nick charles,
there is extensive investigation, including reports from the American Chemical Society, in the TWA800 docket on the NTSB WWW site.
I also wrote a paper on the energy required for ignition, which you can find on my WWW site (EMI, TWA 800 and Swissair 111).
This is not the only documented incident of CWTs exploding on Boeing airframes. (I am using the word "explosion" here to mean a rapid burn, with significant overpressure, after ignition.) Those who favor some other theory have to explain how their theory accounts for those other instances also. (In the case of our missile-theory advocates, it most obviously does not account for those other instances.)
The NTSB, and the American Chemical Society, believe that it is possible to ignite vapors in a CWT with a result similar to that in TWA 800. This contradicts your suggestion (as I understand it) that you don't see how it is possible, so perhaps you should check out the docket materials to see where either they fail or you fail.
PBL