The unit was returned to the manufacture and an evaluation was conducted.Upon initial evaluation, it was determined that the reported complaint of caught on fire could not be confirmed.Visual inspection showed the battery terminals inside the unit and one battery were blackened.Also, the cap was missing, and the device could have been dropped.Further examination revealed that the battery terminals were shorted.It appears that the contacts of the battery terminal became weak over time, from repeated battery insertion.This caused the negative and positive battery terminals to touch, causing a short.Also, the plastic enclosure was found to be blackened.Due to the protection circuitry in the battery and the tube head, it is not possible that the battery would become hot, cause an external fire or melt.It was then determined that the event was not reportable.Upon receiving further information from the dental office, an additional evaluation was conducted.Upon visual inspection, the device appeared to shows signs of damage related to being dropped several times.It also appears that the device has been used extensively.Visual inspection also showed that the battery terminals inside the device and one battery was overheated.Analysis of the battery contacts showed that they shorted together causing a large surge of energy to dissipate there when a battery was inserted.This caused the blackening of the pcb and of the battery.The battery became hot as shown by the blistering of the lower housing.There is evidence of heat damage, possibly due to fire.It is unknown if the contacts became shorted because of the unit being dropped or if they weakened over time from repeated use.The shorting of the contacts caused the negative and positive battery terminals to touch, causing a short.This was the occurrence that lead to the thermal event.The device will not be repaired and is subject to being discarded.This completes the investigation.
|