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Manure gas dangers during liquid manure agitation and pumping

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
  • Eye irritation
  • Odor is obvious and unpleasant
50 ppm
  • Dryness and irritation of the nose and throat
  • Prolonged exposure may cause a runny nose, cough, hoarseness, shortness of breath and pneumonia
100 to 150 ppm
  • Temporary loss of smell
  • Immediately dangerous to life and health
  • Gas seems odorless due to loss of smell
200 to 500 ppm
  • Severe irritation, headache, nausea, vomiting and dizziness
  • Prolonged exposure may cause lung damage
  • Exposure of 1-8 hours can cause death
500 ppm
  • Excitement, headache, dizziness, staggering, unconsciousness and respiratory failure occurs in 5 min to 1 hour
  • Death can occur in 30 min to 1 hour
600 ppm +
  • One or two breaths with as little as 600 ppm can cause a person to lose consciousness
  • Continued exposure can kill

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.

Erin Cortus, Extension engineer

Reviewed in 2019

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