Liquid manure storages are anaerobic systems, meaning without oxygen. As organic material in the manure breaks down, the lack of oxygen in the manure liquid promotes hydrogen sulfide, methane and other gas formation. Hydrogen sulfide is more prevalent when the manure is stored for longer than 21 days, and when the water contains high amounts of sulfur.
Hydrogen sulfide exposure results in significant health problems (Table 1). Methane is a fire/explosion hazard when it reaches flammable limits of 5 to 15 percent by volume. While not always present, foam on the manure surface is an indication of methane and other manure gas production. These dangers are present for both humans and animals in the barn.
Table 1. Human health effects or symptoms from exposure to hydrogen sulfide (H2S)
|H2S exposure level||Expected effect or symptom|
|0.13 to 30 ppm||
|100 to 150 ppm||
|200 to 500 ppm||
|600 ppm +||
When the manure is mixed, through agitation, pumping or other activities like power washing, the pockets of gas formed beneath the manure surface “burst” and move into the airspace above the manure. Actions that reduce the amount of disruption at the manure surface, like keeping the jet of pressurized manure below the liquid surface, lessens the opportunity for gases like hydrogen sulfide to escape.
While we understand some of the risk factors for manure gas production, the release and movement of the gases are not predictable. Therefore, we must always take precautions when working around stored manure.
Table is adapted from “Hydrogen Sulphide Awareness for Liquid Manure Handling Systems,” Prairie Swine Centre Inc. 2004.
Reviewed in 2019