Colyn,
I am a forensic engineer and work quite a bit with fire and explosion as well as mechanical/structural failure.
If I had a way to drain the fuel before crashing, I would get the tanks as dry as possible. A couple ounces of gasoline trapped somewhere in the tank would be plenty to make the space fuel rich. It isn't realistic to expect the entire tank to be fuel rich before impact, but a portion of it certainly will be. It is all a matter of time and temperature. In tank ships, you need around 2 gallons or so to make the space fuel rich. Frequently there is more than this trapped behind the tank scale.
For the reasons stated earlier, I wouldn't be too concerned about an explosion risk of the wing tanks (At least as long as I wasn't standing on it at the time!). My biggest concern would be the size of the fuel puddle the plane came to rest in. A hundred gallons spread out on the runway could make a real big fire real fast and would be difficult to survive if you were caught in the middle. Two cups of gas in the same scenario would be a much more survivable situation.
Another benefit of draining the tanks before impact is the reduction in gross weight and therefore stall/impact speed.
Rob
Rob, interesting info.
So sounds like if you do have a quick drain, you don't want to completely empty it.
I have no idea how to build a quick drain that would not create some leakage risk.
sounds like you are in this business?