Inmates fell ill with symptoms of carbon monoxide poisoning Tuesday morning when a water heater apparently malfunctioned at a minimum-security prison.

The prisoners complained of faintness and trouble breathing, said Dina Tyler, spokeswoman for the Arkansas Department of Correction.Eleven prisoners were sent to Little Rock hospitals and the prison system diagnostic hospital in Pine Bluff, Tyler said. The rest of the 96 inmates whose barracks are served by the boiler were moved to a gym.

While the Wrightsville minimum-security unit has some of the prison system's older buildings, the boiler in question is less than 8 years old, Tyler said.