Waterloo, IA – Authorities say four adults and a toddler have been treated for carbon monoxide poisoning in Waterloo.

Firefighters found a woman unconscious in a doorway at the residence Wednesday night, March 2, 2016 and the rest of the occupants were out of the house and conscious.

Fire Battalion Chief Marty Freshwater says a gas-powered generator placed in a laundry room by the back door was supplying electrical power to the house and had been operating for about 30 minutes. Freshwater says the occupants mistakenly thought leaving a window open on the storm door would provide enough ventilation.

The occupants called 911 for help around 11 p.m. when they became sick at the same time.