How do fire crews handle hot brakes?
(Airbus) A320 landing gear approach paths.
It's important to approach the landing gear from the right angle, because an explosion could throw deadly debris at the firefighters.
Cooling
According to Airbus, water-mist is to be used to cool the brakes.
Water, CO2, or foam, are not to be used. All those cause sudden cooling that can lead to wheel cracks or rim burst.
Fire
If there is fire, then large amounts of water or water-mist is to be used. Foam is to be used if fuel tanks are at risk.
(YouTube) Fire crew attending to 1400°C brakes.

Not an emergency, but interesting:
(airliners.net)

Upon deplaning back in Pyongyang, we noticed the brakes of the main gear were being cooled down with water. Naturally, this led to a mass gathering downstairs, as everyone wanted to take a photo of this event. We learned that this is actually standard procedure, which seemed legit as I remembered seeing water on the apron after our [Ilyushin Il-62] flight as well.


Related: When the brakes are checked, what do the firemen actually do?