A member of Mr. Lear’s staff, who happened to be in Japan at the time of the notebook fire, retrieved the remains. It was taken to a Los Angeles area lab of Exponent, a failure analysis firm, for examination.
The unit worked when it was plugged in to the power cord, despite the fire, which told the investigators that the problem was not with any circuitry or microchips. An X-ray of the battery pack told them the fire was not caused by an overcharged battery because a safety device was still intact.
Rather, Dell said the cause of the fire was a short circuit in one of the fuel cells. It was caused by microscopic metal particles that contaminated the electrolyte, a porous insulator. Dell thinks that the particles were released when the case of the cell was crimped near the end of Sony’s manufacturing process. It was the same problem associated with the 22,000 notebooks that Dell recalled in December.
Sony technicians, who took part in the examination at the Exponent lab, provided additional data on all its batteries, not just those sold to Dell, that suggested that a broader problem in the manufacturing process. “As events trickled in, they seemed to reinforce a conclusion that these Sony cells had an issue,” Mr. Gruzen said. “They don’t show a predictable pattern, which is why we wanted to get them out of the marketplace.”