There are a number of issues, and the odd myth, around working in hot conditions. Safety is number one, but there are other points to think about too.
Heat stroke is a real danger. Companies need to think about how to minimise the risks through the OHS hierarchy (elimination, substitution, engineering controls, administration then personal protective equipment). Does the work in direct sun need to be done now, or can it be deferred to cooler weather? Can you start work earlier in the day to beat the heat? Fans to improve air flow? More breaks, in a cool place, with iceypoles? Work clothes in cool cotton? Also, have someone trained to recognise signs of heat stress, so that action can be taken if something does still go wrong.
Sun safety is important too, with skin cancer still a big issue for workplaces, as well as painful sunburn. Insisting that employees wear sunscreen, hats and suitable protective clothing is a lawful and reasonable order. Also to think about, there is no time limit on somebody putting in a WorkCover claim, so sun damage today, can be a claim decades down the track. And you can never delegate or dilute your duty to supervise and enforce safety.
Some people think that once the temperature reaches a certain level (38 or 40 degrees?) that “the law” says you cannot work and have to go home. False. Some certified agreements (registered with the Fair Work Commission) in the building industry have these limits built in, and only after measurements from recognised weather stations have been observed.
If you do change start and/or finish times to get out of the heat of the day, you may need to check you Modern Award to see if penalty rates apply to these different work times. Also, some Modern Awards contain allowances for working in artificially increased temperatures, such as near a furnace or boiler.
Assess what your risks are, and when, and what you can do it about it. Even better, consult with your workplace about these issues to try and come up with a solution that works. And talk with your friendly, local employee relations consultant!