CONTRA COSTA COUNTY (CBS SF) — Crews say a fire at an Antioch apartment Monday was started by a butane hash oil lab, making it the second fire in four days involving an explosive chemical inside a Contra Costa County home.

“Unfortunately, we are seeing a significant increase in these kinds of fires, in part due to the relative ease of the process, and because of the ability to purchase the pure butane in large amounts,” said Contra Costa County Fire Marshal Robert Marshall.

On Monday night, crews found an extinguished fire on the balcony of a second story apartment in the 2200 block of Sycamore.

They quickly discovered that the cause of the fire was due to an accumulation of high purity butane being used to extract hash oil from marijuana.

Fire investigators from Contra Costa County were called and assisted the Antioch Police with the investigation.

Of the two occupants in the apartment, one was arrested and taken into custody by the Antioch Police Department.

Fire damage was estimated to be $5,000. No injuries were reported.

The fire fire involving a hash oil lab happened Friday in Walnut Creek. The fire caused an explosion, resulting in serious burns to two occupants and $1.2 million in damage to the main building as well as to several adjacent structures.

“Ultra pure butane is extremely dangerous when used in this manner,” Marshall said. “The pure butane is colorless, odorless, and extremely flammable. If the vapor finds an ignition source, a fire can occur, often with disastrous results.”