To make an explosive mixture, it would have to have a source of air. There was no source of air.
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The source of air comes from the atmosphere outside the tank. Are you saying it was some kind of vacuum tank? That would be amazing and would go against the common practice of pumping inert gas into fuel tanks to prevent explosions (something TWA 800 didn’t have).
For what it's worth, I believe someone pointed out earlier that the plane was at 13,000 feet. I believe at 10,000 feet a source of pressurized air is required for passengers.
My recollection of fire is that people can breath levels of oxygen which are so low that a fire cannot be sustained.
So how much air would there have been in the tanks at 13,000 feet? Probably not enough.