ATLANTA (AP) — Potentially lethal carbon monoxide levels in an Atlanta elementary school sent 42 students and six adults to hospitals Monday amid the evacuation of about 500 students, authorities said.

A teacher and a cafeteria worker were among patients treated after firefighters responded to Finch Elementary School shortly after 8 a.m., Atlanta fire Capt. Marian McDaniel told The Associated Press.

Firefighters were initially told people were unconscious at the school, but none were when fire crews arrived. All the patients were conscious and alert as they were being taken to hospitals, McDaniel said.

News footage showed young children strapped to gurneys with oxygen masks on their faces and emergency officials carrying others in their arms.

Firefighters detected high and unsafe levels of carbon monoxide near a furnace at the school, which is on the city's southwest side, McDaniel said. She called the reading — 1,700 parts per million — extremely high.

"It was one of the highest we've seen," she said.

The colorless, odorless gas can be deadly at that level, one expert said.

"Seventeen hundred parts per million is potentially lethal if exposed to it for a period of time," said Stephanie Hon, assistant director of the Georgia Poison Center.

Children could be affected faster than adults and are generally affected at lower parts per million, Hon said.

She said it's easy for initial symptoms of carbon monoxide poisoning to be confused with the flu since both include malaise, headache, nausea and vomiting. A few key differences: Carbon monoxide poisoning generally does not cause a fever and generally a person starts feeling better once he or she is moved to an area with fresh air, Hon said.

Hon said it was fortunate the children do not appear to have suffered severe symptoms and said that was likely due to a short exposure time and perhaps the location of the leak being some distance from where the children were.

"The good news is that they sound like mild to moderate symptoms," Hon said. "Luckily those kinds of exposures do not carry significant long-term health risks, especially with the children involved."

It was not immediately known if the school had a carbon monoxide detector. If it didn't, Hon said, "A carbon monoxide detector, if appropriately used and installed and checked often, could have very well been a warning for this school system."

An Atlanta Public Schools spokesman did not return calls for comment. A district news conference was planned for Monday afternoon.

Bridgette Berry, a grandmother of two students at the school, said the children — ages 6 and 7 — were checked out at the hospital. The family was given a form instructing them to keep a close eye on the children and alert medical officials if they exhibit any symptoms such as a headache, Berry said.

If the school did not have a carbon monoxide detector, Berry said school officials must take action.

"They're not going back unless they get them," Berry said.

Her son and the children's father, Marquis Berry, said the family feels fortunate the situation wasn't worse and frustrated about what he called a lack of communication from the school.

"I had to find out about it on the news," he said.

A total of 42 students and six adults were taken to hospitals, Atlanta Public Schools said on its official Twitter site.

Other students from the school were taken to Brown Middle School for the rest of the day, and were being released to their parents.

Meanwhile, fire officials said they were ventilating the school in an attempt to reduce the amount of carbon monoxide.

In Baltimore last year, school officials vowed to put carbon monoxide detectors in all of the school system's approximately 200 schools after two carbon monoxide leaks within a week's time at one of the schools.

City officials in Baltimore said the battery-powered detectors cost $15 each wholesale.

Source: Jeff Martin from Associated Press. Associated Press writer Christina Almeida contributed to this report as well.