Use and abuse of heat stress limits








Management of heat stress can approached from a number of ways. Two of the most popular are:

  1. Using heat stress indices to apply limits to restrict work and then adopt work/rest regimes
  2. Using indices to identify issues and then assist with the development of controls

We see the first approach far too often in my opinion.

I am not saying that it is not a valid approach as there are some scenarios when this is the only practical option but it should be the exception rather than the rule.

It is far too easy to say “Oh the Regs give us a limit of 29.4⁰C so stop the work and have a break until it gets lower” or “The WBGT is 30.5⁰C so you can work for 15 minutes and rest for 45minutes”.

Managing heat stress is about managing the work environment wherever possible by anticipating these issues and utilising practical controls such as fans, shielding, shade, etc, etc. Educating the individual to understand what is happening to their body in the heat and how to maintain fluid levels to avoid the negative consequences associated with dehydration.

Limits have their place but no matter which level is adopted or what heat stress index is used they are NOT safe/unsafe limits, they are guidelines only. There is a huge variation in the way individuals respond to the heat as well as different work scenarios that will be encountered. If we wanted to guarantee to protect everyone we would need to set the limits so low that there would be no work done north of Sydney before May or after August.

There is considerable discussion about climate change and how it will impact on the work force and productivity going forward. So how is this to be managed? It won’t be by changing our limits, it’s about managing the work environment wherever we can. The limit or index value will give you a starting point, and from there:

  • start cranking up the fans or
  • increasing the shielding and/or insulation around the hot pipes or vessels.
  • make sure workers in the open have access to a shade cover, even an umbrella
  • provide a cool environment for them to rest and rehydrate
  • maybe think about planning the work at a cooler part of the day
  • talk (and listen) to your teams about the impact of heat and how they can take control and manage it. Not “at” them with a 20 slide PowerPoint followed by a 10 question test to prove their competency.

One day we may even start to design our industrial plants taking into consideration potential heat exposure.


Heat stress limits are there as guidelines not guaranteed safe/unsafe limits.  We need to do more about using heat stress indices to inform us about the environment and then controlling not limiting it.

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