The Oregon Department of Environmental Quality and the Environmental Protection Agency are monitoring air quality after diesel sludge and residue caught fire in a tank on Thursday night at the AmeriTies West Plant in The Dalles.  EPA deployed air monitors this afternoon in neighborhoods and other areas downwind from the facility.  Thus far, particulate matter and volatile organic compounds are at normal “background” levels.  Wasco County Emergency Management says the fire is under control, and Mid-Columbia Fire & Rescue is on-site to respond until it is fully extinguished.  The tank normally contains a solution of 99 percent diesel and one percent copper naphthenate.  Crews had taken the tank out of service earlier on Thursday and the copper naphthenate had been safely drained, though some amount of diesel sludge and wood residue remained in the tank and later caught fire.  Vapors inside the tank heated and expanded, causing an explosion inside the tank about 30 minutes after the fire started.  The cause of the fire is still being investigated.  The two firefighters that were hurt in the explosion were released late on Thursday and are home and recuperating.  Neither firefighter sustained long-term injuries.