The flammable (explosive) limits for propane are 2.3 to 9.5%. If there was “too much” propane no explosion. If you were in a room with 15% propane and lit a match, nothing would happen! (Well, you’d pass out from breathing all the propane).
The intent of the designers may have been a vapor explosion, but it takes some careful design to actually get one. The vapor must be mixed with air so that the above limits are met, then set off with multiple sources.
The device would have made a big fire for absolute certain, but the huge vapor explosion is speculation.
My intent here is not to make light of the situation, but the “journalist” is inflating the magnitude of the threat unless he has some detailed information on the car bomb’s design, which has been labeled “crude”. The professor quoted in the article does not even know if there was any high explosive in the car, or a detonator, yet he assumes huge FAB- type explosions.
-—you are a voice of reason—see my tagline—