Heat Stress



The health risks associated with heat stress at work is a subject traditionally studied by occupational hygienists. In the past, in the UK, it was a compulsory component in the modular route to the Certificate examination. Currently it has been “relegated” to an optional module (although that may change in the future). However, questions about are still likely to be asked on heat stress on the Core exam and also in the Oral exam. Candidates for the latter may still be asked about the thermal environment even if they haven’t taken the optional module (M201), so its important that everyone taking the exam knows at least the basics.

Most hygienists don’t come across heat stress problems on a regular basis – it is more likely that they’ll have to deal with a thermal comfort issue. Yet there are still many industries where thermal stress can be a concern. These include traditional industries like steel making, glass manufacture, foundries, mining etc., but other, less obvious types of work may lead to workers being exposed to hot environments – e.g.catering,  bakeries, insulation contractors, firefighters, boiler room workers and anyone working outdoors in hot conditions.  Exposure is often transient and employers may not always identify and consider the risk adequately in their risk assessments. In many cases workers will not be acclimatised to hot conditions making them less tolerant to the heat.

Assessing the risks isn’t easy. There are seven main factors that influence human response to the thermal environment and in an ideal world all of them need to be considered.  Making sense of the data obtained from any measurements can be difficult.

As with most risk assessments it’s sensible to adopt a phased approach. If there is an obvious problem it’s better to look at the control options rather than worrying about what measurements to take. In cases of uncertainty, it may be possible to use the Wet bulb globe temperature (WBGT) index to make a basic evaluation of the risk as there are standards available against which the results can be compared (the ACGIH Threshold Limit Values for heat stress). In extreme cases extensive measurements followed by analysis using a more sophisticated index or even physiological measurements may be needed.

I’ve recently pulled together an introductory talk on heat stress, covering the hazards, measurement, evaluation and control, which I’ve uploaded to Slideshare. You can view it there, or in the embedded version below

Some useful material on heat stress is available on the HSE NIOSH and CCOHS websites

Photo credit: nicootje Stock.XCHNG

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