A Royal Oak high school is open for class on Monday, but its swimming pool remains closed after a weekend carbon monoxide scare, Local 4 reported.

The city fire marshal, maintenance staff and an outside contractor are searching for the source of the leak that caused the evacuation of several people during swimming lessons on Saturday at Dondero High School.

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More than 30 children and adults were treated for carbon monoxide poisoning.

Of the 35 patients seen by doctors at William Beaumont Hospital, six had high levels of carbon monoxide that required placement in a hyperbaric chamber, said Dr. Frank McGeorge, director of emergency medicine at Beaumont.

McGeorge said the patients ranged in age from 6 to 46.

More than 50 people were transported or went to Beaumont after many of those inside Dondero High School were sickened, Royal Oak police Sgt. Barry Gale said. Police were called after 10 a.m. and laid those sickened on a sidewalk outside the school, he said.

The entire school was evacuated as a precaution.

Testing by the fire department indicated that the carbon monoxide levels in the pool area were near 500 parts per million, Local 4 reported. The station learned that the level at which the gas is considered to be dangerous is 32 parts per million.

The leak was believed to have come from a malfunctioning furnace, fire officials said, but the cause was under investigation.

No serious injuries were reported and all of those treated have been released from the hospital.

The high school does not have a carbon monoxide detector, but Local 4 learned that public buildings are not required to have one. School officials are reviewing the incident to determine if a detector on school property is necessary, the station reported.

A regional dive meet that was scheduled to be held at Dondero on Tuesday night has been relocated to Kimball High School on Crooks Road.