Information provided by Centers for Disease Control and Prevention
Do not use generators, pressure washers, charcoal grills, camp stoves, or other fuel-burning devices indoors or in enclosed or partially enclosed areas such as garages, even with doors or windows open. Do not put these devices outside near an open door, window, or air vent. You could be poisoned or killed by carbon monoxide, an odorless, colorless gas from burning fuel such as gasoline, charcoal, or propane. Make sure a battery or electric powered CO detector is functional to alert you to dangerous levels of carbon monoxide in your home.
See also What You Need to Know When the Power Goes Out Unexpectedly.