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Recipe for disaster

Gases are the natural byproducts of manure decomposition. Properly managed, they’re not a problem. Improperly managed, they can destroy property or worse—they can kill unsuspecting workers.

“The four major gases of concern are ammonia, carbon dioxide, methane and hydrogen sulphide,” explains John Tyson, agricultural engineer, Penn State Extension dairy team. “They’re all byproducts of microbial activity in manure.”

Of the four major gases, hydrogen sulphide is most to blame for the asphyxiation of workers. “It’s probably the most deadly on its own,” says Tyson. Interestingly, he says it’s also the gas over which producers have some control. “The limiter of hydrogen sulphide is how much sulphur is available. If you use high-sulphur feeds like distiller’s grains, or if the water the animals are drinking is high in sulphur, that makes more sulphur available for that [chemical] reaction.”

Methane, on the other hand, is most likely to destroy property, if it’s not managed correctly. Tyson says that methane is the only gas, of the four, that’s flammable. However, it requires specific conditions in order to amass concerning quantities.

“The bacteria that make methane live in an anaerobic environment,” Tyson explains. “So if you have manure in a storage facility that’s 10 or 12 feet deep, for example, the bottom of that storage is anaerobic, which means there’s no oxygen there.”

Besides an anaerobic environment, the bacteria that produce methane also need heat. That’s why the microbial activity that makes methane increases in warmer weather. “This means you’re going to get more methane from manure in the summer than in the winter because it’s warmer,” Tyson adds. “In fact, most all those gases are going to be produced at a higher rate in warmer weather.”

The blame game
Barn fires are tragically common, and methane is not always to blame. For example, an April 10 fire at Southfork Dairy Farm, which killed an estimated 18,000 head of cattle, received national news attention due to the scale of distruction. The Texas Fire Marshal office ruled that the fire was an accident that started with an engine fire, with methane not mentioned in the report. Prior to the report, there had been specuation that methane had caused the explosion, including one headline which said the explosion was “ignited by [the cows’] farts”. Tyson warns that without all the facts, it doesn’t make sense to speculate – and there are common misunderstandings of methane at play.

“You have to get to the right methane-to-oxygen concentration, and then you have to have the right spark. [For example], a tank of propane sitting in your backyard is not considered terribly hazardous until you open it up and mix it with the air. Even then, it doesn’t instantaneously ignite or explode, until you hit it with your gas grill igniter or a match or something,” he explains. “So [in the case of the dairy farm], those three components would have had to be mixed at the right time and in the right proportions in order to make an explosion possible.” Moreover, Tyson warns that methane is not the only thing that can catch fire. Building materials can burn, including insulation. 

Better safe than sorry
Although methane wasn’t mentioned in the report out of Texas, it’s still a gas of concern that has to be managed properly. While we think of methane as a byproduct of manure decomposition, Tyson says there are other sources of methane.

“Methane is going to be produced by all types of manure, but it doesn’t only come from manure,” he says. “It can be produced from fruit and vegetable waste, in the right environments. We can take food waste from a commercial kitchen, run it through an anaerobic digester and make methane biogas. So if you have the right foodstuffs to support that methane bug, you can make methane. Manure is not a requirement. It just so happens that manure is a good food source for methane-producing bacteria.”

That said, the amount of methane produced from manure varies, depending on the species of animal and the type of feed. “Different animals have different feed, and their manure produces different quantities of the various gases,” explains Eileen Fabian, professor of agricultural engineering at Pennsylvania State University. “When it comes to methane, you’ll get the most from cattle, much less from swine, and almost none from poultry.”

Best practices
Fabian stresses that managing manure properly is the best way to prevent catastrophes. Fires seldom start spontaneously, regardless of the amount of methane or any other combustible material that may be present. There has to be a spark or an ignition source of some kind that starts the fire.

Preventive measures, like proper ventilation and manure management are key to preventing dangerous gas accumulation. “If you think of an open lagoon, for example, methane is lighter than air, and it will tend to enter the atmosphere on its own,” Tyson explains. “If it’s not contained, we don’t have a problem. However, as soon as we cover that storage, either with a barn or a cover, we capture methane.”

While blowing fresh air into a manure pit is a good way to reduce the concentration of other gases, methane will escape on its own. “Methane is lighter than air, so in its own time, it will actually leave the space. You have to close the lid to keep it in there,” explains Tyson. “With the other gases being heavier than air, the reason we blow air down into a pit, even with an open top, is that we’re trying to push out the carbon dioxide, the ammonia and hydrogen sulphide.”

Most common scenarios
Basic high school physics teaches us that a fire needs three things to start: fuel, oxygen and a spark. If eliminating methane as the fuel source is impossible, due to the normal biological processes that naturally take place when bacteria consume manure, and if eliminating oxygen  is also impossible, then the only element that farmers can and should eliminate is the possibility of a spark setting off the mixture at the wrong time.

Tyson says a spark could come from a variety of sources.

“It could be an electric motor, a hot muffler that’s overheating, a spark from an internal combustion engine, even static electricity,” he says.

“There was an instance here in our county a couple of years ago, where a hay building burned down on a dairy farm,” he continues. “They were grinding hay one Saturday afternoon, [and] they assume that there must have been a rock in one of the bales of hay that went through the grinder and made a spark when hitting the steel blades. The hay started to smolder until it finally got enough oxygen to smolder itself into a fire. By two o’clock in the morning, the barn was on fire.”

Most sparks, he adds, will likely come from equipment, which is why proper maintenance is key. “You’ll want to use sealed electric motors in order to prevent sparks from getting out.”

Fortunately, the kind of fires was saw in Texas earlier this year are rare. “We’re pretty good at managing manure,” Fabian says about producers. That said, we can’t prevent all accidents from happening. We can, however, be as careful as possible keeping in mind the recipe for disaster: fuel, oxygen and a spark. •