Two people are dead after a three-alarm fire erupted at a construction site near downtown Denver on March 7. The mid-day fire, which destroyed a partially completed apartment building and burned hot enough to damage at least 40 cars in the area, forced construction workers to leap to safety from second and third floors.

Some workers were hurt when they jumped; others injured trying to catch them. At least six people were injured, public safety officials said, one of them a firefighter with burns to his hands and face. He was treated at a hospital and released.

Nearly 50 construction workers were on site when the fire broke out. Some tried to extinguish the blaze themselves but were unsuccessful.

Fire officials have not identified the people killed, and said that the investigation into the cause of the fire could take quite some time, possibly weeks. People in the area reported hearing at least two loud explosions several seconds apart as the blaze started.

Denver Fire Captain Greg Pixley said in a news conference on March 7 that the fire spread quickly because of exposed materials on the jobsite. “The building had nothing to protect the wood,” he told reporters at the scene. He noted that officials have no immediate indication of any deviations from city building codes or permitting violations at the site. A progress inspection of the electrical system, conducted earlier in the week, revealed no problems with it.

The fire occurred at the Emerson Place Apartments on East 18th Avenue in Denver’s Uptown neighborhood, near the city’s hospital district. The five-story, 84-unit complex, estimated construction cost of $15 million, featured all studio apartments. The developer is Allante Properties, Greenwood Village, Colo., and the contractor is Vertix Builders, Frederick, Colo. Neither company could be reached for comment.

The project was scheduled for completion this summer.

This story was updated on March 9 after public safety officials confirmed the death of a second person at the site.