According to this summary, available online at NHTSA's Office of Defects Investigation, the potential culprit could be seat belt pretensioners manufactured by two automotive suppliers, ZF TRW and Takata. The latter of the two, Takata, is still embroiled in a massive recall over tens of millions of faulty airbags, which have caused hundreds of injuries and more than 20 deaths globally.
This seat belt investigation covers Ford F-150s manufactured from 2015 through the current model year. Following an accident in which the pretensioner becomes activated, it has been reported that fires soon began in the B-pillar, where the safety system is located.
A seat belt pretensioner itself is there to help cinch down a seat belt during a crash, to pull the occupant firmly into the seat and offer better protection and less movement during an accident.
For the moment, this is not a recall and Ford F-150 owners can continue to use their vehicle. But the potential number of affected trucks is staggering when you consider the F-150 has been the best-selling vehicle in the United States for decades. Ford sold nearly 900,000 units of the F-150 last year. Any potential recall, if one is issued by the NHTSA, could encompass millions of vehicles.
Thankfully, while several trucks have been destroyed or severely damaged, there have been no reports of injuries directly related to the F-150's seat belt pretensioner system.