While there is a legal minimum temperature below which no-one should have to work (16 degrees C), there is no equivalent if it gets too hot.
The TUC is calling for a maximum working temperature of 30 degrees C, or 27 degrees C for those doing strenuous work.
Workers whose exposure to heat cannot be reduced, should be provided with adequate breaks and offered job rotation as hot temperatures cause injuries and illness at work, said the TUC.
Employees suffering in sweltering workplaces run the risk of:
- heat stroke and dehydration
- tiredness leading to accidents
- irritability and the threat of violence
- higher stress levels, with enhanced risks of mental and physical illness
TUC General Secretary, Brendan Barber, said: "Sweatshop conditions can push workers to boiling point. Extreme heat is as bad for you as extreme cold. There is no logic for having a minimum work temperature but no maximum.
"The TUC urges employers to be flexible in these tough temperatures. If they cannot reduce the heat at work they could relax dress codes, and allow more breaks and more shift rotation."
HR professionals agree with the TUC. Nearly three-quarters (73 per cent) of the 230 HR professionals polled by HR Gateway believe an upper limit should be applied, while a quarter said that it depended on the job, and 2 per cent thought no limit was necessary.
Vanessa Stebbings of HR Gateway Consulting said: "While British legislation does not set a maximum working temperature, the World Health Organisation recommends a maximum air temperature of 24 degrees C."
When assessing the risks to heat, it should be remembered that women who are pregnant or menopausal are more susceptible to heat intolerance, she said.