Is it too hot to work?

With temperatures across much of southern Australia reaching heat wave conditions this week, outdoor workers are likely asking themselves; “Is it too hot to work?

We know that a healthy acclimatised worker can cope with temperatures well above the body’s normal core temperature of approximately 37°C, so long as they have the ability to sweat, but how hot is too hot to work?


Legally, how hot is too hot?

There are no regulations in Australia that set a limit on temperature in a work environment, however it is the employers responsibility to identify hazards and put in control measures to reduce the risk to the hazard, if needed. Worksafe Australia identifies extreme temperatures as an example of a common workplace hazard (Worksafe Australia, Code of Practice “How to manage work health and safety risks” December 2011″). The Code provides a simple four step process to identify, assess, control and manage risks in the workplace.


Temperature alone is misleading

Temperature alone, is not an adequate indicator of heat stress. Moisture in the air, radiation heat sources and the amount of air movement also play an important part in determining the amount of heat our bodies will store. The type of work being undertaken, clothing and other personal factors are also important to understand the overall heat burden on an individual.

Heat stress indices have been developed over the years to help quantify the effect of heat stress or to forewarn of its impending approach. These indicies attempt to integrate all the factors affecting the human thermal environment into a single number. There is still much debate as the best one to use and there are over 50 to choose from.

One such index is the Wet Bulb Globe Temperature (WBGT), originally developed in the 1950’s by the US Military as a means to control heat illness experienced in training camps.

The American Conference of Governmental Industrial Hygienists (ACGIH) recommends Threshold Limit Values (TLVs) for working in hot environments. The TLVs for WBGT are reproduced below and can be used as a guide to managing work in high heat conditions.


ACGIH Screening Criteria for Heat Stress Exposure¹ (WBGT TLVs in °C)

Allocation of work
in a work/rest cycle




Very Heavy

100-percent75 – 100%



75-percent50 – 75%




50-percent25 – 50%





25-percent0 – 25%





¹ Canadian Centre for Occupational Health and Safety

Table is intended as a screening tool to evaluate if a heat stress situation may exist. Assumes 8-hour workdays in a 5-day work week with conventional breaks.

TLVs assume that workers exposed to these conditions are adequately hydrated, are not taking medication, are wearing lightweight clothing, and are in generally good health.


How can I get a WBGT for my location?

You have three options to get a WBGT for your location.

  • Portable Monitor – WBGT can be measured using a portable monitor. These can be costly, can only provide a measurement at one location at a time and do not provide any indication of future conditions.
  • BOM web site – WBGT is estimated for a number of towns by the Bureau of Meteorology (BOM) from recent observations. These use an estimation of the WBGT from available measurements, are only available for towns with an automatic weather station and again do not provide any indication of future conditions.
  • KITE®  – Get access to KITE® for a forecast of WBGT for your location over the next four days. (KITE® is our new weather intelligence tool, developed by our talented Meteorology team and scheduled for launch very soon!)


Is it really too hot to work?

KITE® WBGT forecasts for southern Australia this week are predicted to reach a WBGT of 28°C in some parts and may reach as high as 31°C. This means that for healthy acclimatised workers, wearing light summer clothing undertaking moderate to heavy work have the potential to experience heat stress.


What to do if you have to work:

  • Try and work in the shade, or reduce the time in the sun as much as possible. The WBGT can be 5 degrees lower in the shade.
  • Use the work rest regimes (see table for guide) to keep your body temperature below 38 °C.
  • Resting in an air conditioned environment will reduce your temperature far more effectively than resting in a hot environment. If you are out in the field, sit in your car for 20 minutes with the air conditioning on.
  • Drink lots of cool water
  • Air movement can dramatically reduce your temperature so if it isn’t windy see if you can turn a fan on
  • Educate yourself and your follow workers in the early signs of heat illness (see some useful links below)
  • Prepare a Heat Load Action Plan, so you are prepared for future events
If you would like your own heat stress forecast, contact Christine Killip at Katestone for access to KITE®.


Additional information on Heat Stress can be found here:

Work Safe Qld – Injury Prevention Safety Hazardous Exposures: Heat Stress

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