Legislators in Colorado and Washington are considering rules designed to reduce the number of home explosions and injuries caused by people making homemade hash oil.

At least 30 people were injured in Colorado last year in butane explosions involving hash oil—almost three times the number reported the previous year, according to the Associated Press.

Recreational marijuana is legal in both states. In Washington, the production of hash at home is illegal, but people continue to make it, the article notes. In Seattle, federal prosecutors have brought charges in five cases involving hash oil operations that blew up.

People attempting to make hash oil, a marijuana concentrate, use flammable chemicals that can cause an explosion. They pump butane fuel through a tube containing raw marijuana plants, in order to draw out THC, the psychoactive ingredient in marijuana. Volatile butane vapors can fill the room, and be ignited by a flame or spark.

Legislators in Washington have proposed allowing limited home hash oil production, as long as the person making it does not use butane or other explosive gases.

Colorado legislators will consider a similar bill, which would ban the use of explosive gases to make hash oil. “People who make it at home, they can do so with alcohol or methods that are safe,” said Colorado State Representative Yeulin Willett, a sponsor of the bill. Denver has banned several types of home hash production. Aurora, the state’s third largest city, is considering a ban.