Allentown, PA – Nearly three dozen adults and children were evacuated from a day-care center in Allentown, Pa., on Tuesday after emergency workers responding to a report of an unconscious child detected carbon monoxide, an invisible, odorless gas that kills hundreds of people in the United States every year.

Of the 27 children and eight adults who were evacuated from Happy Smiles Learning Center, at least 28 were taken to four area hospitals, officials said. A malfunctioning heating unit and a blocked venting system had caused the leak, investigators told the local Morning Call newspaper.

“Thank you to our neighboring municipalities who also responded quickly and arrived on scene to offer mutual aid,” Allentown’s city government said in a statement. All patients are “stable and there’s no ongoing danger to the neighborhood or the community.” The center’s license has been suspended in the wake of the incident, the statement said.

Allentown’s city council passed a safety ordinance in February mandating that day-care facilities install carbon monoxide detectors. But the Happy Smiles Learning Center and the city’s 160 other day-care centers had until Oct. 27 to comply, and the center had passed an inspection in July. Happy Smiles owner Jesenia Gautreaux told the Morning Call that the center didn’t have detectors but that she intended to have them installed.

The incident prompted a state legislator to renew calls for colleagues to pass a pending bill that would require child-care centers across Pennsylvania to install carbon monoxide detectors.

Tragedy “was narrowly avoided,” state Sen. Wayne D. Fontana (D) said in an email sent to fellow lawmakers that he later posted on his website. “I urge you to pass Senate Bill 129, which is currently in the House Health Committee, that would require inexpensive battery-operated devices” be placed in child-care centers, he said.

The bill passed the Pennsylvania Senate unanimously last month and at least twice before in previous years, according to Fontana. It awaits approval from the lower legislative chamber. State Rep. Jeanne McNeill (D) urged the House to bring the safety bill to a floor vote in a short statement on Twitter that mentioned Tuesday’s incident.

Many unintentional carbon monoxide poisonings occur from December to February, according to figures published by the CDC. “When winter temperatures plummet and home heating systems run for hours the risk of carbon monoxide poisoning increases,” the CDC says.

The gas usually comes from fumes produced by furnaces, kerosene heaters, vehicles with running engines in closed garages, stoves, lanterns, gas ranges, portable generators and burning charcoal or wood.

The CDC recommends that people check or change the batteries of carbon monoxide detectors every six months, check on heating systems and burning appliances every year and never run a gasoline-powered engine less than 20 feet from an open window. Carbon monoxide poisoning is “entirely preventable,” the CDC says.