Chicago, IL – By Brendan McCarthy, Tribune

Three workers were hospitalized Monday afternoon with carbon-monoxide poisoning after using power-washing machines in an underground downtown garage.

The men, employees of a power-washing company, were running two gas-powered machines when they became ill about 2 p.m. in the lower-level garage at 1130 S. Michigan Ave., Chicago Fire Department spokesman Kevin MacGregor said.

One man was found unconscious and was taken in critical condition to Loyola University Medical Center, Maywood, MacGregor said. The other two men were taken to area hospitals in serious condition.

The carbon-monoxide level in the garage was measured at 500 parts per million, MacGregor said. A safe level in a home is considered to be about nine parts per million.

“This was extremely high levels and a deadly condition,” MacGregor said.

The garage is connected to a 43-story residential building, he said. The air exchanges for the garage and building units were not connected, and no one else inside the structure was affected. Emergency personnel checked the building and tested the levels, MacGregor said.

On Friday, a similar incident took place in a building at 1322 S. Wabash Ave. In that case, a resident was seriously injured from high levels of carbon monoxide. The source of the carbon monoxide was a gasoline-powered power-washing device in the basement.

“The building managers need to be aware that they are creating a dangerous atmosphere,” MacGregor said. “This can be deadly.”