The heat rule will likely come into effect on day seven of the Australian Open, with temperatures expected to reach the high 30s.
Organisers have already taken precautionary measures by starting the main draw singles and doubles matches 30 to 60 minutes early, and have advised fans to stay safe in the extreme temperatures.
The Australian Open has its own Extreme Heat Protocol, which takes air temperature, radiant heat, humidity, and wind speed into account.
It also considers “the extent to which a person can control the rise in their body temperature and the physiological cost of doing so”.
These measures are expressed as the heat stress scale (HSS), something Tennis Australia implemented in 2019.
The scale ranges from one to five, and cooling measures, breaks, and a full suspension in play can come into effect depending on the number on the scale.
Heat stress scale readings are continually made throughout every day of the tournament.