3 people injured in 2 hash oil fires in San Diego, suburban Seattle SAN DIEGO, Jan. 3 (UPI) -- Hash oil fires in San Diego and suburban Seattle this week left three people injured, authorities said. A San Diego Fire-Rescue Department official said one man was taken to a hospital Thursday night with burns primarily to his hands after an explosion and fire in a four-story apartment building that allegedly occurred when butane was being used to make hash oil from marijuana, U-T San Diego reported. Police evacuated the building, which sustained damage to several units, the newspaper said. Department spokesman Lee Swanson said investigators determined the explosion happened in a third-floor apartment's kitchen. Initial flames were extinguished by a sprinkler system, but the fire got into a wall and then burned to the roof, U-T San Diego said. In the Seattle suburb of Kirkland, Wash., Wednesday night, roommates Robby W. Meiser, 45, and Bruce W. Mark, 62, suffered minor to moderate burns in an explosion authorities blamed on an attempt to make hash oil with butane in their second-floor apartment, the Seattle Times reported. Attempts to make hash oil, a higher-potency drug derived from marijuana, have been the source of several explosions in recent months, including Mount Vernon, Wash., San Francisco, Chicago and Colorado, authorities said. The dangerous activity involves putting dry marijuana in a glass or steel canister and soaking it with a solvent such as butane to strip away the pot's psychotropic oils, the Times noted. To get rid of the solvent, the mash is then put in a hot-water bath. Since butane is heavier than air, it tends to collect in a puddle when in a poorly ventilated room and sparks can cause fires and explosions. "That is exactly what happened," Kirkland police Lt. Mike Murray said. Murray said Meiser is a designated provider of medical marijuana and had about 40 plants growing in his apartment. The officer said while the practice of extracting hash oil for medical use appears to be allowed under controlled conditions under Washington law, misdemeanor reckless endangerment charges could be sought because it was done in a residential area without proper ventilation, the Times said. The case was to be turned over to prosecutors after the investigation was completed.