LAS VEGAS -- A cell phone battery spontaneously caught fire today, burned through a Defcon attendee's back pants pocket, and fell on the floor, creating burn spots on a carpet and leaving a burn-hole in the attendee's chair.
The man, who asked not to be identified, was not harmed but his trousers were ruined. He told CNET that he was sitting in a mid-day session at Defcon when he started to smell something burning and felt some heat underneath him on his seat. He stood up to find that his back left pocket was on fire.
"I smelled the burn, the smoke, and I stood up and could literally see flames," he said. "I tried to tap it out (with a hand) and it fell to the floor. It burned right through the backside."
The battery, which he said goes with a Droid Bionic smartphone that was not in the pocket, was still burning on the ground. He kicked it and it rolled and burned another spot into the carpet. He then left the room to get help as people around him began taking photos.
His derriere probably would have been scorched as well if he hadn't had his plastic hotel room key-card in between him and the battery. "My hotel key saved my butt," he said, laughing.
A woman who was taking video of the event for Defcon was seated on a platform about 20 feet away and had a good view of what happened. "I saw something glowing out of the corner of my eye," she said. "A guy's butt was in flames."
The room was evacuated and the session continued in a different room. The man said he had nothing else in his pocket but the battery and the hotel card key, and that he had no idea why the battery would have started to heat up.
CNET did not see the phone and was unable to confirm its make and model.
A Motorola representative provided this statement when asked for comment: "Motorola Mobility's priority is the safety of our customers. All Motorola products are designed, manufactured, and tested to meet or exceed international and local standards for consumer safety and performance. We will will look into this matter immediately."
The cause of the overheating remains a mystery.
Don Bailey, a mobile expert at Capitol Hill Consultants, said batteries can heat up if the metal leads touch something conductive. "Something as simple as steel wool can cause a short between the leads on a cell phone battery," he said.
It could been a bad battery, or the man could have damaged the battery somehow. But if there was no metal in the pocket at the time, it's likely the culprit was some conductive material, such as steel wool from a brush used to clean metal, that had somehow worked its way into the fibers of his pocket, Bailey said. "It's rare for manufactured batteries like these to have that kind of a failure."
Updated at 1:58 p.m. PT on July 30 to clarify that the mid-day session was re-started in another room.