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Scott G Winterton, Deseret News
Fire crews respond Sunday, Feb. 9, 2014 to a four-alarm fire at 550 East 500 South in Salt Lake City.

SALT LAKE CITY — Firefighters are still unsure what could have started a fire at a soggy construction site in downtown Salt Lake City, Sunday evening.

About 6 p.m., crews responded to a report of a fire at 550 E. 500 South. An entire multi-residential building went up in flames, despite two days of intermittent rain.

Salt Lake City Fire Department spokesman Jasen Asay said he could feel the blaze's heat from where he parked a block away.

"This was a very intense fire," he said.

Crews found heavy smoke and flames coming from the building and went inside to battle the blaze. They soon exited because of concerns that the building might collapse.

The construction company told fire officials that no one was in the building when the fire started. No workers were on site Sunday and there was no power connected to the building, nor heat sources inside. The fire was upgraded to a four-alarm shortly before 6:30 p.m., bringing about 60 firefighters to the scene.

Smoke and flames from the fire could be seen across the valley, and some witnessed embers shooting out from the building for several feet.

Around 6:45, nearby homes and a Smith's Marketplace across the street to the north were evacuated. Crews were worried about embers from the fire landing on nearby rooftops, especially with wind gusts blowing to the north.

Crews got on top of the Smith's roof and sprayed it down with water so it would not ignite.

A construction crane became a major cause of concern to the firefighters, who worked to prevent the equipment from crashing down from the intense heat and possibly hurting bystanders.

"We worried that if it fell down, we did not know which direction it would fall," Asay said.

Police set up a perimeter between 500 East and 600 East to keep passersby safe while they fought the blaze.

"Anytime you have an incident such as this, it certainly is something that attracts attention, not only for people that are immediately surrounding but the passersby as well," Salt Lake City Police Lt. Josh Scharman said.

Police have since reopened the streets, except for the area between 500 East and 600 East on 500 South, which could stay closed throughout the night.

As of 7:30 p.m., the fire was under control and smoldering.

The building's construction company, U.S. Development, reported that the building was 64,000 square feet and would have contained 61 units, according to a press release from the Salt Lake City Fire Department.

Asay said the only problem they have had with the company was a few weeks ago, when the building lacked a pipe to run up the stairs and assist with firefighting efforts. The company fixed the problem and resumed construction.

Salt Lake City fire officials detained a man in his 20s who they said was dressed as a firefighter at the scene of the fire. According fire officials, he gave false information to law enforcement. Asay said the man has been seen at other fires. He was brought in for questioning.

Damage was estimated at $1.5 million, Asay said. The cause of the fire is still unknown. Investigators will interview witnesses, the construction company and those working on site. They will also look for clues in the building once it is safe to enter.

Around 9:15, Salt Lake City Fire tweeted that their crews would remain on scene throughout the night. The Red Cross has been on scene to provide relief for those firefighters.

Contributing: Richard Piatt

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