The blast and flash fire that rocked a northeast Bend duplex unit March 18 were likely caused by a furnace kicking on and igniting butane that had gathered in the unit’s garage, according to a search warrant affidavit released Tuesday.

A husband and wife sustained serious burns in the explosion, which was associated with an alleged clandestine hash oil lab they were operating in their home.

The couple’s 3-year-old daughter avoided serious injury.

David Carl Paulsen, 32, and Jennifer Rose Paulsen, 32, have been charged with unlawful manufacture of a marijuana item and unlawful delivery of a marijuana item.

Bend Police recently released the request to search a gun safe seized in the investigation.

Just after 7 p.m. March 18, neighbors of the Paulsens reported hearing a loud explosion and seeing the Paulsens rushing around their driveway, according to the court documents. A neighbor who shares a driveway with the couple said Jennifer Paulsen asked if she could use the woman’s shower. The woman reported David Paulsen rinsed himself off outside her residence with her hose.

The witness told police David Paulsen next asked her to tell police that the couple’s 3-year-old daughter had been with her “the whole time.”

The woman said the child had in fact been outside when she first noticed her parents running around.

A different neighbor told police David Paulsen had run to stash a cardboard box and other items in his truck immediately after the explosion, the court documents state. An officer reported looking inside the truck and seeing that it contained butane cannisters. A search of the vehicle turned up other items believed to confirm the existence of a “butane honey oil” lab inside the home of David and Jennifer Paulsen.

Investigators allegedly found drug records, marijuana, butane, multiple firearms, a scale and a “marijuana packed extraction vessel,” the court documents state.

Police believe the Paulsens were extracting THC from marijuana plants using an “open blasting” method. This involves passing butane through marijuana to collect the THC. It’s said to release a large amount of butane into the atmosphere, according to the search warrant affidavit written by Bend Police Detective Nick Lee.

With butane being extremely flammable, it can ignite with as little as a spark from static electricity, Lee writes.

The only legal way to manufacture butane honey oil in Oregon is through the “closed loop” method, which is considered safer. These labs use a system of tubing, valves, tanks and recovery systems to keep the butane from entering the atmosphere. This method is considered safer, yet fires and explosions have occurred in Oregon in closed-loop systems, according to Bend Police.

— Reporter: 541-383-0325, gandrews@bendbulletin.com