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Hot Work Conditions

In the summer, questions come up at which temperature is it too hot to work. OH&S has an information sheet on hot conditions.

The difficulty with this sheet is that it gives the temperature using either a wet bulb globe temperature (WBGT) or a botsball index. These take into account humidity and radiant heat.

OH&S have some data from a paving operation that will give some guidelines as to what temperature may be acceptable.

Table 1

All temperatures are in °C, at 30% relative Humidity

Dry Bulb Temperature °C (Air Temperature)

WBGT °C

29° 22.8°
30° 23.9°
31° 24.7°
32° 25.6°
33° 26.7°
34° 27.5°
35° 28.3°
37° 29.4°
38° 30.3°

For the purpose of OH&S information sheet, most of the work we do would be considered moderate to heavy. It would assume that the workers are reasonably fit and acclimatized to the work and conditions.

Table 1 offers a rough comparison between the WBGT index and Dry Bulb Temperature. Dry bulb temperature is what our thermometers read or the temperature the radio broadcasts.

Based on this a worker doing moderate continuous work would probably be ok to work up to 33°C (air temperature).  Once the temperatures approach the 30°C mark, you should monitor the workers for signs of heat stress. If anybody is starting to show early signs of heat stress, provide the proper first aid.

For heavy continuous work, they should be able to work up to 31°C (air temperature), and monitor for signs of heat stress as temperatures approach 28°C.

Heat Stress Symptoms

  • Severe cramps in legs & stomach.
  • Exhaustion, dizziness, faintness, loss of consciousness
  • Heavy perspiration
  • Shallow breathing

Heat Stress Treatment

  • Move to a nearby cool place, loosen or remove clothing
  • Give water (only if they are conscious and able to drink)
  • If they are conscious, lay on their back with the legs elevated. If the are unconscious place in the recovery position & monitor their breathing.
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