While a hot air dryer was being used to free a coupling in a hydrogen cryostat (an apparatus used to maintain constant low temperatures), a flash fire occurred. The H2 cryostat was being dismantled.
The temperature at the center of the cryostat was sufficiently low to liquefy air. The prescribed requirements for purging and bringing the cryostat to room temperature were circumvented. The H2 - air mixture was formed and ignition was assumed to be a spark from an open filament of the dryer.