I have not tested the main breaker yet but I did get an opportunity to test the 30 amp breaker when we were debugging our current control software. We found it was difficult to get 30 amp breakers back down to an ambient temperature in a minute or two. We did get the 30 amp breakers to still open below 30 amps. Bare in mind we got them really hot (painful to touch) and the adjacent wires were warm to touch but it prompted us to cool these if we have back to back matches. However we only bother to do this under those circumstances and only particular circuits.
Not sure about the main breaker because we are careful with managing our current draw but in rapid practice matches we have gotten our battery lead wires quite warm. I hypothesize that this circumstance would limit the cooling of the breaker or at the very least have a temperature elevated than ambient. Maybe we will try to cook the practice robot this summer to see what happens.
Also to correct some misconceptions about using can air. You can buy non-flammable varieties and they come with lovely little set of warnings explaining the operating temperature. Those are the ones I buy, you can get them on mcmaster even. You even buy varieties designed for rapid cooling so you don't even have to turn the can upside down. The one I have has an operating temperature up to 450 degrees F. Paper burns at 480 F so if your robot is over 450F in any area, you probably should be using a fire extinguisher instead.
For the propellant HFC-134a, its non-flammable.
https://www.chemours.com/Refrigerant...c134a_push.pdf
It should be noted its non-flammable in air in temperatures up to 212F in normal atmosphere conditions. It can be ignited in the presence of oxygen or chlorine.