An explosion that heavily damaged a Tewksbury residence Tuesday night was sparked when someone in an illegal lab used butane to extract the active ingredient from marijuana, the Tewksbury Fire Department said.

“This was a very dangerous situation for the residents and the firefighters,’’ Fire Chief Michael Hazel said.

“The buildup of butane vapors within the apartment came in contact with an ignition source and an explosion ensued,” Hazel said in a statement. “The process was being performed on and around an electric stove within the apartment.’’

The explosion injured two men and a woman and caused an estimated $200,000 in damage to the four-unit residence at 22 Astle St., the department said. The three injured people were taken by medical helicopter to Boston hospitals. Their conditions were not immediately available.


Firefighters responded to the scene from Billerica, while units from Wilmington and Andover also responded for coverage, fire officials said.

A number of full and empty and butane cylinders were found at the apartment, Hazel said.

Dr. Lester Grinspoon, a retired Harvard Medical School professor who has long advocated medical use of marijuana, said the refinery process generates a concentrated form of THC, the acronym for tetrahydrocannabinol, the active constituent of marijuana. The concentrated dose is used in electronic cigarettes, among other applications.

In a telephone interview, Grinspoon said using butane is one of several ways to distill the substance.

He cited two major concerns with the butane process: Sometimes traces of butane survive the extraction process and can be inhaled. The second issue is when untrained people tackle the task.

The incident is under investigation by the Tewksbury fire and police departments, state troopers assigned to the office of State Fire Marshal Stephen D. Coan, and the State Police bomb squad.

John R. Ellement can be reached at ellement@
globe.com. Follow him on Twitter @JREbosglobe.