Iowa State University Extension and Outreach 11/9/16

Denise Schwab ...

Denise Schwab
Extension Beef Specialist

We have heard several reports of cattle deaths while pumping pits, but fortunately no human deaths. The following information comes from Dan Anderson and Jay Harmon from Iowa State University's Department of Agricultural and Biosystems Engineering. They discuss the dangers of gases that can be released when agitating and pumping liquid manure.

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.

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.

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 blocks 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.

Don’t agitate until the manure level is one-and-a-half to two feet below the slats. 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.

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. 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.

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