A construction worker in Florence was rushed to Huntsville Hospital after Florence Fire said he was overcome with carbon dioxide while working in a tunnel on Thursday morning.
It happened while the worker was in a tunnel under Veterans Drive and Cole Avenue.
Firefighters said when they got to the worker in the tunnel he was unresponsive, but revived when taken into the fresh air.
Officials said there was natural gas in the tunnel but believe some of the construction equipment failed to monitor the carbon dioxide levels
"He was about 50 feet into the tunnel," said Dennis Brown, a Battalion Chief with Florence Fire.
"They did have a fan blowing in the tunnel and they had an air monitor also, but it evidently was not working."
Winds prevented the man from being airlifted to Huntsville Hospital, so instead he was taken by ambulance.
The man's name wasn't released. He is only described as being in his 20s.