Ventilation Systems for Confined Space Manure Storage

Pig Barn with Slotted Floor

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


Use the following format to cite this article:

Ventilation systems for confined space manure storage. (2013). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from


Ventilation is crucial in reducing risk exposure when entering a confined space manure storage. A manure storage is considered a confined space based on the criteria established by the Occupational Safety and Health Administration (OSHA). OSHA defines a confined space as 1) being a large enough space and configured in such a way that an employee can bodily enter and perform assigned work; 2) having limited or restricted means for entry or exit; and 3) not designed for continuous employee occupancy.

The following hazards exist in a confined space manure storage:

  1. Lack of oxygen,
  2. Toxic and flammable gases, and
  3. Potential exposure to drowning.

Ventilation Recommendations

The four main types of gases that can be in a manure storage area include hydrogen sulfide, ammonia, methane, and carbon dioxide. Ventilation of the area is recommended to decrease the level of these gases and to replenish the oxygen level in the manure storage.

Ventilation recommendations are based on the ANSI/ASABE S607 standard that was approved in October 2010 by the American Society of Agricultural and Biological Engineers. This standard was developed to reduce risk from asphyxiation, poisoning, and explosions prior to entering a confined space manure storage by specifying the positive pressure, forced ventilation requirements for the manure storage.

The type of flooring that is selected is based on the construction details of the facility and the type of animals being housed. Flooring type affects the type and design of ventilation systems to maximize air movement. The three main types of manure storage flooring and covers are solid, totally slotted, and partially slotted. A solid cover storage can be located beneath or outside the animal housing facility and may have a square, rectangular, or circular footprint. Rectangular and square storage footprints are typically used for partially and totally slotted floors that are located directly below the animal’s living area.

When a manure storage is being ventilated at an air exchange rate of 1.5 AC/m, the ANSI/ASABE S607 standard provides calculated times required to reduce hazardous gases to an acceptable level and to replenish the oxygen level from 0% to 20% within each type of manure storage tank. The standard also provides transformation equations or adjustment factors for alternative ventilation strategies, changes in AC rate, initial gas concentration levels lower than maximum documented levels, and differing fresh air intake locations. Click here for detailed information about calculated ventilation times, adjustments to calculated ventilation times, and information concerning the evacuation of animals from slotted-cover manure pits prior to ventilation.


The ANSI/ASABE S607 standard was designed to reduce the risk of entry into manure storages. In addition to recommended ventilation procedures, agricultural producers and workers should follow these recommendations:

  • Properly post warning signs near the entrance to confined space manure storage facilities.
  • Maintain ventilation instructions near the confined space manure storage for easy access in an emergency situation.
  • Never work by yourself when entering a storage. A second person who does not enter the confined space is needed.
  • Always monitor the gas levels in the storage before and during the entry event.
  • Ventilate the storage for the rate and time outlined in ANSI/ASABE S607 before and during the entry event.
  • Always use a safety harness and emergency retrieval system when entering a confined space manure storage.


To better understand strategies for reducing entry risks, view the following videos from the Pennsylvania State University:

Reducing Risk When Entering a Confined Space Manure Storage

Manure Storage Ventilation Demonstration: Slotted Floor Storage

Manure Storage Ventilation Demonstration: Solid Covered Storage


Click HERE to visit the Manure Pit Safety page by the Pennsylvania State University for additional information including fact sheets, manure pit standards and regulations, and the manure pit safety demonstration trailer.

Click on an article title below to be directed to an article from the Farm & Ranch eXtension in Safety and Health (FReSH) Community of Practice:

Confined Spaces Manure Storage Emergencies

Confined Spaces Manure Storage Hazards

Confined Spaces Manure Gas Monitoring



Use the following format to cite this article:

Ventilation systems for confined space manure storage. (2013). Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from




Manbeck, H., Murphy, D., & Steel, J. (2011) Confined space manure storage ventilation systems. Pennsylvania State University. Retrieved from


Reviewed and Summarized by:
Linda M. Fetzer, Pennsylvania State University –
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 –

Confined Spaces: Emergencies and Rescue

Use the following format to cite this article:

Confined space: Emergencies and rescue. (2012) Ag Safety and Health eXtension Community of Practice. Retrieved from

Entering a confined-space manure storage area can be deadly. Farm and ranch managers, family members, and employees must have a complete understanding of what to do in the event of a confined-space emergency and ways to avoid such an incident.

If you find a victim unresponsive in a manure storage area, immediately call 911. Inform the operator that the incident involves a person in a confined-space manure storage area so that the appropriate emergency response personnel can be dispatched to the scene. Emergency responders trained in confined-space rescue will be equipped with the necessary rescue apparatus and gas detection equipment. Do not enter the manure storage area under any circumstances.

While waiting for an emergency response team, ventilate the area by blowing fresh air into the space, moving the toxic air away from the victim. Keep a ventilation fan readily available specifically for such emergencies. When using a fan, be aware of the following recommendations:

  • Do not use typical barn or home fans to ventilate manure-storage areas because they may emit sparks from static electricity or an electrical short. If flammable methane gas has collected in the storage area, a spark could cause a fire.
  • Never attempt to get fresh air closer to the victim by lowering a fan into the confined space.
  • Make sure that the ventilation fan does not blow the manure gases back toward you, affecting your breathable air.

Preventing Confined-Space Manure Storage Emergencies

Take the following precautions on your farm or ranch to reduce the risk of a confined-space manure storage emergency:

  • Warning Signs: Post warning signs (example is shown below) about the risks of confined spaces and gas hazards at the openings to manure storage areas. Include warnings against walking or driving on crusted manure surfaces.

    Confined Space Sign

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

  • Limited Access: Limit access to manure storage areas to authorized personnel. Take these specific steps to keep people away from manure storage areas:
    • Equip exterior ladders with locking mechanisms.
    • Remove temporary-access ladders from areas surrounding aboveground tanks.
    • When manure storage areas are open, place barricades at the openings of storage areas.
    • Install and maintain fencing around uncovered ground-level storage areas such as manure ponds or lagoons.
  • Education: Educate employees, family members, and visitors about the hazards associated with manure storage in confined spaces.
  • Entry Plan: Prepare and document an entry plan for entering confined spaces where manure is stored. Review the entry plan annually with all employees and family members. The entry plan should include specific physical details about the confined space, descriptions of potential hazards, reasons for entry, procedures for entry, and procedures to follow during emergencies.
  • Two-Person Minimum: Require that two people be present for any confined-space entry and that both individuals be trained in entry and rescue techniques. The person outside the manure storage area should maintain verbal and visual contact with the person inside the confined space at all times. The person outside the storage area should be available to summon help and to implement the rescue and retrieval system if necessary. This person should not enter the manure storage area, even in the event of an emergency.
  • Gas Detection: Use gas detection equipment to monitor oxygen levels and levels of explosive and toxic gases in the confined space.

Gas Monitor

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

  • Ventilation: Prior to entry, ventilate the confined-space manure storage area for a minimum of 15 minutes and continue ventilation during entry and occupancy. A positive-pressure ventilation system is recommended because of the reduced risk of fire or explosion.
  • Body Harness: Require that the person entering the manure storage area carry a portable gas monitor and wear an adjustable body harness with a lifeline attached to a rescue and retrieval system. A typical rescue and retrieval system uses a tripod device equipped with a winch to limit a person’s fall and retrieve a person who has been incapacitated.
  • Power-Source Lockout: To reduce the risk of stray electricity, prior to entry, lock out all power sources in the confined-space manure storage area other than the positive-pressure ventilation system.

Additional Safety Recommendations

  • Remember that youth under the age of 16 are prohibited from working in confined spaces.
  • Provide training about the hazards associated with confined-space manure storage to every person working on, living on, or visiting the farm or ranch.
  • Ventilate manure storage areas appropriately to increase oxygen and decrease explosive and toxic manure gases.
  • Remove personnel and animals from the confinement building during manure storage agitation or pumping. If you are unable to remove the animals, maximize ventilation and begin agitating very slowly while monitoring the animals for abnormal behavior.
  • Prohibit smoking in and around manure storage areas.
  • Operate manure agitators below the surface of liquid manure to reduce the release of manure gases.
  • Leave 1 to 2 cu. ft. of space above the manure to contain released gases. If you are unable to leave the recommended space, lower the manure level prior to agitation.

Use the following format to cite this article:

Confined space: Emergencies and rescue. (2012) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from


Hallman, E. & Aldrich, B. (2007) Hydrogen sulfide in manure handling systems: Health and safety issues. Cornell University Manure Management Program. Retrieved from

Hill, D., Murphy, D., Steel, J., & Manbeck, H. (2011) Confined space manure storage emergencies. Penn State Extension. Retrieved from

Ogejo, J. (2009) Poultry and livestock manure storage: Management and safety. Virginia Cooperative Extension. Retrieved from

Reviewed and Summarized by:
Linda M. Fetzer, Pennsylvania State University –
LaMar Grafft, East Carolina University –
Davis E. Hill, Pennsylvania State University – (has since retired)
Dennis J. Murphy, Pennsylvania State University – (has since retired)
Aaron M. Yoder, University of Nebraska Medical Center –

Manure Foaming

Foaming Manure

Foaming Manure – Source: Schimdt, UMN.


Use the following format to cite this article:

Manure foaming. (2012) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from


Foam in manure pits can be a danger both to animals and workers around the pits. Manure foaming occurs primarily in hog facilities, most commonly in the midwestern United States and Canada. The causes of manure foaming remain a mystery. Manure foaming is not predictable, and no known solutions work in every situation. It is therefore important to understand the risks posed by foaming manure and ways to reduce those risks.

Foam is defined as a mass of bubbles of gas on the surface of a liquid. Rather than being crusty or fluffy, foaming manure has a thick, mucous consistency. In manure pits, the bubbles do not burst but rather cling together.

One theory suggests that a specific microbial population causes foaming in manure pits. Another theory suggests that filamentous microorganisms (bacteria, fungi, or algae) are the cause. Neither theory has been confirmed, and research into the causes of manure foaming continues. Possible triggers include a high content of manure solids resulting from water conservation practices; cool weather patterns; reduced antibiotic use; feeding or diet adjustments; changes in DDGS; changes in corn, including genetic modifications; moldy and/or lightweight corn; and changes in the type or quantity of fat fed to the animals. 

Dangers of Foaming Manure

Foam in manure pits may be linked to suffocation of hogs and incidents of fire and explosion. Methane (CH4) and hydrogen sulfide (H2S) are gases produced during the anaerobic breakdown of manure. Methane is a highly flammable gas that can lead to asphyxiation at high levels. The foam in manure pits captures methane, resulting in concentrations of methane in the foam that can be as high as 60% to 70% (600,000 to 700,000 ppm), which is higher than the concentration at which explosions can occur. When the foam bubbles are disturbed or broken, the captured methane is released at an explosive concentration of 5% to 20% (50,000 to 200,000 ppm). If there is an ignition source near an explosive concentration of methane, an explosion or a flash fire could occur. 

Hydrogen sulfide is a colorless gas that smells like rotten eggs at low levels but can overcome a person’s sense of smell at levels of 100 ppm or higher. Hydrogen sulfide is heavier than air and can collect in the floor or lower areas of the pit. Exposure to hydrogen sulfide can cause eye and nose irritation, headache, nausea, and death.

In addition to the danger of explosion or fire, foaming manure poses an asphyxiation risk for both people and hogs when foam rises through the slats in a barn. Anyone working within the building or in the immediate area should be informed about the dangers of foaming manure, including the hazards of methane and hydrogen sulfide. No smoking should be permitted in or near the building.

Methods of Treatment

There are no proven ways to prevent manure foaming; at present, the focus remains on treating the symptoms. Below are some treatments that have yielded mixed results:

  • Water – Spraying water, running sprinklers, or using soaker systems can break the bubbles in foam, releasing the methane in a relatively safe manner. If you are using water to break down foam, remember to follow recommended ventilation practices.
  • Antifoam agents – There are several antifoam agents on the market. Although some have had limited success in reducing foam, none have proven effective on a consistent basis.
  • Microbial enhancements – Microbial enhancements, typically in the form of feed or manure additives, have been effective on an inconsistent basis.
  • Microbial control – Microbial control refers to changes in pH or oxygen levels or the use of antibiotics.

Due to the unpredictable nature of manure foaming, you should complete an audit of manure pits at least once a month. The purpose of the audit is to monitor pits for changes in manure consistency, increases in foam, and other such indicators of a potential problem. Based on information gathered in the audit, you can make necessary management decisions about using a treatment or changing the pumping schedule.

Emergency Action Plans

Develop an emergency action plan and review it annually with employees. It is especially important that anyone on-site during pit pumping receive training about the action plan. The emergency action plan should include a list of clean-up and containment practices in the event of an overflow, breach, leak, fire, or emergency land application. Due to the potential risk of fire or explosion, include in the action plan an evacuation route for employees. In addition, make sure that all employees know the location of fire extinguishers, hose cabinets, fire blankets, and other types of safety equipment. As a farm or ranch manager, make sure that you have necessary safety equipment and that it is in proper working order.

During pit pumping, remember to keep on hand the contact information of first responders, including the fire department, hospital, and police. When calling 911, give your name, location, contact information, and details about the emergency. 

Precautions during Agitation and Pumping

When foaming manure is present, the risk of explosion necessitates additional precautions during pit agitation and pumping. It is strongly recommended that you pump manure pits when the barn is empty. People should remain outside of the building during agitation and pumping. After checking that everyone is out of the facility, add a physical barrier such as yellow caution tape or place warning signs to ensure that no one enters the facility during the process.

Any ignition sources should be turned off and locked out. Possible ignition sources include welders, heaters, motors, and other equipment, such as a feeding system, that uses electricity. (Because of the importance of ventilation, discussed in the next section, ventilation systems that use electricity may operate during agitation and pumping.) 

Do not agitate the manure until the top of the manure surface is at least two feet below the floor slats. Agitate the manure below the surface of the liquid manure and stop the process if you can no longer agitate below the surface level. Agitate intermittently to reduce the risk of sudden gas release.

When possible, cover pump-out ports unless they are needed for agitation or manure load-out, and cover the pump-out around the agitation with a tarp. After pumping is complete, remember to secure manure pit covers.

Ventilation during Agitation and Pumping

Proper ventilation is one of the most important safety measures during agitation and pumping of manure pits. Regularly check your ventilation system to ensure that it is in proper working condition. Use a ventilation rate of 20 to 30 cfm per animal to dilute the methane concentration below 5%. Ventilation inlets, curtains, and pivot doors should be open during the ventilation process. For naturally ventilated barns, make sure that inlets and outlets are open. Circulation fans used in the summer do not provide the necessary air exchange needed during agitation or pumping, so plan these processes for days when wind is present to increase the amount of fresh air circulating through the building.

Ventilation for Curtain-Sided Barns

Ventilation procedures for curtain-sided barns differ slightly depending on weather conditions. When the weather is warm with winds over 5 mph, run exhaust fans while the curtains are open. On a calm day, the sidewall curtains should remain closed with the fans running. If, however, you are running more than half of the fans, the curtains should remain open during the pumping process. During colder weather, keep the curtains closed while running the exhaust fans.

If you are using a stir fan, use a horizontally directed fan rather than a fan directed downward, to reduce pockets of gas concentrations and to ensure that contaminated gas does not blow back onto hogs. Ventilate for approximately one to two hours after pumping and prior to entering the barn.

Ventilation for Tunnel-Ventilated Barns

During warm or hot weather, run all of the pit fans and a minimum of two tunnel fans. The procedure is slightly different for cold or moderate weather, but you should nevertheless run all of the pit fans and the 36 in. fan and open the tunnel curtain approximately 6 to 12 in. to provide air movement through the entire length of the barn. Remember to reduce the static pressure of the inlet velocity at the tunnel curtain from the regular setting of 800 fpm to 1,000 fpm to a lower setting of 300 fpm to 400 fpm. During both cold and hot weather, partially close mechanized/motorized ceiling inlets to allow air to enter from the tunnel curtain. Ventilate for approximately one to two hours after pumping and prior to entering the barn.





Click here to watch an informative video by Dr. David Schmidt from Iowa State University Extension about foaming manure pits.


Use the following format to cite this article:

Manure foaming. (2012) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from



Burns, R. & Moody, L. (2009) Literature review – deep pit swine facility flash fires and explosions: Sources, occurrences, factors, and management. Iowa State University Department of Agricultural and Biosystems Engineering. No longer available online.

Foaming manure. (2011) Ontario Ministry of Agriculture, Food, and Rural Affairs. Retrieved from

Jacobson, L. (n.d.) Safety measures to prevent barn explosions during pit pumping. University of Minnesota Extension. Retrieved from….

Rieck-Hinz, A., Shouse, S., & Brenneman, G. (2010) A top ten list: Preparing for fall manure application. Iowa State University, Iowa Manure Management Action Group. Retrieved from

Understanding foam and pump-out safety. (2010) Iowa Pork Producers Association. No longer available online.


Reviewers, Contributors and Summarized by:
Linda M. Fetzer, Pennsylvania State University –
LaMar Grafft, East Carolina University –
Davis E. Hill, Pennsylvania State University (Has since retired)
Dennis J. Murphy, Pennsylvania State University (Has since retired)
Ron Odell, Cactus Feeders, LTD. –
Cheryl Skjolaas, University of Wisconsin –
Aaron M. Yoder, University of Nebraska Medical Center –