I very sorry for your loss coptercop.
You seem certain that it was a fire close to the engine or to do with fuel, however a electrical fire cannot be ruled out, which could have occurred in the cockpit.
You don't have much time to react at 800 ft and if your cockpit becomes full of smoke which makes it hard to see and breath, then you are in a very difficult situation.
Here's another thread that you may find interesting reading:
http://www.pprune.org/rotorheads/361...t-what-if.html
Once again I'm very sorry for you loss of a close friend.