How should ground crews act to safely extinguish an airliner's brake unit fire?
Approach from upwind. The source of fire is hot brakes so apply maximum cooling, say water-based. But hydraulic fluids under pressure burn, so if brakes are engaged it's best to ensure with flight crew that the brakes are off as soon as the aircraft is stationary. Stay in the vehicle in case tyre ruptures; chances are it will go sideways. If fuel is leaking, use suitable foam.

I once saw a Harrier with a brake fire.  The burning pressurised brake fluid was acting like a flame thrower on the aircraft structure. The aircraft was written off. This happened about 1981.