A number of Madison residents were evacuated from an east side apartment duplex Thursday after the building’s carbon monoxide reading was nearly five times the level considered toxic for healthy adults.

The Madison Fire Department responded to a call from 1027 Jana Ln. around 11 a.m. after a CO detector sounded in an adjacent unit, a MFD report said.

One Madison woman was hospitalized as a result of continued exposure to 350 parts per million of CO, the report said. A healthy adult encounters toxicity at 50ppm.

Firefighters and paramedics responded after a Madison Gas and Electricity Company employee had arrived to examine the alarm in the neighboring unit, according to the MFD.

All occupants were evacuated from the duplex as crews searched for the source of CO in the building’s exhaust vents.

Lori Wirth, spokesperson for the Madison Fire Department, said some houses’ ventilation systems can experience blockage after significant snow fall.

“When you have a really heavy snow storm as we did this week, particularly with drifting, homes may catch four or five feet of snow drift that can block vents and release toxic gas into living areas,” Wirth said.

Wirth said the Fire Department has received more than a dozen calls since Wednesday from Madison residents reporting CO in their homes.

The houses that turned up high CO levels were ventilated and their furnaces were cleaned and are now perfectly livable, Wirth said.

Although snowdrifts were originally suspected in the Jana Lane case, Wirth said MGE has ruled snow out as the culprit and is currently investigating a possible malfunction in the actual vents.

“It’s fortunate that her neighbors invested in a carbon monoxide detector,” Wirth said. “Madison Fire Department recommends everyone install a detector in their homes.”

Early symptoms of CO poisoning include nausea, disorientation and mimics flu symptoms, Wirth said.

Wirth said the city and Red Cross offer temporary shelters for residents displaced by CO contamination, but none of the victims in the past 72 hours have requested this service.

“This is a case of going to a friend’s house or neighbor’s house as the situation is being dealt with quickly,” Wirth said.