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Police are investigating whether the fire that injured seven people and destroyed 10 apartment units in Bellevue this week was caused by someone cooking a cannabis-related product.

Witnesses reported a loud boom before a fire erupted at The Hampton Greens, in the 4500 block of 148th Avenue Northeast, around 6:30 a.m. Tuesday. Fire officials estimated the damage at $1.5 million to the building and $150,000 to the contents.

A source close to the investigation said Friday that investigators found all the supplies to manufacture a cannabis-related oil — possibly the extremely volatile hash oil — inside one of the burned apartments.

The most popular way of making hash oil now involves flammable solvents, particularly butane, which can be bought in hardware stores.

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Usually a glass or steel canister is stuffed with dried pot. The canister is then flooded with a solvent such as butane, which strips away the psychotropic plant oils. The resulting golden-brown goo is then purged of the solvent. Common methods include boiling it off in a hot-water bath, according to Wired magazine, or using a vacuum system to pull butane from the oil.

The danger comes mainly from improper ventilation. Butane is heavier than air and tends to sink and puddle in a closed room; sparks can cause catastrophes, which the Federal Emergency Management Agency says are sometimes misidentified as meth-lab mishaps.

When asked whether the fire was related to hash oil, Bellevue police spokeswoman Carla Iafrate said the cause of the fire is under investigation.

Bellevue police, the city’s fire marshal’s office and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives are investigating the fire.

Seven people were injured in the blaze, three of whom were transported to Harborview Medical Center. Two of the people remain at Harborview, one in serious condition and the other in satisfactory condition.

Information from Seattle Times archives is included in this report.

Jennifer Sullivan: 206-464-8294 or On Twitter @SeattleSullivan.

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