If people who work with manure are aware of the invisible but ever-present danger of manure gasses, why are there still accidents and fatalities? It’s usually because it’s easy to become complacent and believe ‘it won’t happen to me’. What’s worse is that most farmers are fully aware of the dangers yet fail to take adequate precautions.
Curt Gooch, department of Dairy Environmental Systems and Sustainability Engineering at Cornell University, says farmers should be aware of four gasses from manure: ammonia, carbon dioxide, methane and hydrogen sulfide. “Ammonia and carbon dioxide are by-products of decomposition in aerobic conditions,” he said. “Manure in the barn, smeared on the floor, is generally aerobic. Methane and hydrogen sulfide are only produced in anaerobic conditions. So if someone references ‘a lot of methane coming out of the barn’, it’s coming from anaerobic conditions.”
Gasses produced in anaerobic conditions pose the highest risk, and hydrogen sulfide (H2S) is the most dangerous manure gas. “You smell a little bit, your senses become numb, you don’t know the gas is there and you go down before you know it,” said Gooch. “It’s heavier than air so you might be okay walking around, but if you kneel down or go into a confined space, it can be a real problem.”
At low concentration, hydrogen sulfide smells like rotten eggs, which most people easily recognize. The key to being safe is to recognize that odor and act immediately and without hesitation. Hydrogen sulfide at 2 to 20 ppm causes nausea, watery eyes, headache, fatigue, loss of appetite, poor memory and dizziness. In the best-case scenario, the person who gets to this point has thought ahead and asked someone to be present, and that person can get the victim of manure gas to fresh air and possibly medical treatment. At 100-150 ppm, hydrogen sulfide gas can result in loss of the sense of smell, which means that the person can no longer detect the rotten egg odor and is at greater risk. If hydrogen sulfide reaches 150 to 500 ppm, fatigue and paralysis can occur, and at 500 to 700 ppm, the person will become unable to walk and will likely collapse. Serious eye damage can also occur at this level. A person exposed to hydrogen sulfide at 700 to 1,000 ppm will become unconscious within several breaths and die within minutes.
Gypsum is often the source of hydrogen sulfide on the farm. “Gypsum can be used on a farm in a couple different ways,” said Gooch. “One is as the sole bedding material, and the other is to augment other organic bedding such as straw or wood shavings.”
One of the components of gypsum is sulfur, and hydrogen sulfide contains sulfur. “The problem is that we can get more hydrogen sulfide in manure storages when there’s gypsum on the farm,” said Gooch. “There are pockets in New York where there is a lot of gypsum bedding or gypsum used as an additive.”
Gypsum is a desirable bedding because it keeps animals clean and dry, which can potentially reduce the incidence of mastitis and other health issues. Gypsum alone or added to other bedding is comfortable for cows, which means increased lying time. “It helps the cow’s body conform to its resting area,” said Gooch. “There’s less compaction, and it provides more traction, which helps reduce injuries.”
Gooch says tankers that handle manure containing gypsum bedding are potentially dangerous to work around. “Think of a farm that’s using gypsum bedding, and they’re spreading manure with a liquid tanker,” he said. “If you’ve been around those tankers, you know they need to be serviced. People unknowingly go in them and don’t come out alive.”
One of the dangers of hydrogen sulfide is that exposure is possible without entering a confined space. “It’s heavier than air,” said Gooch, describing the gas. “On a hot day when there hasn’t been any rain for a while, gasses come off the storage and the cloud floats downhill.”
Gooch tells the story of a dairy farm on which a young child was riding a bicycle near the manure storage. The weather was calm and a lot of hydrogen gas was being produced in the storage. The child rode on the downhill side of the storage, through the gas plume, and was knocked out. Fortunately, the child didn’t die, but the potential was there.
Most farmers have heard the tragic story of the young Wisconsin farmer who was agitating manure prior to field application. The pit was full, the air was still and the farmer was overcome by manure gas as he began to break the crust. Although his death was first ruled as suffocation due to methane, further tests showed that hydrogen sulfide was likely the culprit. Adding to the tragedy was the loss of 16 cows near the pit that were also overcome by gas.
In a study of hydrogen sulfide exposure, farmers at 10 lagoon sites were fitted with a personal gas monitor during stored manure agitation to observe and record exposure and develop safety measures. Operators who were very close to the manure during agitation or who leaned over a fence to adjust or maintain equipment had the highest levels of hydrogen sulfide exposure. Those who remained in tractor cabs or were a good distance from potential gas plumes were at a lower risk.
Gooch references on-farm monitoring by Penn State to determine hydrogen sulfide levels. “They measured 150 ppm hydrogen sulfide,” he said. “Hydrogen sulfide can come out of barns. Sometimes gypsum is used in a bedded pack, either a composted bedded pack or housing for dry cows. You go in there in summer with a front end loader and start breaking it loose in a non-ventilated barn, and if there’s gypsum in the bedding, you could be in trouble.”
Good ventilation and air movement will prevent most gas problems, and Gooch reminds farmers that dairy barns for animals of all ages should be well-ventilated. He says gas sensors are useful, but must be kept clean and frequently calibrated to remain accurate.
It seems simple enough to follow simple guidelines for staying safe in confined spaces or in the vicinity of manure storage pits where the potential for accumulated manure gas is high, but unfortunately, there are still close calls and fatal accidents. It’s very tempting to make a quick entry into a confined space to retrieve a dropped tool. Don’t do it. It isn’t worth the risk.