I had the fire suppression system go off while I was in the datacenter once. Scariest thing knowing all the oxygen is being pushed out of the room by the heavier gas.
I've never moved so quick to the exit as I did then. Took 2 breaths along the way, was extremely light headed for about 5 minutes afterwards.
It went off because HVAC guys were using an angle grinder to cut some ducting only feet away from the intake vent. All the smoke got pulled in and set off the fire alarm.
This actually made me laugh out loud while on the can at work.