For the first time since the school was evacuated on Monday, Finch Elementary School will reopen to students Friday morning.

More than 50 students and adults were sent to the hospital Monday when they got sick because of a carbon monoxide leak.

The school’s principal sent a letter home to parents Thursday saying carbon monoxide detectors have now been installed inside Finch. The school system will also put them in across the district.

Investigators originally thought the school’s boiler went bad, but it now looks like the leak was caused by human error.

Atlanta Public School Superintendent Erroll Davis says two maintenance workers did not reset a valve inside the boiler room while they were working on it last Friday. The boiler began to overwork during the weekend and carbon monoxide was building when students arrived Monday.

The two workers did not tell anyone about it until investigators found them Thursday.

"When all of this broke I would have hoped that they would've come forward and at least indicated that they were working on equipment in the building," Davis said. “This is obviously a serious matter. We have now launched a full investigation of that. Again, we hold our employees to the highest ethical standards, and we intend to address these issues swiftly.”

An investigation is under way to determine why that didn't happen.

"I think they should lose their jobs because it is not a mistake that needs to be made. Their mistake put people's lives in danger," parent Desmond Sigers told Channel 2 Action News.

Fire investigators said they measured record high levels of carbon monoxide inside the school that could be lethal within two hours.