A few years back I did a fair few miles (20 minutes) in an EC120 that had developed a "strong smell of fuel". When landed, we found that about 7gal had escaped from the lower fuel bladder (due to over-tightened screws in the 2-part bar that supports the top of the fuel bladder against the underside of the cargo floor) and this was sloshing around inthe bottom of the ship.
Ashen faces, home by train. Bolocking for maintenace who "did not check" to find there is a correct torque setting for the screws and had over-tightened. Never been back to that maintenance provider since.
No "boom", though; in my pyrotechnic experience outside of helicopters it takes more than a spark to light cold kerosene. Usually it takes more than a match.