Warden Mary Sabol said the deadly gas appears to have leaked from the heating and air conditioning system in the York County Jail, The York Dispatch reported. She said a dormitory for women was the only area affected.
The leak was discovered late Wednesday when one inmate became sick. Sabol said 40 to 45 inmates and several guards were treated at local hospitals.
Hospitals said most of the patients had been treated and released by Thursday morning.
"It appears that everyone is going to be OK," Sabol said.