Most Hay Fires Caused by Spontaneous Combustion

Hay fires are burdensome. Not only can they injure or even kill, but they are also a financial burden. They can harm buildings, livestock, crops and even other hay. Even a single hay fire, when it’s all said and done, can result in hundreds of thousands of dollars in total damages. With this in mind, it is necessary to understand what causes hay fires and how to prevent them from happening.

Firstly, hay fires are most typically caused by spontaneous combustion. While this might make it seem like hay fires are unpredictable—and, to some extent, they are—there are still ways to prevent this spontaneous combustion from occurring, or at least to lower the chances of this happening.

The key to preventing hay from combusting is to monitor its percent moisture. The wetter hay is, the more likely it is to combust. When a high percentage of hay is moisture, the hay begins to heat, and the high moisture reduces the hay’s insulation ability. Hay that is above 15 percent moisture, the hay begins to heat. Therefore, it is important to keep the hay’s percent moisture in check. A good rule of thumb is to keep smaller hay bales at a percent moisture of 18 to 22 percent and larger ones at a percent moisture between 16 and 22 percent.

In addition to keeping hay appropriately moist, it is also key to monitor the temperature of the hay, especially if it seems that the hay might be heating up. Generally, if the hay ever reaches 150 degrees Fahrenheit, then it is vital to check temperature daily—as hay that is hotter than this is susceptible to combust. At 160 degrees, the hay is in danger of combusting, and the hay should be inspected once every four hours.

Once the hay gets to 175 degrees, a fire is imminent. To prevent this, wet down the hay, call the fire department and dismantle hay stacks and keep them away from buildings and other (especially dry) hay.

Oftentimes, hay is treated with preservatives, so it is important to examine the consequences of this. Certain preservatives cause hay to produce hydrogen cyanide when heated to above 240 degrees. In this case, extra caution is necessary—as hydrogen cyanide is lethal. In addition, salt, while it may extend the hay’s shelf life, does not prevent spontaneous combustion, but substances like dry ice, liquid nitrogen and gaseous carbon dioxide do.

In the end, preventing spontaneous combustion in hay boils down to vigilance. And this vigilance certainly pays off, as it will not only make people and property safer, but it will maintain the quality of the hay.