LITTLETON, Colo. (CBS4) – Investigators say that the cause of a deadly fire at an assisted living facility in Littleton is accidental, even though they haven’t determined a cause. One man died and 13 others were rushed to the hospital after the fire.

Just after 5 a.m. Saturday, firefighters rushed to the senior living complex where the fire broke out in a first floor apartment.

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Fire investigators are sampling the air in all the units. Once the air sampling is complete, a decision will be made about when residents can return.

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It was not the first time the complex has been ablaze. A bigger fire there in April of 2016 displaced more than one-hundred residents.