Heh, yeah, take fires seriously. My home burned down 3 years ago, pretty traumatic experience. Had nothing to do with growing (wasn't growing anything then, thank god). It was just ancient wiring or something. They never did figure out *exactly* what started it, but it started in the basement. I keep several fire extinguishers around now, two on each floor.
I think an HID light is pretty safe though, if you use it inside an air-cooled reflector. Even if the bulb explodes (which has never happened to me), it's still inside the reflector. As long as you aren't buying shady jury-rigged ballasts off ebay with exposed wires, I don't think there's any more risk of fire than running a beefy gaming computer or a microwave or a hairdryer.
But I think you're doing the right thing using envirolights, because that's not a ginormous cabinet, and the heat of an HID would probably be at least somewhat of an issue in there. Could be done, but not as simply or easily.