BOISE, Idaho (AP) — Federal investigators were working Thursday to try to determine what caused a steel airplane hangar that was under construction in Idaho to collapse the previous evening, killing three people and leaving several others badly injured.

The Boise Fire Department said in the morning that the scene was turned over to OSHA investigators. Though the hangar is at the Boise Airport, it is privately owned by Jackson Jet Center, a charter flight and maintenance company.

The Ada County Coroner’s office was expected to release the names of those killed once family members had been notified.

Nine other people were hurt, including five who had critical injuries and were taken to area hospitals. Officials with Saint Alphonsus Regional Medical Center said they were not able to issue an update on the condition of the injured patients because of privacy laws.

The collapse was reported about 5 p.m., and first responders had to stabilize the massive structure while trying to rescue those who were trapped inside and underneath it. Steel girders and panels were bent, and a large crane was folded in the wreckage.

Inland Crane was hired to provide crane services for the hangar, but that work was largely completed when the accident occured, Jeremy Haener, company vice president, said in a statement. Haener said none of Inland Crane’s employees were injured but the company was mourning the loss of partners and friends.

“Based on accounts of Inland Crane operators, construction workers on site, and the steel erecting contractor, we believe that no action by Inland Crane operators or the crane itself were cause for the structural failure,” Haener said.

At the time of the accident, the crane was being used to place an end truss, Haener said.

“When the building collapsed due to an unknown structural failure, the crane boom — the hydraulic arm of the equipment — snapped on impact.”

Fire Department Operations Chief Aaron Hummel said some of the victims were on a hoist or other elevated platform when the structure fell, and that required specialized rescue efforts.

“Yesterday was a tragic day for our Boise community. Our heartfelt condolences go out to the families and loved ones affected by this incident,” Boise Fire Chief Mark Niemeyer said Thursday. “I commend the actions of all the first responders for their quick and professional response rescuing victims and caring for patients in a chaotic and very dangerous environment.”

Construction work can be hazardous, and steel erection — the type of work being done at the hangar — is one of the top 10 most dangerous occupations, according to data from the U.S. Bureau of Labor Statistics.

The construction industry had the highest number of fatal work injuries in 2002, the most recent year for which data is available, according to the bureau. The agency tallied 1,056 work-related deaths for the sector that year, the equivalent of 13 out of every 100,000 full-time workers.

Boise city permitting records show that the Meridian, Idaho-based contractor Big D Builders obtained permits to build a 39,000-square-foot (3,623-square-meter) hangar for Jackson Jet Center.

The $8.1 million project was to include earth grading, a concrete foundation and a metal building. Phone and email messages seeking comment from Big D Builders were not immediately returned.

Hummel said the rigid steel frame of the building had been erected and crews were still working on the structural components that would have tied the frame together when the “catastrophic” collapse happened.

“I can tell you that it was a pretty global collapse that occurred, and the main structural members came down,” Hummel said.

Officials with the Occupational Safety and Health Administration have not yet released any details about possible causes of the collapse.

The investigation could take up to six months, according to David Kearns, area director for the Boise OSHA office.

“This is a tragedy with a lot of people across the valley grieving today,” Kearns said. “Unfortunately events like these often drive home the importance of ensuring that work site safety and health is a core value at workplaces.”

Wind can sometimes be a factor in the failure of buildings that are under construction, and gusts of up to 20 mph (32 kph) were recorded at the airport just before the collapse was reported, according to the National Weather Service in Boise.

Kearns said he couldn’t talk about whether wind might have been a factor. But he said he has been involved in other, unrelated investigations where wood-frame buildings collapsed under wind pressure because they were inadequately braced.

OSHA records show that Big D Builders received multiple safety violations from the agency in the last 10 years. The first, in 2014, was for having workers who weren’t trained in the proper procedures for erecting extension ladders. Two others in 2017 and 2022 resulted from having subcontractor employees working too close to holes in floors or walls without adequate protection from falls. A fourth violation in 2023 resulted in a $21,875 fine — a higher amount because it was deemed a “repeat violation” — after OSHA said workers were exposed to fall hazards while installing metal sheathing on the roof of a steel building.

There was no indication in the OSHA records that anyone was ever injured in connection with those violations. Fall and ladder hazards are among the most common violations issued by the agency.

Jackson Jet Center officials said in a statement that their “hearts go out to everyone affected by this horrific event.”

“We do not know exactly what caused the hangar collapse,” it said. “Our focus now is on supporting our team and partners during this difficult time.”

Boise Airport operations were not affected by the incident.

Cody McGowan was working about 100 yards (90 meters) from the building Wednesday when he heard a sound like a loud dog whine. When he looked up, he saw a hangar as tall as 3½ to 4 stories tall collapsing in on itself and part of the crane on top.

“When I walked up there, you’re just kind of like, ‘Wow,’” he said. “It’s shocking to see a building falling in on itself.”

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