Offices at 150 Lake Street in Elmira reopened Wednesday afternoon after a carbon monoxide leak was discovered Monday morning.
Five Star Bank, the Trinity of Chemung County, and Moore & Woodhouse were among the offices evacuated on Monday.
First responders arrived around 9:00 a.m. on Monday after receiving a call from the office that people were falling ill.
CO levels as high as 850 parts per million. Levels of 1200 parts per million are considered fatal.
Investigators blamed the leak on a defected furnace.