Propane Generator Room Classification

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Steve Merrick

Anchorage, AK
We have a small 75kVA propane standby generator in one of our process facilities. The propane fuel line has a couple of isolation valves and regulators, so a leak is conceivable, which would dictate a Class I Div II hazardous area classification. However, NFPA 37 4.5.2 states "Engine rooms or other locations shall not be classified as hazardous locations as defined in Article 500 of NFPA 70 solely by reason of the engine fuel, lubricating oil, or hydraulic fluid." This would lead me to believe that generator rooms need not be classified locations, though I frequently see them designated as such.

The wiring in the room is not explosionproof; i.e., it's simple RMC with NEMA 4 boxes and no seal-off fittings. The room used to be protected by propane detectors interlocked with the exhaust fans and louvers per NEC 500.7(K) or 505.8(I), so EP wiring would not necessarily be required. Recently the propane detectors were removed, and I, as the AHJ was asked to rule on whether that was a Code violation. I am inclined to say No, the room need not be classified per NFPA 37, quoted above. Am I off base? Any input from those of you with perhaps more experience than me?

Steve Merrick, PE


Staff member
We have a customer with literally 100s of small to mid size natural gas generators spread across four states, not one of these I have seen is a classified location.

Curios why this propane generator would be treated any differently than a water heater or stove that uses that gas?
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