by Sally Colby
Three brothers went into a manure pit to repair a pipe last summer and none of them made it out alive. Many farmers learned of that story and vowed it would never happen on their farm, but despite understanding the hazards of manure gases in a confined space, there’s a good chance someone else will lose their life thinking “It won’t happen to me.”
“The problem with manure gas is that we can never completely avoid it,” said John Tyson, Penn State ag engineer. “It’s naturally occurring and produced by microorganisms in manure. Microbial activity gives off heat and a respiration byproduct, and respiration is where manure gasses come from.”
The four manure gases of concern include ammonia (NH3), carbon dioxide (CO2), methane (CH4) and hydrogen sulfide (H2S). Regarding ammonia, Tyson explained the nitrogen in manure is converted to ammonia through bacterial degradation. “It’s colorless; however, it will give itself away with a sharp, pungent smell,” he said, adding most people can tell when they’re exposed to ammonia. “It irritates the eyes and makes it difficult to breathe.” Ammonia isn’t usually considered deadly but is highly irritant and can damage eye and lung tissue.
Carbon dioxide is also the result of microbial respiration. Because this gas is colorless and odorless, someone exposed won’t realize what’s happening when CO2 displaces oxygen in the air and causes difficulty breathing. Initial signs of CO2 exposure include shortness of breath and dizziness. “At high enough concentrations, asphyxiation is possible,” said Tyson. “You can suffocate while breathing CO2 because your body will not have enough oxygen to function. Body functions begin to shut down and eventually death will occur.”
Methane, which is odorless and colorless, is formed by bacteria under anaerobic conditions. Since these bacteria don’t require oxygen, methane gas can be present in any sealed area or at the bottom of a liquid storage lagoon where there is no oxygen. “One of the unique characteristics of methane versus other gases is it’s lighter than air,” said Tyson. “Methane will come to the surface as it’s formed by microbes at the bottom of the storage.”
In liquid manure storage without a crust, methane bubbles are often seen at the surface. Because it’s lighter than air, in open storage, methane disperses into normal airstreams. If there’s a structure over the top of the manure storage, such as a slatted floor barn with storage underneath or a covered manure storage, methane will build up in the non-ventilated space. The capture of methane gas for energy is the concept behind methane digesters.
Methane can form in the foam on top of liquid manure storages, especially in swine manure storage. This gas can also bubble up through a slatted floor and form a gaseous layer on top of the storage. Methane is explosive – with the right oxygen/methane mix and a spark of some kind (motor start, lightbulb), an explosion or fire can occur.
The most dangerous gas is hydrogen sulfide, which is the number one cause of manure-related issues. H2S is produced continually by bacteria in anaerobic manure storage systems, is colorless and has a pungent, rotten egg smell. Hydrogen sulfide is heavier than air and will remain at ground level or surface level of manure storage. In most cases, it becomes trapped within manure storage. If the liquid manure storage in anaerobic conditions isn’t agitated, H2S gets stuck within the liquid in gaseous form.
“Hydrogen sulfide causes big issues quickly and at low concentration,” said Tyson. “It can paralyze nerves in the nose, so you get a whiff of rotten egg smell and it deadens the olfactory system.” Too often, someone exposed to H2S notices the initial foul odor but since the nasal nerves can’t smell it anymore, the worker has gotten just enough gas to deaden the senses as the concentration potentially increases.
At H2S levels build up over time, anyone exposed experiences a rapid loss of consciousness. Death can occur within minutes in high concentrations. Tyson said getting out of a H2S environment doesn’t guarantee safety – people can experience delayed reactions up to 24 hours later, and some victims experience long-term neurological damage after exposure.
Tyson compared the flow of H2S on the farm to the flow of water. “As we open manure storages and begin to agitate, that is most often when hydrogen sulfide released,” he said. “What’s down slope and where would the gas flow? Wind also influences gas flow and may push hydrogen sulfide into where humans are working or toward animal housing.” Some farmers have noticed reduced appetites in heifers several days after pumping manure and can attribute it to agitation and the presence of H2S. “When manure storage is agitated, regardless of temperature, turn on the fans and open curtains to increase ventilation during agitation,” he said. “Think about where the hydrogen sulfide can go.”
Some of the initial physical signs of manure gas exposure include feeling hot and clammy, loss of motor skills, irregular heartbeat, chest tightness, difficulty breathing, anxiety and vomiting. “If you don’t feel right, get out of that situation,” said Tyson. “Get away from the manure storage and reevaluate the possibility something might be going on.”
While liquid manure is slightly more dangerous than solid manure, solid systems should be respected. Complacence is often the problem – someone had gone in previously to unplug a pump and nothing happened, so they assume the potentially dangerous practice is safe. Tyson reminded manure handlers that warmer weather “wakes up” microbes, increasing their activity and producing more gas. Proper ventilation for under-barn storage is critical.
For an extra measure of safety and whenever possible, remove any equipment that needs to be repaired out of the pit and work on it away from potential gas, keeping in mind that gas can travel. Gas monitors are good early indicators of potential problems, but Tyson said it’s important to respect the signal and get out of the space when the alarm sounds.
If someone needs to be rescued from a pit or other enclosed space, the rescue should never be attempted without proper safety equipment in place, including extra trained personnel and a call to 911. It’s tough to not jump in an attempt a rescue but the chances are too great that both the victim and rescuer will be at risk.
“What it takes to rescue someone is proper equipment, oxygen tanks and scuba gear,” said Tyson. “Let someone know where you are so they can check on you. Be aware of the position of the pit and how manure gases move – which way does manure gas drain, and what’s in the way of drainage? Increase ventilation in the area. Many times the solution is to increase ventilation to dilute the gases.”