Without wishing to sound doom and gloom here, I have a couple of examples of why fuel tanks can explode, hence my having a very healthy respect of them since:
First one was from a small bodyshop near bromley, in Kent, some 20 odd years ago, that was welding a car during repairs. The fuel tank was still fitted to the vehicle and some fuel somehow became spilt. The fuel vapour got into the air, and was sucked into a wall-mounted gas-fired space heater. The garage exploded, and killed the occupants.
The second one where I was going some gas welding work on a friends beloved Mk 2Cortina 1600E, in his friends garage at the bottom of his garden. I fitted new front wings, panel, and rear wheel arches. Having finished the job and was packing things up, my friend noticed a small rust hole in the boot floor, and asked me to weld that too. Ok, away I went and began to do the job. Though my goggles, I noticed a little fire on the garage floor, from, what I thought, was a bit of underseal or something that had caught alight and dropped onto the concrete. My mate also mentioned it and I told him not to worry - I'd seen that sort of thing plenty of times before, blah.
However, I then noticed that the little fire suddenly became larger, so dropped underneath the car to take a look, and saw that yes, some underseal had caught, but, the flames from that had crept their way along and rose up to the transmission tunnel, and then melted the plastic fuel lines. Fuel then flowed out and immediately caught alight.
The car became TOTALLY consumed in flames faster than you have read this story. Without thinking, we dragged to safety the oxy-acetylene bottles by their 20' hoses, on the sides in the muddy track outside the garages - it had begun to rain, away from the garage as the heat was so intense and I then had to chance going back to get into my own car - a now steaming from the heat, Mk1 Escort RS2000 that was parked opposite to drive it away before that too caught alight.
Basically, the car was completely destroyed, along with his mates garage, and it happened in a few minutes.
The reason I am still on the planet is that because the fuel tank was completely full therefore the flames couldn't get inside the tank to cause an explosion. That's what the fire chief told me afterward anyway. I took his word on that and have removed fuel tanks ever since when welding anywhere near a fuel tank and that rule went for any work done in the workshop by an employee too.
Just thought I'd mention it.
