Quickly changing weather and the rush to harvest the last hay crop of the season increases the risk of hay fires this time of year.

Fires can damage or destroy hay, barns and equipment and cost producers thousands of dollars.

Hay fires usually occur within six weeks of baling, but they can happen in hay several years old. Fire is possible in hay that’s loose, in small or large bales or stacks, and stored inside or outside.

Excessive moisture is the most common cause of hay fires. Odd as it might seem, wet hay is more likely to lead to a spontaneous-combustion fire than dry hay. For example, hay put into a barn or stack when it has more than about 22 percent moisture loses forage quality and has an increased risk of spontaneous combustion.

High-moisture hay stacks can have chemical reactions that build heat. Hay insulates, so the larger the haystack the less cooling occurs to offset the heat. When hay’s internal temperature rises above 130ºF, a chemical reaction begins to produce flammable gas that can ignite if the temperature goes high enough.

Weather conditions greatly influence the rate at which crops dry. Ideal hay curing weather has less than 50 percent relative humidity and some wind. Hay’s moisture content will increase overnight when the air is humid, especially if dew or fog develops.

Heating occurs in all hay above 15 percent moisture, but it generally peaks at 125 to 130ºF in three to seven days with minimal risk of combustion or forage quality losses. Then the temperature in a stack decreases to safe levels in the next 15 to 60 days, depending on bale and stack density, ambient temperature, humidity and rainfall the hay absorbed.

Moisture content should not exceed 18 percent to 22 percent in small, rectangular bales and 16 percent to 18 percent in large, round or rectangular bales. However, a late harvest in cool weather may force producers to take a chance on hay with higher moisture content. If that’s the case, follow this advice:

•Check your hay regularly.
If you detect a slight caramel odor or a distinct musty smell, chances are your hay is heating. At this point, checking the moisture is too late; you’ll need to keep monitoring the hay’s temperature.

•If you suspect your hay is heating, insert a simple probe into the haystack to monitor the temperature.
You can make a probe from a 10-foot piece of pipe or electrical tubing. Sharpen one end of the pipe or screw a pointed dowel to one end, then drill several 0.25-inch diameter holes in the tube just above the dowel. Drive the probe into the haystack, and lower a thermometer on a string into the probe. Insert the probe in several parts of the stack, and leave the thermometer in place for 10 minutes at each site.

•Before surveying the tops of stacks, place long planks on top of the hay.
Do not walk on the hay mass. Always attach a safety line to yourself and have another person on the other end in a safe location to pull you out should the hay surface collapse into what likely is a fire pocket.

•Hay treated with preservatives containing ethoxyquin and butylated hydroxytoluene produce hydrogen cyanide gas at about 240ºF. This gas is deadly, so use extreme caution when fighting a fire in this hay.
In the past, farmers sprinkled salt on wet hay as it was stacked to prevent spoilage, but salt does not prevent spontaneous combustion. Dry ice, liquid nitrogen or carbon dioxide gas pumped into the hay can prevent combustion by eliminating the oxygen from the hay mass.

•Producers who suspect a fire could develop should spread the bales in an area away from other feeds and buildings. Temperatures above 175ºF in hay mean a fire is imminent. The smell or sight of smoke means a fire is burning somewhere in the hay.
In any of these cases, call the fire department immediately. Do not move any of the hay. This would expose the overheated or smoldering hay to oxygen and may result in a fire raging out of control.

The proper procedure for controlling a hay fire is:

•Knock down visible flames. A straight-tip nozzle will penetrate deeper into the hay.
•Probe for hot spots and inject water through the probe to cool the hay and raise it to a moisture content that will prevent burning.
•When the hot spots appear to have cooled sufficiently, begin removing the hay from the barn or stack. Keep a hose handy in case of missed or insufficiently cooled hot spots.

Hay that isn’t too badly damaged may be used as mulch for erosion control on slopes and in gullies. Producers should have a hay sample tested if they are unsure whether it has too much heat damage to be used as feed.  FG

—From North Dakota State University news release

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Dairy Specialist
North Dakota State University

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