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A vehicle that collided with a propane tank sparked the Fourmile Fire that has scorched 7,120 acres since Monday morning, according to an official who called in the blaze to police dispatchers.

Boulder County Sheriff Joe Pelle said officials are still investigating the cause of the fire but confirmed Tuesday afternoon they are looking into whether it was caused by a car hitting a propane tank.

“Part of what they’re doing today is trying to lock that down and confirm it,” he said.

According to a recording of police radio traffic from Monday morning, an unidentified official radioed in at 10:01 a.m. that he saw trees catching on fire at the base of Emerson Gulch.

“Trees are beginning to burn,” the official said. “Call out Fourmile Fire Department.”

About a minute later, a dispatcher sent out a lengthy call for help from Fourmile Fire, Boulder County Emergency Services, the U.S. Forest Service, the Colorado Forest Service and Boulder Fire Wildland Service. The first responders were sent to the 7100 block of Fourmile Canyon Drive, according to the tape.

A few minutes after the call for help went out, dispatchers began receiving calls from residents in the area of the fire.

“They can see flames 10 feet off the ground,” the dispatcher said of one caller.

The official who called in the scene became audibly more anxious as time went on.

“I have a fully involved fire,” he said. “I have trees torching. It’s all at the base of Emerson Gulch. Get Gold Hill fire out now.”

The firefighter’s radio became garbled, and another responder relayed a second report: “There was a collision with a propane tank that caused this fire.”

Reports also came in that a gas tank on a recreational vehicle had exploded.

An incident commander on the radio described the situation to responding crews.

“We have a recreational vehicle fully involved … propane tanks have (exploded),” he said. “Small 20-pound propane tanks have (exploded), immediately threatening a 1,000-gallon propane tank in a steep gulch with up-channel winds … .”

Contact Camera staff writer Heath Urie at 303-473-1328, or urieh@dailycamera.com.