Abstract
Introduction and Background: Occupational heat stress is a complex safety concern that continues to threaten the health and productivity of workers in the mining industry. Mine workers often perform physically demanding work in hot and humid environments, usually while wearing cumbersome work clothing which can restrict heat loss and lead to adverse health, performance and productivity impacts. As such, some mine sites provide employees with personal cooling garments (PCGs). However, their effectiveness in mitigating potentially fatal elevations in body core temperature (Tco) in workers performing their duties in hot conditions remains unclear.
Purpose: We, therefore, conducted a systematic review and meta-analysis to assess the physiological and perceptual effects of PCGs on workers in standard work clothing performing moderate-to-heavy intensity tasks in hot environments.
Methods: A peer-reviewed search strategy was conducted in six academic databases with no language or time limits. Subgroup meta‐analyses were performed to calculate the effect of the PCGs on select physiological and perceptual outcomes and settings/conditions. The realist evaluation framework was then applied to interpret the critical contextual determinants of which PCGs are effective in which setting, other potential influences (e.g., workload, clothing), and the different outcomes achieved from the interaction between each setting and garment.
Results: Thirty-three studies with 764 participants (98% male; 21±34 years), conducted primarily in a laboratory setting (76%), were included. The studies were 193±190 min in duration and consisted of a moderate-to-heavy work effort of 3.3±1.0 METs in hot ambient conditions (temperature: 35.9±3.3°C, 51.4±12.1% relative humidity, wet bulb globe temperature [WBGT] 31.2±2.6°C). The PCGs (n=67) facilitated heat exchange through conduction (n=39), evaporation (n=4), convection (n=2), radiation (n=2), or hybrid combinations (n=20). Conductive and hybrid PCGs offered the most significant thermoregulatory benefit, whereby TCO and heart rate (HR) reductions were consistently observed (TCO: -0.3°C, -0.2°C; HR: -12 beats per minute (bpm), 10 bpm, respectively), while PCGs directed at enhancing evaporative and radiative heat exchange had no or minimal effect on the physiological outcomes assessed (i.e., TCO <0.1°C, HR: <0.7 bpm). WBGT significantly modulated Tco, clothing insultation affected HR, thermal comfort and thermal sensation, and duration of time influenced HR.
Conclusion: While the PCGs had a positive overall effect, conductive options offered the most consistent benefit to workers. As the PCGs analyzed employed different cooling mechanisms, their efficacy was impacted by the context of use, which lead to divergent physiological and perceptual outcomes.
Practical Implications: The findings of our systematic review and meta-analysis highlights various practical considerations for OHS managers in the mining industry to contemplate when making an informed decision on the selection and application of PCGs for mitigating heat strain within their unique workplace. For example, we found that improvement in thermal comfort and thermal sensation was not always paralleled with a physiological effect.Therefore, OHS managers should consider providing additional education for workers to improve awareness about the signs and symptoms of heat‐related illness to ensure employees understand the importance of remaining vigilant to physiological effects, despite the perceptual benefit offered by the PCG.