DENVER >> Alarmed by a rash of explosions and injuries caused when amateurs make hash, lawmakers in Colorado and Washington are considering spelling out what’s allowed when it comes to making the concentrated marijuana at home.

The proposals came after an increase in home fires and blasts linked to homemade hash, concentrated marijuana that can be inhaled or eaten.

In Colorado, at least 30 people were injured last year in 32 butane explosions involving hash oil — nearly three times the number reported throughout 2013, according to officials with the Rocky Mountain High Intensity Drug Trafficking Area, a state-federal enforcement program.

Washington’s legal marijuana law in 2012 did not permit the production of hash or even edibles at home; it technically remains a felony even to use weed purchased at a state-licensed store to make brownies. Nevertheless, many people have done it.

Federal prosecutors in Seattle have brought charges in five cases where hash-oil operations blew up, including at one apartment complex where an 87-year-old former mayor of Bellevue suffered fatal burns after a fire started in another unit.

People make hash oil at home for the same reasons they make beer, wine or booze — to save money, make it to personal taste, or as a hobby.

Though there are safer methods, such as soaking marijuana in a vegetable-based glycerin, one common practice is to force a solvent such as butane or propane gas or liquid through leafy cannabis, a process that separates its psychoactive material from buds, leaves and stems.

After the extraction, the hash-maker then releases the gas or boils off the liquid, leaving behind marijuana’s psychoactive material in a potent goop. The resulting product — called hash oil or shatter or wax in even more concentrated form — can be added to foods without the grassy taste raw pot imparts.

Without proper ventilation, though, the gases can pool in a room, where a spark from an appliance can trigger a severe explosion, knocking buildings off their foundation in some cases.

Washington lawmakers are proposing to allow limited home hash production, though butane or other explosive gases would be banned except for use by commercial producers. Safer methods would be OK, and adults would be allowed to use cooking oil, butter or similar substances to make edibles.

“We have a little problem here with people blowing themselves up,” said Washington state Sen. Ann Rivers, the Republican sponsor of that state’s measure. “Anything we can do to stop that from happening.”

In Colorado, where hash regulations vary by jurisdiction, a bill up for its first vote next week in a House committee would establish a similar ban on the use of explosive gases to make hash.

“People who make it at home, they can do so with alcohol or methods that are safe,” said Colorado state Rep. Yeulin Willett, a sponsor of the bill.

Colorado’s largest jurisdiction, Denver, banned some types of home hash production late last year. A similar ban is under discussion in the state’s third-largest city, Aurora.

But some marijuana activists argue that when pot is legal, concentrating it at home should be legal, too. They compare the hash explosions to fires caused by turkey fryers and call it a problem with a new product that is best addressed by consumer education.

“Sure, there have been numerous dangerous explosions and fires from idiots who are determined to blow themselves up participating in activities which need considerable safety precautions,” said Timothy Tipton of the Rocky Mountain Caregivers Cooperative.

Tipton insisted that butane extraction is perfectly safe with proper ventilation or when done outside.

Supporters of home production also say Colorado’s law is on their side. The state’s marijuana legalization measure specifically included concentrated marijuana and all its production methods.

Just last month, the Denver district attorney dropped a case against a man facing felony charges of manufacturing marijuana concentrate and fourth-degree arson. The man, Paul Mannaioni, was charged last year after a hash oil explosion sent him and two other people to a hospital.

Mannaioni challenged the legality of Denver’s hash oil ban, prompting Colorado’s former attorney general to say the marijuana amendment allows limits on home production.

The charges were later dismissed after prosecutors said they couldn’t tie him to the explosion beyond a reasonable doubt, leaving the legality of the city’s hash oil ban unresolved.

Some marijuana advocates said a statewide ban would invite more legal challenges.

“It’s a patient’s right to make their medicine,” said Jason Warf of the Southern Colorado Cannabis Council.

But Colorado lawmakers backing the homemade limits said the state should err on the side of caution.

“This is something we need to nip in the bud,” Willett said.

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Johnson reported from Seattle.