In the spring of 2006, Sarah Weiss and her two children were evacuated from their Beverly house after dangerous levels of toxic carbon monoxide (CO) fumes filled the basement. The Weisses' oil burner malfunctioned, and the CO detector in the basement — the only one in the house — failed to go off. Sarah Weiss happened to smell the burner's blowback and immediately called the Fire Department.

Had she not detected the scent from the burner, the results could have been fatal. Carbon monoxide is a tasteless, odorless, colorless and toxic gas that causes mild nausea, headaches and shortness of breath at low levels, according to Environmental Protection Agency. At moderate levels, it causes severe headaches, dizziness, mental confusion, nausea and fainting spells. And at high levels — more than 100 parts per million — CO poisoning can be fatal.

At the time, the Weisses' home was not in compliance with a new law that required all Massachusetts homes with fossil-burning fuels (natural gas, oil, wood, propane, gas and coal) to have carbon monoxide detectors installed on every inhabitable floor.

Weiss, who credited the Beverly Fire Department with educating her on the law, said her husband, Eric, immediately bought combination smoke/carbon monoxide detectors for the house.

"We're very vigilant now, absolutely, just because it was a close call," she said.

"Nicole's Law," named after Nicole Garfalo of Plymouth, who died of CO poisoning in January 2005, was passed on March 31, 2006, with the help of now-retired Lt. David Deluca of the Danvers Fire Department.

Deluca, who said he was on the committee that helped to write the law, had a personal connection to CO poisoning: His high school classmate, Edward Arrington, died of it in 2001.

Deluca has a carbon monoxide detector on every inhabitable floor of his Danvers house.

"I'm a big advocate, because they save lives," he said.

While detectors can save lives, many North Shore heating experts agree that the problem can often be eliminated with regular maintenance of heating systems, whether they be oil, gas or wood-burning fireplaces.

David O'Shea, co-owner of All About Chimneys in Marblehead, said that damaged chimneys or those blocked up with accumulated soot can lead to CO gases leaking back into a house. To alleviate this, O'Shea will check and clean a house's entire chimney system and all its flues.

In rare cases, animals block chimney flues, said O'Shea, who added his employees have removed birds and squirrels — dead and alive — from chimneys on the North Shore, as well as bleach bottles and even beer bottles.