This summer, our team has been fielding forage reports for dry hay that have been coming in at moisture levels above our standard 20%. Dry hay with an increased moisture level is a concern not only from a quality perspective, leading to increased dry matter losses and mold growth, but is also at an increased risk for heating, and subsequently fires. With reports of hay fires hitting the news, we think it's a good time to dive into what causes the hay to heat, how to decrease the risk of hay fires, and the hazards associated.

Scientifically speaking, when forages are baled above 20% moisture, it's the ideal environment for mesophilic bacteria, a warm temperature bacterium that traditionally plays a role in forage preservation. It is this bacterium that releases heat, driving temperatures to 130-140?°F. The heat provided by this bacterium creates a breeding ground for thermophilic bacteria, which when multiplying, can raise interior bale temperatures above 170?°F. It's at these temperatures that spontaneous combustion can occur.

The best way to decrease the risk of hay fires is to bale below 20% moisture, as this results in reduced microbial activity. Weather obviously is one of the biggest factors that plays into moisture content. We can also decrease risk using preservatives, such as propionic acid during baling, which will help inhibit/reduce growth of bacteria in the hay. The effectiveness of these preservatives is often good for up to 25% moisture but can have variable results up to 30%.

Another preservation method that we have heard is salting hay. The belief is that spreading salt between layers in a loft would draw moisture out of the hay, therefore stopping mold and preventing this heating (and possible combustion). Though salt does serve as a mild desiccant (absorbs moisture), there are a few things that do not allow it to properly serve as an emergency preservative. This mostly comes down to distribution and quantity. Sprinkling salt on the surface does not reach the internal parts of the bale where this microbial action is occurring. Additionally, the amount of salt you would need to actually absorb enough moisture is cost-prohibitive, as mass quantities would be needed, which would also reduce feed palatability.  

The highest risk for heating and combustion is within the first six weeks after baling. You can monitor the temperature for that period twice daily. The National Resource, Agriculture, and Engineering Service [NRAES] developed a temperature chart outlining further actions that may need to be taken depending on the temperature of the hay.

There are some hazards with a hay fire that need to be considered, the first being a flare up. When hay heats, moving it to cool can be a good strategy. However, exposing the bale to oxygen could cause a flare up to occur. Additionally burned-out cavities or toxic gas could be produced from fires. Burned out cavities occur when a fire has started deep within the hay but may not be openly visible from the outside. Extreme caution should be used if performing activities that require you to get on the hay, such as temperature checks. It is advised not to monitor alone. Lastly, gases such as carbon monoxide, or vapors from chemically treated hay are dangerous to inhale.

In the unfortunate event of a fire, contact the fire department immediately. As farmers, your priority is to protect the farm - animals, inventory, buildings, but you should be the number one priority to protect.

In an ideal world, hay will never be baled above 20% moisture, but trying to produce dry hay here in SWNY with our humidity is a challenge. If you find yourself in a position with high moisture, some strategies to mitigate and reduce the risk of fire include:

• If you find that windrows aren't drying down, there are other forage alternatives such as baleage
• Use a tested preservative
• Monitor the temperature of bales to catch excessive heating sooner rather than later
• Store bales separately to reduce potential losses

Understanding how these fires start and learning how to reduce fire hazards will protect your feed supply, the loss of time and money associated with fires, and your family.  

Resources:

Preventing fires in baled hay and straw. (2012). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://www.extension.org/pages/66577/preventing-fires-in-baled-hay-and-straw.

https://wayne.osu.edu/news/wet-forages-pose-risk-barn-fires