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ARGYLE (CBSDFW.COM) – Federal investigators with OSHA are looking into the cause of a deadly construction collapse at Argyle High School. Construction workers frantically called 911 at around 7:40 a.m. on Thursday morning, after a building’s metal framework suddenly collapsed onto them.

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One worker told the dispatcher, “It’s bad. It is bad. There’s people down”

Another employee said, “We’re erecting a metal building and it collapsed. We need to get emergency personnel out here immediately.”

Employees quickly realized that one of their own was killed. The Tarrant County Medical Examiner’s office has not identified him. Three other workers received minor injuries. Paramedics transported two employees to the hospital, but they were later released.

About 15 workers in all were on site at the time of the collapse. They were building Argyle High School’s new indoor athletic center. “I was just watching it being built yesterday,” said Shawn Cooles, who spotted the commotion when she dropped her daughter off at school. She returned later to leave flowers on the fence for the worker who died. “I just feel sorry for the family.”

People continued to bring flowers through Friday morning.

Annabel Thorpe is a broadcast journalism student who interviewed witnesses. “They just said the structure started to wave. The walls, they started moving, and it all collapsed, like all sides just caved in and it created a huge noise.”

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A source said that the worker who died was in a bucket on a vehicle when the building came down on it. The source said that another employee quickly dove under another large piece of equipment when heard the frame collapsing around him.

OSHA’s team of investigators is inspecting what is left to determine if any workplace safety regulations were violated. The agency said that the employees work for a subcontractor, Warnick Metal Building Erectors of Haltom City. The company has not returned our calls.

Court records show that the company was involved in another building collapse in 2007 in Fort Worth. A lawsuit blamed the company for failing to “properly weld the structure.” In 2012, OSHA fined the same company $2,900 for a serious safety violation.

The general contractor, Northstar Builders of Coppell, declined to comment.

Argyle ISD superintendent Telena Wright said that their police department is also investigating. “My thoughts go out to the family of the deceased — I do not know the identity of the worker yet — and to those workers who were injured. It’s a terrible, terrible, terrible tragedy and I am so very sorry.”

The district said that the building is for athletes, coaches and the band. Before it collapsed, the frame stood 50 feet tall and 180 feet long. The nearly $300,000 project is scheduled to be completed this fall, and there is no word how long construction may be delayed.

Thorpe said that it was a tough day on campus for administrators and students, including herself. “It’s very difficult knowing that someone died and me having to cover it, but that’s part of the job and that’s something you have to learn.”

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There is a baseball game scheduled at Argyle High School on Friday night. Many people are expected to gather there for a candlelight vigil.