My plan, as it now is, is to NOT install the factory floor board system.  That being the case, I'm considering alternate locations for the O2 tank.  At the top of my list of options is in the tail cone, mounted to a custom shelf/bracket system on the right side of fuselage just above(supported in part by) the pitch servo bulkhead.  The concern I have, and the feed back I'm looking for, is regarding the potential ignition source from the battery and relays that are also located in that area (according to the origional plans).  Could any of these electrical components produce arcing???  Could the MH cylinder/valve/fittings possibly leak, producing an explosive mixture???  I suppose the battery and relays could be relocated. Are there any thoughts about putting the battery directly behind the pilot seat, up close to the aft spar???  Heck,  why not redesign the whole airplane?

So, what is the consensus of the readership?  Are these concerns "over the top"?  Perhaps the reply will be:  Whats the big deal, we're already carrying a bomb in each wing...why not throw one in the tail too.  All kidding aside,  I am seriously interested in any thoughts or suggestions.

William,

A leaking O2 cylinder will not produce an explosive mixture—by itself. Mix it with some gasoline vapor, on the other hand, and you have a valid concern. Ditto for the “arcing.” By itself, switches and contacts that produce momentary arcs/sparks are not aggravated/enhanced by being in an O2 environment. Oxygen supports combustion, so if you have a fire from otherwise combustible material, the O2 will enhance the intensity, and usually the heat produced.  BTW, if you’re a smoker, it will cause a “normal” cigarette to burst into flame (the enhanced/intense concept) right on your face…that’s why we have the warning about no smoking around O2…and it’s a real/legitimate one.

Having said that, the direct answer to your question is NO; leaking O2 around switches/relays will not create a fire hazard.

Two things to watch out for as you move things around (“redesign”): Be careful with the weight and balance, and consider carefully whether your changes will alter the airframe structure/strength. We have a classic example in the IV-P world where some builders decided it would be nice to have the aft fuselage inspection panel hinged and latched for easier access. Turns out this panel is a part of the fuselage structure, and not mounting it with multiple screws, as specified in the plans, weakens the rear fuselage. At least two IV-P’s have developed structural cracks from the opening back to the horizontal tail. As far as I know, we’ve not lost an airplane due to this, but on the other hand, we’ve probably been lucky…  To the casual observer, this seems such a trivial mod—the opening is only about 8” x 12” or so—but the cover is designed to be a part of the fuselage structure…an important part. It can’t work that way if not secured all the way around it’s perimeter.

Hope this helps!

Bob