Complex sentence: In the event of a printing stall, and occasionally in normal operation, the fusing oven would heat paper to combustion, which was aggravated by the fact that if the printer continued to operate, it would essentially stoke the oven with fresh paper at high speed.
Split into simpler sentences: In the event of a printing stall, and occasionally during normal operation, the fusing oven would heat paper to combustion. This fire risk was aggravated by the fact that if the printer continued to operate, it would essentially stoke the oven with fresh paper at high speed.