Q: What are your thoughts on using CO2 extinguishers in an HVAC mechanical room, instead of an ABC type?
A: It likely would be a situation where you would be non-compliant with NFPA 10-2010, and therefore you would not be compliant with the 2012 LSC. A CO2 extinguisher carries a BC rating, meaning it is classified for use on flammable liquid fires and electrical fires. But what about fires in your mechanical room that are caused by normal combustibles (paper, cardboard, plastic, linen, etc.)? I’ve yet to see a mechanical room that did not have some level of combustibles stored in the room (filters, boxes of spare parts, trash bags, etc.).
I would recommend ABC fire extinguishers for all mechanical rooms, and the dry powder type is the most common and affordable to use. However, if the mechanical room has sensitive electronic equipment, then perhaps a Clean Agent ABC type extinguisher would be more appropriate.
CO2 extinguishers have a limited value, and should only be used in areas where you have flammable liquids in use and storage, such as laboratories, pharmacies, and perhaps a grounds garage.