started in the cargo hold but no one knew how it could have spread. >> these types of compartments are designed to contain a fire. so why didn't the liner contain the fire? >> the investigators check 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. >> 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 apparently very shoddy workmanship. >> but what