When ignited, manure foam can turn into fire and explosion.
When foaming, methane gas bubbles rise up from manure stored in a deep pit and come in contact with a spark from a heater, welding torch or a cigarette, there can be serious consequences, says a University of Minnesota agricultural engineer.
Larry Jacobson says a pork producer in southeast Minnesota learned the hard way. He noticed a lot of foaming in a manure pit under one of his empty hog barns. “The foam was literally coming up through the slats,” Jacobson explains. “He wanted to knock down the foam, and one of the ways that people have done this is to agitate the manure in the pit.”
The producer went inside the building during pit agitation to make some adjustments. There was 4 ft. of foam in the 8-ft.-deep pit, oozing above the slats and flowing out of the pit's pump-out ports. As he was leaving the barn, it exploded and he was blown 30-40 ft. from the site, Jacobson says. The explosion raised the roof several feet in the air, causing considerable truss and ceiling damage.
There have been several other cases noted in Minnesota, Iowa and surrounding states with the following common denominators:
Ventilation had been turned off or down to minimal levels after animals had been removed.
All barns had deep-pit manure storage.
Only one barn or one room out of several barns or rooms seem to be involved, even with multi-barn sites.
“One of the dangers in barns with deep-pit manure storage is obviously methane gas production, which is a highly flammable gas. Foam on top of liquid manure can contain 60-70% methane,” Jacobson explained in a talk at the Iowa Pork Congress. “When this foam is broken up through agitation or other means, it releases this stored methane (like bubbles bursting) into the air. It can become explosive and it doesn't need that much of a spark to ignite it.”
The foaming problem seems to take some time to develop — months or a year — but once established, it can produce problems quickly.
Foaming also reduces manure storage space and results in dirty pigs when foam pushes above the slats in the pens.
Spray washing the pit area, sprinkling water and pig activity seem to work best to somewhat control the foam issue, Jacobson says.
Foam's Origin Debated
Fortunately, manure pit foaming is a relatively rare problem. Jacobson admits there are no ready answers to why the foam forms in the first place. Could it be due to diet or water source or related to climate?
“Right now we do not have solid answers,” he says. But the University of Minnesota, Iowa State University, the University of Illinois and other organizations are working on getting some answers. Jacobson says more investigations of farm cases will get attention. Plus, he and fellow Minnesota researcher David Schmidt are formulating a survey to send to a targeted group of producers/managers to build a baseline of common factors.
The survey will ask whether distillers dried grains with solubles, antibiotics and pit additives were being used.
Jacobson doesn't think there will be a silver bullet to solve the problem. Rather, he expects to find multiple things that seem to trigger these increasingly frequent events.
Actually, manure foaming is not new. “We have seen foaming for a long time, going back to the '70s and what were called ‘black fires’ where people were welding and you would see this flash. But it was a pretty rare event,” he recalls.
Importance of Ventilation
“If you ventilate swine facilities, make sure you get enough air exchange so that the methane concentration is below the explosive limit (5-15%), and you won't have an explosion,” Jacobson says.
“If there is sufficient ventilation to keep the gas concentration in the barn below 5%, typically four air exchanges per hour — the average minimum ventilation rate — this should keep it under wraps,” he adds.
However, if there is foam present in the pit and manure is being pumped, or the foam is being broken up by spraying water, etc., Jacobson advises up to 10 air exchanges per hour to keep methane concentration in check.
When manure is foaming high enough to block or restrict air flow from pit fans, he recommends that ventilation be provided by wall fans rather than pit fans.
In a curtain-sided barn with only pit fans, make sure the curtains are open to improve ventilation rates. However, if the wind is not blowing enough to retain static pressure, keep the curtains closed and pit fans operating, he suggests.
Obviously, keep people out of the barn when dealing with a manure foaming problem.
Mixing fans can help distribute air in a room or building, but remember they don't exchange air.
“Many times in a mechanically ventilated barn, it is better to not open up (doors and sidewall vents) the barn too much because you lose your static pressure,” he reminds. “It is better to have ceiling inlets open and pit pump-outs closed.”
Avoid pit agitation until manure is at least 2 ft. below the slats and, if possible, only agitate manure intermittently.
“There are really no permanent ways to eliminate foam formation,” Jacobson says. “We do have defoaming agents, but I think in an anaerobic pit situation, they are probably not going to be very effective. Until we understand exactly how that foam is generated in an anaerobic manure pit situation, I think it is going to be difficult to do something permanent to prevent it.”
Iowa Fire Investigations
Robert Burns and his associates Lara Moody and Ross Muhlbauer at Iowa State University's (ISU) Agricultural & Biosystems Engineering Department investigated five of eight fires that occurred in deep-pit swine facilities in Iowa since the fall of 2009. Burns says three explosive gases can be generated in manure storage systems: methane, hydrogen sulfide and phosphine.
Sampling by the ISU team found that foam in Iowa deep-pit swine manure systems contains from 50-70% methane and less than 250 ppm hydrogen sulfide.
Table 1 compares the findings from the five fires investigated. Foaming was present at all five fires, and high foam levels may have reduced the effectiveness of pit fans at some sites, Burns reports. Four of the five sites had fires occur after the foam was broken.
Successive explosions very similar to the Iowa deep-pit fires were also reported in Victoriaville, Quebec, Canada in 2003. In those cases, investigations revealed that explosive levels of methane were captured in foam, and when the foam broke (wash water falling through the slats), it released methane that was ignited by a barn heater, Burns relates.
The action of foaming is not well understood, but Burns says it has been shown to invert the solids profile — meaning that there are more solids at the top of containment than on the bottom.
Possible sources affecting the surface tension of the liquid manure and increasing the potential for foaming include natural and synthetic detergents, oils and greases, proteins, lipids and polymers.
However, Burns admits that in his experience, foaming and fires occurred in facilities that both used and hadn't used detergents.
Literature indicates that DDGS use in pig diets in the last decade has significantly increased manure volume due to reduced dry matter digestibility. But, he stresses, there is no data indicating that DDGS has in any way caused or increased the incidence of these fires.
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|1DDGS stands for distillers dried grains with solubles.|