ATLANTA — Potentially lethal carbon monoxide levels at an Atlanta elementary school with no detectors sent at least 42 students and seven adults to hospitals today and forced 500 more to evacuate, authorities said.

Young children with oxygen masks over their faces were strapped to gurneys and others carried to ambulances by emergency officials at Finch Elementary School in southwest Atlanta. Four students reported passing out at the school, according to hospital officials.

A teacher and a cafeteria worker were also among those treated.

Firefighters found unsafe levels of carbon monoxide near a furnace at the school with a reading at 1,700 parts per million, said Atlanta fire Capt. Marian McDaniel.

The colorless, odorless gas can be deadly at that concentration, said Stephanie Hon, assistant director of the Georgia Poison Center.

Superintendent Erroll Davis praised school officials for quickly evacuating after children started getting sick and said officials were considering installing carbon monoxide detectors in schools. Finch Elementary did not have a detector, he said, though he did not know whether any other district schools had detectors.