Foaming Manure

A warning about the danger of explosions when manure forms a foam, from Robert Chambers, engineer specialising in swine and sheep housing and equipment with the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) in the latest issue of Pork News & Views.
calendar icon 22 June 2010
clock icon 6 minute read

While the problem of foaming manure in storages is certainly not new to Ontario, there have been sporadic reports in the past. There appears to be a new issue on the horizon. In the past year, many swine facilities in the upper Midwest USA have increasingly reported spontaneous foaming in under-barn deep manure pits.

While still a rare occurrence, explosions, property damage and injuries have been reported, though fortunately no deaths.

One of the consequences of manure foaming

This spring in Ontario there was an incident involving a deep pit swine finishing barn. The pit was emptied with the use of a vacuum tanker and the foam brought under control, for now. The operator is still very concerned, and rightly so, that it may come back.

The risk with foam is in the gases that make up the foam. Measurements done at the University of Minnesota have recorded methane (CH4) levels in the 60 to 70 per cent range along with lethal levels of hydrogen sulphide (H2S). These gases are produced from the decomposition of the manure and normally vented out of the barn as they are released from the liquid manure. The foam traps these gases as they are produced and stores them in the foam complex.

As long as the foam is undisturbed, these gases are not an issue. As the foam builds up on the surface of the manure storage it can force its way up into the barn space. It is not uncommon to have three to four feet of manure in the pit and four to five feet of foam in an eight-foot pit. For pit fan-ventilated barns, this foam can block the fans reducing or stopping the normal ventilation. With reduced or no ventilation the risk of explosion is greatly increased. As the foam rises into the barn space the pigs are forced to walk and lay in it and it can even flow into the feeders, rendering the barn useless to the point the animals must be moved.

The danger is when the foam is broken up by pressure washing, aggressive manure agitation or some other method; these gases are released almost immediately into the barn space, overwhelming the capacity of the ventilation system to safely remove them. The specific gravity of methane relative to air is 0.6, therefore it rises quickly. When methane exceeds four to five per cent of the air volume and there is a flame or spark from a heater, electric or gas motor, or light switch, an explosion will result. A Minnesota producer was using a gas-powered pressure washer to hose down a finishing barn in an attempt to lower the foam that had come up through the slats. As it was cold, he had reduced the ventilation to the minimum. Fortunately, he was standing near the door when the explosion blew him 30 plus feet out of the barn; while suffering some burns, he lived to tell the tale.

"The risk with foam is in the gases that make up the foam ... methane and hydrogen sulphide."

The exact cause of the foam is still undecided. The foam consists of bubbles of trapped methane and other manure gases and has thick consistency similar to melted ice cream. It can easily push the wooden lids off the pump-outs.

To date, the only solutions have been to increase the cold air over the manure storage surface, turn on the sprinklers, if present, to knock the foam down. Turn off the heaters and if using a pressure washer, ensure that the motor is outside of the barn space.

In all cases, whenever foam is present, increase the ventilation to ensure at least ten air changes per hour, preferable more; minimum ventilation is usually set for four air changes per hour. Though the pigs may be uncomfortable with the cold, they will be happier than if there is an explosion.

Gas detectors can be purchased from safety suppliers. The gas detectors should be equipped with sensors that monitor LEL (Lower Explosive Limit), which includes methane and hydrogen sulphide. Again, as methane is lighter than air, it will tend to concentrate in the ceiling and hydrogen sulphide is heavier than air and will concentrate near the floor and in rooms or attached buildings lower than the barn, so place the monitor near the ceiling for methane and the floor for hydrogen sulfide. Do not forget to monitor office, utility rooms, showers and feed rooms, as these areas are not ventilated to the same degree as the main barn and gases may become trapped in these spaces.

The upper Midwest states agricultural extension services led by Minnesota have formed a group looking into this issue. What they have found through their survey of affected producers is that while the feeding of DDGS is common in all of the affected barns, not all barns feeding DDGS are foaming. In fact, often one barn can be foaming and another identical barn on the same property can be fine. Sometimes the same barn with a pit divider wall in the middle of the barn can have one side foaming and the other just fine, same pigs, same feed, same management.

The author, Dr Chambers, has an agreement with the University of Minnesota extension service that Ontario producers may participate in a survey on manure foaming conducted by Minnesota investigator, Larry Jacobson. Fill out the form at the link below by selecting 'Other' and entering 'Ontario'. The goal of the survey is to determine the extent of the problem and to determine some common factors that may play into what causes the foaming to start. There is also a Swine Web presentation as well as several fact-sheets [click here].

June 2010

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