BY WILLIAM R. FULTON
Methane fires and explosions are grow-ing issues for rural firefighters with livestock confinement facilities in their response area (photo 1). They occur when a thick foam forms on the surface of the manure in holding pits below the facility. The foam is a concern to firefighters because the bubbles in this foam are filled with a combination of manure pit gases, including methane, a major concern relative to fire and explosion. The foaming problem cannot be traced to one cause. It develops in the deep manure pits in large quantities, sometimes more than four feet thick, and can push through the building’s slatted floor (photo 2).1 A number of major universities in the Midwest are researching this foam-generation issue.
|(1) A typical swine facility at which these fires occur. (Photos courtesy of the University of Illinois Extension unless otherwise noted.)|
|(2) Foam rising through the flooring.|
The foam is typically dark gray (photo 3) and forms on the surface of the manure as the waste decomposes in the pit. Although methane (70 percent) and carbon dioxide (30 percent) seem to be the main gases found in this foam, ammonia and hydrogen sulfide may also be encountered. All these gases are lethal in varied concentrations.2
|(3) Foam collected off the top of manure in the pit.|
Ammonia will usually vent off rather easily but can cause eye and throat irritation. Hydrogen sulfide (H2S), commonly considered the most dangerous pit gas, is highly toxic and can deaden the sense of smell (i.e., you cannot smell it, but it is present in high concentrations). At levels of 600 parts per million (ppm), H2S can kill an individual after only one or two breaths. It can be rapidly released while one is emptying the manure pit or agitating the manure or after any other stirring of the manure in the pit such as is done to blend solids into suspensions. H2S is heavier than air, has a rotten egg odor, and is normally found near the top layer of manure.
Carbon dioxide is another gas formed in the manure pits. This gas can displace oxygen in the lungs and render the victim unconscious. Methane has caused considerable issues in livestock facilities where thick foam is found. Methane is continuously produced in these manure pits and, if no foam is present, will rise off the surface of the manure and be vented out of the facility by controlled pit ventilation systems.
Health and safety problems occur when the foam forms on the top of the manure and traps the methane along with the carbon dioxide. If the foam bubbles burst rapidly and significant quantities are generated as a result of pumping, agitation, or a major temperature change (primarily a rise in temperature), the methane can be released into the upper levels of the livestock facility. If the methane finds an ignition source, a flash fire, an explosion, or a structure fire can result. Ignition sources can also include sparks from a welder, grinder, or torch during normal maintenance.
In some scenarios, when the fire department arrives on scene, the building is damaged, melted plastic watering bowls and electrical lines are present, livestock have been injured, but there is no fire (photos 4-5). In some instances, firefighters arrive and can observe the foam still flaming, much like a candle. From a fire behavior perspective, we have found that as the methane slowly burns, the radiant heat from the fire causes more bubbles to expand and burst, thereby releasing more methane, which ignites, sustaining the combustion process. This sustained burning of the foam can be one of the most problematic situations for the fire department.
|(4) Damage from a methane explosion.|
|(5) Damage done by a flash fire and a methane explosion.|
Explaining the slow burn of the foam is almost as difficult as explaining why it forms on top of the manure in the first place. For the most part, the slow-burn scenario happens when the foam is ignited in the pit—in other words, the ignition source ruptures the foam bubbles and then ignites the methane. The radiant heat from the burning methane causes the expansion of the gases in the foam bubbles. This expansion causes the foam bubbles to stretch to the point of rupture, thereby providing more methane to the fire. These fires would be considered fuel-controlled fires. Furthermore, it could be that the carbon dioxide in the mixture of pit gases within the bubbles has a cooling effect on the fire, which slows the ignition of the methane because of the reduction in temperature.
As noted, nitrogen and carbon dioxide can also be found in the pit area. Both of these gases have a relatively high thermal capacity and can absorb a substantial amount of energy from the combustion reaction. When oxygen concentrations are lower, more energy is lost to heating inert gases, thereby resulting in lower burn temperatures.
The location of the foam within the manure pit can affect the fire’s speed and intensity. If the foam is in the center area of the pit, the open compartment area of the pit would allow any available air to freely be entrained from all directions. The result is a cooling effect on the fire plume and a lowering of the temperature. If the foam is near a pit wall, the amount of air entrained is minimized, and a higher plume and velocity are seen. Depending on the type of construction, this can result in a structure fire (photo 6).
|(6) Damage from a manure pit fire. (Photo by author.)|
Because this is a fuel-controlled fire, venting the pit gases with negative pressure using the pit ventilation system or structural firefighting ventilation fans (make sure they are explosionproof) is a tactical consideration for controlling the fire. Researchers at the University of Minnesota have found that if the foam on the surface of the manure is six inches or more in thickness, it may be possible to sustain the release of methane.3
When the foam is in a sustained burning state, the situation is very unpredictable. When hit with a fog stream, the reaction can be a flash fire because the water ruptures large quantities of methane bubbles and oxygen is introduced. Smooth bore nozzles are not effective and usually cause more foaming by agitating the manure in the pit.
• If dispatched to an incident of this nature, first determine if anyone is still in the facility. Talk to the owner, manager, or employees to make sure the building is clear of all personnel. Next, close all gas valves to heating equipment; realize it may take a long time for pilots to go out after the valves outside the building are closed. Electrical systems should be shut down except for pit ventilation fans (photo 7).
|(7) An explosionproof pit ventilation fan. (Photo by author.)|
• Determine if there is any active fire in the building. Along with normal indicators such as flames and smoke (this type of fire produces very little smoke), try to determine the internal fire conditions. You can use a thermal imaging camera to check pit areas through outside openings to the pit and from the doors.
• Locate a floor plan of the livestock facility and determine if the facility is compartmentalized. In addition, find out if the pit area is constructed the same way. If so, treat each compartment as a separate structure. Accountability is a must at all livestock facility incidents. Buildings are spread out and massive. Knowing what each crew is doing and its location is very important.
• Never enter livestock facilities without wearing full firefighting personal protective equipment including self-contained breathing apparatus. Never enter the pit area if foaming conditions exist. If the incident began with an explosion, be aware of structural damage that may compromise the integrity of the building.
• Ventilate the manure pit area with the building’s negative ventilation fans, which are mandated by specification to be explosionproof. If not effective, use fire service intrinsically safe ventilation fans (not the typical PPV fan) much in the same way as you would at a structure fire, with a focus on the pit area. Make sure that the foam has not blocked the pit ventilation system and reduced the air flow, as this has been a problem in a number of incidents. Monitor the atmosphere for the level of toxic or explosive pit gases. When the fire is completely extinguished, open the side curtains (if equipped). Do this manually; do not use powered systems. Allow pit gases to escape through the top area. If there is no wind or very light winds, ventilation fans may be needed to withdraw exhaust gases from the pit. Apply positive pressure to the pit to force methane up and out. If the facility does not have curtains, first monitor the level of gases. If the level is low, turn on the ventilation system and vent off the remaining gas to safe levels. If curtains are not present, the area will have an air-exchange system to exhaust the pit gases.
• When you are sure there is no active fire and ventilation has been applied, a very fine fog stream (lowest gallonage, wide angle pattern) can be applied to the foam through the slatted floor. This will collapse the foam bubbles and allow the methane to vent off in a controlled condition, neutralizing the situation. Perform air monitoring and ventilation throughout this process. A command decision will have to be made if this step is needed; but without reducing the foam, another incident may occur.
• Applying firefighting foam to the manure pit will only aggravate the situation and can also create long-term problems by killing the bacteria that digest the solids in the manure pit.
• If a structure fire is the result of the ignition of methane, handle it with normal firefighting procedures from the outside of the structure. Use caution if you enter the building, as open pit areas are always a possibility, and any explosion could have caused openings in the flooring. If a number of livestock buildings are tied together and are occupied with animals, begin with the building closest to the building on fire and evacuate the animals. Monitor the air before you enter. If the buildings are connected by enclosed hallways, knocking down these hallways will keep the fire from moving to other buildings. Trench cuts are very effective in containing fires in these large buildings.
These livestock facility incidents can be complicated and sometimes unpredictable. The incidents seem to be on the increase. Awareness that the situation may exist and preplanning the livestock facilities in your response area are imperative. A dialogue between the fire department and those who operate these facilities will be very helpful if an incident occurs.
1. Schmidt, D. (2011). “Manure Pit Foaming.” Power Point , University of Minnesota.
2. “Understanding Foam & Pump-Out Safety,” Iowa Pork Producer Headlines , Iowa Pork Producers Assn., Fall 2010.
3. Funk, T. (2011). “Manure Foaming in Deep Pit Facilities,” (Power Point for the Illinois Pork Expo).
Author’s note: Thanks to Assistant Professor James Pharr, Eastern Kentucky University; Dr. Ted Funk, University of Illinois Extension specialist; and Kurt Glosser, Illinois Fire Service Institute, for their help and guidance with this article.
WILLIAM R. FULTON is a field instructor for the University of Illinois, Illinois Fire Service Institute. He specializes in agricultural rescue programs. He has been a member of the Salem (IL) Fire Protection District for more than 15 years and serves as district fire marshal. He conducts primary fire investigations for the fire district; oversees firefighter safety; and has command duties on fire, rescue, and hazmat scenes. He is an Illinois-certified firefighter II, instructor 1, hazardous materials technician, fire apparatus engineer, and fire investigator. He has an associate degree in agriculture from Kaskaskia College and is pursuing a degree in fire protection administration from Eastern Kentucky University in Richmond, Kentucky.
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