Authorities are pleading with residents not to use generators or gas grills inside area homes left without power by the icy weather.
Robert Kagel, deputy director for emergency management in Chester County, said two dozen or so people were taken to hospitals overnight with carbon monoxide poisoning.
"We ended up sending about 25 people to the hospitals overnight -- four of them fairly critical -- becasue they were using gas grills or generators inside producing carbon monoxide," said Kagel.
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He said some of the more seriously injured were transferred to Philadelphia hospitals for treatment.
Kagel said about 130 people spent the night in emergency shelters in the county, one of the hardest hit by Wednesday's storm.
In past storms officials have repeatedly warned of the dangers of using generators or gas grills inside or keeping cars running with garage doors closed.
People turned to generators and other sources of power to heat and light their homes after more than half a millions customer lost power in the ice storm.
In total, Kagel estimated about 350,000 of the county's 500,000 resident had no power midday Thursday.