A fuel cell forklift operator stated that he observed a "ball of fire" coming from the left side of the forklift that seemed to flash and extinguish. Investigators found no external signs of a fire, but the forklift would not start. The fuel cell power pack access panel was removed to enable investigators to search for any internal signs of a fire. Some areas inside the fuel cell stack appeared to have experienced an electrical arc or some type of overheating. All connections were verified to be tight and secure. The internal fuel cell stack circuit board cover was then removed, and the circuit card on top of the stack also showed signs of overheating. After the fuel cell stack circuit board was removed, a broken drill bit was discovered on top of the fuel cell stack plates.
Evidently, the drill bit was jostled around when the forklift was operated, causing a spark and fire inside the fuel cell stack that burned the circuit card. It is unclear how the drill bit got where it was on top of the fuel cell stack plates. Records indicated that there had not been any maintenance performed on this fuel cell pack that would require drilling. In addition, an inventory check of technician tools used for fuel cell stack assembly accounted for all drill bits.
It appears that this was an isolated event caused by human error. The lessons learned are: (1) to caution workers to maintain their focus during fuel cell stack assembly, (2) to require verification that all tools and spare parts are accounted for prior to closing up the system, and (3) to review quality control procedures and assembly procedures with an eye toward improvement.