Oil Filled Electric radiator heaters do not emit or produce any carbon monoxide.
Oil filled radiators work by a heating element that is powered by electricity to heat the oil up inside the oil filled radiator heater.
Just like an electric water heater works by use of an electric heating element the oil filled radiator heater works the same way to heat the oil up.
The oil never needs replaced as it never burns off inside the oil filled heater.
The electric heater element gets the oil hot enough to heat the inside of the oil filled radiator heater up which then produces the heat.
Oil filled electric radiator heaters are safer than other electric heaters but they still need to be on a dedicated circuit and never use an extension cord with the electric heater unless it's a heavy duty one.
An electric heater should never be plugged into a power strip either as it will overload it and melt it.