More than 3 1/2 months after a fatal, three-alarm fire at a downtown Denver construction site, fire investigators have a long list of what did not cause it.

But they are still trying to determine what ignited the March 7 inferno, which killed two people and destroyed what was to become a five-story, 84-unit apartment building at Emerson Street and East 18th Avenue, in the North Capitol Hill neighborhood.

“Although some possible causes for the fire have been ruled out, it currently is listed as undetermined,” said Greg Pixley, a Denver Fire Department spokesman. “And because of ongoing interviews and investigation, this case will remain open and under investigation.”

After conducting 200 interviews and reviewing 500 photographs, fire investigators have ruled out actions by the following workers as causes: framers, welders, plumbers, drywall installers, insulation workers and electricians. Electrical cords and power units set up to provide a temporary power source for the construction site also have been ruled out.

The fire killed two construction workers — Dustin Peterson Peterson, a 37-year-old electrician, and Roberto Flores-Prieto, 29, who installed insulation. Six other people were injured.

The flames — which caused damaged to seven other nearby buildings and destroyed 45 cars, trucks and fire department vehicles  — rose 200 feet in the air, and the heat was intense enough to be detected from space.

The fire spread rapidly due to open ventilation and the wood-frame construction that did not have active fire stops, Pixley said. Some corridors had drywall, but many rooms were separated by plywood. Doors and windows had not been installed.

Vertix Builders, the company overseeing construction, and Allante Properties, the management group, issued statements saying they are cooperating with investigators and echoed Pixley’s call for people to share more information.

Two of Denver’s three largest fires in recent memory

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