Your trailer has a cargo heater/air conditioner unit. For which materials does federal regulation require that unit be disabled before loading?

49 CFR 177.834(l)

A cargo heater is an ignition and heat source sitting right next to your freight. For explosives and flammable cargo, that combination can turn a mechanical convenience into the cause of a fire or detonation. Knowing which classes require the heater disabled, and which only allow limited heater types, is a simple rule that prevents catastrophic outcomes.