the fire? >> the investigators checked records to see what was being transported in the hold. they find mail, three tires on their way to another valujet plane and then something suspicious. >> they found there were oxygen generators in there. and they found evidence that some of the generators had been discharged. that suddenly would explain why the containment liner had not worked. >> inside the cargo hold, the charred remains of nine activated canisters are recovered. >> oxygen generators use a chemical process to produce oxygen in the event passengers need it during a decompression. >> according to the ntsb, they were improperly secured for shipping. >> it turned out it was just very apparently shoddy workmanship. >> but what causes the fire? according to the ntsb, a disturbance like a bump on the runway makes the spring-loaded levers on the canisters hit the tiny charge on the caps.