The application is a facility for testing helicopter engines at a local air force base. The fuel tank is outdoors, and fuel is pumped into the building and into the engines. I did the electrical design, and the government is its own AHJ, so I am guessing that makes it my call. I declared the test bays to be C1D2 on the basis of a possible fuel spill. My plans instructed the contractor to install all electrical components 18" above the floor, but they did not explicitly state that the room is unclassified above that level. I think they could have; I think they should have. But it turns out to be a non-issue. Reading the citations Bob provided, I concluded that the only requirement for our transformer (112.5 KVA, dry-type) is that it be 12 inches from combustible materials.