FIRE DOORS at the top of the Kaprun tunnel where 156 people died in a blaze last November had been closed but were reopened by two trapped staff escaping the fumes.
Once the doors were opened they did not automatically close again, creating a 'chimney effect' as smoke billowed through the tunnel.
Five independent experts undertook investigations in to the disaster in the Austrian resort (NCEI December 2000).
On the train's fourth trip of the day up the mountain, a faulty heater in the empty rear driver's cabin started the fire, igniting a hydraulic hose above it containing oil. Fire then spread to insulation material that was already soaked in leaked oil.
The resulting drop in hydraulic pressure caused the braking system to stop the train 600m into the tunnel.
Although the driver opened the train doors, most passengers died of smoke inhalation as they tried to escape.
As the tunnel is at a 42.8infinity angle, air was sucked in at the bottom to feed the fire, filling the tunnel and making upward escape impossible.
It is believed that the heater manufacturer specifically stated that it was not for use in a transportation vehicle. It was in the carriage when the train was delivered following refits of the cab in 1994.
Investigators will now focus on the company which refitted the train as well as the Austrian Ministry of Transport and the cable car authority, responsible for safety checks on the train and tunnel.