3 injured in Walnut Creek hash-oil lab explosion

One person was missing and at least two people were hurt in an explosion and fire that tore apart a Walnut Creek apartment complex on Friday, Oct. 31, 2014. The incident was reported at the complex on the 1500 block of Sunnyvale Avenue west of Interstate 680 about 10 a.m., according to the Contra Costa County Fire Protection District. less One person was missing and at least two people were hurt in an explosion and fire that tore apart a Walnut Creek apartment complex on Friday, Oct. 31, 2014. The incident was reported at the complex on the 1500 ... more Photo: Contributed Photo Photo: Contributed Photo Image 1 of / 15 Caption Close 3 injured in Walnut Creek hash-oil lab explosion 1 / 15 Back to Gallery

An explosion caused by a butane-fueled hash oil lab ripped through a Walnut Creek apartment building Friday morning, critically burning two people, injuring a third and forcing 50 others to evacuate.

The explosion occurred about 10 a.m. and was centered in the top unit of a four-unit complex on the 1500 block of Sunnyvale Avenue, two blocks west of Interstate 680.

The blast blew out the walls and roof of the top unit, severely damaged the other units and shattered windows on buildings up to 200 feet away.

Contra Costa County Fire District Capt. George Laing said the apartment was littered with more than 100 butane cylinders.

“When our first responders got there they observed cases of these cylinders,” he said. “As the fire continued to burn these things were shooting off like rockets. It was incredibly dangerous, especially in a multi-unit complex like this.”

Pacific Gas and Electric Co. crews were on-site, but said they had not received reports of gas leaks, said Capt. Kent Kirby of the Contra Costa Fire District.

Neighbors described the explosion as extremely loud and followed by a quick series of smaller blasts.

“I thought it was thunder at first,” said Carol Olson, 55, who lives across the street. “At first I was excited, but then my grandson said someone ran out of the building and his hand was gone.”

Apartment explosion in Walnut Creek multiple injuries pic.twitter.com/wbSNEvpPci — Jodi Hernandez (@JodiHernandez01) October 31, 2014

Two men were transported to a hospital with severe burns. A third man showed up at a hospital later in the day and was determined to have been injured in the blast, Laing said.

The Walnut Creek United Methodist Church, across the street from the damaged building, offered coffee and a place to gather for the 50 or so evacuees. The American Red Cross was also on hand to help those affected.

The street is lined with 1960s-style apartment buildings and is usually quiet, neighbors said.

One woman, who appeared shaken and was standing on the sidewalk with a family member, said she was cooking in her apartment in a building next door when the explosion occurred.

“I thought it was an earthquake,” said the woman, who declined to give her name. “It was very loud. I was scared. My son’s bedroom window was broken. I turned off the gas and ran into the street, and all my neighbors were outside.”

Laing said investigators continued to comb through the site Friday evening.

Chronicle staff writer

Kale Williams contributed

to this report.

Carolyn Jones is San Francisco Chronicle

staff writer. E-mail: carolynjones@sfchronicle.com Twitter: @carolynajones