Portland, OR – Portland fire officials say a man has been found dead in a home with high levels of carbon monoxide and a woman is in critical condition.

Firefighters were called Wednesday evening to the southeast Portland home to find the man dead and the woman unresponsive. Family members who stopped by to visit had called for help.

The woman was listed in critical condition Wednesday night at Providence Portland Hospital.

Fire Department spokesman Lt. Allen Oswalt says investigators think carbon monoxide poisoning is to blame.

KPTV reports that a test of the home showed high levels of the dangerous gas.

Fire officials say the couple had sealed off their windows with plastic and tape and were using a portable natural gas heater that wasn’t properly ventilated. The low temperature overnight Tuesday at Portland International Airport was 12 degrees.