@Drentel - You are taking the negative aspects of propane lawn mowers and not considering the positive aspects. And by the way, gas mowers can release dangerous fumes and cause fires, too. You make it sound like gas engines are perfect when we know that's not true.
And if you don't like propane, there are other mowers that are better for the environment. Electric mowers, cordless mowers and the old push motors that don't use an engine are all environment friendly.