Do you have a fire suppression system?
Mine is keep anything flammable away from the rigs, give them space...not much of a system.
What have to done to deal with chance of a fire?
I keep some extinguishers near by. I really doubt anyone here has a dedicated fire suppression system. Of course you need a smoke alarm near the rigs.
The datacenter at my work uses Novec 1230 gas but that is far beyond the means of a hobbiest. Although, it would be the best type of suppression system since you'd lose the least amount of hardware.
A water based system would be nearly as bad as every card going up in flames, I guess you could use pure demineralized water but not sure how feasible that is. A water based system can ruin a house to the point it needs to be destroyed as well (mold).