Monitoring Manure Gases

Use the following format to cite this article:

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


The four main toxic gases found in manure storage areas are ammonia, carbon dioxide, hydrogen sulfide, and methane. Due to the toxicity of these gases, you must check and monitor gas levels in confined space manure storage areas prior to entering them and while in them.

Additionally, you must monitor oxygen levels to ensure that spaces contain adequate supplies of air.

Portable electronic gas monitors are available to test the levels of both toxic gases and oxygen in a confined space, but it is important to ensure that the monitor you choose will test the level of all the relevant gases.

Portable Electronic Gas Monitors

Handheld Gas Monitor

Handheld Gas Monitor

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

Depending on your budget, you can borrow, lease, or purchase electronic gas detection equipment. There are two types of gas detection devices for monitoring manure storage areas:

  • Installed monitors: Installed, or fixed, gas detection systems are typically more costly and not practical for confined space manure storage areas because such environments corrode a monitor’s electrical components.
  • Portable monitors: These devices are recommended over installed monitors because they can be stored in a protected space when not in use. They include portable electronic single-gas or multigas monitors. 

Methane is explosive at certain concentrations; hydrogen sulfide is lethal at high concentrations; low levels of oxygen can be deadly. A single-gas monitor measures only one of these components. A multigas monitor should have the capability to detect dangerous levels of hydrogen sulfide and methane and dangerously low concentrations of oxygen (0% to 30% by volume). Therefore, a monitor with multigas capabilities provides more information prior to a person entering a potentially dangerous space. 

Gas Monitors with Pumps

Some portable electronic gas monitors are equipped with pumps that allow them to test gas levels without being carried into manure storage areas. During the sampling process, the pump’s plastic tube is lowered into the storage area to within a few inches of the manure surface. The tube should never touch the manure. Measurements should be taken at multiple locations above the manure surface.

Gas levels should be tested at two locations in the confined space for different gases:

  • At the manure surface for the heavier gases carbon dioxide and hydrogen sulfide.
  • In the air approximately 12 inches below the top of the storage unit for the lighter gases ammonia and methane.

Measurements should be done prior to entry and continuously while any person is in the confined space. 

Gas Detection Badges

Another portable device is a gas detection badge, which is worn by a worker to track his or her exposure to contaminants. However, gas detection badges are not recommended for use in confined space manure storage areas because they may give inaccurate readings and they do not provide timely results. In addition, a gas detection badge may not provide readings for oxygen levels.

Gas Detector Tubes

A gas detector tube is a single-use gas detection device that provides a reading for one specific gas. Gas detector tubes do not monitor oxygen levels and provide only an approximate reading for the air being sampled.  

Maintenance of Portable Equipment

Regular maintenance, testing, and calibration of gas monitoring equipment enable it to work properly and extend its life. Maintenance and calibration are generally simple to execute. Follow the manufacturer’s recommendations when calibrating your monitor and use the certified standard gas concentrations. When possible, calibrate your monitor under environmental conditions that are similar to those where you will be using the monitor. As the device ages, calibration often becomes more difficult to complete, and you may need to replace the device or gas sensors. 

Before using a portable electronic gas monitor, remember to fully charge the device or to have fresh batteries available.

Store the device in a clean, dry, dust-free storage container. 


Use the following format to cite this article:


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



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

Steel, J., Murphy, D., and Manbeck, H. (2011) Confined space manure gas monitoring. Penn State Extension. Retrieved from


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