Why Can Hay Spontaneously Combust?

High-moisture haystacks and bales can catch on fire because they have chemical reactions that build heat. ... When hay's internal temperature rises above 130 degrees Fahrenheit (55 degrees Celsius), a chemical reaction begins to produce flammable gas that can ignite if the temperature goes high enough.

What causes spontaneous combustion in hay?

The interface between dry hay and wet hay is an ideal spot for spontaneous combustion. As a wet or green spot of hay in a mow or a large bale heats, moisture is driven into the surrounding dry hay. The area where the wet and dry hay touch, has the heat, dampness and insulation necessary to start a fire.

What makes hay catch on fire?

Fire can occur in loose hay, small bales, large bales or in stacks. The fires can occur in hay stored inside as well as in hay stored outside. Regardless of when or where the fires occur, the most common cause is excessive moisture. Freshly cut forage materials are not dead.