A battery-operated detector was installed within 20 feet of every open flame on district property, CPS officials said. View Full Caption Talcott Fine Arts Academy (file)

CHICAGO — A day after CPS officials said that the installation of approximately 5,900 carbon monoxide detectors at schools citywide was complete, the alarms went off at a South Side elementary school alerting officials to the presence of the poisonous gas.

Some transports from Horace Mann school from high co readings. Alarms tripped early and exposure is low. Transports all good condition — Chicago Fire Media (@CFDMedia) December 3, 2015

Newly installed detectors tripped as designed as school was starting. Students moved quickly to another building — Chicago Fire Media (@CFDMedia) December 3, 2015

More than 100 students and seven staff members required medical attention — including students — but were in good condition late Thursday morning, according to the Chicago Fire Department. Horace Mann Elementary is located at 8050 S. Chappel Ave.

Chicago Public Schools CEO Forrest Claypool ordered detectors to be installed in all schools after the noxious gas seeped into a Jefferson Park school and sickened approximately 89 teachers and students.

An investigation of the incident at Prussing Elementary School on Oct. 30 found "shocking things," he said.

When the boiler malfunctioned at Prussing Elementary School at 9:30 a.m. Oct. 30, the Jefferson Park school had no carbon monoxide detectors, which are not required by state law or city ordinance. A detector in the school's boiler room — in a separate building — was unplugged when the heating system malfunctioned, officials said.

A battery-operated detector was installed within 20 feet of every open flame on district property, including in boiler rooms and kitchens. Additional detectors were installed to cover every 10,000 square feet in schools, district officials said.

District officials agreed last week to replace Prussing Elementary's boiler, bowing to demands from parents who said they did not feel safe sending their children to school knowing the boiler — the subject of a litany of complaints dating back to 2013 — that had sickened their children was still operating.

A permanent engineer has also been assigned to the school at 4650 N. Menard Ave. five days a week to monitor the school’s heating system. City officials will also inspect the boiler once a month to ensure that it is working properly, Claypool said.

District officials have moved to fire Patrick Kelly, the engineer on duty Oct. 30, who was suspended without pay after the incident.

Several lawsuits have already been filed against the CPS in connection with the incident.

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