Wet Hay Can Cause Barn Fires
Periods of rainy weather during the past few months has, at times, pressured farmers to store wet hay and put their barns at a risk of hay-generated fires, say Ohio State specialists.
Fires blamed on spontaneous combustion of stored wet hay have occurred this summer in west-central Ohio causing losses of property and livestock. One reported fire erupted when an electrical spark ignited hay dust.
The storage of wet hay is the most common cause of hay fires. When the crop is stored wet, microbial action can generate internal bale temperatures well above 150 degrees, says Ohio State forage agronomist Mark Sulc. "After a certain point of heating from the mold growth, other chemical reactions begin to take place, and it raises the heat to a point where the hay can burn," he says.
In general, hay is considered too wet for storage if moisture levels are higher than 20 percent in small rectangular bales, higher than 18 percent in large round bales, and higher than 16 percent in large square bales.
To determine moisture levels, farmers can use one of a number of commercial moisture sensors and probes to test hay for moisture content, Sulc says. These sensors are most accurate when put into the bale while it is in the baler chamber. A farmer also can use a microwave oven to determine moisture content. Refer to Ohio State FACT Sheet AGF-004-90, "Using a Microwave Oven to Determine Forage Moisture," which is available on line at
However, persistent rainy weather can give farmers limited choices, Sulc says. "In some places great hay is being made, while other places are getting rained on a lot."
One tactic farmers can use are chemical drying agents that can speed up the drying of legume hay, especially during the summer months, Sulc says. These chemicals are applied to the crop as it is being mowed, he says.
Farmers also can use hay preservatives that allow hay to be baled at higher moisture content without excessive storage losses, Sulc says. A sensor on hay making equipment can efficiently regulate the application rate based on hay moisture levels during harvest. Uniform coverage is essential, he says. However, preservatives are NOT effective on hay with moisture levels above 30 percent.
If equipment is available, farmers can consider using alternative harvesting methods for high-moisture hay. "Under poor drying conditions, put it up as haylage or baleage," Sulc says. "These are other options to go to during periods when only a one- to two-day wilting period is possible."
In addition to wet hay, outside ignitors, such as electrical sparks can spark fires in high levels of hay dust, according to Ohio State agricultural engineer Rick Stowell. These conditions are similar to those that cause grain elevator explosions. However, such fires are less frequent than those caused by wet hay.
Farmers should not be lulled into a false sense of security because they have modern farm buildings made of metal roofing and siding, Stowell says. "Once a barn fire gets started, it's very hard to contain," he says.
Farmers also can take precautions that will limit damage should a fire occur, Stowell says. For example, they should not attach buildings to each other, unless absolutely necessary. Separating structures helps confine fires to the buildings where they start.