Development of a draft British Standard: the assessment of heat strain for workers wearing personal protective equipment

Existing methods for estimating heat stress, enshrined in British/International Standards (the Wet Bulb Globe Temperature (WBGT) index [BS EN 27243] and the Required Sweat Rate equation [BS EN 12515; ISO 7933 modified]), assume that the clothing worn by the individual is water vapour permeable; the WBGT index also assumes that the clothing is relatively light. Because most forms of personal protective equipment (PPE) either have a higher insulative value than that assumed or are water vapour impermeable, the Standards cannot be accurately applied to workers wearing PPE. There was, therefore, a need to develop a British Standard which would allow interpretation of these existing Standards for workers wearing PPE. Relevant information was obtained through reviewing the literature and consulting experts. Two questionnaire surveys of potential users of the Standards were conducted, and physiological data collected both experimentally and in work situations were considered. The information collected was used to develop the draft British Standard. It provides information and data on:

The general effect of PPE on heat balance of the body (the ability of the body to maintain its ‘core’ temperature within an acceptable range)

The effect of specific forms of PPE on metabolic heat production rate

The thermal insulation and evaporative resistance of types of PPE

The effect of the closure of the garments to the body on heat transfer

The effect of the PPE on the proportion of the body covered

The effect of an air supply (for example, Breathing Apparatus [BA]) to the wearer

Guidance is given on conducting an analysis of the work situation, taking account of the impact of PPE. Detailed methods of interpreting both BS EN 27243 and BS EN 12515 for workers wearing PPE are given, taking account of the factors listed above. Three worked examples using BS EN 27243 and BS EN 12515 are given in the Annex of the draft Standard.