REDDING  (AP) — Five people in Northern California suffered serious burns when an explosion blew apart the garage where authorities say the group was cooking concentrated marijuana honey oil with butane.

The Monday morning blast blew the roof off the garage in a quiet residential neighborhood of Redding, a city about 200 miles north of San Francisco, authorities said.

Explosions and fires from botched honey oil labs are on the rise, said Redding Fire Prevention Division Chief Michael J. Bachmeyer, as more people learn via the Internet how to cook concentrated marijuana.

He confirmed a honey oil lab was the cause of Monday’s explosion. Honey oil is also called hash oil, butane hash oil and concentrated cannabis.

“We’re figuring we’ve had about 15 to 20 in the last year,” Bachmeyer said. “There are all kinds of ways to look up how to do the process, even though it’s very dangerous.”

Authorities found cylinders of butane, glass tubes and marijuana at the Redding garage lab. Butane is highly flammable.

Last year, an explosion in a honey oil lab inside an apartment complex in Redding left multiple families homeless.