Garages themselves do not require CO detection.  They are known spaces that may routinely trigger alarms based on the nature and the use of the space.  So that is why the regulation requires classrooms adjacent to any garage to require detection or alarm but not the garage itself; particularly in the example cited, the space is unheated and, therefore, clearly does not have a CO-producing HVAC system, but it is a garage that is used for storage of fuel-fired vehicles.  However, CO coverage in that space is not required, so that may prompt more questions on bus garages and things of that nature.

In general, in bus garage maintenance areas, you are trying to protect the employees.  The  storage areas would not require coverage even if they are covered by gas-fired roof-top units in the storage area.  But we would want to make sure that we are providing adequate coverage wherever those staff are regularly assigned – that might be maintenance bays, bus driver rooms, the corridors, the offices, etc.  Those won’t be classroom zones, but they would be non-classroom zones that should be properly analyzed and covered.

~ Carl Thurnau, P.E., NYSED's Office of Facilities Planning Coordinator, January 20, 2016