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Climate change and heat stress resilient outdoor workers: findings from systematic literature review

BMC Public Health volume 24, Article number: 1711 (2024) Cite this article

Abstract

Purpose

Global warming has led to an increase in the number and intensity of extreme heat events, posing a significant threat to the health and safety of workers, especially those working outdoors, as they often have limited access to cooling strategies. The present systematic literature review (a) summarizes the current knowledge on the impacts of climate change on outdoor workers, (b) provides historical background on this issue, (c) explores factors that reduce and increase thermal stress resilience, (d) discusses the heat mitigation strategies, and (e) provides an overview of existing policy and legal frameworks on occupational heat exposure among outdoor workers.

Materials and methods

In this systematic review, we searched scientific databases including Scopus (N = 855), Web of Science (N = 828), and PubMed (N = 202). Additionally, we identified relevant studies on climate change and heat-stress control measures through Google Scholar (N = 116) using specific search terms. In total, we monitored 2001 articles pertaining to worker populations (men = 2921; women = 627) in various outdoor climate conditions across 14 countries. After full-text assessment, 55 studies were selected for inclusion, and finally, 29 eligible papers were included for data extraction.

Results

Failure to implement effective control strategies for outdoor workers will result in decreased resilience to thermal stress. The findings underscore a lack of awareness regarding certain adaptation strategies and interventions aimed at preventing and enhancing resilience to the impact of climate change on heat stress prevalence among workers in outdoor tropical and subtropical environments. However, attractive alternative solutions from the aspects of economic and ecological sustainability in the overall assessment of heat stress resilience can be referred to acclimatization, shading, optimized clothing properties and planned breaks.

Conclusion

The integration of climate change adaptation strategies into occupational health programs can enhance occupational heat resilience among outdoor workers. Conducting cost-benefit evaluations of health and safety measures for thermal stress adaptation strategies among outdoor workers is crucial for professionals and policymakers in low- and middle-income tropical and subtropical countries. In this respect, complementary measures targeting hydration, work-rest regimes, ventilated garments, self-pacing, and mechanization can be adopted to protect outdoor workers. Risk management strategies, adaptive measures, heat risk awareness, practical interventions, training programs, and protective policies should be implemented in hot-dry and hot-humid climates to boost the tolerance and resilience of outdoor workers.

Peer Review reports

Introduction

Extreme weather events and severe heat pose significant hazards to the safety and health of workers, leading to increased accidents, mortality, and morbidity during hot climate conditions [1,2,3]. Global warming presents a new and formidable challenge for most countries [4, 5]. Global climate change substantially affects physiological and perceptual responses through both direct and indirect effects on core body temperature [6], heart rate, skin temperature, and thermal comfort [7,8,9]. Working in hot and humid environments during long shifts with high physical activity can jeopardize the safety and health of worker populations [7, 10]. Increased exposure to thermal stress among workers in outdoor environments has been documented in tropical and subtropical countries with hot seasons [11]. Exposure to hot working environments, and the resulting elevated physiological and perceptual responses, can lead to occupational heat stress, reducing safety, health, and work capacity [12], and increasing the risk of heat-related illnesses (HRI) [13]. The increment in the levels of ambient temperature, radiation and shifts in the distribution of daily peak temperature can cause indirect and direct effects on outdoor workers [14, 15]. High temperatures and high humidity can exacerbate the effects of physical workload on individuals working outdoors during long shifts in developing and tropical countries [16]. Working in high-temperature and high-humidity environments can have adverse health effects on workers, particularly agricultural workers, construction workers, drivers, sellers, brick-making workers, and daily wage workers [17, 18]. High hot-humid and hot-dry temperatures can lead to occupational heat strain when core body temperature rises above 38 °C [19]. Exposure to heat radiation, either when working outdoors with exposure to the sun or around hot machinery, can greatly increase physiological pressure and lead to reduced work capacity [20].These physiological mechanisms worsen under high climate conditions and climate change, emphasizing the need to identify strategies to increase occupational heat stress resilience and develop solutions and policies to protect the health and safety of outdoor workers [21, 22]. Projected future global warming conditions will dangerously affect the anticipated occupational heat stress resilience of outdoor workers worldwide. There is insufficient knowledge regarding strategies to increase occupational heat stress resilience, necessitating protective measures against heat stress and climate change to reduce health risks and fatalities for future outdoor workers in hot and humid work environments. The findings of this study can inform planning for increasing occupational heat stress resilience, developing heat acclimation strategies, and identifying risk factors to mitigate heat stress caused by global warming, particularly in middle- and low-income communities.

Materials and methods

Search strategy

This systematic literature review was conducted following the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines [23]. We searched scientific databases, including PubMed, Scopus, and Web of Science, and identified additional records through Google Scholar. We used Mesh terms in PubMed to identify synonyms for ‘climate change’ and ‘thermal resistance.’ We also consulted specialists to identify relevant keywords. Our search syntax was developed and applied to title, abstract, or keyword queries in selected databases. To ensure the specificity and accuracy of our search strategy, we tested the number needed to read (NNR) in the Web of Science database. We also investigated the references of included studies and searched key journals via Scopus to identify potentially relevant articles. The full search strategy in three main databases has been mentioned in Appendix 1. Our search syntax was as follows:

PubMed: (“heat wave”[tiab] OR “heat stress”[tiab] OR “climate change*”[tiab] OR (climate[tiab] AND change[tiab]) OR “extreme weather”[tiab] OR “extreme heat”[tiab] OR “global warming”[tiab] OR “hot day*”[tiab] OR “warm day*”[tiab]) AND (“heat tolerance“[tiab] OR “heat resilien*“[tiab] OR (heat[tiab] AND resilien*[tiab]) OR (heat[tiab] AND tolera*[tiab]) OR “Heat resistan*”[tiab] OR thermotolerance[tiab] OR “heat endurance”[tiab] OR (heat[tiab] AND endur*[tiab])) AND (worker*[tiab] OR Firefighter*[tiab] OR “fire fighter*”[tiab] OR firem*[tiab] OR “fire m*”[tiab] OR nurs*[tiab] OR operator*[tiab] OR driver*[tiab] OR farmer[tiab]* OR welder*[tiab] OR miner*[tiab] OR employee[tiab] OR laborer*[tiab] OR labour*[tiab]).

Inclusion criteria

The research question components (PECO) were as follows: P (workers), E (Exposure), C (heat stress), and O (increase occupational heat stress resilience). We included studies that (a) measured physiological and perceptual responses in workplaces and resting environments of workers; (b) studied working populations, including both males and females (healthy and unhealthy populations); (c) assessed the impact of climate change on occupational heat strain, as well as the health, safety, and well-being of workers including work-related variables (income, work type, time), environmental variables (wet-bulb globe temperature (WBGT), relative humidity), physiological variables (heart rate, respiratory, rate of perceived exertion (RPE)), and demographic variables (age, sex, body mass index (kg/m2); (d) focused on air temperature, relative humidity (RH), heat waves, solar radiation, climate change, UV radiation, and thermal stress; (e) considered local and international contexts, countries, and workplaces; and (f) investigated workers’ perceptions of climate change, occupational heat strain, and their knowledge and attitudes toward adaptation strategies.

Exclusion criteria

Studies were excluded if they (a) studied climate change-related phenomena such as storms, cyclones, rainfall, rising sea levels, and drought; (b) evaluated the impact of climate change on plants, crop yields, pest dynamics, soil processes, water availability, and animals; (c) had inaccessible full-texts; or (d) focused on indoor workplaces.

Screening and selection

We entered all identified studies into EndNote and removed duplicates. One team member (PH) screened studies based on their titles and abstracts, and two members of the research team (AH and PH) independently selected relevant studies by reviewing the full texts. Disagreements regarding study inclusion were resolved through team discussion. We also conducted searches in three key journals: environmental research, urban climate, and global environmental change, but did not identify any additional studies.

Data extraction and quality assessment

Two team members (AH and PH) independently assessed the eligibility of included studies based on our inclusion and exclusion criteria. They also evaluated the methodological quality of selected studies using the quality assessment tool for studies with diverse designs (QATSDD), which consists of 16 items and is a reliable and valid tool for assessing the methodological quality of various types of studies [24]. Any disagreements regarding study inclusion were resolved through team discussion.

Results

Search results

The numbers of identified studies and the studies reviewed during the screening and selection stages are presented in Fig. 1. The initial search yielded 2001 articles including the additional articles sourced from Scholar Google. After full-text assessment, 55 studies were selected for inclusion, and finally, 29 eligible papers were included for data extraction. No additional studies meeting our eligibility criteria were identified after the full-text investigation. Similarly, no studies were identified through searches of key journals and the references of included studies. Table 1 provides details on the selected studies, including author/year, study location, document type, population/sample size, climate conditions, assessment of physical, perceptual, and physiological factors, authors’ conclusions, and quality ratings. Table 2 presents suggestions for increasing and decreasing occupational heat stress resilience among outdoor workers.

Fig. 1
figure 1

Flow diagram of the screening process of included studies the strategies to increase occupational heat stress resilience among outdoor workers

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Table 1 Characteristics of included studies examining the strategies to increase occupational heat stress resilience among outdoor workers in the context of climate change
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Table 2 Characteristics of included studies examining the strategies to increase and decrease occupational heat stress resilience among outdoor workers in the context of climate change
Full size table

Descriptive analysis

Out of the 29 selected studies, 18 addressed global warming’s impact on occupational heat stress resilience, risk management strategies, and adaptation strategies for warming conditions. Most of these studies emphasized that climate change will exacerbate the health impacts of extreme heat. The prevalence of negative effects due to climate change will intensify workers’ health risks in future work scenarios, particularly in regions with hot and humid climates and poor economic conditions. As of our selection period until 2023, 20 studies (68.96%) were published between 2016 and 2023. Of the 29 assessed papers, 18 (62.06%) directly investigated the effects of climate change and adaptation strategies for outdoor workers in various countries, including Australia, the USA, China, Japan, Africa, Korea, Slovenia, Taiwan, Indonesia, Ghana, Korea, India, Iran, and Pakistan. The predominant themes identified in these papers revolved around strategies to increase occupational heat stress resilience. In conclusion, the study’s findings were categorized into main themes, including risk factors that decrease occupational heat stress resilience and suggestions for increasing occupational heat stress resilience among outdoor workers.

Thematic content analysis

This systematic review provides a summary of evidence published to date regarding strategies to enhance occupational heat stress resilience, especially in hot outdoor workplaces. Despite variations in study design and analytical approaches, the evidence presented in this systematic review consistently highlights a strong association between thermal stress resulting from global warming and occupational heat stress. Broad findings from these studies indicate that exposure to heatwaves and global warming is linked to adverse health impacts on workers.

Furthermore, several studies underscore the need for sentinel effects and leading indicators to facilitate surveillance of climate-related occupational heat stress effects, as well as strategies and interventions for preventing the impact of climate change on outdoor workers. Finally, the review identifies interventions and adaptation strategies for outdoor workers, including the provision of accessible cool drinking water [13, 26, 41, 44, 47], optimized work-rest schedules [12, 13, 16, 26, 36, 43, 44, 47], the availability of proper resting shade [16, 47, 49], training and awareness programs [20, 38, 40], self-paced work [13, 38, 40, 44, 47], and the use of supportive protective equipment [41].

Factors that reduce resilience to climate change among outdoor workers

Resilience to climate change among outdoor workers can be reduced by various factors, categorized into personal risk factors, environmental risk factors, and occupational-related heat exposure risk factors during work.

Individual-related heat exposure risk factors

Personal factors associated with reduced resilience to climate change, identifiable from outdoor workers’ data, include dehydration [20, 25, 28, 32, 34, 37, 40, 46,47,48], unique medical characteristics [41, 47], pregnancy [38, 40, 47], BMI [29, 30, 37, 40, 47, 49], obesity and body fat [29, 30, 32, 34, 47], overall health status [33, 34, 37, 47], lack of sleep [33, 34, 40, 47], experience of a previous HRI [32, 34, 44,45,46,47], presence of certain concurrent diseases and chronic disease [35, 47], kidney disease [20, 26, 38, 43, 46, 47], consumption of caffeine and alcohol [26, 28, 30, 34, 37, 40, 41, 46, 47], smoking [30], use of drugs [26, 37, 40, 41, 47], age [16, 33, 35, 38,39,40,41, 46, 47], older workers with low education [38, 40, 43, 44, 46, 47], physical fitness [26, 32, 40, 47], metabolism rate [40, 47], type of clothing [40, 47], prior heat injury [40, 46, 47], physical activity and heavy workload [16, 27, 31, 34, 38,39,40, 46,47,48], gender [16, 33, 35, 38,39,40,41, 46, 47], education level [16, 39, 41, 44, 46, 47], wearing PPE [16, 26, 27, 31, 38, 39, 44, 46, 47], and non-acclimatization [29, 32, 37, 40, 41, 43, 44, 47]. Physiological risk factors most frequently expressed by outdoor workers included excessive heart rate [30, 45, 47, 49], oral [47, 49], skin [45,46,47, 49], core temperature [26, 27, 29, 31, 32, 34, 45,46,47,48,49], sweating [39, 47], and blood pressure [45,46,47, 49]. This is often followed by heat exhaustion [47, 48] or tiredness [47], headaches [47], heat rash [47], and fainting [47]. Older adults are more vulnerable to chronic dehydration [28, 45], especially those living with multiple chronic diseases [43, 47]. Aging is also associated with reductions in sweat production [8]. Consequently, studies have generally reported greater elevations in body heat storage and core temperature in older compared to younger adults during environmental heat exposure [26, 37, 46, 47]. Additionally, personal factors correlated with occupational heat strain include the adequacy of water intake [41, 47].

Environmental-related heat exposure risk factors

The environmental factors contributing to thermal stress include high air temperature [12, 16, 26, 27, 31, 34, 40, 45,46,47,48,49], heat wave [43, 47, 48], airspeed and movement around the workplace [16, 43, 45, 47,48,49], high levels of heat exposure (WBGT = 37.5–49 ℃) [38, 46, 47], tropical nights [48], working in sun- exposed conditions [16, 38, 39, 47], solar radiation [26, 40, 43, 46,47,48], high humidity [16, 27, 31, 34, 40, 43, 45, 47,48,49], UV radiation [26, 47,48,49], the moisture content of the outdoor settings or workplaces [16, 39], radiant heat [16, 26, 31, 36, 45, 47, 48], and the air-pollution index [30].

Occupational-related heat exposure risk factors

However, workers encounter various barriers, such as inadequate cool housing designs for rest [38], a lack of management and engineering commitment [41, 42, 47], heavy physical workloads for long hours [16, 47] or physically demanding jobs [44, 46], insufficient awareness and prevention training [38, 40, 41, 43, 47], a lack of knowledge regarding adaptive behavior [41, 43], the absence of occupational heat stress guidelines and adaptation strategies [38, 41, 46, 47], a lack of regular training on adaptation measures [41], limited management commitment [41], the nature of the physical workload [16, 40, 41, 46, 47], the absence of specific thermal stress-related policy regulations [41], working in proximity to heat sources [16, 44, 47], the type of protective clothing [16, 40, 47], limited access to innovative technology and equipment [41], the nature of the work [40, 41, 46, 47], inadequate management commitment, work-break regimes [43, 47] and cooling systems [26, 28, 40, 41, 47, 48]. Additionally, workers face challenges such as inadequate knowledge of adaptive behavior [41, 46], a lack of regular training on thermal stress risk, adaptation, and safety measures [41, 47], a deficiency in specific heat-related policies and regulations [41], limited management commitment to heat-related health and safety measures [41], restricted access to innovative equipment and technology [41], insufficient regular breaks and work-rest time [35, 39, 41, 46, 47], limited access to shade [38, 43, 47], inadequate financial resources [38, 41], the absence of an acclimatization program [41, 43, 47], suboptimal water management [47], and insufficient medical attention when implementing adaptation strategies for climate change and occupational heat stress.

Factors that enhance resilience to climate change among outdoor workers

Enhanced resilience to climate change can be achieved through various means, including personal, managerial, and engineering protective factors.

Personal protective factors

Outdoor workers can take several measures to protect themselves. They should consider adjusting their work schedule [35, 47], maintaining adequate hydration [28, 33, 35, 37,38,39,40, 47], adjusting their clothing [31, 35, 47], drinking more water [35] or drinking plenty of cool water frequently before feeling thirsty [13, 26, 41, 44, 47]. It’s important to take more frequent planned breaks [35, 38, 44], wear broad-brimmed hats [35, 39, 41, 47] and ventilated helmets [28], understand how to self-pace [13, 38, 40, 44, 47], wear sun-protective gear [38, 49], including sunglasses and gloves during hot weather conditions [41], and take work breaks and rest in cooler or shaded areas [13, 28, 33, 35, 38,39,40,41, 43, 44, 47]. Using sunblock [38, 39, 44], and having a higher education level [39, 44, 47], are also beneficial. Workers should consider wearing loose and light-colored clothing [28, 34, 35, 38, 39, 41, 44] and opting for short-sleeved shirts and shorts when possible [13]. Using cooling vests [27, 47], implementing a ‘Buddy system’ [47], acclimatization [26, 29,30,31,32,33,34, 36, 37, 40, 47], maintaining normal anthropometric measures [29], and changing clothing ensembles to more breathable single-layer garments [43] can further enhance personal protection.

Managerial protective factors

Maintaining good quality working conditions and a suitable climate can significantly improve worker performance, productivity, and company profits [37]. Workplace management and training programs [16, 35, 38, 40, 41, 47, 49] are crucial for worker well-being. Developing prevention strategies [12, 13, 38, 48], improving guidelines for worker safety, health, and productivity, and adhering to occupational health standards [12, 38, 47] are essential. Scheduling heavy routine outdoor work during the early morning [47] or evening hours or in shaded areas [13, 41, 44, 49] can help mitigate heat stress. Providing access to cooling systems, such as air conditioning and fans [13, 16, 26, 38,39,40,41, 44, 47], and offering climate change adaptation strategies [13, 48, 49] are beneficial. Adjusting the duration of breaks/rest periods [12, 13, 16, 26, 36, 43, 44, 47], ensuring access to shade [16, 47, 49], and providing access to drinking water or implementing programs to improve hydration status [13, 16, 20, 25, 44, 47, 49] are important managerial measures. Training workers in heat-related illness prevention [20, 38, 40], providing access to medical attention [20], sharing heavier jobs and rotating job assignments on shift schedules [13, 41, 47, 49], offering air-conditioned vehicles [13, 38, 47], promoting climate change awareness to support healthy lives and decent jobs [39], implementing work stoppages if the daily maximum temperature exceeds 40 °C [13, 44, 47], raising worker awareness about heat risks [47] modifying work habits [49], considering the TWL [30], and promoting the understanding of the need for workers to self-pace during hot weather [13, 38, 47] are all valuable managerial protective factors.

Engineering protective factors

Providing and designing regular breaks in shaded areas [38, 47], implementing strategies to eliminate or replace thermal stress risks [37, 44], installing a central cooling system [13, 44, 47], halting work during periods of high thermal stress and supplying mechanical equipment [41, 47], initiating heat-shield projects [47], and enhancing ventilation [38, 39, 44, 47].

Discussion

Our systematic review’s outcomes help us understand strategies for increasing occupational heat stress resilience and assessing the effects of global warming on outdoor workers’ adaptation strategies. This is particularly crucial in numerous warm workplaces, especially in low- and middle-income countries. The implementation of strategies to ensure adequate hydration, including access to drinking water and programs to improve hydration status [13, 16, 20, 25, 44, 47, 49], is one of the most critical interventions for managing warm workplaces. Hydrated workers [28, 33, 35, 37,38,39,40, 47] are more likely to maintain an acceptable work rate and physical activity without health risks in various hot-dry and hot-humid weather conditions [25]. Employers bear the responsibility of providing a safe work environment, conducting training and awareness programs [16, 35, 38, 40, 41, 47, 49], supervision [50], and providing suitable protective equipment to mitigate the negative effects of thermal stress due to global warming on safety and health [26, 49]. Cooling the core body temperature through wearable liquid cooling garments (SCG) [27], evaporative cooling garments (ECGs) [15], fluid cooling garments (FCGs) [51], hybrid cooling (HBCGs) [52], and phase change materials (PCMs) [53] worn by individuals who require personal protective equipment [47, 54], including firefighters and construction workers, significantly reduces occupational heat strain and enhances thermal comfort and performance [32]. Chan et al. recommend implementing appropriate protective measures, such as work-rest schedules and heat tolerance guidelines, to ensure the safety and health of personnel exposed to hot weather conditions [28]. Therefore, it’s advisable to conduct further research on work-rest schedule optimization models for workers, particularly in the context of construction workers [28]. It is recommended that safe work durations should be modified based on expected type of clothing and work intensity [55]. Our review’s results indicate that personal risk factors such as dehydration [20, 25, 28, 32, 34, 37, 40, 46,47,48], smoking [30] and alcohol-drinking habits [26, 28, 30, 34, 37, 40, 41, 46, 47], age [16, 33, 35, 38,39,40,41, 46, 47], BMI [29, 30, 37, 40, 47, 49], and non-acclimatization [29, 32, 37, 40, 41, 43, 44, 47]; as well as work-related factors like work-rest cycles [35, 39, 41, 46, 47] and environmental risk factors such as air temperature [12, 16, 26, 27, 31, 34, 40, 45,46,47,48,49], relative humidity (RH) [16, 27, 31, 34, 40, 43, 45, 47,48,49], heat radiant [16, 26, 31, 36, 45, 47, 48], and Thermal Work Limit (TWL) [30], are significant predictors for determining the physiological responses to HRI among outdoor workers [30]. More efforts should be made to educate workers and employers about the effects of occupational heat stress on safety, health and performance, and appropriate screening protocols (pre-employment and periodic examinations) should be included in health and safety legislation [56].

Educating outdoor workers about physiological and perceptual responses to HRI [20, 38, 40] and heat acclimation under uncompensated thermal stress [26, 29,30,31,32,33,34, 36, 37, 40, 47], as well as emphasizing cooling techniques and fluid intake [28, 33, 35, 37,38,39,40, 47], is essential. Furthermore, it’s necessary to investigate the impact of gender (both women and men) [16, 33, 35, 38,39,40,41, 46, 47] and aging on heat tolerance and psychophysiological adaptation during work in hot-dry and hot-humid environmental conditions. This is especially crucial since elderly workers [38, 40, 43, 44, 46, 47] display increased susceptibility to HRI in future studies, even if they haven’t engaged in prolonged or strenuous physical labor [31]. Pogačar et al.‘s study revealed that the most common symptoms of heat stress include excessive sweating, thirst, and fatigue. Interestingly, there was a significant difference among age groups regarding thirst and excessive sweating [35]. Gender differences in temperature regulation become more apparent under varying heat loads [8]. In general, women lose more heat through convection [11], which is advantageous in hot-humid environments [57], while men lose more heat through evaporation, which is more pronounced in hot-dry environments [58]. The resilience of vulnerable worker groups to heat stress can be compromised despite existing standards and knowledge. This vulnerability is particularly relevant when considering outdoor workers exposed to different climate conditions in tropical and subtropical countries [12, 38, 47]. Kjellstrom et al.‘s study underscores that mine workers remain the most significant population in terms of preventing the impact of thermal stress. This also extends to many construction workers, agricultural workers, and individuals laboring in warm workplaces without effective cooling systems [20]. Lui et al. demonstrated that wildland firefighters experience heat acclimatization across the thermal stress and fire season, leading to significant decreases in physiological and perceptual responses. These adaptations can reduce the risk of HRI [32]. Implementing acclimatization [26, 29,30,31,32,33,34, 36, 37, 40, 47] and adaptation programms [13, 48, 49] for workers exposed to thermal stress is crucial. Adaptation policies aim to increase climate change resilience and reduce climate vulnerability [48]. Managers and occupational health professionals should also assess workers’ health status and individual habits, such as sleep deprivation [33, 34, 40, 47], dehydration, and alcohol consumption before work [34]. International agencies have proposed various climate change adaptation and prevention strategies, including conducting training and awareness programs, using cooling mechanisms [13, 16, 26, 38,39,40,41, 44, 47], and ensuring the availability of cool drinking water [13, 16, 20, 25, 44, 47, 49]. The most effective solutions at mitigating occupational heat strain were heat acclimation [26, 29,30,31,32,33,34, 36, 37, 40, 47], wearing specialized cooling garments [27, 47], cold water immersion [59], improving aerobic fitness [15], and applying ventilation [49]. Extending the exposure time to thermal stress leads to an increase in core body temperature and dehydration levels [60]. Acclimatized workers, with beneficial physiological adaptations like an efficient sweating system, lower heart rate, and core body temperature, can tolerate higher levels of dehydration and lose more water through sweat per shift. This means that the maximum allowable exposure time is greater for acclimatized workers compared to non-acclimatized workers [38, 42, 47]. Venugopal et al. demonstrated a strong correlation between physical workload, thermal stress exposures, Heat Strain Indicators (HSIs), and HRIs, leading to adverse health outcomes among outdoor workers [46]. There is a pressing need for evidence-based reviews and interventions to prevent occupational heat stress and enhance comprehensive resilience labor policies for outdoor workers in low and middle-income countries as climate change progresses. Increased awareness and consciousness among workers can lead to better adaptability to climate change risks [31]. Workers often implement conscious and flexible behavioral attitudes to manage their heat stress, especially in extremely hot workplaces, such as outdoor work [49]. Understanding the relationship between endurance time and WBGT values is crucial for training workers in very hot environments and ensuring their health and safety [43]. Elevated carbon emissions in the atmosphere contribute to extremely hot environments and climate changes, exacerbating occupational heat strains for outdoor workers [61]. A high-quality air and work environment can enhance worker safety, health, productivity, and company profitability [37, 49]. Sustainable adaptation to warming climatic conditions [13] and social protection strategies during exposure to occupational heat stress depend on the availability of financial resources and collaborative efforts to overcome adaptation barriers [48]. The severity of occupational heat stress caused by climate change depends on workers’ sensitivity and vulnerability to different weather conditions. Additionally, the extent of adaptation capacity and resilience planning plays a crucial role [33, 38]. Also, establishing a program that can assess how thermal stress due to climate change may increase heat-related effects on outdoor workers and document future heat-related events leading to relevant occupational health and safety regulations, seems essential [15].

The HEAT-SHIELD project is a customized occupational heat stress-related warning system that provides short- and long-term heat warnings to safeguard workers’ health and productivity. This project represents a useful adaptation strategy aimed at protecting workers, particularly those exposed to the effects of climate change [55, 62,63,64,65,66].

The findings of this study are valuable for policymakers and professionals in the field of occupational health. They can use this information to develop guidelines and regulations aimed at preventing occupational heat stress and strengthening the resilience of outdoor workers during exposure to heat stress caused by climate change. However, it’s important to note that developing countries face a higher risk of negative occupational health outcomes compared to developed countries due to their lower adaptive capacity [46], increased poverty, and insufficient technological progress to combat climate change-induced temperature increases [6, 47]. Outdoor workers often lack awareness of heat-related risks and HRI due to global warming [67, 68]. Therefore, there is a critical need to raise awareness of heat-related hazards, bolster heat stress education, and update existing heat prevention measures. This includes optimizing current heat-related laws and adaptation policies to ensure effective implementation and compliance, especially in hot-dry and hot-humid work environments, particularly in low-middle-income countries [44, 48]. Studies of this nature are essential among workers in these countries to provide health professionals and senior managers with the necessary knowledge to inform occupational heat stress adaptation policies, social protection measures, and resilience strategies for sustainable development.

Limitations

One limitation of this systematic review was the limited focus on female workers. Consequently, the results may not accurately represent the perspectives of women working outdoors, which is an important demographic to consider. Another significant limitation of this study is its heavy reliance on cross-sectional and experimental studies. Incorporating clinical aspects into data collection could greatly enhance and advance occupational health interventions. Furthermore, there is an evident scarcity of research exploring the social dimensions and the broader effects of occupational heat stress. Additionally, there is insufficient investigation into the adaptation strategies employed by workers in the context of increasing thermal stress and climate change, particularly in tropical and subtropical countries. These research gaps highlight the need for further studies to provide a more comprehensive understanding of this critical occupational health issue.

Conclusion

Addressing the health risks associated with occupational thermal stress among outdoor workers requires a multi-level approach that includes standard procedures and safety interventions. Currently, there is a lack of formal guidelines for outdoor workers, and most advisory systems do not adequately support this workforce in implementing solutions to mitigate occupational heat stress and enhance climate change resilience. While many workers acknowledge the importance of increased hydration and clothing adjustments during hot-dry and hot-humid climate conditions, a smaller proportion attempt to modify the nature of their work or seek rest in cooler areas. It is crucial to recognize that occupational heat stress remains a prevalent issue among these populations. To address these challenges, we recommend conducting further research to enhance our understanding of strategies aimed at bolstering the resilience of outdoor workers against heat stress resulting from climate change. This research should encompass diverse fields such as medicine, climatology, occupational health, and epidemiology. Additionally, there is a need to improve information dissemination, develop relevant regulations, and implement protective strategies among outdoor workers. These efforts will aid in identifying and preventing heat stress-related policies, including mitigation and adaptation measures.

Data availability

The datasets used and analyzed during the current study are available from the corresponding author on request.

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Authors and Affiliations

  1. Department of Occupational Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

    Peymaneh Habibi & Farank Mahdavi

  2. Health, Safety & Environment (HSE), Shahid Beheshti University of Medical Sciences and Health Services, Tehran, Iran

    Jaleh Razmjouei

  3. Safety and Risk Engineering, Faculty of Engineering and Applied Science, Memorial University of Newfoundland, St. John’s, Newfoundland, NL, Canada

    Amirhossein Moradi

  4. Department of Health in Emergencies and Disasters, School of Public Health, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

    Saeed Fallah-Aliabadi

  5. Accident Prevention and Crisis Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

    Saeed Fallah-Aliabadi

  6. Department of Health in Disaster and Emergencies, School of Medicine, Kurdistan University of Medical Sciences, Sanandaj, Iran

    Ahad Heydari

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AH and PH were participated in the study design, data collection, data analysis. JR, AM, FM, SFA were participated manuscript writing, revising and editing. Study was done under the supervision of AH and PH. All authors read, revised and approved the final manuscript.

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Habibi, P., Razmjouei, J., Moradi, A. et al. Climate change and heat stress resilient outdoor workers: findings from systematic literature review. BMC Public Health 24, 1711 (2024). https://doi.org/10.1186/s12889-024-19212-3

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