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MIAMI (CBSMiami) — Investigators are trying to find out what is causing a gas leak that sickened dozens of employees in a Sweetwater building.

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The fire department originally believed it had to do with heavy equipment working in the building over the weekend but that has changed.

They then speculated that the source of the carbon monoxide leak could be a slow electrical burn in or behind a wall in an equipment room. The room is located on the second floor and is filled with large batteries meant to supply back-up power.

But that theory was also shot down.

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The fire department announced the carbon monoxide was emanating up from two malfunctioning bathroom drains on the first floor. As for how the gas got into the sewer and flowed up through the drains, that remains unanswered.

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.

The building located at 700 N.W. 107th Avenue houses the company Lennar. In total, the building houses about 400 employees in the building.

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The building will remain closed until the valves are fixed and inspected.