NEWTON (CBS) – Two people were rushed to the hospital after a carbon monoxide leak at a school in Newton Friday morning.

Firefighters were called to the Franklin Elementary School on Derby Street just before 7 a.m. for an incident in the boiler room. Fire chief Bruce Proia says the call came in before any students had entered the school, but a few teachers were inside and called 9-1-1.

A janitor was found staggering around outside the building, and a man who was working on the boiler in the basement. Both were performing routine maintenance on the boiler before the leak occurred.

The fire chief told reporters the CO levels inside the school were “deadly.” Levels have been restored to normal, he added.

The janitor and worker were taken to Massachusetts General Hospital in Boston. They are awake, talking and expected to fully recover.

Classes were cancelled for the day, about a half-hour before the opening bell. Parents say they were well-informed after receiving a reverse 9-1-1 call about the incident.

“I’m glad that they are being careful and cancelling school,” parent Brenda Kostov told WBZ-TV’s Susie Steimle. “It’s the right approach.”

Police urging the public to stay back, saying Derby street is unsafe in front of Franklin School pic.twitter.com/nz6GxNWJRl — Susie Steimle (@SusieWBZ) October 9, 2015

Police were keeping people away from the school as a precaution. The scene was clear by noon.

Newton Mayor Setti Warren says “We will do a full investigation with the fire chief and the building commissioner to determine the cause.”

“We are pleased with the alarm system that was put in place,” said the mayor, “(And) the response that happened in an efficient manner, so that we can let kids know that they couldn’t come. We took precautions so that we didn’t have students and staff in the building today.”

Though the district has no other boilers under construction, every school’s equipment will be inspected by the end of the day Monday.

WBZ NewsRadio 1030’s Mike Macklin reports

