With temperatures of 39 degrees predicted for Friday, students start to believe there is a magic number the mercury can reach which sees the schools close.

But it’s just not the case, according to a Department of Education spokeswoman.

“Generally schools are closed only in extreme circumstances such as during fire or flood or for health and safety reasons such as lack of running water making the site unsanitary,” the spokeswoman said.

“Hot weather is generally not considered to be an emergency and there is no set temperature which forces a school to close.”

She added that many schools in the Illawarra are fully or partly airconditioned.

On Friday, the Bureau of Meteorology is tipping the Mercury to hit a high of 39 degrees in the Illawarra at about 3pm.

Temperatures will still be high in the evening – 27 degrees at 9pm.

It will cool down over the weekend, with 22 degrees and showers predicted.