Pit Gases Pose a Danger in Beef Barns

Gas can be released during times of agitation and pumping and can be potentially dangerous

November 2, 2016, 1:37 pm | Daniel Andersen, Jay Harmon

Dan Anderson and Jay Harmon from Iowa State University's Department of Agricultural and Biosystems Engineering discuss the dangers of gases that can be released when agitating and pumping liquid manure. They offer strategies for safe agitation and ventilation. Anderson is an assistant professor and agricultural engineering extension specialist. Harmon is a professor and extension livestock housing specialist in agricultural engineering.

Pit GasesAMES, Iowa – Hydrogen sulfide gas is a serious issue both in and around barns with liquid manure storage. The decomposition of organic matter in manure results in the release of several gases: ammonia, carbon dioxide, methane and hydrogen sulfide among them. Most of the time these gases are emitted at low levels, but any time manure is being agitated or pumped, or the surface is disturbed, hydrogen sulfide can be rapidly released.

Although all are potentially dangerous, hydrogen sulfide tends to be the most concerning in these cases. Hydrogen sulfide has an intense rotten egg smell, so it is relatively easy to detect its presence, even in very low concentrations, but people quickly suffer olfactory fatigue and lose the ability to smell it. This makes it necessary to use analytical instruments to detect dangerous levels.

Consider monitoring equipment for safety

Hydrogen sulfide monitors can be purchased to help keep those working around manure safe. A monitor, which is small enough to wear, ranges in cost from $99 to $800 and will alert you if the situation is dangerous. There are numerous options available for monitoring hydrogen sulfide levels when working with manure. Below are links to five meters to consider. These meters typically have audible alarms that will sound an alert as dangerous concentrations develop.

  • Honeywell GasAlertMax XT II
  • BW Honeywell GasAlert Clip Extreme GA24XT-H
  • BW Honeywell GasAlert Micro Clip XL 4-Gas Monitor
  • Draeger Pac 3500 H2S Monitor
  • RAE Systems ToxiRAE II

Neither endorsement of companies, individuals or their services mentioned is intended, nor is criticism implied of similar companies, individuals or their services not mentioned.

Best tips for agitation

Hydrogen sulfide can spike quickly and without warning during pit pumping. This can result in hazardous concentrations for both the animals and the farm employees around the facility. Aggressive agitation can contribute to the risk of gas spikes when agitation first begins and when the pit becomes nearly empty. The manure agitation technique used can make a big difference in how much, and how quickly, hydrogen sulfide is off-gassed from the manure.

People should NEVER enter a building being pumped. Use yellow caution tape to mark barn entrances to block door or consider lockout tags during pumping. If possible, remove animals before pumping. For barns with multiple pits, move cattle out of the room with the pit being agitated.

Following are a few best practices regarding manure application.

Agitation strategy

  • Don’t agitate until the manure level is 1.5 to 2 feet below the slats. Hydrogen sulfide is denser than air and as a result will tend to pool on the manure surface; sufficient separation is required to minimize hydrogen sulfide in the animal breathing zone.
  • Avoid aggressive agitation when animals are in the building (no rooster tailing). Surface agitation causes more turbulence and greatly increases the release of hydrogen sulfide.
  • Do not direct agitator nozzles toward pillars, walls or toward a corner. Pillars and walls stop flow quickly and cause the manure to churn, increasing the rate hydrogen sulfide is off gassed from the manure. Corners are often dead air zones; releases of hydrogen sulfide in this area are more likely to result in animal loss
  • Stop agitating when bottom nozzle is less than 6 inches below the manure surface. Keep the agitation below the surface at all times.
  • Avoid sudden changes in agitator depth and intensity. Quick changes can result in large amounts of solids that haven’t previously been agitated and result in rapid gas release. Slower changes in power, flow direction and depth allow for a slower, more continuous release that is safer for animals and workers.


  • Ventilation should be maximized during agitation.
  • Back-wall curtains should be completely opened to allow maximum air flow.
  • A cross wind (through the barn) of at least 7.5 mph is recommended. Wind velocity must maintain this speed and be directed through the barn. If the wind direction is at an angle to the barn, 10 mph wind speeds or greater are recommended.
  • Watch for changing weather conditions, as many times night air is more still than daytime air.
  • Warming air can help disperse hydrogen sulfide; cooling air causes it to settle and pool. As hydrogen sulfide is heavier than air, this can create dangerous conditions.
  • Consider using PTO driven fans to provide extra ventilation. If conditions are calm, use large, PTO driven fans to increase ventilation and air exchange.
  • If present, turn on stir fans in the barn. This moves air around and will decrease the chance of air “dead zones” where inadequate ventilation exists.

Consider adding pump out curtains (tarps) around the manure agitator to limit air exchange of hydrogen sulfide gas near the applicator. This curtain blocks some of the pit air from swirling back towards the pump operator.

For more information on this topic or other manure related issues, please contact the Iowa Manure Management Action Group.

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