Structures for storing manure are necessary on nearly all livestock feeding operations. They provide a way to contain and even treat manure during times when land application of manure is not feasible.
But, as organic matter in manure decomposes, gases that can be harmful or even fatal to humans and animals are produced. These include ammonia, carbon dioxide, methane and hydrogen sulfide. While mechanical and natural ventilation do much to dilute these harmful gases, dangerous conditions can exist in and around manure storages.
Taking time to understand, assess and address potential risks is critical to avoid unnecessary injuries or loss of lives among workers and animals.
“The first step to staying safe around manure storage facilities is to avoid working alone,” Amy Millmier Schmidt, Associate Professor & Livestock Manure Management Engineer at the University of Nebraska-Lincoln, says. “Having a second person available to respond if someone falls into a storage structure or is overcome by dangerous gases could, quite frankly, mean the difference between life and death.”
Along with working in pairs, Schmidt adds, it is critical to assess air quality before entering a manure storage space and avoid entering an area having dangerous gas levels or insufficient oxygen without proper personal protective equipment.
Hydrogen sulfide, with its characteristic "rotten egg" smell is arguably the most dangerous gas that can accumulate in an area of stored manure. Because it is heavier than air, it can collect in the lower levels of a structure and in areas where air movement is not sufficient.
“Even in outdoor slurry storages, hydrogen sulfide released during agitation of the stored manure can settle near the ground around the storage, creating potentially dangerous concentrations of this deadly gas,” Schmidt says. “Evening and early morning conditions – or any time the air is still and temperatures are cool – can produce some of the most hazardous conditions. If you can’t avoid agitation of these types of storage under adverse conditions, use fans or blowers to stir the air and dilute gases.”
Schmidt notes that slurry tank wagons used to haul manure can also accumulate dangerous concentrations of hydrogen sulfide gas if manure remains in them. “No one should ever climb inside a tank wagon to clean it out without first monitoring air quality conditions,” she advises.
At low concentrations, hydrogen sulfide causes paralysis of nerve cells in the nose, deadening the sense of smell. At 500 ppm, rapid loss of consciousness occurs, and death can follow within minutes.
Even brief exposure to high concentrations of hydrogen sulfide can result in reactions that occur within 24 hours. Symptoms include buildup of fluid in the lungs, which may lead to death. Other long-term neurological effects are also possible.
Ammonia has a sharp and distinct odor that is often irritating to the nose, eyes and throat. While it can be deadly at high concentrations (1000 parts per million or greater), most people will leave the area of ammonia accumulation to seek relief before being exposed to dangerous levels.
Methane is an odorless gas that is lighter than air. The most prevalent safety risk associated with methane is combustion. Explosions or flash fires are of greatest concern where manure is covered or contained without sufficient ventilation to dilute and remove methane. This can include deep pit storages beneath slatted floors, and storages with impermeable covers. From a human respiratory perspective, methane that isn't properly ventilated can cause headaches and lead to unconsciousness and death.
Carbon dioxide is also odorless and heavier than air. Like hydrogen sulfide, it can accumulate in low-lying and stagnant areas in and around storages. The greatest risk associated with carbon dioxide is asphyxiation (suffocation) when it displaces oxygen in the air. Even moderate concentrations can lead to shortness of breath and dizziness.
“Again,” Schmidt reiterates, “taking appropriate precautions is absolutely essential to avoid being injured or killed in and around manure storages.”
For open storages at ground level, like lagoons or other in-ground storage basins, drowning is a risk. Fencing to limit access to these types of storages and signage to deter entry without proper equipment and training are simple, yet effective, methods to improve safety. Accessibility to a life preserver or rescue rope are highly recommended.
For enclosed storages, Personal Protective Equipment (PPE) essential to worker safety includes a self-contained air supply, a safety/rescue harness and a second person who remains outside the structure to help rescue the worker if necessary.
“It is absolutely tragic to lose multiple lives when individuals enter an enclosed storage area to rescue someone who has become incapacited, only to be overcome by dangerous gases themselves,” Schmidt says. “Having a rescue harness that can be used to pull someone out of a dangerous situation, and, just as importantly, having the mental wherewithal to utilize that recovery tool rather than jumping in to help the person who is in danger is absolutely critical.”
Handheld and wearable gas monitors are available at a range of prices, from $150 to over $1,000, depending on their capabilities. A gas monitor with a hose provides the ability to sample air quality in an area without physically entering. Handheld or wearable sensors can allow a person to monitor conditions while in the storage. 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.
“The initial investment for a handheld monitor may seem high,” Schmidt says. “However, being able to determine if lethal concentrations of hydrogen sulfide or insufficient oxygen are present in and around livestock housing and manure storage facilities is priceless when it comes to protecting the lives of people and animals.”
If a worker does not own monitoring equipment, contacting local Fire and Rescue teams is recommended. These team members, who are trained and have equipment to complete thorough testing of air quality, may be able to help.
No one should enter livestock housing while manure is being agitated, even when ventilation is operating. Entrances to the building should be marked with caution tape or other bold signage to prevent entry by workers.
Even after nearly all manure has been removed from a storage, hydrogen sulfide can still be deadly.
“When the depth of manure is very low or where a crust or mat has developed on top of the manure, the risk may appear minimal. But agitation of this manure by movement of the worker can release hydrogen sulfide,” Schmidt says.
If animals are present and cannot be removed during agitation of a manure pit underneath livestock housing, ventilation systems should be operated at maximum capacity. Animals should be closely monitored and agitation should be discontinued with any sign of animal stress.
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. Likewise, 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. Distiller’s grains contain greater concentrations of sulfur than corn, resulting in greater excretion of sulfur in manure.
“When cleaning out these types of barns, use large fans or blowers to mix the air,” Schmidt says. “Open all available doors, curtains and other air inlets/outlets. Consider testing gas concentrations during manure removal to ensure that workers aren’t exposed to hazardous conditions.”
Among the signs of being overcome by manure gases are the sense of being hot and clammy, loss of motor skills, irregular/fast heartbeat, tightness of chest, panting, nausea/vomiting and anxiety. If these symptoms occur, it is critical to immediately seek fresh air.
“I cannot overstate the importance of having someone there who knows what to do if you are overcome by gases or are otherwise in need of rescue when working around manure storages,” Schmidt says. “Anyone who works around manure should be well acquainted with and implement the necessary safety basics.”
Funding for this educational article comes from the Central States Center for Agricultural Safety and Health and the University of Nebraska Medical Center.