Firefighters came across a makeshift marijuana lab—possibly used to extract "honey oil" from the plant—when they responded to a call in the Hollywood Hills area on Thursday morning, reports the L.A. Times.

Erik Scott, spokesman for the Los Angeles Fire Department, told LAist that firefighters received a call about "water flowing" at 2:44 a.m. on Thursday at an apartment on 1963 North Cahuenga Boulevard. When they arrived, they discovered that the apartment complex's sprinkler system had been set off by a fire in one of the apartments.

Scott said that, while the "small fire was extinguished quickly," a man in an apartment was discovered to be suffering from third-degree burns to his hands and face. He was taken to a hospital and was listed in critical condition. Scott says that a "possible explosion" may have occurred. The fire was confined to the room, and there were no reports of other injuries

Upon inspection of the scene, firefighters discovered a makeshift lab that may have been used to extract hash oil, or "honey oil," from marijuana plants, Lt. Brent McGuire of the LAFD told Fox 11. Also referred to as "wax" and "dab," hash oil has a higher concentration of THC—the psychoactive chemical in pot—and is thus often more potent that a regular marijuana plant.

According to NBC 4, officials were preparing to serve a search warrant Thursday morning to collect evidence from the apartment.