Information Bulletin Number 0907300

Prevent Hay Fires On Your Farm
Brian S. Aldrich, Agriculture Resource Extension Educator, Cornell University Cooperative Extension Cayuga County
Eric M. Hallman, Director, Cornell Agricultural Health and Safety Program
Risk of Fires Caused by Wet Hay
Farmers who make dry hay face problems in field drying most every season. In some seasons, it is extremely challenging to
make dry hay. Frequent showers, constant cloudiness and wet field conditions increase the risk of putting up hay that is not
dry enough to cure well in the barn. Spontaneous combustion is a real problem for hay producers and buyers. To prevent
fires in the haymow, it is extremely important to know the weather conditions under which the hay was made,
especially if it is hay you are purchasing and did not make yourself! Stacking small, rectangular bales at 20% moisture
or higher, and large or round bales at 16% moisture or more, potentially creates the conditions for a fire. Fires in freshly cut
hay usually occur within the first two to six weeks after baling.
How to Tell if You Have a Problem
Some heating in new hay is normal. The quickest way to tell if you have a problem is to drive a long pipe (8-10 ft., 3/8-inch
diameter) or an iron or copper rod into the center of the stack. Leave it in for 20 minutes and then pull it out. If it's too hot
to hold in your hand, the hot hay should be removed immediately. Another warning sign is that smoldering hay gives off a
strong, pungent odor.
If you suspect you have a problem for any reason, monitor the temperature of the haystack. A temperature of 150°F or
higher means that hay is entering the danger zone. The following table provides guidance for actions to take depending on
the temperature of the hay. We have put this table together using several published references, and have chosen the most
conservative values where there were differences.
Temperature Action Steps
120F or below No concern, no action needed.
120 to 140F Check temperature daily.
140 to 150F Check temperature twice a day.
150F Entering the danger zone! Check temperature every two hours.
150 to 160F Begin moving hay out of the structure. At a minimum, stacked hay should be
disassembled to allow more air to move around heated bales to cool them.
160 to 175F Call fire department; have them on-site before moving hay.
The danger of spontaneous combustion is rapidly increasing. Hot spots or fire
pockets are likely. If possible, stop all air movement around hay. Call 911 to
alert of a possible hay fire.
Remove hot hay. This should be done with the assistance of the fire service.
Fire service should be prepared for hay to burst into flame when it contacts
fresh air. Move hay away from buildings with bucket-loader or bulldozer.
200F or higher
Hay is almost sure to ignite. Remove hot hay. This should be done with the
assistance of the fire service. Fire service should be prepared for hay to burst
into flame when it contacts fresh air. Move hay away from buildings with
bucket-loader or bulldozer.
Sources: 1. Hall, Marvin. 2006. Penn State Field Crop News Vol.06:04.
2. Murphy, Dennis J., and William C. Arble. 2000 (revised). Extinguishing Fires in Silos and Hay Mows. NRAES-18. Natural Resource,
Agriculture, and Engineering Service, Ithaca, NY. Table 6-1, p.27. . 607-255-7654.
How to Check the Temperature of a Haymow
Commercial hay thermometers are too short to monitor the interior temperature of a haymow. The National Ag Safety
Database (, “Hay Fire Prevention and Control”, offers the following instructions on how to fabricate
and use a longer probe to measure temperatures deeper inside the haystack:
…A simple temperature probe can be made in the farm shop from a 10-foot piece of 3/4-inch diameter iron pipe. Drill eight
3/16-inch diameter holes about three inches from one end then hammer that end of the pipe together to form a sharp edge
(Figure 1). Check hay temperature in the center of the stacked hay. The easiest way to do this is from the top of the stack.
Do not walk directly on the stacked hay; pockets may have already burned out under the hay surface. Place boards,
plywood, or a ladder on the hay and walk on those instead (Figure 2). This will spread the weight of the person monitoring
the temperature over a larger area and help keep him from falling into burned out cavities. Be sure to use a lifeline in case
the hay surface collapses into a fire pocket. A second person, standing safely away from the hay, should hold the other end
of the rope to pull the person monitoring the temperature out in case the hay surface collapses into a fire pocket. Drive the
probe from the top of the haystack into the inner most bales (Figure 3). Lower a thermometer to the end of the probe with a
piece of light wire. After 10 to 15 minutes, retrieve the thermometer and read the temperature.
Figure 1. Homemade hay temperature probe with thermometer.
Source: National Ag Safety Database .
Role of Ventilation Depends on Hay Temperature
At lower temperatures, ventilation helps to disperse the heating that normally occurs in stored hay. But at temperatures of
175F or greater, ventilation will fuel a fire and should be avoided.
If Hay Starts On Fire
Call 911 immediately if a fire starts in your haymow. Do not wait to see if you can put the fire out yourself. Hay fires can
spread very rapidly and soon become uncontrollable. The National Ag Safety Database advises, “Let firefighters take
control of the situation once they arrive. Do not move hay if signs of fire are present. Moving hay exposes the overheated or
smoldering hay to oxygen and may cause the fire to burn uncontrollably.”
Further Information
The National FARMEDIC Training Program has instructors who can train and assist rural firefighters with the best methods
for extinguishing fires on the farm. Contact them at 1-800-437-6010, e-mail, website