IONIA, Mich. (WOOD) — The Ionia County Jail says a carbon monoxide leak that sent nine inmates to the hospital was detected because of a chemical smell that turned out was coming from a boiler ventilation pipe.

The jail said the leak was first detected just after midnight Saturday when staff was made aware of a chemical smell in a housing unit and inmates reported feeling sick. The nine inmates were moved outside for fresh air and the Ionia Department of Public Safety was called. Officers found a concentration of carbon monoxide and maintenance identified that the smell was coming from a ventilation pipe on a boiler supplying hot water to the unit.

The prisoners were taken to hospitals, including a few in Grand Rapids due to overflow at the Ionia hospital.

Meanwhile, the jail says repairs were made to the leak and Ionia Department of Public Safety made sure carbon monoxide levels were back below acceptable levels at the housing unit.

The inmates were treated and cleared by medical staff. Seven inmates returned to the jail by Saturday afternoon. One was granted an early release because his sentence was supposed to end in a few days. The last inmate was being detained by another agency but it released its hold on him so he left on bond, the jail said.

The problem unit had been inspected in November, the jail said, and “regularly maintained.” The jail was inspected by the Michigan Department of Corrections in February and passed its standards. Calling it an “isolated incident,” the Ionia County Jail said measures have been put in place to identify the problem quickly if the mechanical failure should happen again.

“Our staff did a great job identifying an issue and taking swift actions to ensure that all the inmates were removed from any danger and then getting them the appropriate medical attention,” the jail wrote in a Tuesday release.

But loved ones say Ionia County Jail inmates complained of feeling ill for days before they were finally hospitalized. The girlfriend of one inmate told News 8 that her boyfriend went through the jail’s designated channels to ask for help. An email from one inmate to a loved one said they begged for ambulances, but it wasn’t until a group of inmates threw up in the middle of the night that anything happened. The jail did not confirm that any symptoms were noticed before Saturday.

The inmates who returned to the jail after being hospitalized said they continued to experience symptoms. The jail says inmates affected are still being monitored by medical staff.