The Occupational Safety and Health Administration (OSHA) defines a confined space as a space that:
Confined spaces on a farm or ranch in which manure handling may occur include manure pits, manure transfer pipes and deep gutters, transfer storage areas, and liquid manure spreaders. Farms and ranches continue to expand their operations to include larger manure handling systems. While these new systems are more efficient and reduce manual labor, farmers and ranchers must understand the hazards associated with working in and around confined spaces where manure is stored.
The breakdown of manure is a biological process, and environmental factors such as temperature, humidity, and air flow can impact the release rate of gases produced during this process. High temperature, lack of air exchange, and humidity can increase the levels of manure gases that are produced and released. The following hazardous gases form naturally in manure storage areas and are difficult to detect because of their properties, impact on a person's sense of smell, and similarity to other odors on a farm or ranch:
Handheld gas detection equipment should be used to monitor gas levels prior to entry into and while occupying confined-space manure storage areas. Some equipment used to detect manure gases is configured to measure oxygen level, explosive gases (methane), and toxic gases (hydrogen sulfide).
For each of the hazardous gases mentioned above, OSHA has identified safe exposure levels for humans. Table 1 outlines the acceptable exposure limits in ppm over an eight-hour period. The oxygen level in a given space should be between 19% and 23%.
|Hazardous Gas||Acceptable Exposure Limits|
|Carbon dioxide||5,000 ppm|
|Hydrogen sulfide||10 ppm|
One way to reduce levels of hazardous gases is to ventilate the manure storage area using a mechanical ventilation system that forces fresh air into the space, increasing the oxygen level and decreasing the levels of explosive and toxic gases. By using a specially designed positive-pressure mechanical forced-air ventilation system, you can reduce the buildup of dangerous levels of gas. Forcing fresh air through a fan into the storage area reduces the possibility of fire or explosion caused by explosive gas coming into contact with electric fan motors. Fans should be able to move a volume of air equal to one-half the volume of the empty manure storage area every minute. Use the ANSI/ASABE S607 standard, provided by the American National Standard Institute (ANSI) and American Society of Agricultural and Biological Engineers (ASABE), for guidance about ventilation capacity and ventilation time prior to entry and during occupancy. Click HERE for more information from Penn State Extension about the standard. To avoid the failure of a critical ventilation system during a power outage, connect the system to a standby power source that is regularly maintained and tested.
If possible, avoid entering confined-space manure storage areas. If entry is unavoidable, you should fully understand the risks of entering such a space and have an entry plan that outlines your actions.
Complete the following steps when entering and working in a confined-space manure storage area:
See the Penn State Extension video below to learn more about safety concerns associated with manure storage in confined spaces.
Confined space: Hazards of manure gases. (2012) Farm and Ranch eXtension in Safety and Health (FReSH) Community of Practice. Retrieved from http://www.extension.org/pages/63141/confined-spaces:-hazards-of-manure-....
Confined spaces. (n.d.) United States Department of Labor. Retrieved from http://www.osha.gov/SLTC/confinedspaces/index.html.
Harshman, W., Yoder, A., Hilton, J., & Murphy, D. (2004) Confined spaces. HOSTA task sheet 3.8. National Safe Tractor and Machinery Operation Program. Retrieved from http://www.extension.org/sites/default/files/NSTMOP%20Task%20Sheets%20Se....
Harshman, W., Yoder, A., Hilton, J., & Murphy, D. (2004) Manure storage. HOSTA task sheet 3.11. National Safe Tractor and Machinery Operation Program. Retrieved from http://www.extension.org/sites/default/files/NSTMOP%20Task%20Sheets%20Se....
Steel, J., Murphy, D., & Manbeck, H. (2011) Confined space manure storage hazards. Penn State Extension. Retrieved from http://extension.psu.edu/business/ag-safety/confined-spaces/manure/manur....
Zhao, L. (2007) How to work safely around manure storage. Ohio State University Extension. Retrieved from http://ohioline.osu.edu/aex-fact/pdf/0739.pdf.