Gases produced during manure decomposition can build up in confined spaces and be released in deadly concentrations during agitation and pumping of slurry pits and removal of bedded-pack manure. Recent deaths of cattle in the Midwest have been attributed to lethal concentrations of hydrogen sulfide gas released during slurry manure agitation. Even more devastating are the losses of human lives resulting from manure gases.
As crops come out of fields, farmers and custom manure haulers are focused on getting manure applied before snow or frozen soils preclude application. Removing manure from storages, particularly slurry storages and pits located beneath a facility housing animals, requires careful attention and practices to avoid hazards to both workers and animals. Likewise, entering a manure pit to access equipment or other items is simply not acceptable without personal protection equipment. The following manure handling guidelines apply when working around manure storages.
Never enter a manure storage structure without proper personal protection equipment (PPE): a self-contained air supply, a safety/rescue harness, and a second person who remains outside the structure and can rescue the worker from the pit, if necessary, using the safety harness. Entering a structure to retrieve an unconscious person can easily result in multiple casualties. Being able to retrieve an unconscious person via safety harness may save their life by minimizing their length of exposure to manure gases.
Never enter livestock housing while manure is being agitated. Even when ventilation is operating, workers should avoid entering a building where a pit beneath the production area is being agitated. Entrances to buildings should be marked with caution tape or other bold signage to prevent entry by workers.
Always operate ventilation systems at their maximum capacity when agitating manure in a pit below where animals are housed. Hydrogen sulfide gas is heavier than air. In a recent report of cattle deaths during manure agitation, those animals lying down were lost to asphyxiation while those that were standing survived.
If possible, remove animals from building before manure agitation begins. If animals must remain in the buildings, monitor animals from outside the building and discontinue agitation and pumping if signs of animal stress are observed.
Be aware that hydrogen sulfide can "settle" near the ground during agitation of outdoor slurry storages, particularly when the ambient air is still and temperature is cooling. Evening and early morning conditions can produce some of the most hazardous conditions. Avoid agitation of storages under these conditions or utilize fans/blowers to mix the air and dilute gases.
To minimize release of gases during manure agitation:
- Agitate below the manure surface to minimize turbulence, which can cause greater gas releases.
- Maintain a steady agitator intensity and depth below surface, which minimizes turbulence.
- Direct agitator nozzles towards the center of the pit to avoid “churning” of manure near walls and pillars.
- Maintain at least 18” of clearance between stored manure and slatted floors to minimize hydrogen sulfide dispersion into the breather zone of animals.
Bedded-pack barns can also be a source of hydrogen sulfide release during clean-out due to the minimal oxygen present in the bedded pack. The use of gypsum for cow bedding in these systems may contribute to greater hydrogen sulfide generation. When cleaning out these types of barns: use large fans or blowers to mix air; open all available doors, windows, and other air inlets/outlets; and consider testing gas concentrations during manure removal to ensure that workers are not exposed to hazardous gas levels.
Distiller's grains contain greater concentrations of sulfur than corn resulting in greater excretion of sulfur in manure. Therefore, feeding distiller’s grains to cattle in a slatted floor or bedded pack confinement system may contribute to greater risk of hydrogen sulfide release during manure removal.
Handheld and wearable hydrogen sulfide monitors are available from a number of online sources (enter search term: hydrogen sulfide monitor) for around one hundred dollars. Less expensive “test kits” that require monitoring a color change on a piece of reagent paper are not recommended as they require a liquid sample and cannot be used to monitor the changing gas concentration during manure removal activities. While the initial investment for a handheld monitor may seem high, being able to determine if lethal concentrations of hydrogen sulfide are present in and around livestock housing and manure storage facilities is priceless when it comes to protecting the lives of people and animals.
Amy Millmier Schmidt, Nebraska Extension Livestock Bioenvironmental Engineer
University of Nebraska–Lincoln
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