A couple of yrs ago. Two people in my county who were camping in a tent[Fall time]. Died from from useing a kerosine heater in a "closed" tent...No exhaust or fresh air to circulate.
Personally any appliance that puts out CO[exhaust] into the living quarters. I would use "sparingly" for a "temporary" heat source. Generally, the elderly & children are the 1st to develope signs of CO poisioning. But, not etched in stone.
Some yrs ago, we carried out a whole family with CO poisioning[bad furnace]. One of them was unconscious.
Severe CO poisioning victims, generally are treated in a Hyper Baric Chamber with saturated oxygen.