Minimizing Hay Storage Loss from Heating

From iGrow.org Blog

Successful hay storage is essential to preserving high quality forage, while ensuring desired performance from livestock and deterring economic losses from unwanted hay storage fires. The predominant reason that fires occur in hay is because of excessive moisture in the plant residue that results in heating when it is baled or stacked for long term storage.

Plant cell respiration burns plant sugars to produce energy. This is a normal process as the hay plant tissue dries down and is often referred to as “sweating” or “heating” and occurs until the plant material is less than 15% moisture. When the plant material has more than 20% moisture it can cause the mesophilic bacteria present to grow rapidly, which is encouraged by the excessive moisture present. This produces heat in the bale. The higher the moisture content the longer it takes for the bale to dry down. Correspondingly, the higher the temperature in the bale’s core will be as it works through the cycle of heating and drying. It is important to note that spontaneous combustion of hay bales can occur at interior bale temperatures of 170° F.

Minimizing heat damage and fire risk at harvest.
How do we minimize the risk of heating or damage from fire? It is recommended to put up dry hay at a moisture content of 20% or less as this is when mesophilic bacteria growth is minimized, reducing the risk of overheating.

• Baling when the weather is appropriate for putting up hay is often challenging. However, to achieve the desired moisture content, one should keep the following in mind. If humidity is high or there is heavy dew, the hay will “pick up” moisture content. Often baling later in the day helps minimize extra moisture from accumulating. However, as night approaches it can also increase the moisture present, so constant checking of the moisture content throughout baling is recommended.
• Use a moisture tester which will give an automatic reading of the moisture content in the field or conduct a moisture test to determine the moisture content before baling. View Using a Microwave Oven to Determine Moisture Content of Forages to learn how to do a moisture test at home with a microwave.
• Use equipment that will enhance quicker dry down of the forage. This includes hay rakes and conditioning equipment, tedders and windrow inverters.
• Preservatives such as propionic acid that are applied at the time of baling can reduce or inhibit the growth of bacteria reducing the potential for excessive heating.

Minimizing heat damage and fire during storage.
Once the hay has been baled it is best to minimize losses or the potential of enhanced heating especially if the hay has been put up at marginal moisture levels (close to 20% moisture).

• Storing inside is best to minimize losses from weather. In doing so, make sure it is weather tight and has adequate drainage to inhibit water from entering the building.
• If storing outside is your option, cover the hay with a waterproof type material. To help moisture absorption from the ground, hay should be stored on a bed of gravel or by lifting them above the ground via tires, poles or pallets. If you are unable to cover them, provide enough room between bales to allow for adequate air flow for drying to continue.

Check stored hay temperature.
If stored hay has been put up at a moisture content higher than recommended it will cause heating to occur. Stored hay should be monitored twice daily for a period of six weeks as it continues to dry down.

Checking of stacked bales should be done in teams of two people, along with a life harness being worn by the person on top of the stack. A life harness is recommended as a burned-out cavity can develop in the hay stack, which a person may fall into as they monitor bale stack temperatures. It is also recommended that planks or plywood be placed to help with weight distribution as a prevention measure for falling into a burned out cavity.

To monitor the temperature of baled hay one can use a commercial thermometer or a home fabricated probe can be used to meet your monitoring needs. A piece of 3/8 inch - 8 to 10 ft. iron pipe with a pointed tip can also be used. If you are using a commercial thermometer probe this should be left in the bale for 10-15 minutes to get an adequate reading. If you are using a home-made probe it should be left in the bales for 20 minutes before removing. The guidelines for using a homemade probe is that after removal, if the probe is too hot to hold in your hand, then you have hay that is too hot and should be removed.

The following temperature chart provides a guidelines for actions in correlation to the temperature of the stored hay.

Table 1. Critical Temperatures and Action Steps

Temperature    Condition and Action