Occupational Heat Stress in Compressed Air - Validity of current heats stress indices

Abstract

The risks of decompression sickness and osteonecrosis associated with working in compressed air tunnels have been well researched and documented. To date though, the risk of heat stress in compressed air tunnel environments has largely been ignored. This is surprising because both the high humidity and increased atmospheric pressures affect the mechanisms by which heat is lost from the human body to the environment. Current British Standards for the assessment of heat stress require the application of two heat stress indices: “Wet Bulb Globe Temperature Index” (WBGT); and the “Required Sweat Rate Index” (SWreq). In their current form, neither index allows for the effects of atmospheric pressure on the mechanisms of human thermoregulation to be evaluated. This report discusses whether the indices can be modified to account for the influence of atmospheric pressure and, if so, evaluates their possible validity. The study demonstrated that although modifications to both indices are possible, neither the WBGT nor the SWreq index provided valid results. These findings suggest that neither index would be suitable for the assessment of heat stress in compressed air tunnels. Furthermore, it is clear that scientific data collected from compressed tunnelling sites is required to identify, quantify and describe the heat stress and the resultant heat strain that miners may be experiencing. To this end, future research recomm endations are also provided. 1 Introduction 2 The Wet Bulb Globe Temperature (WBGT) Index 3 The Required Sweat Rate Index (SWREQ) 4 Theoretical validity of SWreq in Compressed Air Tunnelling 5 Conclusions 6 Recommendations for Further Research References