Hay fires cost farmers millions of dollars in building and feed replacement costs, lost revenue and increased insurance rates.
Wet hay: a fire hazard
Proper moisture at baling is the single biggest hay fire risk factor. Hay baled at less than 15 percent moisture has a very low risk of fire (table 1). As bale moisture increases, fire risk increases.
Table 1. Moisture guidelines at the time of baling
| Moisture (%) | Comments |
|---|---|
| Less than 10 | Hay may be brittle and dry. |
| 10-15 | Recommended moisture. Least risk of fire. |
| 16-20 | Could mold without preservative. Slight fire risk. |
| 21-25 | Will likely mold without preservative. Moderate risk of fire. |
| Over 25 | Severe heat damage. High fire risk. |
Baled hay becomes a potential fire hazard when the temperature inside the bale doesn’t decline. Heat comes from bacteria respiration following baling. Table 2 lists the effects of bale temperature and fire potential.
Table 2. Effects of internal bale temperature and fire potential
| Temperature (F) | Comments |
|---|---|
| Less than 130 | Least risk of fire. |
| 130-140 | Little risk of fire. Keep checking. |
| 150 | Moderate fire risk. Check often. |
| 175-190 | Fire is imminent. Contact the fire department. |
| Over 190 | Use extreme caution. Bales may combust when moved. |
Maximum temperature isn’t the only concern with potential hay fire. You should also monitor and consider the rate of temperature increase when addressing a fire risk. A gradual increase in bale temperature usually has little fire risk. A rapid rise in temperature creates a high fire risk.
Hay damage
Besides fire, wet hay is also at risk of heat damage and mold. Moldy hay is especially dangerous to horses by causing,
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Colic
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Heaves
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Respiratory illness
Moldy hay is also a health risk for horse owners. Farmer's lung is an allergic reaction that can occur from breathing in dust with spores and dried fungi commonly found in moldy hay. Farmer’s lung can be disabling for people and repeated exposures can cause scarring and fibrosis.
Reviewed in 2021