Texas is by far the biggest producer of hay in the United States; with Missouri and Nebraska a distant second and third. Feeding livestock is the number one use of hay, as almost any animal on a farm or ranch (horses, cattle, sheep, goats, etc.) will eat hay. It is usually fed to livestock when they cannot graze or be in a pasture because of winter or a drought. Last year, Texas suffered the 11th driest year in the past 128 years, and 2023 is on pace to beat that. As you can imagine, there is a lot of hay currently being harvested and stored in Texas.
Every year in North America insurers pay out tens of millions of claim dollars resulting from fires and feed damage caused by the spontaneous combustion and heating of hay mow – a pile of hay stored in or near a barn. Spontaneous combustion is the result of a chemical reaction that occurs when combustible materials combine with oxygen, generating heat which eventually ignites the hay. We normally think of spontaneous combustion with regard to the storage of rags which are soaked with cleaning products, linseed oil, or other oils used to finish wood. Subrogation opportunities abound once you realize that the careless storage of hay can result in a catastrophic fire and that the wetter the hay, the more likely it is to start on fire.
Not many people outside of the agriculture industry understand what “hay” is. Oat, barley, and wheat plant materials are often cut green. The harvested product is made into hay for animal fodder or turned into straw – a harvest byproduct used primarily for animal bedding – where the stems and dead leaves are baled after the grain has been harvested and threshed.
Good storage practices will avoid spontaneous combustion. But, before we discuss these storage practices, it is important to understand spontaneous combustion and how a wet pile of hay can destroy a lifetime of work. Rural fires can be the result of overheated exhaust pipes or a thoughtless passerby throwing a cigarette out a car window. However, hay mow fires on farms are much more likely to be caused by spontaneous combustion. In one year alone, in one state alone, the Montana Fire Marshall’s office recorded 148 agricultural-product fires that resulted in injury and millions of dollars in damage.
The Science of Spontaneous Combustion
Although spontaneous combustion commonly occurs in piles of moist organic material, such as mulch and hay, the scientific mechanism of how it occurs is not entirely understood. Initially, heat is generated by the respiration of bacteria, molds, and microorganisms. This biological process naturally raises the heat of the material, explaining the steam and smoke you see from a pile of garden mulch in your driveway. This process can raise the temperature of the materials to between 122°F and 212°F (50°C to 100°C), above which point the living organisms perish.
- 150°F (65°C) is the beginning of the danger zone. At this point, the temperature of the hay must be checked daily.
- 160°F (70°C) is dangerous. The owner must check the temperature every four hours and continuously inspect the stack.
- 175°F (80°C), the owner should call the fire department. The owner should also wet down the hay and attempt to remove it from the barn and away from buildings and other dry hay.
- 185°F (85°C), hot spots and pockets may be expected. Flames will likely develop when heating hay comes in contact with the air, so even attempting to move the hay at this point will cause ignition.
- 212°F (100°C) is critical. The hay is on fire.
As is suggested from the above, there are a lot of things that the owners or persons baling and storing hay can do to both detect and prevent spontaneous combustion and damage.
Moisture content is a critical factor affecting self-heating of vegetable material. Spontaneous combustion may occur when moisture content ranges from about 20 percent to 45 percent. Ironically, it is wetter hay which produces the most risk of fire. Dryer hay will not support the necessary biological activity. Large piles of hay retain more heat than smaller piles and are, therefore, more likely to combust. Scientists refer to the “critical radius” of a pile of stored material, below which spontaneous ignition cannot occur. Bulkier products, such as wood chips, permit more air flow than finer or denser products, such as hay, and can safely be stored in larger piles. Products that degrade slowly, like dry wood chips, can be safely piled higher than those that degrade more rapidly, like wet wood chips or hay. The spontaneous combustion of hay mow will usually not occur in less than two weeks after the hay is stored, with a more common timeline being five to ten weeks. In investigating a hay fire, your expert will make note that hay ignited by an external source, such as an electrical failure, discarded smoking materials, or a spark, will almost always show evidence of burning from the outside. To the contrary, a spontaneous combustion fire will ignite in the interior of the pile and burn outward, often forming a sort of chimney to the exterior. Moreover, unburned hay from a stack that self-ignited is very dark in color and may be more acidic than normal.
The main culprit in spontaneous hay combustion is moisture. Moisture can get into stored hay in many ways, all of which can lead to spontaneous combustion, fires, damages, and subrogation potential. Farmers and those storing hay must make efforts to avoid moisture getting into hay, an impossible task when the roof of the barn leaks or the hay is stored close to other machinery which sprays water or moisture. Also, heating often occurs when the plants are baled too “green” due to the plant’s internal moisture or sap content being too high, providing additional third-party liability potential. Regardless how the moisture gets into the hay, it allows microbial activity or plant respiration and enzyme activity to continue, increasing as more moisture and heat is generated by this activity. Spontaneous combustion and a significant insurance claim are the result.
Hay which contains moisture in excess of what is considered satisfactory to store hay safely will result in increased microbial activity and plant respiration, both of which, in the presence of the moisture and oxygen (O2), causes the hay to carbon dioxide, water, and heat.
Avoiding Spontaneous Combustion
There are a number of ways the owner (purchaser or seller) of hay can contribute to and/or prevent such losses. Each presents a subrogation opportunity, should the negligent failure to follow the best practices in the production and storage of hay result in a fire.
Process of harvesting. Dangerous moisture can be introduced when the hay is not “cured” enough (i.e., too green) resulting in their internal cell moisture being too high at baling. This is referred to as “sap” moisture and is simply the moisture in the plant cells which also contain the soluble sugars and proteins.
Process of curing. How hay is cured can also play a big role in determining who is at fault. Ideally, well-cured hay is dried externally (free moisture) and internally (plant sap or juices) to such an extent that only minimal or negligible heating will occur. Hay baled at 10-12 percent moisture will not heat at all, but due to the dryness of the hay, substantive and nutritional losses will occur when this extremely dry material breaks up during transportation and storage.
As a result, most hay is baled at around 15 percent. At this moisture level, hay will experience some heating in the first few weeks. Moisture or dampness resulting from this minor heating is commonly referred to as “sweating.” The product eventually reaches its own equilibrium moisture content, depending on climate.
Farmers are rewarded for skirting the edges of safe hay storage with higher yields, and this phenomenon should be remembered when investigating such a claim. Dry matter loss reduces the value of the hay and can result if the hay is too dry. As a rule of thumb, the yield loss of a round bale of hay is 1 percent of original yield for each 1 percent moisture that is lost as stored hay reaches its equilibrium storage moisture. When hay is baled at 22 percent moisture, which then dries to 14 percent moisture, yield loss will be approximately 8 percent.
A windrow is a row of mowed hay which is allowed to dry before being baled, combined, or rolled. This windrow is often formed by a hay rake, which rakes hay that has been cut by a mower machine or by scythe into a row, or it may naturally form as the hay is mowed. Spontaneous hay combustion is often the direct result of excess surface or “free” moisture present on hay windrows at baling. This moisture may arise from excess dew overnight, sections of the windrows not being cured enough such as the bottoms of windrows, or a rain-affected windrow insufficiently dried before baling. Well-cured hay will almost never self-combust. Allowing excess moisture and/or insufficient curing are often the culprit in such fire losses. Even if the majority of the forage is well-cured and ready to bale, a single bale or few bales may be unsafe to bale and can potentially cause a fire which destroys the entire product. All of these things provide potential third-party liability.
Process of baling. The size, shape, and mass of hay bales have a direct impact on its moisture content and, therefore, its propensity for spontaneous combustion. Excessive moisture in windrows can be the result of “hard-to-dry” capeweed or other foreign vegetation being in the harvested product, low lying or shaded areas, an excessively heavy outside windrow, and the like. Excessive rain after baling, but before the hay is covered, can soak into bale exteriors for several centimeters and create an inconvenience for farmers. Condensation may accrue quickly on the underside of tarps used to cover freshly baled hay and could cause the same problem as if the baled hay wasn’t covered at all. This is especially true after heavy rains. The bales must be “re-dried” and if they are stacked before they are sufficiently dry, the upper bales will trap evaporating moisture and generate heat.
Storing hay. Properly baled hay with the correct amount of moisture can get excessive moisture added even after it has been baled and stored. A leaking barn roof, open window, or nearby rain downspout which allows rainfall to seep down between bales of hay can also lead to dangerous moisture content. In addition, flood water can saturate the bottom layers of bales stored in a shed or outside bale stack.
Monitoring moisture. If hay is put into a barn or stack when it has more than about 22% moisture, not only does the hay lose forage quality, but it has an increased risk of spontaneous combustion. Hay moisture meters are cheap and easy to use. Farmers must closely monitor the amount of moisture in the windrows before the hay is baled. Once it is baled, it is too late. Recommended moisture content depends on the type of bale or hay mow involved:
Small Rectangular Bales 16 – 18%
Round Bales (Soft Center) 14 – 16%
Round Bales (Hard Center) 13 – 15%
Large Rectangular Bales 12 – 14%
Export Hay Under 12%
Hand-held moisture meters, even when used properly, provide only a rough guide at best, to help ascertain the suitability of material for baling. The meter must be calibrated before use and the manner in which the meter is used is critical. In investigating such losses, always inquire into and obtain, if possible, the actual meter or meters used, if any, to measure the hay. It is important that the hay samples tested be representative of the material to be baled. This requires sampling along windrows and throughout its depth and then repeating this throughout the pasture. It is a time-consuming process that often sees short cuts. Areas which are in the shade or in lower-lying areas of the pasture need careful attention.
There are reliability issues regarding the accuracy of hay moisture meters in these extreme conditions—such as not being able to measure sap moisture. Stripping the stems of the hay to look for moisture, or closely examining the knots of cereal hay, will help give good indications of the extent of curing. Failure to carefully follow any of the above procedures and practices can result in significant errors in moisture readings. The higher the moisture content in hay, the less accurate are most hay moisture meters.
Monitoring temperature. Once the hay mow is stored, farmers must continually monitor and observe the product, and must be knowledgeable as to the signs of heating hay. Symptoms that indicate a haystack is heating are:
- Bale Temperature;
- Steam Rising from Hay Stack;
- Unusual Odors;
- Moisture or Corrosion on Rafters or Metal Roofs;
- Mold on Barn Surfaces;
- Slumping of an Area of Bales
If a haystack heats excessively, and the farmer recognizes this, there is action that can be taken (note that this also contributes toward contributory negligence of our insured). Hay mow should be monitored for heating within days of stacking and storing. If any heat is detected, monitoring should continue until heating subsides. Spontaneous combustion occurs at between four and fourteen weeks after baling, but can occur much earlier or even up to six months later.
The crowbar method of testing for heat involves pushing a crowbar into the center of the stack from several locations, preferably near the top of the stack because heat rises. After leaving it for two hours, the farmer pulls it out and feels it with his hands. If he can handle the bar without discomfort, he should continue to check daily. If he can only handle the bar for a short time, he should check the temperature twice daily and remove any machinery from the barn and storage area. If he can touch the bar only briefly, he should check the temperature every two to four hours and begin moving the hay to provide air flow. If the bar is too hot to hold, the farmer must immediately call the fire department and avoid walking on the top of the stored hay. A problem with the crowbar method is that the bar can only be pushed in to shallow depths and the heating could be located much deeper into the hay mow. Alternative techniques include the use of a probe and a thermometer.
If the stack heats to excessive levels, action must be taken to prevent spontaneous combustion. Years ago, farmers spread salt on wet hay as it was stacked to prevent spoilage. However, this will not prevent heating or combustion. Dry ice, liquid nitrogen, or carbon dioxide gas may be pumped into the hay to prevent combustion by eliminating oxygen from the hay mow.
Weather conditions. Weather conditions during the growth of the product and during and after harvest dramatically affect how hay is baled and stored. Excessive rain requires adaption in the procedures used. Conversely, the risk of spontaneous hay combustion actually increases during periods of drought. There are several alternative theories for this, including the fact that the demand for fodder is very high during droughts and can result in shortcuts being taken and hay being baled before it is properly cured. It could also be that plants in drought conditions produce a waxy layer on the leaves and stems to help conserve plant moisture, reducing the rate of curing.
Subrogating Hay Fire Losses
Typical spontaneous combustion of hay facts can be found in the Washington case of Thompson v. King Feed & Nutrition Serv., Inc., 70 P.3d 972 (Wash. App. 2003) aff’d, 105 P.3d 378 (Wash. 2005). Glen Thompson rented his barn to King Feed & Nutrition Service, Inc. to store baled hay collected from the Thompson farm and surrounding properties. The Thompsons were not involved in any aspect of the operation other than renting their barn as the storage site for the hay. The dry hay was stored on the second story of the barn. Wet hay was stored outside on the north wall of the barn under a lean-to roof. In August 1998, the hay on the north wall caught fire, and the barn and its contents were destroyed.
Thompson sued King Feed for negligence in failing to properly and safely store hay next to and in their barn. Thompson’s expert testified that spontaneous combustion was “the most likely” cause of the fire. King Feed defended itself by arguing that spontaneous combustion of hay in Western Washington was extremely rare and suggested that something Thompson did actually started the fire. King Feed also argued that testimony about electrical repairs done on the barn five to six months before the fire suggested that the system was somehow faulty. The judge granted a directed verdict against King Feed and the jury granted $300,000 to Thompson.
In every agricultural fire claim, early and thorough investigation is critical. Do not wait until the claim has been adjusted and paid before engaging an expert and/or investigator. Visit the scene early. Meet with the insured and obtain copies of any storage agreements, lease contracts, etc., Subrogating for damage caused by spontaneous combustion will only be viable where there is a third party involved – i.e., situations where a third party has harvested, cured, baled, and stored the hay in the premises of the insured, or where third parties are hired by the owner of the damaged building to assist in these processes. Always contact subrogation counsel if the loss is likely to be significant.
For more information on subrogating damages caused by the spontaneous combustion of hay, contact Lee Wickert at firstname.lastname@example.org.
Lee R. Wickert is a senior associate attorney in our Austin, Texas branch office. Lee was located in in our Wisconsin office, but transferred to our Austin, Texas branch office when it was opened in May 2019. Lee’s practice focuses on insurance litigation, subrogation, workers’ compensation, health insurance and ERISA, automobile insurance, property and casualty, and insurance coverage. Lee is a graduate of the University of Wisconsin-Milwaukee and obtained his law degree at Marquette Law School and his M.B.A. at Marquette University. Lee is licensed to practice in Texas and Wisconsin.