Two people working in a marijuana processing business in Astoria were taken to Legacy Oregon Burn Center late Wednesday after an explosion rocked the building.

The blast - the first involving a legal cannabis enterprise in Oregon -- remains under investigation but early indications point to butane as a possible cause, officials said.

The business, Higher Level Concentrates, uses the highly volatile gas to make hash oil. The explosion is under investigation by Oregon OSHA, an agency whose mission is worker safety and health.

Two OSHA compliance officers were dispatched to the scene Thursday, said Aaron Corvin, an agency spokesman, who stressed the inquiry is in its early stages.

Higher Level Concentrates is on the Oregon Health Authority's list of 127 state-authorized marijuana processors who can make oil for the medical marijuana market.

The business also has submitted its application for a processor license to the Oregon Liquor Control Commission, the agency overseeing recreational marijuana; that application is pending, said agency spokesman Mark Pettinger.

Astoria police and firefighters responded to a report of an explosion about 6:30 p.m. Wednesday near Portway and Industry streets in the city's west end. In addition to Higher Level Concentrates, the building houses a dispensary, Sweet Relief, which was damaged in the blast.

Officials said the explosion occurred in the basement where the extraction business is located.

Gary Reynolds, owner of Sweet Relief, said two of his employees were in the shop when they felt the building rumble.

"One of the guys came from down below and told everyone to get out," Reynolds said. "He was burned up pretty good."

He said his employees ran from the building, which was quickly engulfed in smoke.

Three people working in Higher Level Concentrates escaped; two were burned and are being treated at the Portland burn center.

The blast victims were identified as William "Chris" West, 40, and Jacob Alan Magley, 34, both of Astoria. West is one of the owners of the business. The extent of their injuries is unknown; both men were in stable condition late Thursday, police said.

Jason Oei, 43, a second business owner, was at the scene at the time and wasn't injured.

Making hash oil using butane can be a dangerous endeavor. For years, the activity was unregulated and underground, carried out by home producers who often misunderstand the risks associated with butane. The gas, a cheap and flammable solvent, is used to extract tetrahydrocannabinol, or THC, from marijuana flowers and leaves. It can quickly fill an enclosed space, where something as ordinary as a pilot light can ignite a fireball.

The dangers led to a law, signed earlier this year by Gov. Kate Brown, that makes unlicensed production of marijuana extracts a felony. The provision is intended to target homemade butane hash oil operations.

The law left existing commercial - yet unregulated - processors in in a gray area as the state transitioned to a fully regulated recreational market. As a stopgap, the state allowed these businesses to apply for an interim registration that protects them from criminal prosecution.

State officials said none of the businesses that applied for registration have followed through, most likely because they plan to pursue a license with the liquor control commission.

But even without being registered, extraction companies must follow state rules for processing, officials said.

"There are limitations on what they can do when they make those extracts and prohibitions on how they can make those extracts," said Andre Ourso, manager of the state's medical marijuana program. "If we went in there and we found they were doing things they weren't allowed to do, they would not get a registration from us."

The liquor control commission hasn't yet inspected the extraction facility and the business hadn't submitted paperwork showing its equipment meets state safety standards for marijuana processing.

Pettinger said it's premature to say how the blast might impact the company's prospect for a state license.

"Perhaps they had all the correct and adequate safeguards in place," he said. "I don't want to prejudge them before we have all the information."

Butane-fueled explosions are relatively common in Oregon and elsewhere in the country. Earlier this year, a butane-fueled explosion shook a Parkrose home, where three children, including an infant, were present. No one was injured.

In August, a BHO-related explosion leveled a Medford home. In 2013, a blast in a Gresham garage killed a Portland man and severely burned his friend.

-- Noelle Crombie

503-276-7184; @noellecrombie