The delayed arrival of spring weather, constant rains this summer and saturated fields have producers wondering when to harvest hay.

The wet conditions also impede hay’s dry-down. Thus, the chances of putting up hay that is too wet are much higher this year, also increasing the risk of hay fires, warns J.W. Schroeder, the North Dakota State University Extension Service’s dairy specialist.

“Excessive moisture is the most common cause of hay fires,” Schroeder says.” Odd as it might seem, wet hay is more likely to lead to a spontaneous-combustion fire than dry hay.”

High-moisture haystacks and bales can catch on fire because they have chemical reactions that build heat. Hay insulates, so the larger the haystack, the less cooling that occurs to offset the heat. When hay’s internal temperature rises above 130 degrees Fahrenheit (55 degrees Celsius), a chemical reaction begins to produce flammable gas that can ignite if the temperature goes high enough.

Fire is possible in hay that’s loose, in small or large bales or stacks, and stored inside or outside. Hay fires are a danger at any time in stacked small bales when the hay’s moisture content is 20 percent or higher, and in stacked big square or round bales when the hay’s moisture content is more than 16 percent. Hay fires usually occur within six weeks of baling.

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

Weather conditions greatly influence a crop’s drying rate. 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

Finding a dry spot to pile hay also is a challenge.

“This year, it may be prudent to consider not piling all of your harvest in one area of the yard or field,” Schroeder says.” If it does overheat to the point of creating a fire, you don’t want to lose the entire harvest. Fires can damage or destroy hay, barns and equipment, and cost producers thousands of dollars.”

Schroeder recommends these steps to minimize the risk of hay fires:

Check your hay regularly. If you detect a slight caramel odor or 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 1/4-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 240 F (115 C). This gas is deadly, so use extreme caution when fighting a fire in this hay.

Producers who suspect a fire could develop should spread the bales in an area away from other feeds and buildings. Temperatures above 175 F 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,” Schroeder advises. “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, Schroeder says. Producers should have a hay sample tested if they are unsure whether it had too much heat damage to be used as feed.

NDSU Agriculture Communication - July 29, 2011