My company seems to have had some problems with the ovens recently. Some bent or broken bits in the racks containing the meal plates have caused the whole rack to slide back and make contact with the oven fan. The results varied but were never too pleasant: be it a simple CB pop, the fan grinding up the rack or massive overheating.
Maybe these parts could be made more solid with proper spacers or a protective basket installed around the heating filaments and the fan.