“It was a hot day in JFK, the plane was delayed several hours on takeoff. The packs (air conditioning system on Boeing Airplanes) are directly below the center wing tank. The area became very hot. “
I live in AZ. I understand hot.
How many times did this exact plane and/or hundreds like it sit on runways in Saudi/Iraq/Middle East/Las Vegas/Phoenix under almost, if not identical circumstances? Numbers would indicate that in your 4 cases, something else happened.
Since 1960's the FAA and aircraft manufacturers have had two choices to prevent undesired fuel combustion. Either remove oxygen, or remove the ignition source. Removing oxygen (and replace with nitrogen) has been available since the 1960's. FAA and commercial airliners chose ignition source removal, because of weight considerations. That has been largely successful, but not entirely so. Just like many other safety considerations.