Three people were injured Wednesday when a small explosion erupted at a marijuana growing operation in southwest Denver.

According to fire department spokesman Mark Watson, the explosion occurred at 12:44 p.m. while workers apparently wer using butane gas to extract THC illegally from plants behind a building on the 1200 block of South Lipan Street.

“We heard these booms,” said Cindy Gilmore, who works in a neighboring building.

“A big ball of flame was coming out the back of the building.”

Gilmore said that she heard 10 booms in total and that she saw several people run from the building and get into their cars and speed away after the explosion. One woman and two men remained who appeared to be burned, Gilmore said. The fire department confirmed that three people suffered second-degree burns and were taken to a hospital.

According to Watson, fire crews arrived quickly and extinguished the blaze and every plant outside of the building was destroyed.

He estimated that there were 36 plants inside the building and said that authorities seized them.

The name of the operation was not released, but fire officials said that it identified itself as a medical marijuana co-op and that it operated in a space in the building.

The investigation is ongoing, but Watson said that charges could range from arson to violations of the fire code.

He said charges in the case likely will be filed Thursday.

The Denver Police Department was on scene Wednesday waiting for a warrant to enter the building to investigate possible illegal activities relating to marijuana growing and selling.

Kate Gibbons: 303-954-1016, kgibbons@denverpost.com or twitter.com/ByKateGibbons