Intensity of Fire
“This test resulted in venting with smoke but no fire,” the NTSB reported.
Boeing also consulted with other companies about their experience with the use of similar lithium-battery cells and “based on this information, Boeing assessed that the likelihood of occurrence of cell venting would be about one in ten million flight hours.”
Yet all of this analysis badly missed the mark. The probabilities proved to be off by a factor of 200.
The 787 that caught fire in Boston had logged just 169 flight hours.
And the entire operational fleet of 787s had logged a total 51,662 in-service hours, plus about 6,000 flight-test hours.
On the day of the Boston fire, the battery did not behave as predicted.
The battery’s power discharge was “not at the constant rate described by the Boeing or Thales documents and included large changes and reversals of power within short periods of time,” the report states.
The fire that day was small but intense.
Boston airport firefighters encountered heavy smoke in the passenger cabin and had to forcibly extract a smoking, hissing, popping, chemical-spewing battery from the belly of the plane.
Interviews by the NTSB revealed the firefighters did not know they were dealing with a lithium-ion battery, and they had great difficulty putting out the fire.
When Capt. Mark Munroe of the airport’s aircraft rescue and firefighting unit entered the plane, he “saw heavy white smoke billowing through the floor” of the passenger cabin.
After locating the fire inside the electronics bay in the belly of the airplane, firefighters entered the compartment through dense smoke and applied shots of Halotron fire extinguisher to the battery.
Lt. David Hoadley of the firefighting unit reported that “it seemed like the fire did not want to go out, it kept rekindling.”
Then the battery, in munroe’s words, “exploded.”
“Capt. Munroe heard the battery hissing still and pushing white smoke or steam. There was liquid sizzling over the sides of the battery and still heavy smoke conditions. ... The battery continued to hiss before exploding.”
Munroe related that “he felt something hit him in the neck while he was in the airplane,” and he was sent for medical treatment. “Something had burned his neck.”
Firefighters attempted to remove the battery from the jet but found the “quick disconnect” mechanism Boeing had included to allow the battery to be removed for maintenance was “melted and unrecognizable” and a metal plate was preventing access.
The firefighters cut away the metal plate, severed the battery wires, then “pried the battery loose with hydraulic spreaders and removed it.”
The battery was passed down to a firefighter and placed on the tarmac about 50 feet from the airplane.
100 minutes
The fire was declared under control an hour and 40 minutes after the initial notification.
Still, for all the intensity, no one was badly hurt and details in the report suggest it could have been worse.
NTSB investigators found no heat damage to any primary airplane structure — that is, any part of the airframe critical to flight.
Only the floor panel and carbon-fiber floor support material, which are considered to be secondary structure, “were found to be heat damaged beneath where the APU battery had been installed.”
And sitting on a rack above the battery that burned was a smaller lithium-ion battery, also supplied by Japanese manufacturer GS Yuasa, that is used to provide emergency power for the jet’s flight controls for 10 minutes or more “when no other electrical power is available.”
Investigators found the exterior of this battery had been “lightly scorched” by the fire below and noted its case had openings at the corners.
The firefighters suppressed the fire before it could spread to that second battery.
By Dominic Gates
Seattle Times aerospace reporter
Last edited by dabrat; 11th March 2013 at 23:03.
Reason: Adding more info