Hay barn fires a real hazard when mother nature keeps sending rain

Jason Hartschuh, OSU Extension Field Specialist, Dairy management and Precision livestock

At over 20% moisture, mesophilic bacteria release heat, causing stored hay temperature to rise.

 

Mother Nature has been at it again, hardly giving us enough days to make silage or balelage, let alone dry hay. It seems like there is a risk of pop-up showers every afternoon. Some areas of the state are better off than others, but the ground is often wet, so the forage lying against the ground does not dry very well. When it is not raining, the humidity is often high. When the relative humidity is 90%, the hay will never get dry enough to bale. Even when the relative humidity is 80% the moisture won’t fall below 20% to safely bale dry without propionic acid. These conditions are hazardous for hay harvest, as wet hay not only rots but also may burn. 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 the temperature to rise to 130 to 140ºF, with the temperature staying high for up to 40 days. As temperatures rise, thermophilic bacteria can proliferate in your hay, raising the temperature into the fire danger zone, exceeding 175°F.

Assessing your risk
Monitoring haystack temperature is a good idea whenever hay is stored above 18% moisture. All hay with a moisture content over 15% undergoes a heating and sweating period, typically peaking in temperature between 125-130°F, within three to seven days after baling, with minimal risk of combustion or forage quality loss. After the peak temperature is reached, hay generally returns to normal temperature over the next 15 to 60 days.

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. Having a moisture tester on your baler can help you know the variability across your field in moisture and when to use hay preservatives. Without a moisture tester, if you occasionally find darker green damp spots or the humidity is high, be sure to monitor for heating. Most propionic acid-based products are effective when applied at the correct rates to inhibit bacterial growth in hay with up to 25% moisture, with variable effectiveness at 25-30% moisture. Some products contain preservatives such as ethoxyquin or butylated hydroxytoluene, which, at very high temperatures of 240°F or above, produce hydrogen cyanide gas, which is deadly. Products that contain primarily propionic acid do not have this risk.

Temperature assessment
125° F/51.6° C – 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.

160° F/71.1° C – Hay has reached the danger zone. Carefully check hay temperature every few hours. Disassemble stacked hay to promote air circulation to cool hay be very careful of even hotter spots. Have a tank of water present while unstacking.

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 the fire service, remove hot hay. Be aware that bales may burst into flames, so keep tractors wet so the tractor does not catch fire.

200°+ F/93.3°+ C – Fire is present within the haystack near the temperature probe. With the assistance of the 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 to where bales will be stacked.

Monitoring the haystack
There are a couple of options available to monitor hay temperature. One of these uses technology, like the cables that can be used to monitor the temperature in stored grain. There are a couple of companies that produce cables that can be placed between bales in a stack. Monitoring probes are also available, which are placed in bales and use radio frequency signals to communicate with a receiver that uploads these temperatures to the web.

If you believe that your hay is at risk of heating, monitoring temperature is critical.  It should be done daily until temperatures stabilize in the safe zone or reach 150°F, when monitoring needs to be increased twice daily. This can be done with technology or manual temperature probes. 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 approximately six weeks, until values stabilize within the safe zone.

Temperature monitoring depends on the stack size but should be taken close to the center of the stack. In larger stacks, ideally, this is 8 feet down in the stack. This can be done by purchasing a long probe thermometer or building your own. This length of probe will be hard to push into the stack, so handles will be helpful. Building your own can be done with a 3/8-to 3/4-inch piece of pipe or electrical tube cut to a closed point. The pipe size will depend on the size of the thermometer probe that you will insert into the pipe. A digital or dial thermometer with a remote probe sensor works well. A larger pipe can be used, and a thermometer on a string can be 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 of fire. An infrared thermometer can also be used to assess the temperature of the pipe as soon as you pull it out. Any time temperatures are above 175ºF, hay should not be removed from the barn until the local fire department is present; you are at risk for fire. Once the fire department is present, hay should be carefully removed from the barn, with charged fire hoses ready in case spontaneous combustion occurs.

Have a safe and well-drying hay season this year!

Source: Ohio State University