A spate of home explosions caused by amateur hash oil makers is an unexpected consequence of legal marijuana in Colorado, The New York Times reports.

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.

While these accidents have occurred around the country, they are causing a special problem for courts and lawmakers in Colorado, the article notes. Criminal defense lawyers argue making hash oil can no longer be considered illegal now that the state has made it legal to grow, smoke, process and sell marijuana. The state attorney general has said marijuana legalization does not apply to butane extraction.

In 2014 there were 32 hash-oil explosions in Colorado, up from 12 the previous year. Dozens of people have been injured, including 17 who were treated for severe burns.

“This is uncharted territory,” State Representative Mike Foote told the newspaper. “These things come up for the first time, and no one’s dealt with them before.”

In Grand Junction, the Fire Department responded to four hash oil explosions last year. “They get enough vapors inside the building and it goes off, and it’ll bulge out the walls,” said Fire Marshall Chuck Mathis. “They always have a different story: ‘Nothing happened’ or ‘I was cooking food, and all of a sudden there was an explosion.’ They always try to blame it on something else.”