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Module 7: Manure Pit Safety


Of the approximately 2 million farms in the United States [USDA 2022], an unknown number contain manure pits or tanks.  Manure pit systems are used primarily on livestock farms (including dairy operations) to allow for the easy cleaning of animal confinement buildings and the efficient underground storage of large amounts of raw manure.  Because large areas of the confinement building can be cleaned with a water hose or other similar methods, such handling of manure is more efficient than the historical method of shoveling solid animal waste.  

Inside the pit, the manure undergoes anaerobic digestive fermentation to form fertilizer.  The digestive process can generate four potentially dangerous gases.  The accumulation of these gases within the confined space of the manure pit can produce an oxygen-deficient, toxic, and/or explosive environment.

Often, these farms use manure as a fertilizer.  The manure in the pit is agitated, pumped into a manure spreader, and spread.  Manure contains valuable nutrients that helps feed crops grow.

Recognizing the Hazard

Common manure pit hazards are:

  • Atmospheric
  • Immersion
  • Machine-related.


  • The most dangerous gas associated with a manure pit.
  • Accumulates low in the space because it is heavier than air.
  • H2S smells like rotten eggs initially, but deadens your sense of smell.
  • At high levels, H2S affects the nerves that make you breathe.
  • H2S is flammable.
  • Odorless and colorless.
  • CO2 displaces breathable air.
  • Like H2S, it is heavier than air and accumulates low in the space.
  • Has a distinct smell, and burns your eyes, nose and throat.
  • Found in almost all animal storage buildings.
  • Heavier than air and accumulates close to the ground also.
  • Methane is odorless and lighter than air.
  • Methane is highly flammable and explosive when it accumulates in a space.


Manure can also be stored as a liquid in areas like this.  Be sure that there is appropriate fencing and signage.


The consistency of manure in these pits makes rescue much more difficult than from ponds or water.


Equipment used to agitate or pump manure from the pit can break, jam, or otherwise need servicing or maintenance.


Only persons trained and properly equipped to work on the equipment should do so.

Evaluate & Control the Hazards

Dangerous gases may accumulate anywhere manure accumulates and breaksdown.  Using your sense of smell is no way to judge how much of a particular gas there is.  


Purchasing a monitor to check for gases may be a life saver.  Units like these can monitor several gases at one time.  

Check access points to manure pits or ponds and make sure there are secure to prevent someone from entering.  

Perform regular maintenance on pumps and other pit related equipment.  When equipment fails, you don't want to make the mistake of thinking it will ba a quick fix and the gases won't harm you.