A woman is suing the maker of a portable heater over the deaths of her parents and two daughters in Madison from carbon monoxide poisoning. They were using the heater to keep warm while sleeping in a horse trailer before last year's World Clydesdale Show.

The lawsuit that Karina Clay filed in Dane County Circuit Court claims the company knew the heater was dangerous but sold it without safety warnings.

Found dead a year ago were 68-year-old DeVere Clay and his 57-year-old wife Barbara Clay, who were Clydesdale breeders from Tomah, and their granddaughters, 10-year-old Erin Briney and 13-year-old Hope Briney.

They were at the Alliant Center for the World Clydesdale Show, which opened the next day.

The lawsuit seeks unspecified damages from Mr. Heater Corporation and its parent company, Enerco Group, of Cleveland.