A leak in the machine that puts the fizz in a Rochester bar's soda dispenser released suffocating amounts of carbon dioxide into the basement and left an employee unconscious, authorities said.

Several of the man's would-be rescuers Monday morning in Rooster's Barn and Grill had their heroics foiled when they realized they also couldn't breathe, according to Deputy Fire Chief Steven Belau.

Firefighters toting oxygen supply tanks as part of their self-contained breathing apparatus entered the basement and carried Jerry Johnson outside to safety, Belau said.

Johnson, 63, was taken to St. Marys Hospital and was listed in fair condition Tuesday night.

Carbon dioxide "is not toxic," Belau said, "but it can displace oxygen, meaning that not enough oxygen is left in the air to sustain life."

Belau said the drama began about 9:45 a.m. at the bar at 2280 Superior Drive NW., when employees went to check on a hissing sound in the basement.

They found a leak in the carbon dioxide system that puts the fizz in carbonated beverages and powers the bar taps.

"The employees tried to shut off the CO2 tanks, but found they were having trouble breathing and turned around," Belau said. That's when Johnson collapsed.

Patrons and other ­employees "heroically tried to get into the basement and pull the victim out," Belau said, "but were turned back because they found they were unable to breathe."

Police hustled everyone out of harm's way, and firefighters soon arrived to rescue Johnson and get the carbon dioxide cylinders turned off.

"The survivor surely would have perished if not for the [properly equipped] firefighters," the deputy chief said.

Paul Walsh • 612-673-4482