The focus of this review is upon acute exposure to hot environments and the accompanying physiological changes. The target audience includes physiologists, physicians and occupational health and safety practitioners. Using the principles of thermodynamics, the avenues for human heat exchange are explored, leading to an evaluation of some methods used to assess thermally-stressful environments. In particular, there is a critique of the wet-bulb globe temperature (WBGT) index, and an overview of an alternative means by which such assessments may be undertaken (the heat stress index). These principles and methods are combined to illustrate how one may evaluate the risk of heat illness. Three general areas of research are briefly reviewed: the physiological impact of wearing thermal protective clothing, heat adaptation (acclimation) and whole-body pre-cooling. These topics are considered as potential pre-exposure techniques that may be used to reduce the threat of hyperthermia, or to enhance work performance in the heat.
The purposes of this review are to show pathophysiological mechanisms for heat illness during working in a hot environment and accordingly provide some preventive considerations from a viewpoint of body fluid homeostasis. The incidence of the heat illness is closely associated with body temperature regulation, which is much affected by body fluid state in humans. Heat generated by contracting muscles during working increases body temperature, which, in a feedback manner, drives heat-dissipation mechanisms of skin blood flow and sweating to prevent a rise in body temperature. However, the impairment of heat-dissipation mechanisms caused by hard work in hot, humid, and dehydrated conditions accelerates the increase in body temperature, and, if not properly treated, leads to heat illness. First, we overviewed thermoregulation during working (exercising) in a hot environment, describe the effects of dehydration on skin blood flow and sweating, and then explained how they contributes to the progression toward heat illness. Second, we described the advantageous effects of blood volume expansion after heat acclimatization on temperature regulation during exercise as well as those of restitution from dehydration by supplementation of carbohydrate-electrolyte solution. Finally, we described that the deteriorated thermoregulation in the elderly is closely associated with the impaired body fluid regulation and that blood volume expansion by exercise training with protein supplementation improves thermoregulation.
Homeothermic animals regulate body temperature by autonomic and behavioral thermoeffector responses. The regulation is conducted mainly in the brain. Especially, the preoptic area (PO) in the hypothalamus plays a key role. The PO has abundant warm-sensitive neurons, sending excitatory signals to the brain regions involved in heat loss mechanisms, and inhibitory signals to those involved in heat production mechanisms. The sympathetic fibers determine tail blood flow in rats, which is an effective heat loss process. Some areas in the midbrain and medulla are involved in the control of tail blood flow. Recent study also showed that the hypothalamus is involved in heat escape behavior in rats. However, our knowledge about behavioral regulation is limited. The central mechanism for thermal comfort and discomfort, which induce various behavioral responses, should be clarified. In the heat, dehydration affects both autonomic and behavioral thermoregulation by non-thermoregulatory factors such as high Na+ concentration. The PO seems to be closely involved in these responses. The knowledge about the central mechanisms involved in thermoregulation is important to improve industrial health, e.g. preventing accidents associated with the heat or organizing more comfortable working environment.
This paper presents heat stress Standard ISO 7243, which is based upon the wet bulb globe temperature index (WBGT), and considers its suitability for use worldwide. The origins of the WBGT index are considered and how it is used in ISO 7243 and across the world as a simple index for monitoring and assessing hot environments. The standard (and index) has validity, reliability and usability. It is limited in application by consideration of estimating metabolic heat and the effects of clothing. Use of the standard also requires interpretation in terms of how it is used. Management systems, involving risk assessments, that take account of context and culture, are required to ensure successful use of the standard and global applicability. For use outdoors, a WBGT equation that includes solar absorptivity is recommended. A `clothed WBGT' is proposed to account for the effects of clothing. It is concluded that as a simple assessment method, ISO 7243 has face validity and within limits is applicable worldwide.
The work of the main European research teams in the field of thermal factors was co-ordinated in order to improve significantly the Required Sweat Rate model published as an international standard. Many significant modifications were brought, in particular concerning the effects of forced convection, body movements and exercise and the prediction of the skin temperature as a function of the rectal temperature and in case of severe conditions of radiation, humidity and clothing. The criteria for acceptable work durations in hot environments were updated concerning the maximum increase in core temperature and the acceptable water loss. The revised model, called Predicted Heat Strain model, was validated through a set of lab and field experiments involving stable and fluctuating conditions with high and low radiation, humidity and air velocity. It is meanwhile adopted as an ISO and CEN standard.In addition, a strategy was developed to assess the risks of heat disorders in any working situation. It is based on the three highest stages of the SOBANE strategy: an "Observation" method for improving simply the thermal conditions of work; an "Analysis" method to evaluate the magnitude of the problem and optimise the choice of solutions and an "Expert" method for in depth analysis of the working situation when needed.
Thermal stress is an important factor in many industrial situations, athletic events and military scenarios. It can seriously affect the productivity and the health of the individual and diminish tolerance to other environmental hazards. However, the assessment of the thermal stress and the translation of the stress in terms of physiological and psychological strain is complex. For over a century attempts have been made to construct an index, which will describe heat stress satisfactorily. The many indices that have been suggested can be categorized into one of three groups: "rational indices", "empirical indices", or "direct indices". The first 2 groups are sophisticated indices, which integrate environmental and physiological variables; they are difficult to calculate and are not feasible for daily use. The latter group comprises of simple indices, which are based on the measurement of basic environmental variables. In this group 2 indices are in use for over four decades: the "wet-bulb globe temperature" (WBGT) index and the "discomfort index" (DI). The following review summarizes the current knowledge on thermal indices and their correlates to thermal sensation and comfort. With the present knowledge it is suggested to adopt the DI as a universal heat stress index.
Recently, a novel environmental stress index (ESI) which is composed from commonly used meteorological variables: ambient temperature (Ta), relative humidity (RH), and solar radiation (SR) was suggested as follows: ESI=0.63Ta-0.03RH+0.002SR+0.0054(Ta·RH)-0.073(0.1+SR)-1; (°C) The purpose of the present study was to evaluate and validate the ESI for hot dry and hot wet climatic conditions. The ESI was applied to large meteorological databases from 2 different locations resembling hot/wet and hot/dry climates. Data analysis revealed high correlation between ESI and the wet bulb globe temperature (WBGT) index for each of the two databases: P<0.05, R2=0.985 and 0.982, for the hot/dry and hot/wet conditions, respectively. Therefore, it is concluded that ESI, which is constructed from fast response and commonly used weather variables (Ta, RH, SR), and also found in a microsensor format is validated for hot/dry and hot/wet zones and as a potential index to serve as an alternative to the WBGT for heat category assessment.
The high level of protection required by personal protective clothing (PPC) severely impedes heat exchange by sweat evaporation. As a result work associated with wearing PPC, particularly in hot environments, implies considerable physiological strain and may render workers exhausted in a short time. Recent development of algorithms for describing the heat transfer, accounting for pumping and wind effects, comprises improvement of the prediction of thermal stress. Realistic corrections can then be made to the available measures of thermal insulation and evaporative resistance of a given clothing ensemble. Currently this information is incorporated in international standards for assessment of thermal environments. Factors, such as directional radiation and wetting of layers, were studied in a recently completed EU research project. The development of advanced thermal manikins and measurement procedures should provide better measures for predictive models. As with all methods and models, the results need validation in realistic wear trials in order to prove their relevance and accuracy.
This report provides a summary of research conducted through a grant provided by the Workplace Safety Insurance Board of Ontario. The research was divided into two phases; first, to define safe work limits for firefighters wearing their protective clothing and working in warm environments; and, the second, to examine strategies to reduce the thermal burden and extend the operational effectiveness of the firefighter. For the first phase, subjects wore their protective ensemble and carried their self-contained breathing apparatus (SCBA) and performed very light, light, moderate or heavy work at 25°C, 30°C or 35°C. Thermal and evaporative resistance coefficients were obtained from thermal manikin testing that allowed the human physiological responses to be compared with modeled data. Predicted continuous work times were then generated using a heat strain model that established limits for increases in body temperature to 38.0°C, 38.5°C and 39.0°C. Three experiments were conducted for the second phase of the project. The first study revealed that replacing the duty uniform pants that are worn under the bunker pants with shorts reduced the thermal strain for activities that lasted longer than 60 min. The second study examined the importance of fluid replacement. The data revealed that fluid replacement equivalent to at least 65% of the sweat lost increased exposure time by 15% compared with no fluid replacement. The last experiment compared active and passive cooling. Both the use of a mister or forearm and hand submersion in cool water significantly increased exposure time compared with passive cooling that involved only removing most of the protective clothing. Forearm and hand submersion proved to be most effective and produced dramatic increases in exposure time that approximated 65% compared with the passive cooling procedure. When the condition of no fluid replacement and passive cooling was compared with fluid replacement and forearm and hand submersion, exposure times were effectively doubled with the latter condition. The heat stress wheel that was generated can be used by Commanders to determine safe work limits for their firefighters during activities that involve wearing their protective clothing and carrying their SCBA.
In spite of increased environmental cold stress, heat strain is possible also in a cold environment. The body heat balance depends on three factors: environmental thermal conditions, metabolic heat production and thermal insulation of clothing and other protective garments. As physical exercise may increase metabolic heat production from rest values by ten times or even more, the required thermal insulation of clothing may vary accordingly. However, in most outdoor work, and often in indoor cold work, too, the thermal insulation of clothing is impractical, difficult or impossible to adjust according to the changes in physical activity. This is especially true with whole body covering garments like chemical protective clothing. As a result of this imbalance, heat strain may develop. In cold all the signs of heat strain (core temperature above 38°C, warm or hot thermal sensations, increased cutaneous circulation and sweating) may not be present at the same time. Heat strain in cold may be whole body heat strain or related only to torso or core temperature. Together with heat strain in torso or body core, there can be at the same time even cold strain in peripheral parts and/or superficial layers of the body. In cold environment both the preservation of insulation and facilitation of heat loss are important. Development of clothing design is still needed to allow easy adjustments of thermal insulation.
The objectives of the present study were to define the lowest ambient air and cabin temperatures at which aircrews wearing immersion protection are starting to experience thermal discomfort and heat stress during flight operations, and to characterize during a flight simulation in laboratory, the severity of the heat stress during exposure to a typical northern summer ambient condition (25°C, 40% RH). Twenty male helicopter aircrews wearing immersion suits (insulation of 2.2 Clo in air) performed 26 flights within an 8-month period at ambient temperatures ranging between -15 and 25°C, and cabin temperatures ranging between 3 and 28°C. It was observed based on thermal comfort ratings that the aircrews were starting to experience thermal discomfort and heat stress at ambient and cabin air conditions above 18°C and at a WBGT index of 16°C. In a subsequent study, seven aircrews dressed with the same clothing were exposed for 140 min to 25°C and 40% RH in a climatic chamber. During the exposure, the aircrews simulated pilot flight maneuvers for 80 min followed with backender/flight engineer activities for 60 min. By the end of the 140 min exposure, the skin temperature, rectal temperature and heart rate had increased significantly to 35.7 ± 0.2°C, 38.4 ± 0.2°C and between 110 and 160 beats/min depending on the level of physical activity. The body sweat rate averaged 0.58 kg/h and the relative humidity inside the clothing was at saturation by the end of the exposure. It was concluded that aircrews wearing immersion suits during the summer months in northern climates might experience thermal discomfort and heat stress at ambient or cabin air temperature as low as 18°C.
A thermal manikin is a useful tool to evaluate thermal environments such as clothing, houses and others. A manikin needs to have the following properties: shape and size, heat production, skin temperature, sweat rate, physiological responses and others. So far, no manikin satisfying all these criteria has been available. In the present study, a two-layer movable sweating thermal manikin was newly developed as a trial to compensate for the differences between conventional thermal manikins and the human body. The manikin consisted of two layers, a core section in the trunk and a shell section divided into 17 parts over the whole body, the temperature and heat supply of which could be independently controlled. The manikin is possible to change the posture and to walk. The sweat rate from 180 pores on the skin was controlled by peristaltic pumps. The temperature performance of the manikin was investigated using thermograph. As a result, the surface temperature of the manikin decreased more in the extremities than in the trunk when the manikin was exposed to 18°C after being exposed to 28°C for 20 min. This is analogous to the skin temperature decline in the extremities of the human body.
The incidence of heat disorders in July and August during 10 yr (1995-2004) reported for the population of Yamanashi prefecture was analyzed, with special consideration of an aging society, in relation to levels and patterns of phases with high daily maximal temperatures. There was an increasing tendency for years with hot summers in comparison to preceding decades. Two climatic characteristics associated with increased incidence of heat disorders have become apparent: first, sustained phases of atmospheric temperatures exceeding ≈32°C, second, rapid onset of phases with high maximal temperature after preceding phases of relatively cool weather. The influence of age expressed itself in a peak of heat disorder incidences among older children and adolescents and in an elevated plateau at ages higher than ≈60 yr. Up to that age, exertional heat disorders prevailed. At higher ages classical, non-exertional heat disorders constituted an increasing fraction. Lethal outcomes among patients suffering from heat disorder was low. Patients older than 70 yr clearly prevailed among the lethal cases. The frequent occurrence of heat disorders among persons of old age puts emphasis on the importance of maintaining social activity to improve well-being in general and physiological resistance against heat in particular, including adequate fluid supply. Because physiological heat defense is limited in an aging population, adequate air conditioning will gain increasing importance in view of the observed tendency for the increasing occurrence of phases with excessively high atmospheric summer temperatures.
Nowadays, no studies have been published on the relationship between meteorological conditions and work-related mortality and morbidity in Italy. The aim of this study was to evaluate the relationship between hot weather conditions and hospital admissions due to work-related accidents in Tuscany (central Italy) over the period 1998-2003. Apparent temperature (AT) values were calculated to evaluate human weather discomfort due to hot conditions and then tested for work accident differences using non-parametric procedures. Present findings showed that hot weather conditions might represent a risk factor for work-related accidents in Italy during summer. In particular early warming days during June, characterized by heat discomfort, are less tolerated by workers than warming days of the following summer months. The peak of work-related accidents occurred on days characterized by high, but not extreme, thermal conditions. Workers maybe change their behaviour when heat stress increases, reducing risks by adopting preventive measures. Results suggested that days with an average daytime AT value ranged between 24.8°C and 27.5°C were at the highest risk of work-related accidents. In conclusion, present findings might represent the first step for the development of a watch/warning system for workers that might be used by employers for planning work activities.
As the percentage of shifts in hot working conditions in German Coal mines had increased to more than 50% during the last decade, a study was carried out to record the physiological strain of miners. Thirty-eight miners participated during 125 shifts. Heart rate and rectal temperature were measured continuously. Sweat losses as well as food and fluid uptake were estimated from measurements before and after shifts. During all shifts mean heart rates resulted in 102.8 min-1, mean rectal temperature was 37.7°C. Mean sweat loss per shift was 3,436 g; mean sweat rates resulted in 494 g/h. Rehydration during the shift at high climatic stress decreased to about 60% of sweat losses. In order to state the organizational frame of work at hot working places in German coal mines, the main features of regulations of work at hot working places are presented.
The aim of this research was to understand hot working environment at a construction site in summer and its effects on health of workers. In the subjective construction site, some measures, such as taking a break during work, setting tents and electric fans, and drinking cool water, had already been taken to reduce heat stress. Twelve male workers were examined. The WBGT outdoors during work varied from 23 to 34°C. The time-motion study revealed that one subject worked exceeding 7 hours, and that the other one had little rest time and drank little water during work. Few items of subjective symptoms increased after work compared with before work. In blood chemical data, electrolytes and blood urea nitrogen did not change. Blood sugar before work was significantly higher than before lunch and after work. Two subjects showed serum osmotic pressures increased after work. Two had the tendency to increase the blood pressure during work. The measures seemed effective, because the effects of work were not remarkable in general. However, some problems were still pointed out. Thus, stricter work control and health care for workers are necessary, such as controlling working hours strictly and monitoring the water intake during work.
A cross-sectional study was performed on 225 textile workers from a wool production company in Montenegro to test the hypothesis of a relationship between exposure to intense industrial noise and tooth abrasion. The group exposed to intense noise (104 dB (A) Leq) consisted of 111 weavers (82 males and 29 females), while the control group (81 dB (A) Leq) consisted of 114 blue-collar workers (32 males and 82 females) in preparation departments. A specialist in dental prosthetics clinically examined all the subjects and additionally analyzed tooth statuses on hard plaster models. Gender, age, socioeconomic status and tooth brushing habits of workers were controlled as confounding factors. Significantly high adjusted odds ratios for tooth abrasion of 3.74 (95%CI=1.42-7.85; p<0.01) were found among female workers exposed to intense noise in comparison with the control group. The analysis of the subclass of male workers with severe tooth abrasion (grades III-IV) revealed significantly high adjusted odds ratios for tooth abrasion of 5.48 (95%CI=1.76-14.50; p<0.01) among the noise exposed group compared to the control group. This study suggests that extremely high levels of occupational noise might be related to tooth abrasion in exposed textile workers.
The associations between health behaviors and depressive symptoms have been demonstrated in many studies. However, job strain has also been associated with health behaviors. The aim of this study was to analyze whether health behaviors such as physical activity, sleeping, smoking and alcohol intake are associated with depressive symptoms after adjusting for job strain. Workers were recruited from nine companies and factories located in east and central areas of Japan. The Center for Epidemiologic Studies Depression (CES-D) Scale was used to assess depressive symptoms. Psychological demand and control (decision-latitude) at work were measured with the Job Content Questionnaire. Multiple logistic regression analysis was used to determine the independent contribution of each health behavior to depressive symptoms. Among the total participants, 3,748 (22.7%) had depressive symptoms, which was defined as scoring 16 or higher on the CES-D scale. Using the multiple logistic regression analysis, depressive symptoms were significantly associated with physical activity less than once a week (adjusted relative risk [ARR]=1.18, 95% confidence interval [CI], 1.14 to 1.25) and daily hours of sleep of 6 h or less (ARR, 1.25; 95%CI, 1.14 to 1.35). Smoking and frequency of alcohol intake were not significantly associated with depressive symptoms. This study suggests some health behaviors such as physical activity or daily hours of sleep are associated with depressive symptoms after adjusting for job strain.
This work investigated how wearing a new design of back belt affects erector spinae activity, hand force, and body stability. The belt was first tested with static holding tasks and found to significantly decrease the back muscle activity. Actual lifting tasks were further carried out to test the effect of the belt. Ten male subjects performed a symmetric lifting task of low-lying loads (11 and 16 kg) at natural toting velocity, using either a squat or stoop lifting posture, both with and without a belt. The study measured various independent variables using electromyography (EMG), load cells, and motion capture device. The results demonstrated that the belt reduced the load on the erector spinae, as well as the triceps brachii and biceps brachii. The overall mean values of the peak (hand) force did not appear significantly affected while wearing the belt, but the force peaks appeared postponed. The belt did not alter body stability while lifting. From the present findings, the belt effectively changed the force distribution during lifting, at least reducing the muscle load on the back. The belt may be a potentially useful device for symmetric industrial lifting tasks.
The purpose of this study was to investigate the time dependent effects among factors affecting duration of work disability after compensated low-back pain. A postal survey involving 238 compensated workers at 39 companies was performed between January 5, 2004, and March 23, 2004. Cox proportional hazard regression analysis was used to model the effect of demographic, work-related, and injury factors affecting the duration of work disability. The variables that significantly affected the duration of work disability were age, company size, compensation benefit, pain radiation, and diagnosis. In addition, company size and pain radiation showed statistically significant time dependent effect. Consequently, this study found that there were time dependent factors affecting the duration of work disability. A phase-specific analysis would be useful to make policy for the prevention of long term disability after back injury.
Pregnant Sprague-Dawley (CD IGS) rats were orally administered doses of bisphenol A (BPA) at 4, 40, and 400 mg/kg, from gestation days 6 to postnatal day 20. Neurotransmitters such as dopamine (DA) and serotonin (5HT) were extracted from the brains of dams and female offspring, and measured using liquid chromatography. BPA at 400 mg/kg was toxic and dosed rats died. At 3 wk after birth, brain levels of 3,4-dihydroxyphenylacetic acid (DOPAC, a DA metabolite), homovanillic acid (HVA, a DA metabolite), 5HT, 5-hydroxyindoleacetic acid (5HIAA, a 5HT metabolite) in female offspring were increased and the HVA/DA ratio was high in some brain areas of BPA-treated groups as compared with controls. At the age of 6 wk, levels of choline (Ch) in BPA-treated groups at 4 and 40 mg/kg were higher than control in all of eight brain areas. No changes were observed in acetylcholine (ACh) contents. In 9-wk-old offspring, changes in monoamines and metabolites were scattered and not great. At 3 wk after delivery, levels of 5HIAA in some brain areas of dams treated with BPA were higher than in control dams. Dose dependent increases in HVA and the HVA/DA ratio of the occipital cortex, and in the HVA/DA ratio of the frontal cortex were observed. The turnover of DA and 5HT was accelerated in 3-wk-old offspring and dams. BPA possesses very weak estrogenic activity. Changes in cerebral neurotransmitters observed in offspring and dams in this study may have been related to the estrogenic activity of BPA. However, further investigation is needed to examine the contribution of hormonal activity to such neurotransmitter changes.