The midday explosion that convulsed a quiet North Portland neighborhood last month showered the street with glass and debris and hurled a 150-pound door into nearby Peninsula Park.

It blasted a 91-year-old home to pieces, scattering glass and scraps of the roof. The two men inside died. The sheer force of the blast suggested someone, maybe a contractor, nicked a natural gas line.

Then veteran Portland fire investigator Richard McGraw noticed something on the ground nearby -- a small red nipple common on butane cans. It couldn't be a butane blast, McGraw thought. This was too destructive, too powerful.

But then McGraw and his partner, Portland police Detective Joe Luiz, found butane cans strewn along the curb. By the time they'd sifted through what was left of Matt McCrann's home on North Kerby Avenue, investigators uncovered more than 400 butane cans - the telltale signs of an illegal butane hash oil lab and a growing hazard across the state.

The cans were used to extract tetrahydrocannabinol, or THC, from more than 100 pounds of marijuana leaves and flowers. The end product, a potent amber-hued oil known as BHO, is in high demand on the regulated and underground markets in Oregon and beyond. Stronger than smoking a joint, the oil is typically consumed using discreet portable pen-like devices or specially outfitted pipes called oil rigs.

Though recreational marijuana sales have been legal in Oregon since 2015, illicit labs like McCrann's have proliferated as the marijuana supply has increased in the era of legalization. With the hash oil labs have come a raft of serious injuries associated with butane-fueled explosions.

Police in Oregon last year investigated at least 25 illegal hash oil labs statewide, far eclipsing the number of methamphetamine labs reported by police. Since January, police have identified at least 19 illegal labs, seven of them involving explosions.

Oregon doesn't routinely collect data on hash oil labs and explosions; police agencies voluntarily submit that information to state and federal authorities so the numbers likely underrepresent the scope of the problem.

Medford police Lt. Mike Budreau, who oversees a regional drug and gang task force, said police in the unit have investigated nine illegal labs since early last year. He's seen butane blasts powerful enough to knock a home off its foundation.

"You don't have time to evacuate," he said. "Most of the time it catches people by surprise. ... That initial explosion can be traumatic and dangerous."

Oregon lawmakers this year took steps to crack down on illegal hash oil labs by making explosions tied to butane hash oil operations a felony. Yet the trend continues and in July reached a grim milestone: Portland's first fatalities from a butane blast.

The two North Portland men were among three people who died from processing BHO this year. A Grants Pass man asphyxiated in February when a bathroom filled with the odorless gas.

BIG PROFITS FUEL RISK

Explosions related to illicit hash oil production have hit two places the hardest: Southern Oregon, the epicenter of outdoor marijuana production in the state, and the Portland, data collected by federal authorities show.

Oregon marijuana growers and processors say the trend is driven by a variety of factors.

Red tape has led to a short supply of hash oil in regulated stores. Processing marijuana into oil is a lucrative outlet for surplus cannabis coming from medical marijuana operations and illegal grows.

Oregon's entrenched black market continues to flourish unchecked on sites including Craigslist, where hash oil made by illegal processors sells for $5 to $10 a gram compared to $30 to $50 at a licensed shop.

"It's a risk-reward thing right now and the reward on the black market is great enough that they take the risk," said Don Morse, owner of the Human Collective, a marijuana store in Southwest Portland.

Steve Marks, executive director of the Oregon Liquor Control Commission, which regulates the marijuana industry, acknowledged that a patchwork of local fire safety requirements statewide has slowed licensing for legal hash oil makers. The commission has so far licensed 119 marijuana processors to make cannabis oils.

State safety rules typically require the manufacturers to make six-figure financial investments in facilities and equipment.

Marks said his agency is working with state and local fire officials to speed up the approval process so more hash oil can enter the regulated market and, he hopes, dent black market production.

"Any illegal marijuana operation," he said, "is a concern of the state."

INJURIES ARE 'STEADY PROBLEM'

Dr. Niknam Eshraghi has seen the damage butane can cause up close.

Eshraghi, a surgeon, directs the Legacy Oregon Burn Center in Portland, which has treated 45 patients, mostly young men, burned in butane explosions since 2014.

"Unfortunately, it's a steady problem," Eshraghi said.

Butane hash oil burn injuries are extremely painful and can be disfiguring. They often require surgery, unusually long and costly hospitalizations and recoveries that take months. Charges for burn center care can run up to $5,000 a day, Eshraghi said.

Last week, two men were sentenced to three years of probation for their role in a butane hash oil explosion in Astoria last fall that sent one man to the Legacy burn unit for a month. Fire officials found hundreds of punctured butane cans at the scene.

The largest burn center serving Northern California, the heart of that state's outdoor marijuana industry, has also seen a steep climb in butane blast victims since 2014.

The regional burn center at UC Davis Health has admitted about 30 patients a year for the past three years, said Dr. David Greenhalgh, the center's chief of burns.

The problem has taken on such urgency that Greenhalgh and firefighters this year pressed the California State Assembly to limit the sales of odorless butane, a move similar to limits that states placed on ephedrine and pseudoephedrine in response to the methamphetamine crisis. Butane is easy to buy in stores or online, where a case of butane costs as little as $22.

A similar push is underway in Oregon. Portland Fire & Rescue officials say they plan to lobby lawmakers to impose limits on the sale of butane.

Care for butane blast patients comes at extraordinary expense given the extensive nature of the burns, said Greenhalgh, who pointed to one patient whose burns covered 90 percent of his body. The bill: $12 million.

"It's a big problem for us and it costs society a lot of money," Greenhalgh said. "It keeps our burn units full."

PORTLAND'S LATEST BLAST TURNS DEADLY

Portland fire officials first realized butane hash oil labs were a problem three years ago when firefighters responded to a fiery blast tied to butane in a freezer, McGraw said.

Officials combed through previous explosions and linked a handful to butane. In all, the city has seen eight butane explosions since 2012.

The latest blast killed McCrann, 42, and Richard Cisler, 68, a Vietnam vet who had been working on the home at the time.

Don't do this at home

Oregon bans butane hash oil production in a residence.

Hash oil processing with butane or CO2 must be done only in licensed facilities and meet a host of safety regulations, including using professional-grade "closed loop" systems. These machines are designed to contain butane during the manufacturing process. The butane used can't come from pressurized cans.

An engineer must verify that the closed-loop system keeps flammable gas from leaking into a room. The room itself must be well ventilated.

And the space and equipment, along with all electrical installations, must meet structural safety code and state and local fire code requirements.

McCrann wasn't licensed to process marijuana for the recreational market and he wasn't registered with the Oregon medical marijuana program.

Fire investigators don't know where he got the marijuana; though he had growing equipment, investigators didn't find plants.

Firefighters found signs of a busy hash oil operation in the basement, where they recovered a machine used to process marijuana, along with 289 punctured butane cans, another 142 cans that had exploded or were damaged. Marijuana leaves and flowers that had been processed were stashed in a half-dozen large garbage bags. Other bags at the site had exploded, spraying the yard with cannabis.

Investigators said they increasingly see some underground processors moving away from primitive processing that relies on Pyrex and PVC pipes in favor of more sophisticated systems intended to contain butane. These systems, which resemble Rube Goldberg contraptions complete with tanks and hoses, are generally considered safer because they keep butane from leaking into the room. But if used improperly or if the system has a loose fitting, gas can still escape.

"Every time you puncture a can you are losing some into the basement atmosphere," McGraw said.

In all, officials estimated McCrann had gone through at least 120 pounds of marijuana. Depending on quality, that amount could translate into as much as $50,000 in hash oil on the black market.

Before he died, a stricken McCrann managed to drag himself from the alley behind the house onto a neighbor's patio, where he told the neighbor, Mike Cook, that he was sorry and that he shouldn't have turned on the dryer. He later died at the hospital.

Investigators haven't confirmed that the dryer ignited the blast, but it doesn't take much for butane to explode. Something as ordinary as flipping a light switch or plugging in a phone charger can ignite the heavy gas, which quickly fills an unventilated room.

The damage to McCrann's home was so complete that it took firefighters hours to sift through the rubble to locate Cisler's remains, McGraw said.

"There was so much debris, we didn't know where to begin to look," McGraw said.

Cisler's son, Boomer, 28, meanwhile, is raising money for a memorial for his father. He said in a recent Facebook post that he plans to start a blog about his father's life and achievements.

"I'm still finding my own ways of dealing with this loss," he wrote.

-- Noelle Crombie

503-276-7184; @noellecrombie