Be very cautious with ANY heat source
Quoting Kevin above: "Be very cautious with a 'vent-free' heat source"
You could remove 'vent-free' from the line. All heat sources carry inherent risks.
"With no vent or flue pipe the combustion gases from the heater end up in the room/house with you."
Modern kerosene and gas heaters have combustion efficiency exceeding 99.9% which reduces CO production down to miniscule levels. The combustion gases then are essentially water vapour and carbon dioxide. If a heater is properly maintained, the greater risk is O2 depletion.
"Your life will be in your hands"; your life is always in your hands.