ATLANTA — It’s odorless, colorless and deadly. And if carbon monoxide is leaking in a school, it might not be detected until people are ill.

A leak at an Atlanta elementary school that sent 42 students and seven adults to hospitals had school officials considering whether to install carbon monoxide detectors, a possibly life-saving move that is only required in a handful of states.

The detectors are not required in schools by law in Georgia and other states. Connecticut requires them in schools, while Maryland requires them in newly built and remodeled schools. Building codes and local rules can require them in schools elsewhere. When properly installed, the detectors give a warning when carbon monoxide reaches unsafe levels.

“To me, it’s somewhat of a no-brainer in the sense that you’ve got fire alarms,” said Doug Farquhar, program director for environmental health at the National Conference of State Legislatures. “There’s no school in the country that’s going to open unless there’s a fire alarm system. Why not add carbon monoxide?”

The leak in Atlanta proved serious but not fatal. Superintendent Erroll Davis credited officials at Finch Elementary School with quickly evacuating the school after children started getting sick. The kids are attending classes at a nearby middle school until the problem is fixed. Fire department officials Tuesday said the school is not allowed to reopen until a deficient boiler system is inspected and certified.

Carbon monoxide, a byproduct of combustion, was discovered at unsafe levels near a school furnace. When it builds up in enclosed spaces, people exposed to the gas can experience headaches, dizziness, weakness, nausea and confusion, according to the U.S. Centers for Disease Control and Prevention. Inhaling high levels of the gas can eventually cause loss of consciousness and even death. The poisoning can be difficult for doctor to diagnose since its symptoms mirror those of other ailments.

Leaks are not unheard of. A malfunctioning water heater was blamed for sending higher-than-normal levels of carbon monoxide through an elementary school in Glen Rock, Penn., in September, sickening around 40 people. In February 2011, about 40 students and faculty were treated for suspected carbon monoxide poisoning at Snow College in Ephraim, Utah. Another carbon monoxide leak forced the evacuation of an elementary school in St. Paul, Minn., in 2010. Firefighters traced a leak back to basement boilers.

A model environmental policy for schools published by the U.S. Environmental Protection Agency recommends that schools install carbon monoxide detectors near combustion sources, such as boilers, stoves and water heaters. It also advises that ventilation systems receive regular maintenance.

“Improperly managed ventilation and filtration systems can contribute to airborne mold, infectious diseases, and carbon monoxide poisoning,” the report said.

Commercially available carbon monoxide alarms designed for homes range in cost from around $13 to more than $100. Alford said Atlanta school officials have recently discussed models that cost around $15.

Facility managers in school sometimes must make financial decisions on which safety upgrades they can afford, especially when those fixes are not required by law. Still, Farquhar said the alarms are relatively cheap for the protection they provide.

“It’s not asbestos where you need to go in and rip everything out and close the school for months on end,” he said. “You just put the detector in and it’s pretty cheap and cost-effective.”