Let's talk science: Elements of fire suppression at Pasco Landfill

Nota: Está disponible en español

Since June, contractors have taken several measures to extinguish a fire in a localized portion of the Pasco Sanitary Landfill in Franklin County. Underground temperature probes and gas monitors were installed to gather details about the area of the fire. Significant progress to extinguish the underground fire has been made although data suggests it isn’t completely out yet.
Extinguishing a fire is no easy task. Tack on that this particular fire is underground and in an old landfill with a variety of wastes currently being treated to avoid further groundwater contamination. Several methods and approaches can be used. Each has pros and cons including cost, worker safety and effectiveness.
The project team and parties responsible for cleanup of the landfill thoughtfully and carefully weighed options to suppress the fire and adequately protect human health and safety and the environment.

Science of fire

Fire is a chain reaction. The reaction continues in a cycle as long as fuel, oxygen, and heat are interacting to create combustion. In order to stop combustion, one of the components of the fire triangle must be removed.

fire chart, showing in corners fuel, oxygen and heat, with chemical chain reaction in middle.

Let’s use a campfire as an example. Clean, dry wood provides fuel and it should be stacked in a way that allows air to pass through. Once you add and sustain heat, the triangle is completed and a chain reaction begins.
Smokey Bear taught us well. We can put out our campfire by applying water, which removes heat from the chain reaction faster than the fire can produce it. Or we can smother the fire with something that doesn’t burn, like soil, which prevents oxygen from reaching the fuel (wood) and heat (flame). Either would effectively break the fire triangle’s chain reaction.

Managing the Pasco Landfill underground fire

In the case of the underground fire at the Pasco Landfill, careful consideration for fire suppression was made because of the location and source of the fuel. The fire is currently localized in a portion of the landfill that contains household garbage and construction debris. Heat is part of the natural cycle at landfills – it’s produced by bacteria that breaks down and decomposes the trash.
So how is oxygen reaching the waste and completing the fire triangle underground? We can’t be completely sure, but it could have been from air pockets in the landfill and cracking in the protective soil cover that contractors observed on site.
Part of Pasco Landfill, showing a large dirt pile with broken fence on side, four yellow pilings in dirt.

Click on the above photo to view the Flickr photographs.

Adding to the complexity of the underground fire is treatment of an adjacent section of the landfill containing drums of hazardous waste. This area, known as Zone A, has a system in place that uses technology to draw air through the soil preventing pollution from reaching groundwater and building up in the soil.  As a precaution, the operations of the treatment system were modified.

The right elements for the job

Water wasn’t the right choice for many reasons. First and foremost, it would have required digging up the smoldering waste to add water. Excavation could also potentially add more oxygen to the fire triangle and fuel the chain reaction. All parties involved prefer to avoid excavation in order to extinguish the fire, if possible. But most importantly, using water to extinguish the fire could potentially carry additional pollution down through the soil and into groundwater – the very groundwater we are trying to protect with the treatment system in Zone A.
Working closely with technical experts, including local fire departments, Ecology and the parties responsible for cleanup chose to smother the underground fire with an engineered cover, soil, and by injecting liquid carbon dioxide. The liquid carbon dioxide cools the burning materials and displaces oxygen from the areas actively burning underground.
Temperature probes inserted in and around the underground fire are showing results. Much of the area has cooled, indicating the fire is subsiding. There is still a small hot spot, but we are continuing to monitor the situation and act responsively to manage and extinguish the fire.
There is no immediate threat to people living near the landfill or to workers and businesses in the area, based on our current knowledge.

Landfill cleanup progress

Cleanup activities have been ongoing at the closed landfill site for many years. The public will have an opportunity to provide feedback on additional cleanup options for the site in 2015.
Stay current on the fire suppression efforts and cleanup progress at our Pasco Sanitary Landfill webpage.