The tank vent lines do route over the cabin roof to the opposite side of the airframe and are fitted with "NRVs". In addition the tank compartments are vented. If the fuel tanks are ruptured (highly likely in a crash where the aircraft ends up on its side) then fuel will probably end up out of the bag and in the tank bay and then overboard. With a high C of G and a narrow undercarriage, most Puma accidents end up on their side. Most Chinook accidents stay the right way up and generally just rip the wheels off, hence it's good safety record.