Four family members were found dead Monday in their home of apparent carbon monoxide poisoning, bringing the death toll from the Northwest's worst windstorm in a decade to 14.

The four — one woman and three males — were found in a home in Burien, a south Seattle suburb, along with another relative who was clinging to life, said King County sheriff's Sgt. John Urquhart. Like many in the area left without power after the storm, they had been running a generator in their garage, authorities said.

"Other family members had last talked to them around Saturday," Urquhart said. "They called us to make a welfare check. We broke into the house and found them."

Carbon monoxide — an odorless, colorless and highly toxic gas — was also responsible for killing two men over the weekend. One had been using a portable generator in his living room; the other was using a charcoal grill to heat his bedroom.

At least 100 people have developed symptoms of exposure to carbon monoxide since the winds knocked out power to more than a million homes and businesses late last week. Dozens were treated in a hyperbaric chamber that re-oxygenates the blood at Virginia Mason Medical Center, officials said.

Of the 14 storm-related deaths, 12 were in Washington and two were in Oregon.

"We're dealing with a carbon-monoxide epidemic in Western Washington," said Dr. Neil B. Hampson at Virginia Mason's Center for Hyperbaric Medicine. "This has the potential to be the worst case of carbon monoxide poisoning in the country."

The region's worst windstorm in more than a decade struck on Thursday, knocking out power to more than 1.5 million homes and businesses. Wind gusted to 113 mph during the storm near Mount Rainier and to a record 69 mph at Seattle-Tacoma International Airport.

About 200,000 customers were still without power in western Washington, utilities reported, as temperatures were in the low to mid 20s over most of the affected area early Monday. Authorities said it could be days before power is restored.

Washington Gov. Chris Gregoire declared a statewide disaster and the state National Guard was mobilized to help get fuel and supplies to hard-hit areas.