and skin temperatures and heart rate for garments with higher air permeability. For heart rate and core temperature the two lowest and the two highest air permeabilities formed two distinct groups, but they did not differ within these groups. Based on protection requirements, it is concluded that air permeability increases can reduce heat strain levels allowing optimisation of chemical protective clothing. Statement of Relevance: In this study on chemical, biological, radiological and nuclear (CBRN) protective clothing, heat strain is shown to be significantly higher with selectively permeable membranes compared to air permeable ensembles. Optimisation of CBRN personal protective equipment needs to balance sufficient protection with reduced heat strain. Using selectively permeable membranes may optimise protection but requires thorough consideration of the wearer's heat strain. [ABSTRACT FROM AUTHOR]

We compared the effects of an ice-slush beverage (ISB) and a cool liquid beverage (CLB) on cycling performance, changes in rectal temperature (T (re)) and stress responses in hot, humid conditions. Ten trained male cyclists/triathletes completed two exercise trials (75 min cycling at ~60% peak power output + 50 min seated recovery + 75% peak power output × 30 min performance trial) on separate occasions in 34°C, 60% relative humidity. During the recovery phase before the performance trial, the athletes consumed either the ISB (mean ± SD -0.8 ± 0.1°C) or the CLB (18.4 ± 0.5°C). Performance time was not significantly different after consuming the ISB compared with the CLB (29.42 ± 2.07 min for ISB vs. 29.98 ± 3.07 min for CLB, P = 0.263). T (re) (37.0 ± 0.3°C for ISB vs. 37.4 ± 0.2°C for CLB, P = 0.001) and physiological strain index (0.2 ± 0.6 for ISB vs. 1.1 ± 0.9 for CLB, P = 0.009) were lower at the end of recovery and before the performance trial after ingestion of the ISB compared with the CLB. Mean thermal sensation was lower (P < 0.001) during recovery with the ISB compared with the CLB. Changes in plasma volume and the concentrations of blood variables (i.e., glucose, lactate, electrolytes, cortisol and catecholamines) were similar between the two trials. In conclusion, ingestion of ISB did not significantly alter exercise performance even though it significantly reduced pre-exercise T(re) compared with CLB. Irrespective of exercise performance outcomes, ingestion of ISB during recovery from exercise in hot humid environments is a practical and effective method for cooling athletes following exercise in hot environments. [ABSTRACT FROM AUTHOR]

Background. Thermal protective clothing (TPC) worn by firefighters provides considerable protection from the external environment during structural fire suppression. However, TPC is associated with physiologic derangements that may have adverse cardiovascular consequences. These derangements should be treated during on-scene rehabilitation periods. Objective. To examine heart rate and core temperature responses during the application of four active cooling devices, currently being marketed to the fire service for on-scene rehabilitation, and compare them with passive cooling in a moderate temperature (approximately 24°C) and with an infusion of cold (4°C) saline. Methods. Subjects exercised while they were wearing TPC in a heated room. Following an initial exercise period (bout 1), the subjects exited the room, removed the TPC, and for 20 minutes cooled passively at room temperature, received an infusion of cold normal saline, or were cooled by one of four devices (fan, forearm immersion in water, hand cooling, or water-perfused cooling vest). After cooling, the subjects donned the TPC and entered the heated room for another 50-minute exercise period (bout 2). Results. The subjects were not able to fully recover core temperature during a 20-minute rehabilitation period when provided rehydration and the opportunity to completely remove the TPC. Exercise durations were shorter during bout 2 when compared with bout 1 but did not differ by cooling intervention. The overall magnitudes and rates of cooling and heart rate recovery did not differ by intervention. Conclusions. No clear advantage was identified when active cooling devices and cold intravenous saline were compared with passive cooling in a moderate temperature after treadmill exercise in TPC. [ABSTRACT FROM AUTHOR]

The article presents a study which identifies the effect of environmental heat stress with modest hyperthermia on aerobic performances and pacing strategies. It cites that eight euhydrated men have performed a 15-minute time trial on a cycle ergometer in temperature environments at 21 degrees Celcius and 40 degrees Celsius respectively after a 30-minute cycling preload at 50% peak pulmonary oxygen uptake (VO2). The performance was assessed by the total work in kilo Joules completed in 15 minutes, while pacing was quantified through comparison of the percent difference in actual work performed in each of five 3-minute blocks normalized to the mean work performed per 3-minute block. The results showed degradation of aerobic exercise in hot environments without marked hyperthermia.

An abstract of the article " Prior Heat Stress: Effect on Subsequent 15-min Time Trial Performance in the Heat," by Robert W. Kenefick, Brett R. Ely, Samuel N. Cheuvront, Laura J. Palombo, Daniel A. Goodman and Michael N. Sawka is presented.

This study tested a new portable cooling device for fire fighting recovery. Participants (N = 8) walked and did arm curls (time-weighted VO2: 1.6 L· min-1 on a treadmill for 40 min in a heated chamber (wet bulb globe temperature: 33.7°C; relative humidity: 40-45%) while wearing firefighter turn-out gear and self-contained breathing apparatus (SCBA). Immediately on finishing exercise, participants recovered for 40 min with either a hand-cooling device or seated passive recovery at an ambient temperature of 22°C, 35% RH in a repeated-measures counterbalanced design. The cooling device had little impact on recovery during the first 30 min; however, compared with passive cooling, the cooling device resulted in significantly lower rectal temperature (Tre) during the last 10 min. Relative to starting Tre of the recovery period, ΔTre at 35 min had fallen 0.51 ± 0.19°C (passive) and 0.76 ± 0.30°C (active) (p = 0.03); and at 40 min ΔTre had fallen 0.63 ± 0.17°C (passive) and 0.88 ± 0.31°C (active) (p = 0.03). Cooling capacity of the device calculated from ΔTre over the whole recovery period averaged about 144% of passive. Reductions in heat storage enhance worker safety and performance in hot environments. [ABSTRACT FROM AUTHOR]

There is a need to rapidly screen individuals for heat strain and fever using skin temperature (Tsk) as an index of deep body temperature (Tb). This study's aim was to assess whether Tsk could serve as an accurate and valid index of Tb during a simulated heatwave. Seven participants maintained a continuous schedule over 9-days, in 3-day parts; pre-/post-HW (25.4 °C), simulated-HW (35.4 °C). Contact thermistors measured Tsk (Tforehead, Tfinger); radio pills measured gastrointestinal temperature (Tgi). Proximal-distal temperature gradients (ΔTforehead–finger) were also measured. Measurements were grouped into ambient conditions: 22, 25, and 35 °C. Tgi and Tforehead only displayed a significant relationship in 22 °C (r: 0.591; p < 0.001) and 25 °C (r: 0.408; p < 0.001) conditions. A linear regression of all conditions identified Tforehead and ΔTforehead–finger as significant predictors of Tgi (r2: 0.588; F: 125.771; p < 0.001), producing a root mean square error of 0.26 °C. Additional residual analysis identified Tforehead to be responsible for a plateau in Tgi prediction above 37 °C. Contact Tforehead was shown to be a statistically suitable indicator of Tgi in non-HW conditions; however, an error of ~1 °C makes this physiologically redundant. The measurement of multiple sites may improve Tb prediction, though it is still physiologically unsuitable, especially at higher ambient temperatures. [ABSTRACT FROM AUTHOR]

Heatwaves are one of the most dangerous natural hazards causing more than 166,000 deaths from 1998–2017. Their frequency is increasing, and they are becoming more intense. Electric fans are an efficient, and sustainable solution to cool people. They are, for most applications, the cheapest cooling technology available. However, many national and international health guidelines actively advise people not to use them when indoor air temperatures exceed the skin temperature, approximately 35 °C. We used a human energy balance model, to verify the validity of those recommendations and to determine under which environmental (air temperature, relative humidity, air speed and mean radiant temperature) and personal (metabolic rate, clothing) conditions the use of fans would be beneficial. We found that current guidelines are too restrictive. Electric fans can be used safely even if the indoor dry-bulb temperature exceeds 35 °C since they significantly increase the amount of sweat that evaporates from the skin. The use of elevated air speeds (0.8 m/s) increases the critical operative temperature at which heat strain is expected to occur by an average of 14 °C for relative humidity values above 22 %. We also analyzed the most extreme weather events from 1990 to 2014 recorded in the 115 most populous cities worldwide, and we determined that in 93 of them the use of fans would have been beneficial. We developed a free, open-source, and easy-to-use online tool to help researchers, building practitioners, and policymakers better understand under which conditions electric fans can be safely used to cool people. [Display omitted] • Electric fans can safely be used even if the air temperature is higher than 35 °C. • Electric fans can cool people even when air temperature exceeds skin temperature. • Health guidelines should not discourage people from using fans during heatwaves. • Health guidelines regarding the use of electric fans should be reviewed. • Our open-source tool calculates humidity-dependent temperature thresholds. [ABSTRACT FROM AUTHOR]

Summary: This study examined the effects of active warm up on thermoregulatory responses and intermittent-sprint cycle performance in hot conditions (35.5±0.6°C, RH 48.7±3.4%). Eight trained males performed a 36-min, intermittent-sprint test (IST) after no (WUP 0), 10-min (WUP 10) or 20-min warm up (WUP 20). The IST contained 2-min blocks consisting of a 4-s sprint, 100s active recovery and 20s passive rest. Twice during the IST, there was a repeated-sprint bout (RSB) comprising five, 2-s sprints separated by ∼20s. There were no significant differences between trials for mean work (3870±757 versus 4028±562 versus 3804±494Jsprint−1), peak power (W) or work decrement (%). However, mean work was significantly less in RSB2 than RSB1 for WUP 20 only (P <0.05). Plasma lactate was significantly higher after active warm up (WUP 20=WUP 10>WUP 0; P <0.05), but not significantly different between conditions following either RSB. Rectal temperature (T re) was significantly higher after active warm up (37.0±0.3 versus 37.3±0.3 versus 37.7±0.1°C for WUP0, WUP10 and WUP20, respectively) and throughout the IST. The longer active warm up resulted in a greater increase in T re and was associated with a decrease in short-term repeated-sprint ability (with incomplete recovery), but not prolonged, intermittent-sprint performance in the heat. As active warm up did not improve performance (<40min), team-sport athletes may minimise changes in T re (and the likelihood of heat illness) by avoiding excessive warm up when competing in the heat. [Copyright &y& Elsevier]

The article examines the effects of different types of personal cooling equipment (PCE) on the alleviation of heat strain during red pepper harvest simulated in a climatic chamber in Korea. The study shows that rectal temperature (Tre) is effectively maintained under 38°C by wearing PCE. The study suggests that heat strain of farm workers can be eliminated by the combination of the cooling vest, a scarf and a brimmed hat.

The present study was conducted in order to evaluate whether physiological strain is alleviated by a new personal cooling system (CS) consisting of a layered vest and integrated blower that generate a flow of air. Twelve male volunteers were exposed to climatic conditions of 40°C, 40%RH (40/40), and 35°C, 60%RH (35/60) during a 115 min exercise routine, followed by 70 min resting recovery, while wearing a battle dress uniform (BDU) and a ballistic vest, with (COOL) or without (NOCOOL) CS. The CS was able to attenuate the physiological strain levels during exercise, when compared to identical exposures without the CS. Temperature elevation, (Δ T re) after 100 min of exercise, was lower by 0.26 ± 0.20 and 0.34 ± 0.21°C in 40/40 and 35/60, respectively, ( p < 0.05). Mean skin temperature $$ {\left( {\ifmmode\expandafter\bar\else\expandafter\=\fi{T}_{{{\text{sk}}}} } \right)} $$ was lower by 0.9 ± 0.4 and 0.6 ± 0.5°C for 40/40 and 35/60, respectively. Heart rate (HR) was not significantly different for COOL versus NOCOOL for 40/40. At 35/60, HR was lower by 10 beats per min (bpm) ( p < 0.05). Physiological strain index (PSI) was 9 and 21% lower for the 40/40 and 35/60, respectively, for COOL versus NOCOOL ( p < 0.05). Heat storage ( S) rates were 19 and 24% lower and sweat rates were 21 and 25% lower for the 40/40 and 35/60, respectively, for COOL versus NOCOOL ( p < 0.05). However, the CS was not effective in alleviating physiological strain during resting recovery with no difference in T re cooling rate, S, or HR drop rate between groups over resting recovery periods. The CS tested in this study was found to be an effective tool for lowering physiological strain while exercising but not during resting recovery. Therefore, the CS should be further developed in order to achieve greater attenuation of the thermal strain during exercise and improve effectiveness during rest. Overall, it has the potential to be useful for both military and sports personnel. [ABSTRACT FROM AUTHOR]

The study examined the impact of chemical protective (CP) clothing on the performance of lifesaving tasks in thermoneutral and cold conditions. Eleven males performed pre-exercise followed by lifesaving tasks wearing either field combat uniform at 21°C (U) or CP clothing at 21°C (CPN) and-;5°C (CPC). The tasks were ventilating a doll (VA) and connecting an intravenous line (IV). Mean skin temperature was significantly higher for CPN compared to U and CPC during pre-exercise, VA and IV. Changes in blood pressure were significantly greater with CP clothing than without during VA and IV. The number of breaths per min (in VA) and time needed for IV increased by 19% (p < 0.05) and 18%, respectively, for CPN compared to U. Due to the cold, the additional increment was 5% and 17%, respectively, for CPC. Wearing of CP clothing in thermoneutral or in cold conditions may not prevent but, especially in the cold, significantly impede the performance of basic medical tasks. The findings of this study showed that performing medical tasks while wearing nuclear, biological and chemical protective clothing is impaired due to significant changes in physiological strain. This suggests that realistic training in local conditions as well as in cold conditions is needed to realise the restrictions due to protective clothing. [ABSTRACT FROM AUTHOR]

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on–off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30°C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 ± 5 W · m -2 . Water temperature to the LCG was held constant at 21°C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 ± 0.2°C) in NC, which was greater than IC (0.5 ± 0.2°C) and CC (0.5 ± 0.3°C) ( p [ABSTRACT FROM AUTHOR]

Exercise-heat exposure results in significant sweat losses due to large biophysical requirements for evaporative heat loss. Progressive body water losses will increase plasma tonicity and decrease blood volume (hypertonic–hypovolemia). The result is reduced dry and evaporative heat exchange through alterations in the core temperature threshold for initiation of skin blood flow and sweating as well as changes in the sensitivity of these thermo-effectors. Regulation of reduced sweating conserves body water, which reduces heat loss and increases exercise hyperthermia, but the magnitude of this effect is modified by environmental heat transfer capabilities. The focus of this paper is to (1) examine the major mechanisms by which hypohydration alters thermoregulatory responses in the heat, and (2) illustrate how important differences in environmental airflow characteristics between laboratory and field settings may modify these effects. [Copyright &y& Elsevier]