Article Source: Preventing fires in baled hay and straw. (2012). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice.

Most hay fires occur within the first six weeks after baling.  Understanding the causes of fires in stored hay and learning how to reduce fire hazards will protect your feed supply and could prevent the loss of time and money associated with a fire. Moisture content is the main factor that causes hay to spontaneously combust.  Additional factors that contribute to the risk of hay fires include the volume of the bale stack, bale density, and ventilation or air flow around the stacked bales.  Bales with a lower density that are stacked lower and have good air flow and ventilation have a lower risk of overheating.

The best way to reduce the risk of a hay fire is to bale hay at a moisture content of 20% or less because at this moisture level, microbial activity decreases.  There are several ways of reducing moisture content in baled hay:

·Baling under appropriate conditions: Weather plays a critical role in achieving the appropriate moisture level in baled hay.  The recommended weather conditions for haymaking are a slight wind and a humidity level of 50% or less.  Because hay has a higher moisture content in the morning, it is recommended that you bale later in the day.  The recommended practice for haymaking is to mow hay in the morning and allow it to dry in the field for a minimum of one full day prior to baling.

·Using specialized equipment: Another way of decreasing moisture content is to use specialized haying equipment designed to increase drying rates.  Such equipment includes tedders, windrow inverters, hay rakes, and conditioning equipment.

·Using hay preservatives: Hay preservatives, such as liquid propionic acid, applied to the hay during baling inhibit or reduce the growth of bacteria in hay with a high moisture content.  Another way to reduce the risk of a hay fire is to ensure that stored hay remains dry.

· When storing hay inside, make sure the barn or storage area is weather tight and has proper drainage to prevent water from entering the barn.

·When storing hay outside, cover the hay with plastic or another type of waterproof material.  If you are unable to cover the bales, arrange the bales so that air can circulate between them to promote drying.  Bales can be protected from ground moisture by storing them on a bed of gravel or lifting them off the ground on used tires, poles, or pallets.  DO NOT STORE BALES UNDER TREES OR IN THE FENCEROW.

If you are concerned that hay may have been baled at too high a moisture content, monitor the internal bale temperature twice daily for the first six weeks after baling.  For safety reasons, you must work with a partner when checking the temperature of stacked bales.  One of you stands atop the bales to measure the internal temperature while the other observes.  The person testing the hay should wear a harness and a lifeline that is attached to a secure object.  In the event of an emergency, such a system allows the observer to pull the person checking the temperature out of the hay.  Due to the potential dangers of this situation, this task should not be assigned to youth workers.

The following temperature chart outlines further actions that may need to be taken depending on the temperature of the hay.

Temp chart

(Source: National Resource, Agriculture, and Engineering Service [NRAES])