two days ago I broke couple of ice fishing rules and almost bought the farm. went fishing alone,mid week and my propane heater nearly co2 me to death. two days to recover! seems the heater I btg has had legal issues and was the kind that lawsuits were brought against mfg. I was in flip style shanty in open wind with I thought was plenty of air but was way wrong! I was barely able to make it to shore with gear in tow. sat in truck till I could see and move again. be carefull. I now have heard from many that they carry battery operated co2 units with spare batterys in their safety gear.