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MIAMI (CBSMiami) — Firefighters say they know what caused a gas leak that sickened dozens in a South Florida business.

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Miami-Dade Fire officials said carbon monoxide was leaking from two bathroom drains on the first floor of the Lennar building in Sweetwater.

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The leak sickened employees in the building earlier Monday. Crews rushed seventeen people to the hospital and about 30 others were treated at the scene. Another 80 people went home not feeling well.

In total, the building houses about 400 employees.

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The building, located at 700 N.W. 107th Avenue, will remain closed until the valves are fixed and inspected.