Four Los Angeles firefighters remained hospitalized Monday and seven others had been discharged after they were injured while fighting a blaze in the city's downtown.
The firefighters were injured and hospitalized Saturday after an explosion erupted during a warehouse fire, the Los Angeles Fire Department said.
Officials have said none of suffered life-threatening injuries, but two firefighters had been placed on ventilators to protect their airways. On Sunday, they were removed from the devices but were in intensive care for significant burn injuries.
The federal Bureau of Alcohol, Tobacco, Firearms and Explosives said Monday it has activated a team to assist in the investigation into the fire, which was reported around 6:30 p.m.
Investigators are looking into a business connected to the warehouse, law enforcement sources have said.
The business, Smoke Tokes, is reported to be a supplier for butane honey oil, the LAFD has said.
An initial assessment found that the company might be a wholesaler of products used to make concentrated cannabis, a process that usually requires highly flammable butane.
The LAFD says the firefighters "encountered increased pressurized smoke and heard a rumbling high-pitched sound," while battling the fire, and they started to exit the building and roof due to deteriorating conditions.
Then "a significant explosion created a massive fireball" that enveloped firefighters, and the heat melted helmets and burned through protective coats and hoods, the department said.