Emergency crews in two cities responded Saturday to carbon-monoxide alerts in buildings where heating vents had been clogged by snow from the historic blizzard.

In Biddeford, five people were being treated at Southern Maine Medical Center for possible carbon-monoxide poisoning Saturday afternoon.

Biddeford Fire Department Deputy Chief Kevin Duross said the residents of a single-family home at 49 Green St. heard their carbon-monoxide detector sounding at 1:45 p.m. They were transported to the hospital with non-life-threatening symptoms.

Duross said it appears that carbon monoxide built up inside the house after the outside vents to the propane furnace became clogged with snow. He advised residents to make sure their own vents are operating properly and not blocked by drifts.

Carbon-monoxide buildup apparently caused by a blocked roof vent pipe also brought firefighters to the Turnpike Mall in Augusta on Saturday.

No one was injured, and all the pets inside Petco — about 50, including a chameleon, reptiles, ferrets and other animals — were safe, if temporarily chilly because the doors were opened to allow fresh air inside.

Derek Allee, who works for Taurus Management Services LLC, called the fire department after a worker at Olympia Sports reported an unusual odor.

Augusta Fire Department Battalion Chief Daniel Guimond said a carbon-monoxide reader measured 62 parts per million when he entered the common area at the mall — prolonged exposure at 35 parts per million can be lethal.

Guimond ordered doors opened and went inside Petco, where he found elevated levels as well.

Firefighters then turned their attention to the roof-mounted propane heaters.

“One of the vents was completely covered over with snow,” Guimond said.

Firefighters shoveled off the snow. With the vent cleared, the doors open and fire department fans operating, the carbon monoxide dissipated quickly.

A furnace repair service was called as well, and the worker said a mechanical problem might have contributed to the carbon-monoxide buildup.