Since the early 1960s, nearly 150 people have died in the U.S. because of manure-related gas incidents in confined spaces (NCERA 2016). Of those cases, about half occurred on dairy operations. Almost 25% involved a young person under the age of 16. The most common activity at the time a person died was conducting repairs or maintenance on manure handling equipment (34% of the deaths) followed by actions associated with trying to rescue another person entrapped or overcome in a manure storage/reception pit (22% of the deaths) (Beaver and Field 2007).
Gases are continuously released from manure storage systems as organic compounds degrade. A variety of gases can be released from manure based on the manure’s characteristics and other compounds that may be added. The most common gases of concern are carbon dioxide (CO2), methane (CH4), ammonia (NH3) and hydrogen sulfide (H2S).
Hydrogen sulfide is the gas of greatest acute concern when agitating manure storage systems, as it can cause human health impacts (including respiratory irritation, pulmonary edema, and death) at low concentrations (see Hydrogen Sulfide Health Hazards). At concentrations as low as 0.001 ppm, H2S can have a strong rotten egg odor. While this is a good indicator of the presence of H2S at low levels, one should not rely on smell. At slightly higher concentrations, H2S can begin to affect the olfactory nerve, which is responsible for the sense of smell, preventing humans from smelling this highly toxic gas. Hydrogen sulfide can build up in stagnant air that does not disperse, resulting in increased concentrations especially during times when there is little or no air movement. Children may encounter higher exposure levels due to their proximity to the source of H2S. Children also have additional exposure risk since they have smaller diameter airways and a higher lung-surface-area-to-body-weight ratio (ATSDR 2014). Although H2S does not build up in the body, low-level chronic exposure over time can lead to a variety of physical and neurological disorders, including significant potential for eye injury and damage (ATSDR 2014).
For more information regarding agriculture safety, please visit UW-Extension Agricultural Safety & Health Information Clearinghouse and UW-Center for Agricultural Safety & Health.