(Reno, NV) — Spontaneously combusting rags are to blame for a fire at the University of Nevada, Reno’s College of Engineering. Investigators say oily rags on a roof burst into flames during triple-digit heat on Monday afternoon. Construction workers had left them up there about an hour prior. The ambient air temperature was 102 degrees at the time and the temperature on the roof was at least 120 degrees. Firefighters kept the flames from spreading to the rest of the building.