Silo Fire Prevention and Management

Rescue trucks at silo

Photo source: Penn State University


Use the following format to cite this article:
Silo fire prevention and management. (2015) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from….

Because the ingredients needed for a fire to occur are present in silos, agricultural producers who have silos should take steps to minimize the likelihood of silo fires and be prepared to manage silo fires should they occur. Fire prevention steps are similar regardless of what type of silo you have. The approach to managing a fire, however, is based on the type of silo in which the fire is burning.

Ingredients for Fire

Three ingredients are needed for anything to burn: a heat source, air, and fuel.

  • The heat source for a silo fire is bacterial action within the silage. When forage material is cut, bacterial action on the forage begins. This action produces heat until all the oxygen in the pile is consumed. Microorganisms are killed at 250°F–400°F, causing a breakdown in the forage through an oxidation process called pyrolysis. Pyrolysis allows oxygen in the silo to support a smoldering fire that can result in charred cavities in the silage. Once the oxygen is consumed, the fermentation process begins and continues until the forage becomes stable. 
  • The air source for a silo fire includes air that is trapped in chopped forage during harvest and air that blows into the silo. The dryer the material, the more trapped air there is.
  • The fuel source for a silo fire is the silage, although it typically is not a highly effective fuel source because of its moisture content. Even dry silage is too wet to burn quickly.

Causes of Silo Fires

The three main types of upright silos found on farm operations are conventional, oxygen-limiting, and modified oxygen-limiting. Typically, silo fires occur more frequently in conventional silos than in oxygen-limiting silos because oxygen is present in greater amounts in conventional silos. Many silo fires occur in the top layer (approximately the top 10 feet) of dry, loosely packed silage. Such fires can be the result of an overheating unloader motor but more often are caused by spontaneous combustion. Spontaneous combustion can occur when new silage having a too-low moisture content (less than 45%) is placed in the silo, when fresh silage is placed on top of old silage, or when the silo has poorly maintained doors and walls. Putting new silage on top of old silage is especially risky if the old silage is too dry. The dryer the material is, the more air that will be trapped when fresh, wetter material is placed on top of it. That trapped air can allow excessive heating and support a smoldering fire.

A silo fire can start from a source outside the silo as well. The two most common examples of these types of fires are a fire in the chute from a shorted-out electrical wire or a fire from an adjacent barn fire.

Prevention of Silo Fires

Prevention of silo fires involves performing proper maintenance on silos and unloaders and taking appropriate steps when harvesting and storing forages.

Silo and Unloader Maintenance

When a silo is empty, inspect the silo walls (especially the lower 10–15 inches), the silo doors, and the unloader system. Make any necessary repairs. If you have an oxygen-limiting silo, pressure-test it on a regular basis (at least once every other year, preferably when empty). If air is allowed to leak into an oxygen-limiting silo, forage quality can decline, and the chance of a fire developing increases. Many fires have started in oxygen-limiting silos that have been unused for several years but not emptied.

For the unloader system, examine belts, bearings, wiring, and the motor. Lubricate the lift cables, and immediately replace any lift cable showing signs of kinks, cuts, or corrosion. Check for damaged insulation or terminals on the unloader power cable, and repair or replace damaged materials as needed.

Harvesting and Storage Recommendations

Implementing the following steps for harvesting and storing forages will decrease the risk of a silo fire occurring:

  1. Minimize drying time to reduce respiration.
  2. Chop forage at the correct theoretical length cut (TLC). The TLC for hay crop silage is 3/8 inch; the TLC for corn silage is 1/4 inch. Follow the silo manufacturer’s recommendations.
  3. Ensile at 30%–50% dry matter content (i.e., 50%–70% moisture content), based on the silo manufacturer’s recommendations. Using this approach will optimize fermentation.
  4. Leave the silo sealed for at least 14 days to allow complete fermentation to occur.
  5. Unload 2–6 inches per day, and maintain a smooth surface. Using this unloading schedule will help you stay ahead of any spoilage. Spoilage is caused by the bacterial action that can cause heating.
  6. Discard deteriorated silage. Performing this step will help eliminate a fuel source for potential fires and minimize animal health problems.

Management of Silo Fires

Managing silo fires involves monitoring silage to detect a fire early, taking the proper steps when you suspect or discover that a fire is burning, and understanding how fires in different types of silos are extinguished.

Monitoring of Silage

Silage is costly to replace, so one of the main goals of managing a silo fire is to locate the fire and control the area so that only a minimum amount of silage is affected. The first step in managing a silo fire is early detection, so monitor a silo for three weeks postharvest. This length of time is the critical period for fermentation and heating to occur. Because silage burns slowly, detecting a fire early allows you time to evaluate your options and develop a plan for addressing the fire.

Response to the Presence of a Fire

If you suspect or discover a silo fire, contact your local fire department immediately. A silo is a confined space, and firefighters are obligated to follow the US Department of Labor, Occupational Safety and Health Administration (OSHA) Confined Space Standard for entry into a silo. When you contact the fire department, indicate the type of fire so that the fire department can dispatch the correct personnel and equipment (e.g., thermal imaging camera, infrared heat gun, self-contained breathing apparatus).

Wait for the fire service personnel to arrive. Do not enter the silo or climb the chute because unknown factors, such as fire gases or burning embers falling down the chute, may exist. Only rescue personnel with self-contained breathing apparatuses or supplied-air respirators should enter an upright silo because of toxic gases that can be present due to the fermentation process or the fire. The most typical gases in silos include carbon monoxide, carbon dioxide, nitric oxide, nitrogen dioxide, and nitrogen tetroxide. Additional gases can be present due to the burning of substances such as silo liners and epoxy coatings.

While waiting for fire service personnel to arrive on the scene, take the following steps:

  1. Close the bottom of the chute to reduce airflow that may be fanning the fire. Use sheet metal or another noncombustible material to close the chute.
  2. Remove all livestock from any exposed or adjacent buildings.
  3. Spray water to wet down the area around the silo chute to prevent the fire from spreading.
  4. Place noncombustible shields (metal siding, etc.) over any openings in the silo or chute to prevent sparks and embers from flying into or onto other buildings.

Fire Management Approaches for Various Silo Types

It is important to understand how silo fires are managed in various silo types. A fire in a conventional silo will not burn out; instead, it must be extinguished. A fire in oxygen-limiting silo may be managed so that it burns out, or it may have to be extinguished. To extinguish a silo fire, it is necessary to eliminate one of the ingredients needed for fire to occur. Trained fire service personnel are needed to extinguish a fire in any type of silo.

Conventional Silo

Because a conventional silo is not airtight, fire service personnel cannot smother the fire by eliminating the air source. The best approach is to locate the heat source and remove it. If possible, fire service personnel should avoid flooding the silo with water for the following reasons: doing so could ruin good feed; it is difficult to unload wet silage with an unloader; water can damage the silo; and the introduction of water can actually cause additional fires in the silo.

Oxygen-Limiting Silo

With proper management, you may be able to allow a fire in an oxygen-limiting silo to burn out. To reduce any additional air from entering the silo, close the top hatch cover (without latching it) and the bottom unloading door. CAUTION If the silo is heavily smoking or rumbling (vibrating), do not attempt to close the top hatch; rather stay off the silo! The assumption is that after you close the top hatch cover and bottom unloading door, no air will go into the silo, so the fire eventually will use up the residual air in the silo and burn out over time. However, this process can take up to three weeks. If this approach does not work, trained personnel—usually representatives of the silo manufacturer/dealer—can inject carbon dioxide or liquid nitrogen into the silo, causing any oxygen trapped by the silage to be consumed and allowing the fire to burn out.

A concern related to a fire in an oxygen-limiting silo is the potential buildup of confined gases within the silo. Through pyrolysis, a smoldering fire will produce large quantities of carbon monoxide and other products that can result in an explosion when combined with air from outside the silo. Consequently, you should do nothing that will cause air to go into the silo. For example, do not add water or foam or open any portals into the silo.

Modified Oxygen-Limiting Silo

For fire management purposes, you can treat an oxygen-limiting silo that has been modified through the installation of a top unloader the same way as a nonmodified oxygen-limiting silo, at least initially. However, in spite of such modification, these structures are still airtight enough to allow for a dangerous buildup of carbon monoxide in a smoldering fire. In more than one case, an explosion has occurred during firefighting operations involving a modified oxygen-limiting silo.

Additional Recommendations

  • Specialized training in proper techniques for responding to silo fires is available for fire department personnel. If your local firefighters have not had such training, encourage them to locate and participate in a training program.
  • If you no longer use a silo, make sure that it is completely empty. Residual silo material can dry out and pose a fire risk.
  • In the event of a silo fire, do not apply cool or cold water to the outside of a silo because doing so may cause structural damage.
  • After a silo fire, inspect the silo, and make any necessary repairs.


Click here for a guide to assisting firefighters at the scene of a silo fire. 

Use the following format to cite this article:
Silo fire prevention and management. (2015) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from….


Florida Forage Handbook. (2008). University of Florida Institute of Food and Agricultural Sciences (IFAS). Retrieved from

Hill, D. (2009) Silo fires—protect your investment. Pennsylvania State University. Retrieved from

Murphy, D., and Arble, W. (2000) Extinguishing fires in silos and hay mows. New York: Natural Resource, Agriculture, and Engineering Service.

Article Contributor: 
Davis E. Hill, Pennsylvania State University–
Reviewed and Summarized by:
Linda M. Fetzer, Pennsylvania State
Carol Jones, Oklahoma State University–
Dennis J. Murphy, Pennsylvania State University–
Aaron M. Yoder, University of Nebraska Medical Center–



Horizontal Silo Safety

Bunk Silo

Bunk Silo

(Source: Penn State Ag Safety and Health)


Use the following format to cite this article:

Horizontal silo safety. (2013). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from


The term horizontal silo refers to a storage system in which silage is piled in low, long piles in a space that may or may not have sidewalls. Horizontal silos vary in size depending on the scale of the farm operation. There are several common types of horizontal silos: 

  • A bunker silo (shown above) is a horizontal silo with construction-grade materials for sides.
  • A trench silo is cut into the earth. 
  • Drive-over piles are piles of silage that are dumped on the ground or a hard surface without walls.

Silo Inspection

All types of horizontal silos can have damage from wear and tear, so it is important to inspect bunker silos for cracks in the sidewalls before harvesting silage. Sidewall cracks should be repaired immediately to maintain the integrity of the wall. Sidewalls in a trench silo can slip and the floors in trench silos and drive-over piles can become muddy or rutted.

Sighting rails (shown below) made of iron or steel pipe should be installed and maintained on bunker silos to provide visual clues for the operator as he or she backs up and unloads and packs forages. Note that these railings will not prevent a tractor or truck from overturning, but they can serve as fall protection for workers placing plastic and weights on the packed silage.


Sight Rails on Bunk Silo

Sight Rails on Bunk Silo. Photo Source: Keith Bolsen, Kansas State University


Packing Safety

Silage should be packed tightly, and packing of silage should be completed quickly. Packing in this manner helps to exclude oxygen from the silage, which in turn promotes effective fermentation. In the rush to complete the packing process, especially when multiple trucks and tractors are used, the prevention of rollover incidents is a primary safety concern. To reduce the risk of a rollover incident, packers should use a safe slope or progression wedge (shown below) with a maximum slope of 3:1 (3 ft. of horizontal run to 1 ft. of vertical drop). The slope should be maintained on all sides of drive-over piles. Tractors used for packing silage should be equipped with rollover protective structures (ROPS), and operators should always wear seat belts.


Exiting Progressive Wedge Trench

(Source: Pennsylvania State University, Agricultural Safety and Health)

Some farm operations utilize dump trucks to haul forage to the silo. Like tractors, dump trucks can also overturn, so operators should always wear their seat belts and should keep the truck’s center of gravity between the frame rails of the truck. When the dump bed is raised, the truck becomes less stable, especially on uneven or sloped terrains. The following hazards can cause dump trucks to roll over:

  • Tire ruts
  • Depressions
  • Wind gusts
  • Uneven loads 
  • Low tire pressure on one side of the truck

Operating dump trucks and packing equipment away from the sidewall will help prevent damage to the sidewalls of a horizontal silo and will help reduce the risk of overturn incidents.

Once the packing process is completed, the silage should be covered with plastic and weights, requiring workers to stand or walk on the sidewalls of a bunker silo. Fall protection is necessary to reduce injury risk to workers completing this task. Fall-protection standards require that anytime workers are on a walking or working surface with unprotected sides that are 6 ft. or more above a lower level, the workers should be protected through the use of guardrails or other fall-protection systems. Sighting rails on the sides of a bunker silo can be considered guardrails if their construction meets standard handrail specifications. Click here for the specific fall-protection standard outlined by the U.S. Department of Labor, Occupational Safety and Health Administration (OSHA).

Safety Precautions during Feedout

There are several potential causes of injury during the feedout process, including the following:

  • Equipment rollover
  • Entanglement
  • Silage collapse due to undercutting

Undercutting occurs when silage-loading machines (for example, tractor front-end loaders, skid steers, and so on) are not able to reach the top of the silage face. Silage in horizontal silos can be packed to heights of 20 to 40 ft., and most pieces of equipment on traditional farm operations are too small to reach the top of the silage. If a machine is not able to reach the top of the silage and instead continually removes silage from the bottom, the process creates an overhang (shown below) that could potentially collapse and bury workers, bystanders, and equipment beneath tons of silage.

Undercut Silage Face


(Source: Keith Bolsen, Kansas State University)

One way to reduce undercutting is through the use of a silage defacer. A silage defacer has a hydraulic set of rotating knives mounted in an open framework. The defacer is mounted to a skid steer or material handler’s boom (shown below). The purpose of the defacer is to loosen silage vertically from the top to the bottom of the silage face in the horizontal silo, eliminating the undercutting that causes an overhang hazard.

NH Telehandler

(Source:New Holland North America)

Operators using a silage defacer must read the operator’s manual prior to using the equipment to understand how to operate the equipment safely. Anyone operating the silage defacer should first clear the work area of all bystanders. The defacer should be operated only from the operator’s station. The defacer should be positioned at the top of the silage feedout area before the motor is engaged. Once the motor has reached full speed, the unit should be slowly lowered to cut through the recommended depth (that is, 1 to 3 in. per pass). As with all equipment, the operator should not leave the operator’s station until the unit has been shut down, parts have stopped moving, and the keys have been removed from the ignition switch.

It is recommended that no one stand at a silage face that exceeds his or her height. Silage faces can collapse even if an overhang hazard is not present (for example, when a frozen chunk of silage breaks loose). This type of hazard is especially dangerous for individuals, such as nutritionists or students, collecting silage samples. To reduce the risk of a silage-face collapse, those collecting samples should use a loader to scoop up silage and move it away from the silage face before gathering samples from the loader bucket.

Regulations Regarding Hired Labor

Any agricultural operation employing 11 or more workers should adhere to the following standards under OSHA:

  • Rollover Protective Structures (ROPS) for Tractors Used in Agricultural Operations (1928.51): The ROPS standard requires that employees use only tractors equipped with a ROPS and seatbelt.
  • Guarding of Farm Field Equipment, Farmstead Equipment, and Cotton Gins (1928.57): This standard requires that power take-off (PTO) shafts and other moving parts of machinery and equipment be equipped with proper guarding.

The U.S. Department of Labor governs regulations regarding youth employed in agricultural operations. Youth aged 14 and 15 can be employed on farms and ranches, but they must complete a course and receive a certificate of training under the regulations of the Agricultural Hazardous Occupations Order (AgHOs) before operating tractors or powered farm equipment. AgHOs regulations do not apply to youth age 16 or older or to youth working on their own family farms. Safety training is important for all agricultural workers, but it is especially important for youth working on any farm.

Producers who hire custom operators should ensure that the operators are familiar with the farm or ranch’s fields, roads, lanes, and silage storage facilities. It is the responsibility of the farm owner or producer to provide a safe workplace for contractors and warn them of any hazards that cannot be eliminated. All custom operators that have employees should have proof of workers’ compensation and insurance coverage and should provide their workers with safety training.

Additional Safety Recommendations

Producers and workers should adhere to the following safety recommendations when working around horizontal silos: 

  • Allow only mature, experienced individuals to operate equipment.
  • Use tractors that have a low clearance and wide front end.
  • Use tractor weights to improve stability.
  • When packing on sloped surfaces, move by backing the tractor up the slope.
  • When packing, use a tractor equipped with front-wheel drive or front-wheel-assist drive for additional traction and stability.
  • When using a dump truck on the forage slope, back the truck up the slope to reduce the risk of a side overturn.
  • Do not fill a bunker or trench silo higher than the sidewalls.
  • Know where workers are located and use standard agricultural hand signals to communicate.

Use the following format to cite this article:

Horizontal silo safety. (2013). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from



Harshman, W., Yoder, A., Hilton, J., and Murphy D. (2013) HOSTA Task Sheet 3.9.2: Packing forage in a horizontal silo. The Pennsylvania State University. Hazardous Occupations Safety Training in Agriculture. Retrieved from….

Harshman, W., Yoder, A., Hilton, J., and Murphy D. (2013) HOSTA Task Sheet 6.9: Silage defacers. Retrieved from….

Murphy, D. and Harshman, W. (2007) Horizontal silo safety. The Pennsylvania State University College of Agricultural Sciences. Retrieved from


Reviewed and Summarized by:

Linda M. Fetzer, Pennsylvania State University –
LaMar Grafft, East Carolina University
Gail Lapierre, University of Vermont
Dennis J. Murphy, Pennsylvania State University (Has since retired) 
Aaron M. Yoder, University of Nebraska Medical Center –



Dangers of Silo Gases

Use the following format to cite this article:

Dangers of silo gases. (2012) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from


After harvested forages are placed in a silo, they often produce gases during the early stages of the fermentation process. Silo gases are difficult to detect because they are almost invisible, but signs of such gases may include:

  • the formation of a faint yellow or red haze that appears from the top of a conventional silo to the bottom of the ladder chute, 
  • staining on the silo and silage, and
  • a bleach-like odor that may be present even at the base of the silo and in the milking parlor.

If you detect silo gases, leave the area immediately. Physical reactions to silo gases may not be noticeable immediately after your exposure, but damage to your lungs may have already occurred. (Click here to learn more about respiratory illnesses related to farming practices in production agriculture.)

The most common silo gases are carbon dioxide (CO2and nitrogen dioxide (NO2). Types and concentrations of silo gas vary depending on whether the silo is a conventional silo or oxygen-limiting silo and how much time has passed since the silage was placed in the silo.

Conventional Silos

Conventional Silo

Conventional Silo

(Source: Pennsylvania State University. Agricultural Safety and Health)

Conventional silos are often constructed of concrete staves held together with steel hoops, but some are made of reinforced concrete, steel, galvanized tile, or brick.

The most abundant type of gas in a conventional silo is nitrogen dioxide, which has a bleach-like odor and produces low-lying yellow, red, or dark brown fumes. Because it is heavier than air, nitrogen dioxide settles on top of the silage or flows down the chute and collects in adjoining feed rooms or other low-lying areas in the barn near the base of the silo.

Nitrogen dioxide begins to form within hours after the forages are ensiled, with the amount of gas peaking about three days after harvest. From that point, the amount of gas begins to decrease rapidly.

Nitrogen dioxide is harmful because it causes severe irritation to the nose and throat, which can lead to lung inflammation. After low-level exposure to nitrogen dioxide, a person may experience very little immediate pain or discomfort but may later suffer from fluid collection in the lungs that may be fatal. Prolonged or recurring pneumonia-like symptoms can occur two to six weeks after initial exposure. Any person who has been exposed to any level of nitrogen dioxide, for even a short period of time, should seek immediate medical attention.

Oxygen-Limiting Silos


(Source: Pennsylvania State University. Agricultural Safety and Health)

An oxygen-limiting silo is constructed of dark blue or green enamel-coated steel, poured reinforced concrete, or concrete staves. Oxygen-limiting silos are designed so that entering the silo is typically unnecessary. 

In this type of silo, the fermentation process produces both nitrogen dioxide and carbon dioxide. The conditions in an oxygen-limiting silo promote greater production of carbon dioxide, which helps maintain high-quality silage.

Carbon dioxide is an odorless and colorless gas that displaces the life-sustaining oxygen in a silo. When levels of carbon dioxide are high, a person may have little warning before being overcome by this gas. 

Modified Oxygen-Limiting Silo

A modified oxygen-limiting silo is an oxygen-limiting silo that has been modified with a different type of unloading system. The unloading system is located on the top of the silage and unloads through a hollow center chute. An oxygen-limiting silo can also be modified with the addition of a conventional top-unloading system, unloading doors, and a chute along the outside of the silo tower. Silos with a top-unloading system typically have a domed roof to provide space for the tripod that suspends the unloader.

As in an unmodified oxygen-limiting silo, the respiration and fermentation process converts the oxygen in the silo into carbon dioxide. The design of a modified oxygen-limiting silo typically makes entry unnecessary.  

Decreasing the Risk of Exposure to Silo Gases in Conventional Silos

  • Ventilation: When you use a conventional silo on your farm or ranch, ventilation is the best defense against nitrogen dioxide buildup in areas of your barn and the best away to lower the risk to your livestock.

    • Provide adequate ventilation in and around your silo during the first 72 hours of silage fermentation and for at least two to three weeks after filling the silo.
    • Keep the door between the silo room and the barn closed.
    • Consider using barn exhaust fans to blow air into the silo or feed room to decrease quantities of silo gases that may have flowed down the chute.
  • Timing: Avoid the silo during critical periods when silo gases are forming. Gas concentrations are highest between 12 and 72 hours after filling.

    • If at all possible, do not enter the silo for two to three weeks after filling because of the high level of silo gases. If you must enter the silo during that time to level silage or set up an unloader, enter immediately after the last load is in and before the fermentation process begins—a period that may be only a few hours. (Follow the same precautions below if entry is required within four to six weeks after filling.)
      • Prior to entry, run the silo blower for 15 to 45 minutes and keep it running while you are in the silo.
      • Wear a self-contained breathing apparatus (SCBA) and a harness attached to a lifeline and anchor point.
      • Always maintain visual contact with a second person outside the silo.
      • If the level of the silage is low, a silo blower will not provide enough ventilation to dilute the silo gases. Do not enter the silo without wearing an SCBA.
    • Prior to entering any silo at any time, make sure that the power supply for all unloading mechanisms is locked out.
  • Personnel: Never enter a silo unless there is another person present outside the silo who can quickly get help if necessary. This person should maintain visual contact with you at all times because if you are overcome by silo gas, you may not be able to call out for assistance.
  • Personal Protective Equipment (PPE): If, in an emergency, it is necessary to enter a silo containing silage, the individual entering the silo must wear an SCBA. Click here to learn more about respiratory protection equipment. 
  • Signage: Post appropriate signage warning people of the potential for silo gases. By posting “Danger—Deadly Silo Gas” signs around the base of the silo, you are warning visitors, family members, and workers to stay away from the area.

Additional Recommendations

  • Keep children away from the silo and adjoining areas during filling and for at least two weeks after.
  • When uncovering the filler opening, stay positioned on the ground and use a rope to pull the cover off the filler opening. Remove the cover several days before you start using the silage.
  • If you begin to cough or experience throat irritation while working near a silo, move to a source of fresh air immediately.

Use the following format to cite this article:

Dangers of silo gases. (2012) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from




Atia, A. (2004) Silo gas (NO2) safety. Agri-Facts. Retrieved from$department/deptdocs.nsf/all/agdex9036/$file/726-1.pdf?OpenElement.

Cyr, D. and Johnson, S. (2002) Upright silo safety. University of Maine Cooperative Extension. Retrieved from

McFadden, M. (2011) Beware of silo gases. Michigan State University Extension. Retrieved from

Murphy, D. (2013) Silo gases—the hidden danger. Pennsylvania State University Cooperative Extension. Retrieved from .

Murphy, D. and Arble, W. (2000) Extinguishing fires in silos and hay mows. New York: Natural Resource, Agriculture, and Engineering Service.


Reviewed and summarized by
Linda M. Fetzer, Pennsylvania State University –
Dave Hill, Pennsylvania State University (Has since retired)
Dennis J. Murphy, Pennsylvania State University (Has since retired)
J. Samuel Steel, Pennsylvania State University (Has since retired)
Aaron M. Yoder, University of Nebraska Medical Center –