With the Bureau of Meteorology forecasting a hot summer this year WorkSafe WA commissioner Darren Kavanagh said employers need to make sure workers are not exposed to extremes in temperature which can lead to heat stress or even heat stroke in indoor workplaces like foundries.

In extremely hot places workers can lose up to a litre of fluid every hour, so drinking water is vital and air circulation also helps to evaporate sweat.

Kavanagh said sweating caused by the heat depletes the body of fluids and causes symptoms like tiredness, irritability, inattention and muscular cramps.

He said these don't just cause physical discomfort; they take the worker's attention away from the task at hand, which increase the risk of workplace injuries.

Heat stroke is a more serious affliction that demands immediate medical treatment, he said, with the tell-tale signs high body temperature and hot and dry skin, and no sweating.

The worker may also be confused or lose consciousness.

Kavanagh said the effects of extreme or sustained heat can seriously affect a worker's concentration levels and the consequences of this can also be very serious.

"Guarding against heat stress and heat stroke is part of providing a safe and healthy workplace and I urge employers to ensure that preventative measures are in place," he said.