Assess your stacked hay for fire risk


Tony Nye - OSU Extension



The last couple of weeks have provided for a lot of field work, hay making and planting.

As I drive around the county, I feel we are at least 80 to 85 percent complete with this year’s planting season. The hot, dry summer-like weather has also prompted many producers to get several acres of hay cut and put in the barn.

My family, too, was busy with many farm activities this week, including hay harvest. While getting hay out of the field and put in the barn, I thought about the potential risk of hay fires.

Hay fires are caused when bacteria in wet hay create so much heat that the hay spontaneously combusts in the presence of oxygen. At over 20% moisture, mesophilic bacteria release heat-causing temperature to rise between 130°F to 140ºF with temperature staying high for up to 40 days.

As temperatures rise, thermophilic bacteria can take off in your hay and raise temperature into the fire danger zone of over 175°F.

If hay was baled between 15-20% moisture and acid preservatives were used, there is still potential for a hay fire, but not as great as on non-treated hay. Without a moisture tester, if you occasionally find darker green damp spots or humidity is high, be sure to monitor for heating.

Most propionic acid-based products are effective at inhibiting bacteria growth in hay up to 25% moisture, with variable effectiveness at 25-30% moisture, if applied at the correct rates.

The following information can help in assessing the temperature of hay:

• At 125°F/51.6°C, there is no action needed.

•150°F/65.6°C, hay is entering the danger zone, check temperatures twice per day. Disassemble haystacks moving bales outside to allow air circulation to cool the hay.

• Hay that is approaching 160°F/71.1°C has now reached the danger zone. Carefully check hay temperature every few hours. Unstack hay to promote air circulation to cool hay. It is important to be careful of even hotter spots and to have a tank of water present while unstacking.

• Once hay reaches 175-190°F/79.4-87.8°C, hot spots or fire pockets are likely. Alert fire service to the possible hay fire incident. Close barns to minimize air movement around the hay. With the assistance of fire service, remove hot hay. Be aware that bales may burst into flames, keep tractors wet so the tractor does not catch fire.

• Temperatures above 200°F/93.3°C will likely see fire present within the haystack. Utilizing a temperature probe can help locate the hot spots. Fire service should be notified immediately and with the assistance of fire service, remove hot hay. If possible, inject water into the hot spot to cool hay before moving. Most likely a fire will occur, keep tractors wet and fire hose lines charged in the barn and along the route of where bales will be stacked.

It is important to realize that it can take several days for hay to heat up to dangerous levels so do not rest easy until you are assured the hay temperatures have stabilized and back to a safe zone.

There are a couple options available to monitor hay temperature. One of these is high technology, like the cables that can be used to monitor temperature in stored grain. Most of us do not have these available to us. Another method would be the use of manual temperature probes.

If you believe that you may be at risk for hay heating, monitoring temperature should be done daily until temperatures stabilize in the safe zone or reach 150°F when monitoring needs increased too twice daily.

When monitoring hay temperature, be very cautious — hot hay can burn within the stack and cause cavities underneath that you can fall into.

Use planks to spread out your weight while walking on the stack and have a harness system attached to the ceiling in case you fall into a burned-out cavity. Also work in pairs with someone on the ground within voice range to assist you if you find yourself in a bad situation.

Temperature monitoring should continue for possibly six weeks until values stabilize in the safe zone.

Building your own can be done with a 3/8-3/4 piece of pipe or electrical conduit cut into a closed point. The pipe size will depend on the thermometer probe size you will put in the pipe. A larger pipe can be used and a thermometer on a string lowered into the pipe.

Drill 3/16-inch holes in the bottom four feet of the pipe. Leave the thermometer in the stack for about 10 minutes to get an accurate reading.

A less accurate method is to leave a pipe in the stack all day, and if a section is too hot to hold in your hand when removed you are at risk for fire. Or even better, use an infrared thermometer to measure the temperature of the pipe.

Any time temperatures are above 175ºF hay should not be removed from the barn until the local fire department is present.

Once the fire department is present, hay should be carefully removed from the barn with charged fire hoses ready if spontaneous combustion occurs.

Have a safe a well drying hay season this year!

Tony Nye is the state coordinator for the Ohio State University Extension Small Farm Program and has been an OSU Extension Educator for agriculture and natural resources for over 30 years, currently serving Clinton County and the Miami Valley EERA.

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Tony Nye

OSU Extension