Napa Valley, CA – One man died and another went to Queen of the Valley Medical Center in critical condition on Monday after what appeared to be carbon monoxide poisoning.

Details were sketchy at the scene on the 1000 block of Foster Road at 1:30 p.m. Napa Police Sgt. Ryan Cole said the occupants may have been heating the home with propane.

“That’s preliminary,” Cole said as paramedics, police and firefighters walked around in the front yard. “There will be a full investigation by police.”

The house is on a large lot against a hill, making it seem like a rural pocket within city limits. Emergency crews tried vainly to revive one of the victims on the front lawn before covering the deceased with a yellow tarp.

Two fire trucks, a paramedic unit, an ambulance and four police cars blocked off Foster Road to traffic in front of the house at 1:30 p.m. Firefighters had hooked up a hose to a hydrant near Snow Elementary School as a precaution against a possible gas leak.