An Evaluation of the Physiological Strain Experienced by Electrical Utility Workers in North America

Agreement between measured and self-reported physiological strain in males and females during simulated occupational heat stress

RATIONALE

Monitoring physiological strain is recommended to safeguard workers during heat exposure, but is logistically challenging. The perceptual strain index (PeSI) is a subjective estimate thought to reflect the physiological strain index (PSI) that requires no physiological monitoring. However, sex is known to influence perceptions of heat stress, potentially limiting the utility of the PeSI.

OBJECTIVES

The objective of this study was to assess whether sex modifies the relationship between PeSI and PSI.

METHODS

Thirty-four adults (15 females) walked on a treadmill (moderate intensity; ~200 W/m2) for 180 min or until termination (volitional fatigue, rectal temperature ≥39.5°C) in 16°C, 24°C, 28°C, and 32°C wet-bulb globe temperatures. Rectal temperature and heart rate were recorded to calculate PSI (0-10 scale). Rating of perceived exertion and thermal sensation were recorded to calculate PeSI (0-10 scale). Relationships between PSI and PeSI were evaluated via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis. Mean absolute error between measures was calculated by summing absolute errors between the PeSI and the PSI and dividing by the sample size.

FINDINGS

PSI increased with PeSI (p < 0.01) but the slope of this relation was not different between males and females (p = 0.83). Mean bias between PSI and PeSI was small (-0.4 points), but the 95% LoA (-3.5 to 2.7 points) and mean absolute error were wide (1.3 points).

IMPACT

Our findings indicate that sex does not appreciably impact the agreement between the PeSI and PSI during simulated occupational heat stress. The PeSI is not a suitable surrogate for the PSI in either male or female workers.

"Breaking down in tears, soaked in sweat, and sick from the heat": Media-based composite narratives of first responders working during the 2021 Heat Dome

BACKGROUND

During the summer of 2021, a deadly, unprecedented multiday Heat Dome engulfed western Canada. As a result of this extreme heat event (EHE), emergency dispatchers received an unparalleled increase in incoming 911 calls for ambulance, police, and fire (as first responders) services to attend to hundreds of heat-vulnerable community members succumbing to the heat. With 103 all-time heat records broken during this EHE and indoor temperatures of nearly 40°C, the first responders attending these calls faced extensive job demands and highly challenging operating conditions. Initial investigations have explored the health system-level impacts; however, little has been done to explore the impact on the first responders themselves. Therefore, this study aimed to improve our understanding of EHEs' impacts on the operational capabilities and health of first responders, specifically police, fire, ambulance, and dispatch services.

METHODS

A systematized review and content analysis of media articles published on the 2021 Heat Dome in Canada was conducted (n = 2909), and four media-based composite narratives were developed highlighting police, fire, ambulance, and dispatch services. The Job Demands-Resources (JD-R) model was applied as a theoretical framework for occupational burnout.

RESULTS

The media-based composite narratives highlighted that first responders faced record-breaking call volumes, increased mental-health-related claims, and exhaustive heat-related physiological stress. Using the JD-R model as a theoretical framework for occupational burnout, we identified three measures of stressful job demand: work overload (e.g., the surge in call volume, firefighters responding to medical emergencies), emotional demands (e.g., severe medical emergencies, sudden deaths, unresponsive patients, distraught family members), and physical demands (e.g., resuscitation in personal protective equipment, heat-related illness).

CONCLUSION

The experiences described underscore the importance of supporting first responders during work in extreme heat conditions. These findings have important implications for addressing rising rates of burnout during and following public health crises, such as EHEs, a problem that is increasingly being recognized as a threat to the Canadian public healthcare system.

Working under the 2021 Heat Dome: A Content Analysis of Occupational Impacts Mentioned in the Canadian Media

Extreme heat events directly impact worker health and cause additional cascading and transitional workplace impacts. However, current investigations on these impacts often rely on specific datasets (e.g., compensation claims, hospitalizations). Thus, to continue to work towards preventing and mitigating the occupational risks posed by extreme heat events, this study aimed to explore the occupational impacts of the 2021 Heat Dome in Canada using a qualitative content analysis method on a news-based dataset. A systematized review of news articles published before, during, and after the 2021 Heat Dome was conducted on academic (n = 8) and news (n = 5) databases, along with targeted grey literature. Two researchers qualitatively coded the articles in NVivo for occupational impacts or references mentioned within the articles. Overall, 52 different occupations were identified as being impacted by the 2021 Heat Dome. Impacts were diverse and ranged from work cancellations or delays to work modifications and reports of heat-related illnesses. The 2021 Heat Dome impacted the health and safety of many occupational groups and provided new insights into the expanding impacts that extreme heat events can have on the Canadian workforce. With climate projections showing a growing trend of more hot days and intense heat waves in Canada, addressing these concerns should be a critical priority.

Limitations associated with thermoregulation and cardiovascular research assessing laborers performing work in the heat

PURPOSE

To quantify the current literature and limitations associated with research examining thermoregulatory and cardiovascular strain in laborers working in the heat.

METHODS

PubMed, SCOPUS, and SPORTDiscus were searched for terms related to the cardiovascular system, heat stress, and physical work. Qualifying studies included adult participants (18-65 years old), a labor-intensive environment or exercise protocol simulating a labor environment, a minimum duration of 120 min of physical work, and environmental heat stress (ambient temperature ≥26.0°C and ≥30% relative humidity). Studies included at least one of the following outcomes: pre- and peak physical work, core temperature, heart rate (HR), systolic blood pressure, diastolic blood pressure, HR variability, and rate pressure product.

RESULTS

Twenty-one out of 1559 potential studies qualified from our search. There was a total of 598 participants (mean = 28 ± 50 participants per study, range = 4-238 participants per study), which included 51 females (8.5%) and 547 males (91.5%). Of the participants, 3.8% had cardiovascular risk factors (diabetes: n = 10; hypertension: n = 13) and 96.2% were characterized as "healthy". Fifty-seven percent of the included studies were performed in a laboratory setting.

CONCLUSIONS

Studies were predominantly in men (91.5%), laboratory settings (57%), and "healthy" individuals (96.2%). To advance equity in protection against occupational heat stress and better inform future heat safety recommendations to protect all workers, future studies must focus on addressing these limitations. Employers, supervisors, and other safety stakeholders should consider these limitations while implementing current heat safety recommendations.

Elevations in serum brain-derived neurotrophic factor following occupational heat stress are not influenced by age or common chronic disease

With global warming, workers are increasingly exposed to strenuous occupations in hot environments. Given age- and disease-associated declines in thermoregulatory function, older workers are at an elevated risk of developing heat-related injuries. Brain-derived neurotrophic factor (BDNF) is thought to confer neuroprotection during acute exercise, however, the influence of environmental heat on BDNF responses during prolonged work remains unclear. Therefore, we evaluated serum BDNF concentrations before and after 180 min of moderate-intensity treadmill walking (200 W/m2) and after 60 min of post-exercise recovery in temperate (wet-bulb globe temperature (WBGT) 16°C) and hot (WBGT 32°C) environments in 13 healthy young men (mean [SD; 22 [3] years), 12 healthy older men (59 [4] years), 10 men with hypertension (HTN) (60 [4] years), and 9 men with type 2 diabetes (T2D) (60 [5] years). In the temperate condition, all but one participant (1 HTN) completed the 180 min of exercise. While exercise tolerance in the heat was lower in older men with HTN (117 min [45]) and T2D (123 min [42]) compared to healthy older men (159 min [31]) (both p ≤ 0.049), similar end-exercise rectal temperatures (38.9°C [0.4]) were observed across groups, paralleled by similar elevations in serum BDNF across groups at end-exercise (+1106 pg/mL [203]) and end-recovery (+938 pg/mL [146]; all p ≤ 0.01) in the heat. No changes in serum BDNF were observed in the temperate condition. Our findings indicate similar BDNF responses in individuals with HTN or T2D compared to their healthy counterparts, despite exhibiting reduced tolerance to heat.

Effects of wetted inner clothing on thermal strain in young and older males while wearing ventilation garments

The present study examined the effect of wearing a water-soaked inner t-shirt with a ventilation garment on thermal and cardiovascular strain in eight young (26 ± 4 years) and eight older (67 ± 3 years) men undertaking moderate-intensity work (metabolic rate: 200-230 W m^-2) in a hot environment (37°C, 50% RH, 2.8 kPa). While intermittent walking in hot conditions for 60 min, as a control (CON), the subject wore a dry inner t-shirt (long-sleeved) without fanning of a ventilation jacket (single-layered cotton, 0.21 clo). On separate days, under a fanned ventilation jacket, the subject wore a dry inner t-shirt (DRY) or an inner t-shirt soaked with 350 mL of tap water (WET). In the young group, increases in rectal temperature from pre-exercise baseline in the WET trial (0.7°C ± 0.2°C) were lower than in the CON (1.3°C ± 0.3°C) and DRY (1.1°C ± 0.2°C) (both p < 0.05) trials during exercise in hot conditions. In the older group, the increases were also attenuated in WET (0.7°C ± 0.4°C) compared with CON (1.3°C ± 0.4°C) and DRY (1.1°C ± 0.4°C) (both p < 0.05) without differences between age groups. Heart rate and whole-body sweat loss were lowest in the WET, followed by DRY, and then CON conditions in both groups (all p < 0.05). These findings demonstrate that wearing a water-soaked inner t-shirt while using a ventilation garment is an effective and practical cooling strategy to mitigate thermal and cardiovascular strains in young and older individuals during moderate-intensity work in hot conditions.

The serum irisin response to prolonged physical activity in temperate and hot environments in older men with hypertension or type 2 diabetes

Current labor demographics are changing, with the number of older adults increasingly engaged in physically demanding occupations expected to continually rise, which are often performed in the heat. Given an age-related decline in whole-body heat loss, older adults are at an elevated risk of developing heat injuries that may be exacerbated by hypertension (HTN) and type 2 diabetes (T2D). Elevated irisin production may play a role in mitigating the excess oxidative stress and acute inflammation associated with physically demanding work in the heat. However, the effects of HTN and T2D on this response remain unclear. Therefore, we evaluated serum irisin before and after 3-h of moderate intensity exercise (metabolic rate: 200 W/m²) and at the end of 60-min of post-exercise recovery in a temperate (wet-bulb globe temperature (WBGT) 16 °C) and high-heat stress (WBGT 32 °C) environment in 12 healthy older men (mean ± SD; 59 ± 4 years), 10 men with HTN (60 ± 4 years), and 9 men with T2D (60 ± 5 years). Core temperature (T_co) was measured continuously. In the heat, total exercise duration was significantly lower in older men with HTN and T2D (both, p ≤ 0.049). Despite T_co not being different between groups, T_co was higher in the hot compared to the temperate condition for all groups (p < 0.001). Similarly, serum irisin concentrations did not differ between groups under either condition but were elevated relative to the temperate condition during post-exercise and end-recovery in the heat (+93.9 pg/mL SEM 26 and + 70.5 pg/mL SEM 38 respectively; both p ≤ 0.014). Thus, our findings indicate similar irisin responses in HTN and T2D compared to healthy, age-matched controls, despite reduced exercise tolerance during prolonged exercise in the heat. Therefore, older workers with HTN and T2D may exhibit greater cellular stress during prolonged exercise in the heat, underlying greater vulnerability to heat-induced cellular injury.

Heat-Related Illness in Emergency and Critical Care: Recommendations for Recognition and Management with Medico-Legal Considerations

Hyperthermia is an internal body temperature increase above 40.5 °C; normally internal body temperature is kept constant through natural homeostatic mechanisms. Heat-related illnesses occur due to exposure to high environmental temperatures in conditions in which an organism is unable to maintain adequate homeostasis. This can happen, for example, when the organism is unable to dissipate heat adequately. Heat dissipation occurs through evaporation, conduction, convection, and radiation. Heat disease exhibits a continuum of signs and symptoms ranging from minor to major clinical pictures. Minor clinical pictures include cramps, syncope, edema, tetany, and exhaustion. Major clinical pictures include heatstroke and life-threatening heat stroke and typically are expressed in the presence of an extremely high body temperature. There are also some categories of people at greater risk of developing these diseases, due to exposure in particular geographic areas (e.g., hot humid environments), to unchangeable predisposing conditions (e.g., advanced age, young age (i.e., children), diabetes, skin disease with reduced sweating), to modifiable risk factors (e.g., alcoholism, excessive exercise, infections), to partially modifiable risk factors (obesity), to certain types of professional activity (e.g., athletes, military personnel, and outdoor laborers) or to the effects of drug treatment (e.g., beta-blockers, anticholinergics, diuretics). Heat-related illness is largely preventable.

Analysis of occupational stress and its correlation with oxidative-antioxidant levels among employees of a power grid enterprise in Guangdong

BACKGROUND

Occupational stress and its health effects on occupational populations have attracted extensive attention from researchers in public health. The stressors faced by employees of power grid enterprises are increasing progressively, which is easy to cause occupational stress. The balance of the body's oxidative-antioxidant levels plays an essential role in maintaining the body's health status. This study aims to explore occupational stress and its correlation with oxidative-antioxidant levels in employees of a power grid enterprise.

METHODS

A cluster random sampling method was used to investigate the basic information of 528 employees in a power grid enterprise and investigate the two occupational stress models of employees by using the Job Content Questionnaire based on the job demand-control-support (JDC) model, and the Effort-Reward Imbalance Questionnaire based on the effort-reward imbalance (ERI) model, respectively. Peripheral blood samples were collected from the employees to measure the levels of malondialdehyde (MDA), total antioxidant capacity (TAC), and superoxide dismutase (SOD). The correlation between different models of occupational stress level and the body's oxidation-antioxidation level was further explored.

RESULTS

The detection rate of high JDC model occupational stress was 50.6% and the detection rate of high ERI model occupational stress was 50.9%. The JDC model occupational stress was significantly associated with high-temperature and high-altitude operation, visual display terminal operation, monthly income, and exercise (all P < 0.05). The ERI model occupational stress was significantly associated with visual display terminal operation (all P < 0.05). The results of the generalized additive model showed that SOD levels had a non-linear relationship with the D/C ratio as well as the E/R ratio. With the D/C ratio close to 1, SOD levels raised rapidly. When the E/R ratio exceeded 1, the SOD level raised rapidly (all P<0.05) . TAC levels were negatively associated with the E/R ratio (P < 0.05).

CONCLUSION

The detection rates of occupational stress in both models among employees in a power grid enterprise are higher. ERI model occupational stress was associated with body TAC and SOD levels, and JDC model occupational stress was associated with body SOD levels.

Heat Strain Evaluation of Power Grid Outdoor Workers Based on a Human Bioheat Model

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.

Occupational heat strain in outdoor workers: A comprehensive review and meta-analysis

The present comprehensive review (i) summarizes the current knowledge on the impacts of occupational heat stress on outdoor workers, (ii) provides a historical background on this issue, (iii) presents a meta-analysis of published data, (iv) explores inter-individual and intra-individual factors, (v) discusses the available heat mitigation strategies, (vi) estimates physical work capacity, labour productivity, and metabolic rate for the year 2030, and (vii) provides an overview of existing policy and legal frameworks on occupational heat exposure. Meta-analytic findings from 38 field studies that involved monitoring 2,409 outdoor workers across 41 jobs in 21 countries suggest that occupational heat stress increases the core (r = 0.44) and skin (r = 0.44) temperatures, as well as the heart rate (r = 0.38) and urine specific gravity (r = 0.13) of outdoor workers (all p < 0.05). Moreover, it diminishes the capacity of outdoor workers for manual labour (r = -0.82; p < 0.001) and is responsible for more than two thirds of the reduction in their metabolic rate. Importantly, our analysis shows that physical work capacity is projected to be highly affected by the ongoing anthropogenic global warming. Nevertheless, the metabolic rate and, therefore, labour productivity are projected to remain at levels higher than the workers' physical work capacity, indicating that people will continue to work more intensely than they should to meet their financial obligations for food and shelter. In this respect, complementary measures targeting self-pacing, hydration, work-rest regimes, ventilated garments, and mechanization can be adopted to protect outdoor workers.

Indicators to assess physiological heat strain – Part 3: Multi-country field evaluation and consensus recommendations

In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this third paper, we conducted field experiments across nine countries to evaluate the efficacy of 61 meteorology-based TSIs for assessing the physiological strain experienced by individuals working in the heat. We monitored 372 experi-enced and acclimatized workers during 893 full work shifts. We continuously assessed core body temperature, mean skin temperature, and heart rate data together with pre/post urine specific gravity and color. The TSIs were evaluated against 17 published criteria covering physiological parameters, practicality, cost effectiveness, and health guidance issues. Simple meteorological parameters explained only a fraction of the variance in physiological heat strain (R² = 0.016 to 0.427; p < 0.001), reflecting the importance of adopting more sophisticated TSIs. Nearly all TSIs correlated with mean skin temperature (98%), mean body temperature (97%), and heart rate (92%), while 66% of TSIs correlated with the magnitude of dehydration and 59% correlated with core body temperature (r = 0.031 to 0.602; p < 0.05). When evaluated against the 17 published criteria, the TSIs scored from 4.7 to 55.4% (max score = 100%). The indoor (55.4%) and outdoor (55.1%) Wet-Bulb Globe Temperature and the Universal Thermal Climate Index (51.7%) scored higher compared to other TSIs (4.7 to 42.0%). Therefore, these three TSIs have the highest potential to assess the physiological strain experienced by individuals working in the heat.

Effects of sex and wet-bulb globe temperature on heart rate variability during prolonged moderate-intensity exercise: A secondary analysis

Sex-differences in heart rate (HR) and heart rate variability (HRV), a surrogate of cardiac autonomic modulation, are evident during rest and exercise in young healthy individuals. However, it remains unclear whether sex impacts HRV during prolonged exercise at differing levels of environmental heat stress. Therefore, we completed a secondary analysis upon the effects of sex and wet-bulb globe temperature (WBGT) on HR and HRV during prolonged exercise. To achieve this, HR and HRV were assessed in non-endurance-trained and non-heat-acclimatized healthy men (n=19) and women (n=15) aged 18-45 years during 180-min treadmill walking at a moderate metabolic rate (200 W/m2: equivalent to ~35% peak aerobic power) in 16, 24, 28, and 32°C WBGT. In the final 5 min prior to exercise termination, HR was observed to be higher in women relative to men in all but the 32°C WBGT. Although no sex-differences were observed for the HRV metric of root-mean-square of successive differences, high frequency power was higher in women relative to men across WBGT conditions. These findings indicate that, in healthy non-heat-acclimatized individuals, women respond to prolonged exercise-heat stress with a greater increase in HR despite cardiac vagal autonomic modulation remaining equal or increasing compared to men. Novelty points. • Prior to exercise termination, females respond with a greater increase in heart rate under all wet-bulb globe temperatures except the hottest (32°C). • Sex influenced heart rate variability (HRV) metrics during all wet-bulb globe temperatures, but results were mixed. • Further characterisation of HRV sex differences remains an important area of research.

Heat tolerance and the validity of occupational heat exposure limits in women during moderate-intensity work

To mitigate excessive rises in core temperature (>1°C) in non heat-acclimatized workers, the American Conference of Governmental Industrial Hygienists (ACGIH) provide heat stress limits (Action Limit Values; ALV), defined by the wet-bulb globe temperature (WBGT) and a worker's metabolic rate. However, since these limits are based on data from men, their suitability for women remains unclear. We therefore assessed core temperature and heart rate in men (n=19; body surface area-to-mass ratio: 250 (SD 17) cm2/kg) and women (n=15; body surface area-to-mass ratio: 268 (SD 24) cm2/kg) aged 18-45 years during 180-min walking at a moderate metabolic rate (200 W/m2) in WBGTs below (16 and 24°C) and above (28 and 32°C) ACGIH ALV. Sex did not significantly influence (i) rises in core temperature, irrespective of WBGT, (ii) the proportion of participants with rises in core temperature >1°C in environments below ACGIH limits, and (iii) work duration before rises in core temperature exceeded 1°C or volitional termination in environments above ACGIH limits. Although further studies are needed, these findings indicate that for the purpose of mitigating rises in core temperature exceeding recommended limits (>1°C), ACGIH guidelines have comparable effectiveness in non heat-acclimatized men and women when working at a moderate metabolic rate. Novelty points • Sex did not appreciably influence thermal strain nor the proportion of participants with core temperatures exceeding recommended limits. • Sex did not significantly influence tolerance to uncompensable heat stress • Despite originating from data obtained in only men, current occupational heat stress guidance offered comparable effectiveness in men and women.

The impact of age, type 2 diabetes and hypertension on heart rate variability during rest and exercise at increasing levels of heat stress

PURPOSE

In older adults with type 2 diabetes (T2D) and hypertension (HTN), cardiac autonomic modulation is markedly attenuated during exercise-heat stress. However, the extent to which this impairment is evident under increasing levels of heat stress remains unknown.

METHODS

We examined heart rate variability (HRV), a surrogate of cardiac autonomic modulation, during incremental exercise-heat stress exposures in young (20-30 years) and middle-aged-to-older individuals (50-70 years) without and with T2D and HTN. Thirteen young and healthy (Young, n = 13) and 37 older men without (Older, n = 14) and with HTN (n = 13) or T2D (n = 10) performed 180-min treadmill walking at a fixed metabolic rate (~ 200 W/m²; ~ 3.5 METs) in a differing wet-bulb globe temperature (WBGT; 16 °C, 24 °C, 28 °C, and 32 °C). Electrocardiogram (ECG) and core temperature measurements were recorded throughout. Data were analysed using 5-min averaged epochs following 60-min exercise, which represented the last common timepoint across groups and conditions.

RESULTS

Ageing did not significantly reduce HRV during increasing exercise-heat stress (all p > 0.050). However, T2D and HTN modified HRV during exercise-heat stress such that Detrended Fluctuation Analysis (DFA) α₁ (p = 0.012) and the cardiac sympathetic index (p = 0.037) were decreased compared to Older in all except the warmest WBGT condition (32 °C).

CONCLUSION

Our unique observations indicate that, relative to their younger counterparts, HRV in healthy older individuals is not perturbed during exercise heat-stress. However, relative to their age-matched healthy counterparts, HRV is reduced during exercise-heat stress in individuals with age-associated chronic conditions, indicative of cardiac autonomic dysfunction.

Determinants of heat stress and strain in electrical utilities workers across North America as assessed by means of an exploratory questionnaire

Previous field studies monitoring small groups of participants showed that heat stress in the electrical utilities industry may be detrimental to worker health and safety. Our aim in this study was to characterize heat stress and strain in electrical utilities workers across North America. A total of 428 workers in the power generation, transmission, and distribution industry across 16 U.S. states and 3 Canadian Provinces completed a two-part on-line questionnaire anonymously. The first part comprised 13 general questions on the employee's workplace location, role in the organization, years of experience, general duties, average work shift duration, and other job-related information. It also included two questions on self-reported heat stress. The second part consisted of the "Heat Strain Score Index" (HSSI), a validated questionnaire which evaluates heat stress at the workplace as "safe level" (score ≤13.5: worker experiences no/low heat strain), "caution level" (score 13.6 to 18.0: moderate risk for heat strain), and "danger level" (score >18.0: high risk for heat strain). In addition to the survey, we obtained meteorological data from weather stations in proximity (12.3 ± 12.2 km) to the work locations. Based on the HSSI, 32.9%, 22.3%, and 44.4% of the responders' workplaces were diagnosed as "safe level," "caution level," and "danger level," respectively. The HSSI varied significantly depending on the occupation from 4.9 ± 3.2 in contact center workforce to 19.1 ± 5.4 in mechanics (p < 0.001), and demonstrated moderate linear relationships with summertime (June, July, August) midday air temperature (r = 0.317, p < 0.001) and outdoor midday Wet-Bulb Globe Temperature (r = 0.322, p < 0.001). The highest HSSI was observed in mechanics, machine operators in line installations, line workers, electricians, and meter-readers. We conclude that electrical utilities workers experience instances of severe environmental heat stress resulting in elevated levels of heat strain, particularly when performing physically demanding tasks (e.g., manually climbing utility poles, installing lines).

An exploratory survey of heat stress management programs in the electric power industry

Workers in the electric power industry commonly perform physically demanding jobs in hot environments, which combined with the protective clothing worn, places them at risk of disease and health problems related to occupational heat stress. With climate change fueling an increase in the occurrence of hot weather, a targeted approach to heat stress management within the industry is needed. To better understand current heat management practices and identify opportunities for refinement, we conducted an exploratory survey among 33 electric utility companies operating in the United States (n = 32) and Canada (n = 1). Forty-six employees responsible for health and safety of company workers completed 26 questions assessing heat stress as a workplace hazard and heat management practices within five categories: (1) use and administration of heat stress management program; (2) surveillance of heat stress and heat strain; (3) job evaluation and heat-mitigation guidance; (4) education and training programs; and (5) treatment of heat-related illness. While a majority of the respondents (87.0%) indicated heat stress is a workplace hazard and their organization has a heat stress management program (78.3%), less than half reported performing real-time monitoring of heat stress in the workplace (47.8%) or tracking worker heat strain (19.6%) (i.e., physiological response to heat stress). However, most organizations indicated they conducted pre-job evaluations for heat stress (71.7%) and implemented an employee training program on managing heat stress (73.9%). The latter included instruction on various short- and long-term heat-mitigation guidance for workers (e.g., use of work exposure limits, hydration protocols) and the prevention (52.2%) and treatment (63.1%) of heat-related illnesses. Altogether, our survey demonstrates that although many companies employ some form of a heat management program, the basic components defining the programs vary and are lacking for some companies. To maximize worker health and safety during work in hot environments, a consensus-based approach, which considers the five basic components of a heat management program, should be employed to formulate effective practices and methodologies for creating an industry-specific heat management strategy.

Hot weather and heat extremes: health risks

Hot ambient conditions and associated heat stress can increase mortality and morbidity, as well as increase adverse pregnancy outcomes and negatively affect mental health. High heat stress can also reduce physical work capacity and motor-cognitive performances, with consequences for productivity, and increase the risk of occupational health problems. Almost half of the global population and more than 1 billion workers are exposed to high heat episodes and about a third of all exposed workers have negative health effects. However, excess deaths and many heat-related health risks are preventable, with appropriate heat action plans involving behavioural strategies and biophysical solutions. Extreme heat events are becoming permanent features of summer seasons worldwide, causing many excess deaths. Heat-related morbidity and mortality are projected to increase further as climate change progresses, with greater risk associated with higher degrees of global warming. Particularly in tropical regions, increased warming might mean that physiological limits related to heat tolerance (survival) will be reached regularly and more often in coming decades. Climate change is interacting with other trends, such as population growth and ageing, urbanisation, and socioeconomic development, that can either exacerbate or ameliorate heat-related hazards. Urban temperatures are further enhanced by anthropogenic heat from vehicular transport and heat waste from buildings. Although there is some evidence of adaptation to increasing temperatures in high-income countries, projections of a hotter future suggest that without investment in research and risk management actions, heat-related morbidity and mortality are likely to increase.

Challenges arising for older workers from participating in a workplace intervention addressing work ability: a qualitative study from Germany

OBJECTIVE

Studies examining what renders workplace interventions to sustain and promote work ability of older workers successful have largely neglected older workers´ perspective. This paper outlines the results of a study with regard to older workers´ experiences and expectations of a workplace intervention. Based on these findings, some reflections on how to improve the design and the implementation of workplace interventions for older workers are provided.

METHODS

Semi-structured interviews were conducted with older workers (N = 8) participating in a workplace intervention undertaken at one production site of a large manufacturing company in Baden-Wurttemberg/Germany. The interview guide included questions on participants´ experiences with and expectations of the intervention. The interviews were recorded, transcribed verbatim and analyzed using qualitative content analysis according to Mayring (2014).

RESULTS

Older workers´ reported some challenges they face due to their participation in the workplace intervention. These resulted from the work environment (physical challenges), the work process design (new long work cycle), the work organization (tight time allowances, little job rotation, change of teams, age stereotypes) and the management of the workplace intervention (bad information, feeling of occupational insecurity and lack of being valued).

CONCLUSIONS

The study shows that challenges arising for older workers from their participation in the workplace intervention may have counteracted the promotion of work ability. As findings suggest, some of these challenges might have been avoided either by considering workers´ perspective during design and implementation of an intervention or by referring to evidence on aging and work ability.

Occupational heat exposure and the risk of chronic kidney disease of nontraditional origin in the United States

Occupational heat exposure is linked to the development of kidney injury and disease in individuals who frequently perform physically demanding work in the heat. For instance, in Central America, an epidemic of chronic kidney disease of nontraditional origin (CKDnt) is occurring among manual laborers, whereas potentially related epidemics have emerged in India and Sri Lanka. There is growing concern that workers in the United States suffer with CKDnt, but reports are limited. One of the leading hypotheses is that repetitive kidney injury caused by physical work in the heat can progress to CKDnt. Whether heat stress is the primary causal agent or accelerates existing underlying pathology remains contested. However, the current evidence supports that heat stress induces tubular kidney injury, which is worsened by higher core temperatures, dehydration, longer work durations, muscle damaging exercise, and consumption of beverages containing high levels of fructose. The purpose of this narrative review is to identify occupations that may place US workers at greater risk of kidney injury and CKDnt. Specifically, we reviewed the scientific literature to characterize the demographics, environmental conditions, physiological strain (i.e., core temperature increase, dehydration, heart rate), and work durations in sectors typically experiencing occupational heat exposure, including farming, wildland firefighting, landscaping, and utilities. Overall, the surprisingly limited available evidence characterizing occupational heat exposure in US workers supports the need for future investigations to understand this risk of CKDnt.

Heat Tolerance and Occupational Heat Exposure Limits in Older Men with and without Type 2 Diabetes or Hypertension

PURPOSE

To mitigate rises in core temperature >1°C, the American Conference of Governmental Industrial Hygienists (ACGIH) recommends upper limits for heat stress (Action Limit Values; ALV), defined by wet-bulb globe temperature (WBGT) and a worker's metabolic rate. However, these limits are based on data from young men and are assumed to be suitable for all workers, irrespective of age or health status. We therefore explored the impact of aging, type 2 diabetes (T2D), and hypertension (HTN), on tolerance to prolonged, moderate-intensity work above and below these limits.

METHODS

Core temperature and heart rate were assessed in healthy, non-heat acclimatized young (18-30 y, n=13) and older (50-70 y) men (n=14), and non-heat acclimatized older men with T2D (n=10) or HTN (n=13) during moderate-intensity (metabolic rate: 200 W/m2) walking for 180 min (or until termination) in environments above (28 and 32°C WBGT) and below (16 and 24°C WBGT) the ALV for continuous work at this intensity (25°C WBGT).

RESULTS

Work tolerance in the 32°C WBGT was shorter in men with T2D (median [IQR]; 109 [91, 173] min; p=0.041) and HTN (109 [91, 173] min; p=0.010) compared to healthy older men (180 [133, 180] min). However, aging, T2D, and HTN did not significantly influence (i) core temperature or heart rate reserve, irrespective of WBGT, (ii) the probability that core temperature exceeded recommended limits (>1°C) under the ALV, and (iii) work duration before core temperature exceeded recommended limits (>1°C) above the ALV.

CONCLUSION

These findings demonstrate that T2D and HTN attenuate tolerance to uncompensable heat stress (32°C WBGT); however, these chronic diseases do not significantly impact thermal and cardiovascular strain, or the validity of ACIGH recommendations during moderate-intensity work.

A modified physiological strain index for workplace-based assessment of heat strain experienced by agricultural workers

BACKGROUND

As global temperatures rise, increasing numbers of individuals will work in hot environments. Interventions to protect their health are critical, as are reliable methods to measure the physiological strain experienced from heat exposure. The physiological strain index (PSI) is a measure of heat strain that relies on heart rate and core temperature but is challenging to calculate in a real-world occupational setting.

METHODS

We modified the PSI for use in field settings where resting temperature and heart rate are not available and used the modified physiological strain index (mPSI) to describe risk factors for high heat strain (mPSI ≥ 7) experienced by agricultural workers in Florida during the summers of 2015 through 2017. mPSI was calculated for 221 workers, yielding 465 days of data.

RESULTS

A higher heat index (β = 0.185; 95% CI: 0.064, 0.307) and higher levels of physical activity at work (0.033; 95% CI: 0.017, 0.050) were associated with a higher maximum mPSI. More years worked in US agriculture (-0.041; 95% CI: -0.061, -0.020) were protective against a higher maximum mPSI. Out of 23 workdays that a participant experienced a maximum mPSI ≥ 7, 22 were also classified as strained by at least one other measure of high heat strain (core temperature [Tc] >38.5°C, sustained heart rate >(180 - age), and mean heart rate > 115 bpm).

CONCLUSIONS

This study provides critical information on risk factors for elevated heat strain for agricultural workers and suggests a practical approach for using PSI in field-based settings.

Heat Stress and Kidney Function in Farmworkers in the US: A Scoping Review

Chronic kidney disease of unknown etiology (CKDu) has been well described in farmworkers in Latin America. Agricultural workers in the United States (US) are exposed to similar hot and humid working conditions, but CKDu in the US is under-described. This review aims to better understand the current literature describing the connection between heat stress and kidney function in farmworkers in the United States. Utilizing a scoping review methodology, we searched CINAHL, Embase, PubMed, and Web of Science databases to better understand the current state of the heat stress and kidney function research in farmworkers within the United States. In this review, 229 pieces of literature were screened. Ultimately, 4 articles were chosen to be included in the scoping review. Common themes within the articles were variations in study protocol lengths and type of heat stress measurement. Additionally, the majority of the work completed was quantitative to date, with only one study providing a critical social lens for analysis of CKDu in the United States. We found evidence that more work is needed within the US to understand the relationship between working in the heat and kidney function in agricultural and other workers who experience high heat conditions at work and are susceptible to the deleterious effects of working in said conditions.

Exploratory narrative text analysis to characterize tasks associated with injuries among electric utility line workers: EPRI Occupational Health and Safety Database 1995-2013

BACKGROUND

Injury prevention is an important goal for electric utility line workers who are among the top 10 U.S. occupational groups sustaining fatal injuries on the job.

METHODS

Using narrative text fields, we identified 10 high-risk tasks among electric utility line workers. We performed a case-control study of task-injury associations using data from the Electric Power Research Institute Occupational Health and Safety Database (1995-2013).

RESULTS

Drawn from 12,323 line worker injuries, cases were individuals with a major injury (5 or more days lost work) matched to controls, individuals with a minor injury (less than 1 day lost work), on company and year of injury. Conditional logistic regression estimated adjusted odds ratios (OR) and 95% confidence intervals (95% CI). Some tasks associated with higher odds for major injuries among line workers included: climbing up/down ladder/stairs/elevator (OR = 4.3; 95% CI = 2.6, 7.4); climbing down poles and transmission towers (OR = 5.5; 95% CI = 3.6, 8.4); entering/stepping out/approaching utility trucks, bucket, or vaults (OR = 5.8; 95% CI = 4.0, 8.4); and performing repetitive work/overtime (OR = 5.5; 95% CI = 3.2, 9.5).

CONCLUSIONS

Knowledge gained can be used to focus efforts and plan efficient preventive measures that reduce injury rates, time lost from work, and costs within the electric power industry.

Influence of age, geographical region, and work unit on heat strain symptoms: a cross-sectional survey of electrical utility workers

This study assessed self-reported heat strain symptoms in workers of a state wide electrical utility distributor to determine risk differences between age groups, geographical work regions and work units. Out of a total 3,250 workers, 918 (∼28%) outdoor staff completed an online survey, which assessed the frequency of self-reported heat strain symptoms in the work and post-work settings, factors contributing to symptoms and symptom management. Heat strain symptoms were grouped into chronic low-grade cases and isolated high-grade cases based on the severity and frequency of symptoms. The risk (likelihood) of an employee being classified as either a chronic low-grade or isolated high-grade case was calculated and compared to the mean risk of all categories to determine risk difference, expressed as -1.00 to 1.00. For chronic low-grade cases, the 41-50 years age group had significantly increased risk (+0.08, p < 0.05) while the over 60 years age group had significantly decreased risk (-0.14, p < 0.05). Two of the three regions (p < 0.01) and three of the nine work units also demonstrated risk differences (p < 0.01) for chronic low-grade cases. Work units were the sole grouping to demonstrate risk difference for isolated high-risk cases. Work units with greater exposure to heat and higher requirement for protective clothing, such as Underground (+0.19, p < 0.05), Overhead - Predominantly Live Line (+0.18, p < 0.01), and Overhead - Distribution and Transmission (+0.11, p < 0.05) were at greater risk of reporting heat stress symptoms. This study demonstrates that the pattern of self-reported chronic low-grade heat strain cases differs to isolated high-grade cases within the electrical utility industry. Age, geographical location, and work unit independently alter the risk of chronic low-grade heat strain, while the risk of isolated high-grade heat strain was only related to work unit. These outcomes support implementation of a flexible and targeted approach to heat stress management in large and diverse organizations in which employees are routinely exposed to heat.

Whole-body heat exchange in women during constant- and variable-intensity work in the heat

PURPOSE

Time-weighted averaging is used in occupational heat stress guidelines to estimate the metabolic demands of variable-intensity work. However, compared to constant-intensity work of the same time-weighted average metabolic rate, variable-intensity work may cause decrements in total heat loss (dry + evaporative heat loss) that exacerbate heat storage in women. We therefore used direct calorimetry to assess whole-body total heat loss and heat storage (metabolic heat production minus total heat loss) in women and men during constant- and variable-intensity work of equal average intensity.

METHODS

Ten women [mean (SD); 31 (11) years] and fourteen men [30 (8) years] completed two trials involving 90-min of constant- and variable-intensity work (cycling) eliciting an average metabolic heat production of ~ 200 W/m² in dry-heat (40 °C, ~ 15% relative humidity). External work was fixed at ~ 40 W/m² for constant-intensity work, and alternated between ~ 15 and ~ 60 W/m² (5-min each) for variable-intensity work.

RESULTS

When expressed as a time-weighted average over each work period, total heat loss did not differ between men and women (mean difference [95% CI]; 4 W/m² [- 11, 20]; p = 0.572) or between constant- and variable-intensity work (1 W/m² [- 3, 5]; p = 0.642). Consequently, heat storage did not differ significantly between men and women (- 4 W/m² [- 17, 8]; p = 0.468) or between constant- and variable-intensity work (0 W/m² [- 3, 3]; p = 0.834).

CONCLUSION

Neither whole-body heat loss nor heat storage was modulated by the partitioning of work intensity, indicating that time-weighted averaging is appropriate for estimating metabolic demand to assess occupational heat stress in women.

Heart rate variability in older workers during work under the Threshold Limit Values for heat exposure

BACKGROUND

The Threshold Limit Values (TLV) of the American Conference of Governmental and Industrial Hygienists indicate the levels of heat stress that all workers may be repeatedly exposed to without adverse health effects. In this study, we evaluated heart rate variability (HRV) during moderate-to-heavy work performed continuously or according to different TLV work-rest (WR) allocations in healthy physically active older workers.

METHODS

Nine healthy older (58 ± 5 years) males performed three different 120-minute conditions in accordance with TLV guidelines for moderate-to-heavy intensity work (360 W fixed rate of heat production) in different wet-bulb globe temperatures (WBGT): continuous cycling at 28°C WBGT (CON), as well as intermitted work performed at WR of 3:1 in 29°C WBGT (WR3:1), and at WR of 1:1 at 30°C (WR1:1). Rectal temperature and HRV (3-lead electrocardiogram [ECG]) were assessed throughout.

RESULTS

Coefficient of Variation, Poincaré SD2, and Shannon Entropy were decreased during the CON compared with the WR3:1 when core temperature exceeded 38°C and after 1 hour of continuous work (P < .05). Also, 4 of the 12 HRV indices studied were reduced at CON compared with WR1:1 after 2 hours of accumulated work time (P < .05). Participants worked longer before core temperature reached 38°C during the WR1:1 and the WR3:1, compared with CON (P < .05).

CONCLUSIONS

Incorporating breaks during moderate-to-heavy work in the heat for older adults can reduce autonomic stress and prolong the work performed at safe core temperature levels. The TLV WR1:1 provides increased cardiac protection for older workers, as compared with the CON and the WR3:1.

Heat strain in children during unstructured outdoor physical activity in a continental summer climate

The purpose of this study was to assess the heat strain experienced by children during unstructured physical activity outdoors in a temperate continental summer climate. Eighteen children (7 girls, 12.1 ± 1.7 years) performed up to 4 h of outdoor free-play (duration: 218 ± 33 min; air temperature of 24.5 ± 3.9°C and relative humidity of 66.2 ± 9.2%). Urine specific gravity (USG) was measured pre- and post-free-play, while body core temperature (Tco, ingestible pill) and heart rate (HR) were measured continuously. Physiological strain index (PSI) was calculated from Tco and HR (scale: 0 (none) to 10 (very high)). Activity levels were categorized as rest, light, moderate, and vigorous based on the metabolic equivalent of task, estimated from video analysis. Most children were euhydrated pre (78%, USG ≤ 1.020), but not post-free-play (28%, USG ≤ 1.020). Mean and peak Tco, HR, and PSI responses were 37.8 ± 0.3°C and 38.4 ± 0.3°C, 133 ± 14 bpm and 180 ± 12 bpm, and 4.7 ± 1.1 (low) and 7.4 ± 1.0 (high), respectively. All children reached peak Tco≥38.0°C, with seven ≥38.5°C, and the highest at 38.9°C. The children spent 58 ± 15% of free-play engaged in moderate-to-vigorous intensity physical activity. During free-play, all of the children performed moderate-to-vigorous intensity physical activity, which was associated with pronounced elevations in heat strain.

Heat Exchange in Young and Older Men during Constant- and Variable-Intensity Work

PURPOSE

Current occupational heat stress guidelines rely on time-weighted averaging to quantify the metabolic demands of variable-intensity work. However, variable-intensity work may be associated with impairments in whole-body total heat loss (dry + evaporative heat loss), especially in older workers, which exacerbate heat strain relative to constant-intensity work eliciting the same time-weighted average metabolic rate. We, therefore, used direct calorimetry to evaluate whether variable-intensity work would cause decrements in the average rate of whole-body total heat loss that augment body heat storage and core temperature compared with constant-intensity work in young and older men.

METHODS

Eight young (19-31 yr) and eight older (54-65 yr) men completed four trials involving 90 min of work (cycling) eliciting an average metabolic heat production of ~200 W·m in dry-heat (40°C, 20% relative humidity). One trial involved constant-intensity work (CON), whereas the others involved 10-min cycles of variable-intensity work: 5-min low-intensity and 5-min high-intensity (VAR 5:5), 6-min low-intensity and 4-min very high-intensity (VAR 6:4), and 7-min low- and 3-min very, very high-intensity (VAR 7:3). Metabolic heat production, total heat loss, body heat storage (heat production minus total heat loss), and core (rectal) temperature were measured throughout.

RESULTS

When averaged over each 90-min work period, metabolic heat production, total heat loss, and heat storage were similar between groups and conditions (all P ≥ 0.152). Peak core temperature (average of final 10 min) was also similar between groups and conditions (both P ≥ 0.111).

CONCLUSIONS

Whole-body total heat loss, heat storage, and core temperature were not significantly influenced by the partitioning of work intensity in young or older men, indicating that time-weighted averaging appears to be appropriate for quantifying the metabolic demands of variable-intensity work to assess occupational heat stress.

Determinants of heat-related injuries in Australian workplaces: Perceptions of health and safety professionals

INTRODUCTION

Hot workplace environments can lead to adverse health effects and contribute to a range of injuries. However, there is limited contextual understanding of heat-related injury occurrence. Gaining the perspectives of occupational health and safety professionals (HSPs) may elucidate the issue and inform targeted interventions.

METHODS

A cross-sectional national online survey was conducted in Australia to characterise HSP perceptions of heat-related injuries; current preventive measures; training, policies and guidelines; and perspectives on barriers for prevention. Results were analysed descriptively and a log-Poisson regression model was used to identify risk factors associated with HSP reported injury occurrence, assessed through prevalence ratio (PR).

RESULTS

Of the 307 HSP survey participants, 74% acknowledged the potential for increased risk of occupational injuries in hot weather. A variety of injury types and mechanisms were reported, including manual handling injuries, hand injuries, wounds or lacerations, and loss of control of power tools. Correlates of reported heat-related injuries included working in the sun without shade [PR: 1.26; 95% CI: 1.07-1.48] and too few rest breaks [PR: 1.28; 95% CI: 1.04-1.44]. Other factors of significance were inadequate hydration; issues with personal protective equipment (PPE) and poor supervision of workers. Only 42% reported that adequate heat training was available and 54% reported the provision for outdoor work to cease in extreme temperatures. It was acknowledged that the frequency of injuries could be reduced with wider adoption of self-pacing, and work/rest regimes. Perceived barriers for prevention included: lack of awareness of physical injury risks, and management concerns about productivity loss and/or deadlines.

CONCLUSION

The findings indicate a range of potentially modifiable work and organisational risk factors such as more suitable PPE and better supervision. More attention to these factors, in conjunction with traditional interventions to reduce heat effects, could enhance injury prevention and labour productivity in people working in hot environments.

Workers' health and productivity under occupational heat strain: a systematic review and meta-analysis

BACKGROUND

Occupational heat strain (ie, the effect of environmental heat stress on the body) directly threatens workers' ability to live healthy and productive lives. We estimated the effects of occupational heat strain on workers' health and productivity outcomes.

METHODS

Following PRISMA guidelines for this systematic review and meta-analysis, we searched PubMed and Embase from database inception to Feb 5, 2018, for relevant studies in any labour environment and at any level of occupational heat strain. No restrictions on language, workers' health status, or study design were applied. Occupational heat strain was defined using international health and safety guidelines and standards. We excluded studies that calculated effects using simulations or statistical models instead of actual measurements, and any grey literature. Risk of bias, data extraction, and sensitivity analysis were performed by two independent investigators. Six random-effects meta-analyses estimated the prevalence of occupational heat strain, kidney disease or acute kidney injury, productivity loss, core temperature, change in urine specific gravity, and odds of occupational heat strain occurring during or at the end of a work shift in heat stress conditions. The review protocol is available on PROSPERO, registration number CRD42017083271.

FINDINGS

Of 958 reports identified through our systematic search, 111 studies done in 30 countries, including 447 million workers from more than 40 different occupations, were eligible for analysis. Our meta-analyses showed that individuals working a single work shift under heat stress (defined as wet-bulb globe temperature beyond 22·0 or 24·8°C depending on work intensity) were 4·01 times (95% CI 2·45-6·58; nine studies with 11 582 workers) more likely to experience occupational heat strain than an individual working in thermoneutral conditions, while their core temperature was increased by 0·7°C (0·4-1·0; 17 studies with 1090 workers) and their urine specific gravity was increased by 14·5% (0·0031, 0·0014-0·0048; 14 studies with 691 workers). During or at the end of a work shift under heat stress, 35% (31-39; 33 studies with 13 088 workers) of workers experienced occupational heat strain, while 30% (21-39; 11 studies with 8076 workers) reported productivity losses. Finally, 15% (11-19; ten studies with 21 721 workers) of individuals who typically or frequently worked under heat stress (minimum of 6 h per day, 5 days per week, for 2 months of the year) experienced kidney disease or acute kidney injury. Overall, this analysis include a variety of populations, exposures, and occupations to comply with a wider adoption of evidence synthesis, but resulted in large heterogeneity in our meta-analyses. Grading of Recommendations, Assessment, Development and Evaluation analysis revealed moderate confidence for most results and very low confidence in two cases (average core temperature and change in urine specific gravity) due to studies being funded by industry.

INTERPRETATION

Occupational heat strain has important health and productivity outcomes and should be recognised as a public health problem. Concerted international action is needed to mitigate its effects in light of climate change and the anticipated rise in heat stress.

FUNDING

EU Horizon 2020 research and innovation programme.

On the use of wearable physiological monitors to assess heat strain during occupational heat stress

Workers in many industries are required to perform arduous work in high heat-stress conditions, which can lead to rapid increases in body temperature that elevate the risk of heat-related illness and even death. Traditionally, effort to mitigate work-related heat injury has been directed toward the assessment of environmental heat stress (e.g., wet-bulb globe temperature), rather than toward the associated physiological strain responses (e.g., heart rate and skin and core temperatures). However, because a worker’s physiological response to a given heat stress is modified independently by inter-individual factors (e.g., age, sex, chronic disease, others) and intra-individual factors both within (e.g., medication use, fitness, acclimation and hydration state, others) and beyond (e.g., shift duration, illness, others) the worker’s control, it becomes challenging to protect workers on an individual basis from heat-related injury without assessing those physiological responses. Recent advancements in wearable technology have made it possible to monitor one or more physiological indices of heat strain. Nonetheless, information on the utility of the wearable systems available for assessing occupational heat strain is unavailable. This communication is therefore directed toward identifying the physiological indices of heat strain that may be quantified in the workplace and evaluating the wearable monitoring systems available for assessing those responses. Finally, emphasis is placed on the barriers associated with implementing these devices to assist in mitigating work-related heat injury. This information is fundamental for protecting worker health and could also be utilized to prevent heat illnesses in vulnerable people during leisure or athletic activities.

Impact of climate change on occupational health and productivity: a systematic literature review focusing on workplace heat

Background:

With climate change, mean annual air temperatures are getting hotter and extreme weather events will become more and more common in most parts of the world.

Objectives:

As part of the EU funded project HEAT-SHIELD we conducted a systematic review to summarize the epidemiological evidence of the effects of global warming-related heat exposure on workers’ health and productivity.

Methods:

Three separate searches, focused, respectively, on: i) heat-related illness (HRI), cardiovascular, respiratory and kidney diseases; ii) traumatic injuries; and iii) vector-borne diseases or vectors distribution, were conducted in PubMed. EMBASE was also consulted to retrieve relevant studies focused on the health effects of climate change. A fourth search strategy to assess the effects on work productivity was conducted both in PubMed and in the SCOPUS database.

Results:

A significant proportion of studies reported findings regarding the Mesoamerican nephropathy issue. This is a disease occurring especially among young and middle-aged male sugarcane workers, without conventional risk factors for chronic kidney disease. For injuries, there is a reversed U-shaped exposure-response relationship between Tmax and overall daily injury claims. Outdoor workers are at increased risk of vector-borne infectious diseases, as a positive correlation between higher air temperatures and current or future expansion of the habitat of vectors is being observed. As for productivity, agriculture and construction are the most studied sectors; a day with temperatures exceeding 32°C can reduce daily labour supply in exposed sectors by up to 14%.

Conclusions:

The present findings should inform development of further research and related health policies in the EU and beyond with regard to protecting working people from the effects of workplace heat during climate change.

Screening criteria for increased susceptibility to heat stress during work or leisure in hot environments in healthy individuals aged 31-70 years

Population aging and global warming generate important public health risks, as older adults have increased susceptibility to heat stress (SHS). We defined and validated sex-specific screening criteria for SHS during work and leisure activities in hot environments in individuals aged 31-70 years using age, anthropometry, and cardiorespiratory fitness. A total of 123 males and 44 females [44 ± 14 years; 22.9 ± 7.4% body fat; 40.3 ± 8.6 peak oxygen uptake (mlO2/kg/min)] participated, separated into the Analysis (n = 111) and Validation (n = 56) groups. Within these groups, participants were categorized into YOUNG (19-30 years; n = 47) and OLDER (31-70 years; n = 120). All participants performed exercise in the heat inside a direct calorimeter. Screening criteria for OLDER participants were defined from the Analysis group and were cross-validated in the Validation group. Results showed that 30% of OLDER individuals in the Analysis group were screened as SHS positive. A total of 274 statistically valid (p < 0.05) criteria were identified suggesting that OLDER participants were at risk for SHS when demonstrating two or more of the following (males/females): age ≥ 53.0/55.8 years; body mass index ≥29.5/25.7 kg/m2; body fat percentage ≥ 28.8/34.9; body surface area ≤2.0/1.7 m2; peak oxygen uptake ≤48.3/41.4 mlO2/kg fat free mass/min. In the Validation group, McNemar χ2 comparisons confirmed acceptable validity for the developed criteria. We conclude that the developed criteria can effectively screen individuals 31-70 years who are at risk for SHS during work and leisure activities in hot environments and can provide simple and effective means to mitigate the public health risks caused by heat exposure.

The physiological strain incurred during electrical utilities work over consecutive work shifts in hot environments: A case report

PURPOSE

In this article, we evaluated physiological strain in electrical utilities workers during consecutive work shifts in hot outdoor conditions.

METHODS

Four highly experienced electrical utilities workers were monitored during regularly scheduled work performed in hot conditions (∼34°C) on two consecutive days. Worker hydration (urine specific gravity) was assessed prior to and following work. The level of physical exertion was determined by video analysis. Body core temperature (T_core) and heart rate (HR; presented as a percentage of maximum, %HR_max) were monitored continuously. Responses were reported for each worker individually and as a group mean ± standard deviation.

RESULTS

According to current guidelines, all workers were dehydrated prior to work on both days (urine specific gravity: day 1, 1.025 ± 0.005; day 2, 1.029 ± 0.004) and remained dehydrated following work (urine specific gravity: day 1, 1.027 ± 0.015; day 2, 1.032 ± 0.004) except for one worker on day 1 (urine specific gravity of 1.005). On day 1, the proportion of the work shift spent at rest (as defined by the American Conference for Governmental and Industrial Hygienists, ACGIH) was 51 ± 15% (range: 30-64%). Time spent resting increased in all workers on the second day reaching 66 ± 5% (range: 60-71%) of the work shift. Work shift average T_core was 37.6 ± 0.1°C (range: 37.5-37.7°C) and 37.7 ± 0.2°C (range: 37.5-37.9°C) on days 1 and 2, respectively. Peak T_core surpassed the ACGIH recommended threshold limit of 38.0°C for work in the heat in three workers on day 1 (38.1 ± 0.2°C, range: 37.8-38.2°C) while all workers exceeded this threshold on day 2 (38.4 ± 0.2°C, range: 38.2-38.7°C). By contrast, work shift average (day 1, 67 ± 7%HR_max, range: 59-74%HR_max; day 2, 65 ± 4%HR_max, range: 60-70%HR_max) and peak (day 1, 90 ± 6%HR_max, range: 83-98%HR_max; day 2, 87 ± 10%HR_max, range: 73-97%HR_max) HR were similar between days.

CONCLUSION

This case report demonstrates elevations in thermal strain over consecutive work shifts despite decreases in work effort in electrical utilities workers during regular work in the heat.

Increasing age is a major risk factor for susceptibility to heat stress during physical activity

We evaluated the extent to which age, cardiorespiratory fitness, and body fat can independently determine whole-body heat loss (WBHL) in 87 otherwise healthy adults. We show that increasing age is a major predictor for decreasing WBHL in otherwise healthy adults (aged 20–70 years), accounting for 40% of the variation in the largest study to date. While greater body fat also had a minor detrimental impact on WBHL, there was no significant role for cardiorespiratory fitness.

The recommended Threshold Limit Values for heat exposure fail to maintain body core temperature within safe limits in older working adults

PURPOSE

The American Conference of Governmental and Industrial Hygienists (ACGIH®) Threshold Limit Values (TLV® guidelines) for work in the heat consist of work-rest (WR) allocations designed to ensure a stable core temperature that does not exceed 38°C. However, the TLV® guidelines have not been validated in older workers. This is an important shortcoming given that adults as young as 40 years demonstrate impairments in their ability to dissipate heat. We therefore evaluated body temperature responses in older adults during work performed in accordance to the TLV® recommended guidelines.

METHODS

On three occasions, 9 healthy older (58 ± 5 years) males performed a 120-min work-simulated protocol in accordance with the TLV® guidelines for moderate-to-heavy intensity work (360 W fixed rate of heat production) in different wet-bulb globe temperatures (WBGT). The first was 120 min of continuous (CON) cycling at 28.0°C WBGT (CON[28°C]). The other two protocols were 15-min intermittent work bouts performed with different WR cycles and WBGT: (i) WR of 3:1 at 29.0°C (WR3:1[29°C]) and (ii) WR of 1:1 at 30.0°C (WR1:1[30°C]). Rectal temperature was measured continuously. The rate of change in mean body temperature was determined via thermometry (weighting coefficients: rectal, 0.9; mean skin temperature, 0.1) and direct calorimetry.

RESULTS

Rectal temperature exceeded 38°C in all participants in CON[28°C] and WR3:1[29°C] whereas a statistically similar proportion of workers exceeded 38°C in WR1:1[30°C] (χ²; P = 0.32). The average time for rectal temperature to reach 38°C was: CON[28°C], 53 ± 7; WR3:1[29°C], 79 ± 11; and WR1:1[30°C], 100 ± 29 min. Finally, while a stable mean body temperature was not achieved in any work condition as measured by thermometry (i.e., >0°C·min^-1; all P<0.01), heat balance as determined by direct calorimetry was achieved in WR3:1[29°C] and WR1:1[30°C] (both P ≥ 0.08).

CONCLUSION

Our findings indicate that the TLV® guidelines do not prevent body core temperature from exceeding 38°C in older workers. Furthermore, a stable core temperature was not achieved within safe limits (i.e., ≤38°C) indicating that the TLV® guidelines may not adequately protect all individuals during work in hot conditions.

Recruitment, Methods, and Descriptive Results of a Physiologic Assessment of Latino Farmworkers: The California Heat Illness Prevention Study

OBJECTIVE

The California heat illness prevention study (CHIPS) devised methodology and collected physiological data to assess heat related illness (HRI) risk in Latino farmworkers.

METHODS

Bilingual researchers monitored HRI across a workshift, recording core temperature, work rate (metabolic equivalents [METs]), and heart rate at minute intervals. Hydration status was assessed by changes in weight and blood osmolality. Personal data loggers and a weather station measured exposure to heat. Interviewer administered questionnaires were used to collect demographic and occupational information.

RESULTS

California farmworkers (n = 588) were assessed. Acceptable quality data was obtained from 80% of participants (core temperature) to 100% of participants (weight change). Workers (8.3%) experienced a core body temperature more than or equal to 38.5 °C and 11.8% experienced dehydration (lost more than 1.5% of body weight).

CONCLUSIONS

Methodology is presented for the first comprehensive physiological assessment of HRI risk in California farmworkers.

Physiological and perceptual effects of a cooling garment during simulated industrial work in the heat

OBJECTIVE

Evaluate physiological and perceptual responses using a phase change cooling (PCC) garment during simulated work in the heat.

METHODS

Twenty males wearing compression undergarments, coverall suit, gloves, and hard-hat, completed two randomly assigned trials (with PCC inserts or control, CON) of simulated industrial tasks in the heat (34.2 ± 0.05 °C, 54.7 ± 0.3%RH). Trials consisted of two 20 min work bouts, a maximum performance bout, and 10 min of recovery.

RESULTS

Physiological strain index (PSI) was lower during PCC after the second work bout and during recovery (all P < 0.05). PCC reduced heat storage (27.0 ± 7.6 W m^-2) compared to CON (42.7 ± 9.9 W m^-2, P < 0.001). Perceptual strain index (PeSI) was reduced with PCC compared to CON (P < 0.001), however performance outcomes were not different between trials (P = 0.10).

CONCLUSIONS

PCC during work in the heat attenuated thermal, physiological, and perceptual strain. This PCC garment could increase safety and reduce occupational heat illness risk.

Restoration of thermoregulation after exercise

Performing exercise, especially in hot conditions, can heat the body, causing significant increases in internal body temperature. To offset this increase, powerful and highly developed autonomic thermoregulatory responses (i.e., skin blood flow and sweating) are activated to enhance whole body heat loss; a response mediated by temperature-sensitive receptors in both the skin and the internal core regions of the body. Independent of thermal control of heat loss, nonthermal factors can have profound consequences on the body's ability to dissipate heat during exercise. These include the activation of the body's sensory receptors (i.e., baroreceptors, metaboreceptors, mechanoreceptors, etc.) as well as phenotypic factors such as age, sex, acclimation, fitness, and chronic diseases (e.g., diabetes). The influence of these factors extends into recovery such that marked impairments in thermoregulatory function occur, leading to prolonged and sustained elevations in body core temperature. Irrespective of the level of hyperthermia, there is a time-dependent suppression of the body's physiological ability to dissipate heat. This delay in the restoration of postexercise thermoregulation has been associated with disturbances in cardiovascular function which manifest most commonly as postexercise hypotension. This review examines the current knowledge regarding the restoration of thermoregulation postexercise. In addition, the factors that are thought to accelerate or delay the return of body core temperature to resting levels are highlighted with a particular emphasis on strategies to manage heat stress in athletic and/or occupational settings.

Age, human performance, and physical employment standards

The proportion of older workers has increased substantially in recent years, with over 25% of the Canadian labour force aged ≥55 years. Along with chronological age comes age-related declines in functional capacity associated with impairments to the cardiorespiratory and muscular systems. As a result, older workers are reported to exhibit reductions in work output and in the ability to perform and/or sustain the required effort when performing work tasks. However, research has presented some conflicting views on the consequences of aging in the workforce, as physically demanding occupations can be associated with improved or maintained physical function. Furthermore, the current methods for evaluating physical function in older workers often lack specificity and relevance to the actual work tasks, leading to an underestimation of physical capacity in the older worker. Nevertheless, industry often lacks the appropriate information and/or tools to accommodate the aging workforce, particularly in the context of physical employment standards. Ultimately, if appropriate workplace strategies and work performance standards are adopted to optimize the strengths and protect against the vulnerability of the aging workers, they can perform as effectively as their younger counterparts. Our aim in this review is to evaluate the impact of different individual (including physiological decline, chronic disease, lifestyle, and physical activity) and occupational (including shift work, sleep deprivation, and cold/heat exposure) factors on the physical decline of older workers, and therefore the risk of work-related injuries or illness.

The physical demands of electrical utilities work in North America

We assessed the physical demands associated with electrical utilities work in North America and how they influence the level of thermal and cardiovascular strain experienced. Three common job categories were monitored as they are normally performed in thirty-two electrical utility workers: (i) Ground Work (n = 11), (ii) Bucket Work (n = 9), and (iii) Manual Pole Work (n = 12). Video analysis was performed to determine the proportion of the work monitoring period (duration: 187 ± 104 min) spent at different levels of physical effort (i.e., rest as well as light, moderate and heavy effort). Core and skin temperatures as well as heart rate were measured continuously. On average, workers spent 35.9 ± 15.9, 36.8 ± 17.8, 24.7 ± 12.8, and 2.6 ± 3.3% of the work period at rest and performing work classified as light, moderate, and heavy physical effort, respectively. Moreover, a greater proportion of the work period was spent performing heavy work in Ground Work (1.6 ± 1.4%) relative to Bucket Work (0.0 ± 0.0%; P<0.01) and in Manual Pole Climbing (5.5 ± 3.6%) in comparison to both other work job (both P≤0.03). Furthermore, the proportion of time spent during work classified as heavy physical effort was positively correlated to the mean (r = 0.51, P<0.01) and peak (r = 0.42, P = 0.02) core temperatures achieved during the work period as well as the mean heart rate response (presented as a percentage of heart rate reserve; r = 0.40, P = 0.03). Finally, mean and peak core temperatures and mean heart rate responses increased from the first to the second half of the work shift; however, no differences in the proportion of the work spent at the different intensity classifications were observed. We show that Manual Pole Work is associated with greater levels of physical effort compared to Ground or Bucket Work. Moreover, we suggest that the proportion of time spent performing work classified as heavy physical exertion is related to the level of thermal and cardiovascular strain experienced and that workers may not be employing self-pacing as a strategy to manage their level of physiological strain.