Development of a modified predicted heat strain model for hot work environments

Excessive exposure to heat can lead to injuries, illness, and death among mineworkers. The actual cost of heat-related injuries and illnesses is unknown because of underreporting and lack of symptom recognition. Multi-factorial, evidence-based, and field-ready guidelines for identifying–and predicting–physiological markers of heat strain are currently unavailable. The predicted heat strain (PHS) model, is the latest attempt by mining companies to aid in the evaluation and management of occupational heat exposures. The adopted algorithm relies on worksite environmental measurements and an estimate of individual metabolic rate for mine workers to provide an estimate of the workers’ core temperature during a work shift. There are several known limitations of the PHS model, including the assumption that the subject worker is hydrated and fit. A modified PHS model was presented based on eight physical parameters that are measured at different intervals during a work shift; these parameters are air temperature, relative humidity, air velocity, radiation, metabolic rate, acclimatization, clothing insulation and posture. To validate the results, the predictions from the modified PHS model were compared with direct physiological measurements obtained from ingestible pills and heat stress monitors under different environmental and working conditions.