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.

A Denver man who suffered severe burns while he was making hash oil at home, shows how he made the marijuana concentrate. The Associated Press

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.

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 died after sustaining an injury while trying to escape a fire that started in another unit.

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.

Without proper ventilation, though, the gases can pool in a room, where a spark from an appliance can trigger a severe explosion.

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