Abby says the gas filler tube was torn by a loose belt in the differential housing. The differential housing is part of the rear axle of the van, some distance away from the gas filler, and contains no belts.
The oxygen tanks in the back of the ambulance are labeled 'Flammable Gas'. Oxygen is not flammable. Oxygen will accelerate a fire, but doesn't burn in and of itself.
Abi says either that the accelerant is O2 or NO2. Either would be incorrect - O2 is oxygen which promotes burning but isn't inflammable itself, NO2 is nitrogen dioxide which is not inflammable. If she said NO2, presumably she means N2O, nitrous oxide, which has anaesthetic use as well as being inflammable.
Gibbs tells Danforth that his the DNA from the charred body wasn't Danforth's son because it didn't match the records in AFIS. AFIS is a fingerprint search database. CODIS is the database that law enforcement searches for DNA matches. The military keeps its own records of service person's DNA for matching to remains of their dead.