Hazardous waste materials exploded Sunday when a fire broke out at the Richland landfill and destroyed the hazardous waste facility.
No one was injured and the runoff water from fighting the fire was contained as planned in collection pools, officials said.
The cause remains under investigation.
Paints, solvents, propane tanks, pesticides and other household hazardous material were stored at the facility, but Jim Jordon, Richland assistant fire marshal, said he doesn't think the fire was caused by spontaneous combustion.
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"It would surprise me if it were," Jordon said. "Some chemicals can (spontaneously combust) depending on the mixture, but the people who work at the facility are trained ... and know the hazards."
The fire at the Benton County Household Hazardous Waste Facility at Richland's Horn Rapids Landfill broke out around 5:15 p.m.
It was reported by someone at the nearby ORV track who spotted the smoke.
Workers had left the landfill around 4:30 p.m. after their shift ended, officials said.
When fire crews arrived, the building was engulfed in flames and contents inside were exploding, fire officials said.
Firefighters kept a safe distance from the fire by using two "deck guns" to propel about 1,000 gallons of water a minute at the fire.
"The crews did a very professional job," Jordon said. "They handled it the right way."
Firefighters had the flames mostly contained in 20 minutes, but one crew stayed on the scene until 1:30 a.m. Monday to ensure the fire was out.
The storage area and its contents were destroyed. An adjacent secured building that houses flammable materials sustained only exterior damage, officials said.
Representatives from the hazardous material team and state Department of Ecology were at the scene Sunday night to make sure there were no safety or environmental issues from the chemicals.
"They were really happy with the containment," Jordon said. "All the systems worked the way they were supposed to."
Residents with hazardous materials to dump are advised to use common sense to store the materials the best they can in the meantime or to call other facilities that accept hazardous waste.
Richland city officials also are expected to provide information to the public about what to do with hazardous materials until the facility is rebuilt.