The Occupational Safety and Health Administration is investigating after a worker falls to his death during an expansion project at Lockheed Martin's Cobb County campus.

Van Winkle Construction Company Spokesman Thornton Kennedy tells WSB 22-year-old Kevin Michael Yager was an employee of a roofing subcontractor when he fell more than 40 feet from a hangar around 7:15 a.m. Wednesday.  He says it has been a very difficult day and their thoughts and prayers are with the young man's family.

"From what I understand, he was not tied off, so at some point he fell from a high area and died from injuries resulting from that fall," said Kennedy.

Kennedy said there were close to 100 workmen on the site including a safety director.

"I think that is the responsibility of the person to make sure that they are properly tied into the system.  It's a harness system, a four point harness system.  There are guide wires that you should be tied into with a rope to make sure that if anything were to happen or if you were to fall, you'd be caught by the guide wires," said Kennedy.

This is the first fatal accident for the company in 40 years.

"Van Winkle Construction has been around for a long time and this is something that has really rocked Van Winkle Construction to its core because it's such a rarity," said Kennedy.

The company has been expanding three hangars at Lockheed Martin since March.

"We really put employee safety and worker safety first.  Everybody goes through rigorous training.  That's our employees as well as anybody that works on our sites," said Kennedy.