Wufi
40 cars in a basement garage
I take it you are you ventilating this space?
If not then prepare to die by carbon monoxide poisoning.
In the UK we would have to ventilate to a constant rate of 6ac/hr and go to high speed (10ac/hr) if initiated by either a carbon monoxide detector or a fire alarm.
The fans would need to be fire rated at 300C for an hour and the system would need to be in 2 parts (we assume this means run/standby plant)
Ciao
Friar Tuck of Sherwood