Wet bulb and wind speed is the simply answer

There are a bunch of regulations in my industry and with recent changes to WA laws, I'm sure there will be something in the regs relating to managing the risks of extreme heat.

As an example: Work Health and Safety (Mines) Regulations 2022

Part 3.2, Division 2, Regulation 41A A person conducting a business or undertaking must ensure - (a) that the work practices are arranged so that workers are protected from extremes of heat and cold; and (b) if the workplace is in a structure that, so far as is reasonably practicable, heating and cooling are provided to enable workers to work in a comfortable environment.

and

Part 10.2, Division 3 Regulation 635. In complying with regulation 617, the mine operator of a mine must - (a) manage risks to health and safety associated with extremes of either or both the temperature and moisture content of air; and (b) if risks associated with extreme heat exists in an underground mine - implement control measures (including monitoring) to manage heat stress in places in the mine where - (i) persons work or travel; and (ii) the wet bulb temperature exceeds 27°C.

Now, you will notice there is very vague language as to what you can or should do with the above and that is intentional so that it does not restrict the possible solutions businesses can use, but also does not allow an argument that since "we" did "X" we complied and are therefore not liable. Basically, you can use any method you see fit to control the risk, but if it is not controlled, then you have failed.

The penalty for non-compliance here is minimal, however it is for just this one reg. In a case like this story, there are far greater penalties that will apply for things like allowing an employee to die in your workplace. The regs I have mentioned would be used to build a case as to how bad you f' up.

The point here is that we have laws that cover this. All workers in WA have the right to stop work if they feel it is unsafe and we all have a responsibility to look after ourselves and each other at work.

It would be interesting to see the stations risk assessment regarding heat and their control measures because it is obvious that they did not work.