November 19, 2007 | General

Tennessee Composting Facility Rises From The Ashes

BioCycle November 2007, Vol. 48, No. 11, p. 28
Quick action on the part of the firefighting team saved five rotary digesters, but the Memorial Day fire destroyed the compost building and tip floor.
Robert Spencer

ON A hot and hazy Memorial Day morning this past May, when all five of Pigeon Forge Fire Department’s full-time firefighters were enjoying a day off, the alarm went out for a fire at Sevier County, Tennessee’s solid waste cocomposting facility. Over the 15 years that the plant has been in operation, the fire department has responded to small fires, usually a “hot load” on the tipping floor that one truck could contain. So when Fire Chief Tony Watson saw the unusually large, black plume of smoke gushing from the direction of the plant from more than three miles away, he associated it with the combustion of hydrocarbons, and wondered if a jet had crashed in the middle of the building. His read of the smoke said this was a much larger fire than his mostly volunteer crew should tackle themselves, so he immediately started calling in neighboring fire departments in Sevierville, Gatlinburg and other communities in Sevier County.
“When I arrived, the compost building was on fire from one end to the other, and I could not believe that compost would cause this type of fire,” recalls Watson. “My first concern was if everyone was out of the building, and I was told by the operator who called in the fire that all five employees were accounted for. I then turned my attention to the fire and frankly I was scared since I did not know what would happen next. We could let the fire burn, but we also wanted to save the five digesters that were not yet on fire. I knew that the compost digesters are the most expensive pieces of equipment at the plant. So, one ladder truck was set up to spray 2,000 gallons per minute of water on the ends of the digesters, particularly one discharge conveyor that was burning, as well as trash in one of the digesters that had caught fire. That digester had been shut down for several months and had a small amount of dry garbage in it that caught fire.”
Tom Leonard, Solid Waste Director for Sevier Solid Waste Inc., who was out of town with his family for the weekend, arrived around 4:00 pm at his burning plant, and was relieved to see that the digesters had been saved. “The other four digesters were full of trash and if they had caught fire it would have been a disaster,” explains Leonard. Eight hours after they started fighting the fire at 8:30 am, Watson said he knew they had saved the five digesters and each of the hydraulic rams that feed them. Leonard estimates that the replacement cost for each digester would have been about $3 million.
He adds that although it was a holiday, the facility was open for a half day, receiving MSW until noon. The goal was to load the 300 tons of trash into the digesters, and go home to enjoy the rest of the holiday. The compost building was full of compost in various stages of processing, with approximately 10,000 cubic yards of material in the building.
By late afternoon, it was time to deal with the fire in the garbage on the tipping floor. After inspecting the roof to see if it was safe to enter the building, Leonard and Watson decided to move the garbage out of the building to the parking lot.
“We made a decision to remove all of the MSW from the tip floor, even though some of it was on fire, because it would have been nearly impossible to put out the fire with 300 tons in one big pile inside the building,” recalls Leonard. “Two of our operators, one who is also a volunteer fireman, started moving the trash with our two loaders into the parking lot where it was spread out with the loaders so firefighters could soak it with a combination of Class A firefighting foam and water. That took all night to make sure the fire was out. For the following four days, our employees loaded it into trailers for transport to the adjacent landfill.”
He adds that the other priority was to try and save equipment. “We were able to save our two CAT loaders. However, our Backhus windrow turning machine was destroyed, along with all of the conveyors, screens and electrical equipment.”
The 102,000 square foot compost facility was essentially one large building surrounding three sides of the five digesters; the tipping building was at the loading end of the digesters; the discharge ends of the digesters were in a building at the other end; and the primary screening, aeration floor and final product screening and storage area were in a large building to the side of the digesters. Residuals from the primary trommel are conveyed back to the tipping floor, and are ultimately disposed. The tipping floor is approximately 15 feet higher than the discharge end of the building, with the digesters below the tipping floor. “This design allows for charging of the hydraulic rams by pushing MSW into the pits in the floor, rather than some facilities where the MSW is fed into a hopper and up conveyors into the digesters,” explains Leonard.
The fire spread rapidly through the 102,000 square foot compost building, consuming accumulated dust and ceiling panels that then fell down onto the compost below, creating a smoldering fire that was very difficult to extinguish. For that reason, the County hired a contractor to pull back the roof to gain access to the interior piles. Leonard points out that the upper two feet of the compost piles were burning so they peeled that layer off with a track excavator, took it outside and soaked it to put out the fire.
The fire was so intense that it was burning in the underground HDPE ducts that carried air to the adjacent biofilter, and would have ignited the 30,000 square foot wood chip biofilter had the fire in the ducts not been contained.
Almost 24 hours after arriving at the fire, Chief Watson left the fire scene at 6:00 am to get some sleep. Watson says that after two days there were still 30 firefighters on the scene. Overall, approximately 400 firefighters were at the plant over the five days it took to completely put it out. Watson and Leonard are grateful to the many other citizen volunteers who helped set up a relief center at the armory building directly across the road from the plant, where firefighters and county employees could shower, rest, eat and rehydrate with water and Gatorade. Most importantly, Watson points out that there were no injuries to anyone involved with the fire.
Critical to the success of this firefighting effort was the City of Pigeon Forge’s plentiful water supply system from a reservoir with 12 million gallons of storage, and a water treatment plant that can process 12 million gallons per day. “We estimate that we used 2 to 3 million gallons of water to contain the fire,” says Watson.
The motor at the top of the conveyor – where it entered the tipping building through an opening in the wall – that carries residual materials from the primary trommel screen back to the tipping floor is where the fire is thought to have started. “Due to the negative air pressure in the compost building, air flow was from the tipping building and into the compost building, which probably contributed to the rapid speed in which the fire spread from the conveyor and into the compost building,” says Leonard. “It then apparently raced to the other end of the compost building, and it was a number of hours before it spread to the tipping floor, even though it appears to have started close to the tipping building.”
Roger Price, Fire Inspector for the Pigeon Forge Fire Department, was also out of town on Memorial Day, and did not arrive on the scene until the following day. He began his investigation as to the cause of the fire, interviewing employees and firefighters, looking at the pattern of the fire and building design. The loader operator on the tipping floor that morning saw an orange glow coming from the opening in the wall through which a conveyor returns residue to the tipping floor from the primary trommel screen. He dragged a water hose over to the location but quickly realized he should call 911 since the fire was already too large for one hose to quench.
“It appears the fire was probably ignited by a spark from a conveyor motor or gear box, and the insurance company has had electrical and mechanical engineers involved in the investigation,” Price speculates. “A slight breeze blowing through the wall opening for the conveyor probably created a flue fire that was burning the accumulation of dust on the walls and ceiling beams and panels. That little glow turned into a huge ball of fire in a few minutes. We think we had a dust explosion, and a sprinkler system would have helped.”
As described in the accompanying MSW Composting Survey article, Sevier Solid Waste plans to rebuild the cocomposting facility, and hopes to have it operational in 2008.
Chief Tony Watson offered the following lessons from the compost facility fire:
o Compost facility operators should build a relationship with the fire chief prior to having a major fire, including periodic inspections of the facility so that the chief understands what is in the facility and how it operates.
o Have periodic tours of the compost facility by the firefighters so they too understand the plant.
o Install fire suppression sprinklers throughout the facility. This will save 15 to 20 percent on insurance costs, and potentially reduce losses from a fire, but will not work for internal fires such as in the compost and garbage.
o Make sure there is plenty of water to fight a fire, looking at hydrants as well as fire ponds to fill tanker trucks.
o Plan a location where firefighters can rest and eat, such as the armory.
o Have a contingency plan for garbage disposal in the event it must be removed from the building, and then diverted to another disposal facility until a reconstructed plant is operating.
o To put out a fire in a pile of garbage or a pile of compost, auger a hole at least 10 feet deep into the pile and inject a Class A foam. The foam increases surface area and helps the water penetrate the material. This also helps reduce rekindling of fires. Also use foam on compost and garbage hot spots as the material is spread out and soaked with water.
o Determine where the excess water from firefighting will go and if there are sensitive streams or water bodies that could be damaged, and therefore should be protected if possible. The Sevierville fire water mostly flowed to the adjacent fire pond or into the woods down gradient of the plant. (Editor’s Note: A 1995 fire at the Cobb County, Georgia composting facility resulted in firefighting water flowing into a stream, a fish kill and a regulatory fine).
o Refrain from training compost plant employees to fight fires, except for ones that can be put out with an extinguisher. Instead, rely on getting the fire department on the scene as soon as possible.
o The first question to ask when you get to a fire, “Is everyone out of the building?”
Editor’s Note: The information in the article on the Sevierville composting facility fire was presented at the 4th Annual Rotary In-Vessel Users Group meeting on September 12-13, 2007 in Pigeon Forge, Tennessee. The meeting included a tour of the burned facility.
AT the eastern entrance to the Great Smoky Mountain National Park, the most visited national park in the U.S., a rapidly growing tourist industry brings millions of visitors to the mini-golf courses, thrill rides, musical acts, restaurants and hotels. The Dollywood theme park is one of the largest draws, and is located just one mile “as the crow flies” from the Sevierville cocomposting facility. Pigeon Forge Fire Chief Tony Watson, along with county and city managers, had to decide if the fire and smoke were a threat to the thousands of visitors at Dollywood on this Memorial Day. By early afternoon, the fire had become a media event, and reporters and TV camera crews were covering the fire and asking questions. “As Chief, I needed to get approval from government management about a number of issues, and we decided we did not need to close Dollywood or other attractions since the wind was not sending excessive amounts of smoke into those areas, but was basically going straight up or in a direction away from Dollywood,” he says.

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