Background: Global climate change is already increasing the average temperature and direct heat exposure in many places around the world. Objectives: To assess the potential impact on occupational health and work capacity for people exposed at work to increasing heat due to climate change. Design: A brief review of basic thermal physiology mechanisms, occupational heat exposure guidelines and heat exposure changes in selected cities. Results: In countries with very hot seasons, workers are already affected by working environments hotter than that with which human physiological mechanisms can cope. To protect workers from excessive heat, a number of heat exposure indices have been developed. One that is commonly used in occupational health is the Wet Bulb Globe Temperature (WBGT). We use WBGT to illustrate assessing the proportion of a working hour during which a worker can sustain work and the proportion of that same working hour that (s)he needs to rest to cool the body down and maintain core body temperature below 38°C. Using this proportion a ‘work capacity’ estimate was calculated for selected heat exposure levels and work intensity levels. The work capacity rapidly reduces as the WBGT exceeds 26-30°C and this can be used to estimate the impact of increasing heat exposure as a result of climate change in tropical countries. Conclusions: One result of climate change is a reduced work capacity in heat-exposed jobs and greater difficulty in achieving economic and social development in the countries affected by this somewhat neglected impact of climate change. Keywords: climate change; work; heat; occupational health; productivity (Published: 11 November 2009) Citation: Global Health Action 2009. DOI: 10.3402/gha.v2i0.2047

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Workplace heat stress, health and productivity - an increasing challenge for low and middle-income countries during climate change.

With predicted increasing frequency and intensity of extremely hot weather due to changing climate, workplace heat exposure is presenting an increasing challenge to occupational health and safety. This article aims to review the characteristics of workplace heat exposure in selected relatively high risk occupations, to summarize findings from published studies, and ultimately to provide suggestions for workplace heat exposure reduction, adaptations, and further research directions. All published epidemiological studies in the field of health impacts of workplace heat exposure for the period of January 1997 to April 2012 were reviewed. Finally, 55 original articles were identified. Manual workers who are exposed to extreme heat or work in hot environments may be at risk of heat stress, especially those in low-middle income countries in tropical regions. At risk workers include farmers, construction workers, fire-fighters, miners, soldiers, and manufacturing workers working around process-generated heat. The potential impacts of workplace heat exposure are to some extent underestimated due to the underreporting of heat illnesses. More studies are needed to quantify the extent to which high-risk manual workers are physiologically and psychologically affected by or behaviourally adapt to workplace heat exposure exacerbated by climate change.

https://www.jstage.jst.go.jp/article/indhealth/advpub/0/advpub_2012-0145/_pdf

Health Impacts of Workplace Heat Exposure: An Epidemiological Review

The WBGT heat stress index has been well tested under a variety of climatic conditions and quantitative links have been established between WBGT and the work-rest cycles needed to prevent heat stress effects at the workplace. While there are more specific methods based on individual physiological measurements to determine heat strain in an individual worker, the WBGT index is used in international and national standards to specify workplace heat stress risks. In order to assess time trends of occupational heat exposure at population level, weather station records or climate modelling are the most widely available data sources. The prescribed method to measure WBGT requires special equipment which is not used at weather stations. We compared published methods to calculate outdoor and indoor WBGT from standard climate data, such as air temperature, dew point temperature, wind speed and solar radiation. Specific criteria for recommending a method were developed and original measurements were used to evaluate the different methods. We recommend the method of Liljegren et al. (2008) for calculating outdoor WBGT and the method by Bernard et al. (1999) for indoor WBGT when estimating climate change impacts on occupational heat stress at a population level.

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Calculating Workplace WBGT from Meteorological Data: A Tool for Climate Change Assessment

It is accepted that the earth's climate is changing in an accelerating pace, with already documented implications for human health and the environment. This literature review provides an overview of existing research findings about the effects of heat stress on the working population in relation to climate change. In the light of climate change adaptation, the purpose of the literature review was to explore recent and previous research into the impacts of heat stress on humans in an occupational setting. Heat stress in the workplace has been researched extensively in the past however, in the contemporary context of climate change, information is lacking on its extent and implications. The main factors found to exacerbate heat stress in the current and future workplace are the urban 'heat island effect', physical work, individual differences, and the developing country context where technological fixes are often not applicable. There is also a lack of information on the effects on vulnerable groups such as elderly people and pregnant women. As increasing tempera- tures reduce work productivity, world economic productivity could be condensed, affecting devel- oping countries in the tropical climate zone disproportionately. Future research is needed taking an interdisciplinary approach, including social, economic, environmental and technical aspects.

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Effects of Heat Stress on Working Populations when Facing Climate Change

Personal cooling technologies locally control the temperature of an individual rather than a large space, thus, providing personal thermal comfort while supplementing cooling loads in thermally regulated environments. This can lead to significant energy and cost savings. In this study, a new approach to personal cooling was developed using an infrared-transparent visible-opaque fabric (ITVOF) that provides passive cooling via the transmission of thermal radiation emitted by the human body directly to the environment. Here, we present a conceptual framework to thermally and optically design an ITVOF. Using a heat transfer model, the fabric was found to require a minimum infrared (IR) transmittance of 0.644 and a maximum IR reflectance of 0.2 to ensure thermal comfort at ambient temperatures as high as 26.1 °C (79 °F). To meet these requirements, an ITVOF design was developed using synthetic polymer fibers with an intrinsically low IR absorptance. These fibers were then structured to minimize IR reflection ...

Infrared-Transparent Visible-Opaque Fabrics for Wearable Personal Thermal Management

The farmers in tropical climate are exposed to high heat during the summer months. The study examined the physiological strains of farmers (N=26) to six combined exposures of work and high heat, with moderate and heavy work (26 to 50%, and 51 to 75% VO2max) and three ambient conditions, i.e., 34.4 to 42.2°C WBGT (inside) in an environmental chamber. While the cardio-respiratory responses and Tcr were predominantly influenced by the work severity (p<0.001), the environmental warmth greatly influenced the sweating response (p<0.001). The importance was placed on the segmental Tsk as the first rank indicator of the bodily heat strain. Both the environmental warmth and work severity had independent discernable effects on the dynamic equilibrium of the central and peripheral mechanism to regulate the body temperature. The segmental and compartmental (core, muscle, fat and skin) heat balance analysis indicated the span of convergence of the segmental core and muscle temperatures to the divergence of skin and fat temperatures (CORE-SHELL) as a quantitative estimate of the segmental gradient for heat transfer. The summation of heat exchange across the compartments and segments yielded the transient change in Tcr (0.06 to 0.12°C/min), with significant difference between the moderate and heavy work. The Tcr of 39°C was taken as the limit of tolerance for the farmers, and by defining the criteria limit of Tcr of ~2.5°C gradient from the basal Tcr and the rate of change in Tcr, the tolerance times were estimated. Corollary to the development of ISO 7933 standard (PHS index), the predictions of tolerance times from the transient change in Tcr or the exponential relationship with the WBGT (tolerance time, min = 1,841 e -0.103 WBGT) were useful to suggest the protective limit for men at work in extremely hot environment. The simplicity of prediction lies in using WBGT as a criterion. The exponential equation estimated the tolerance time of 55 min at 34°C WBGT, and up to 38°C WBGT, the decrease in tolerance time was 4 to 5 min per degree increase in environmental warmth. Beyond 38°C WBGT, the estimated tolerance time decreased by 2 to 3 min per degree increase in WBGT. Further optimization and validation of the knowledge for men and women farmers in different age groups will have application in managing heat illnesses and disorders in tropical farming.

Thermal limits of men in moderate to heavy work in tropical farming

Ergonomics in sickle operation

The efficacy of a water-cooled jacket for auxiliary body cooling was examined under a simulated hot environment. The personal garment comprised of a water re-circulating three-layered vest of cotton fabric lined with 2 mm diameter latex tubing and inter-spaced coating of rubberized solution. Four subjects wearing the water-cooled jacket were tested in the environment chamber (30, 35 and 40 degrees C DB, 50-60% RH, air velocity 0.3, 0.6 and 0.9 m/s, with corresponding average effective temperature of 26 +/- 2.3, 33 +/- 1.1 and 36 +/- 1.5 degrees C). The inlet water temperature was maintained at 10-12 degrees C, with flow rates of 2.6 +/- 0.3, 4.3 +/- 0.3 and 5.1 +/- 0.3 l/h). At 30 degrees C DB, variation in water flow had marginal effect on microclimate, while at higher temperatures (35 and 40 degrees C DB), the re-circulating cooled water had noticeable effects in lowering microclimate, trunk and other skin temperatures, and maintaining the body core within 36.7 +/- 0.2 to 37.5 +/- 0.2 degrees C, over 2 h exposure at 35 and 40 degrees C DB. The observation indicates that the water-cooled jacket provided auxiliary cooling to maintain comfortable microclimate, skin and body core temperatures. This enabled subjects to sustain comfortable heat balance over 2 h heat exposure without any noticeable heat strain.

Efficacy of a water-cooled garment for auxiliary body cooling in heat

Construction workers are at high risk of heat-related illnesses during summer months in India. The personal cooling garment (PCG) is a microclimate assistive device that provides protection from heat stress. The applicability and efficacy of wearing PCG for the physiological and subjective responses were tested on 29 healthy construction workers at actual field worksites. During the test, the climatic conditions were 103.64 ± 38.3°F dry bulb temperature, 41.2 ± 13.4% relative humidity, and wet bulb globe temperature 91.43 ± 39.92°F. Mean weighted skin temperature was significantly lowered by 38.66 ± 33.98°F when wearing PCG as compared with wearing habitual clothing (HC), 32.36 ± 33.44°F ( p < .05). Mean sweat loss was also significantly lower when wearing PCG: 0.365 ± 0.257 kg as compared with wearing HC: 0.658 ± 0.342 kg ( p < .05). Heart rate, along with back and chest skin temperatures were significantly reduced with wearing PCG. The present study suggests that PCG provides an affordable way of alleviating the discomfort and physiological strain caused by environmental heat exposure.

https://journals.sagepub.com/doi/pdf/10.1177/2165079918785388

Workplace Heat Exposure Management in Indian Construction Workers Using Cooling Garment.

The working capacity of young, healthy, unacclimatized men (N = 11) was studied under long-duration (8 to 9 days) exposure to combined work and heat (dry and humid). The dry (Gr A, N = 5) and humid (Gr B, N = 6) groups were exposed to 41.3 +/- 0.6 degrees C DB, 40-50% RH and 39.2 +/- 0.6 degrees C DB, 70-80% RH, respectively, for all days of exposure. The experimental protocol was divided into: (i) direct determination of maximal oxygen uptake (VO2max) by stepped increases in bicycle ergometry everyday in the morning in the initial hours before exposure to heat, after which the recovery process of oxygen debt contraction was examined; and (ii) exposure to heat in a climatic chamber for 2 h where the subjects performed two spells of ergometric work (10 to 12 min each) at a relative intensity of 50 +/- 12 to 69 +/- 11% VO2max. The average heat exposure time for Gr A was higher (108 +/- 12 min) as compared to Gr B (95 +/- 10 min), but Gr B sustained a high heat load as reflected from the high deep-body temperature maintained during the exposure. The high body temperature load of Gr B had a significant effect on the cardiorespiratory capacity, indicating an upward trend in VO2max. This was statistically significant (p < 0.05) for the first four days of exposure. Subjects of Gr B had a relatively higher working capacity compared to those in Gr A on all days. The VO2max and analysis of the fractions of oxygen debt contraction (fast and slow component) indicated that the subjects showed a better training/heat acclimatization effect under hot, humid conditions.

S. P. Ashtekar

Papers

Thermal limits of men in moderate to heavy work in tropical farming

Ergonomics in sickle operation

Efficacy of a water-cooled garment for auxiliary body cooling in heat

Workplace Heat Exposure Management in Indian Construction Workers Using Cooling Garment.

Human work capacity under combined stress of work and heat