in order for gasoline to be ignited there must be an open flame or spark with an extremely high temperature. the smoldering tobacco in a cigarette is not sufficent to ignite gasoline as shown in the video above.
the temperature of the burning section of a lit cigarette is as follows
Side of the lit portion: 752 deg F
Middle of the lit portion:1112 deg F)
These temperatures are theoretically high enough to ignite concentrated petrol vapors however in the case of an open lawnmower outside, there is an insufficient vapor to air ratio.
You also have to consider the fact that outdoors there is a breeze and the lawnmower is in motion so the potential flammable vapors have no chance to gather and build up to any concentration even remotely close to the air to fuel mixture necessary for ignition.
Gas is designed for use in an engine which is driven by a spark. The fuel should be premixed with air within its flammable limits and heated above its flash point, then ignited by the spark plug. The fuel should not pre-ignite in the hot engine. Therefore, gasoline is required to have a low flash point and a high auto-ignition temperature.
For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel. 7% gas, 93% air. This may seem like an easily attainable amount of vapors but in fact it is unrealistic and requires an enclosed environment to achieve this kind of ratio.
In theory a stoichiometric mixture has just enough air to completely burn the available fuel.
In the case of operating a lawn mower outdoors the air ratio greatly outweighs the possibility of residual gasoline vapors.
Thus a cigarette will not light gasoline.
If you throw a lit match in a can of gasoline, the gasoline will put the match out.
If you throw a lit cigarette in a can of gasoline, the gasoline will put the cigarette out.
SO, IN CONCLUSION, SMOKING A CIGARETTE WHILE MOWING THE LAWN HAS MINIMAL RISK OF IGNITION. IN FACT THE HEAT OF THE ENGINE REACHING A TEMPERATURE HIGH ENOUGH TO IGNITE THE POSSIBLE RESIDUAL VAPORS IS MORE LIKELY THAN THE VAPORS BEING IGNITED BY THE OPERATOR'S CIGARETTE.
So you may wonder, if a cigarette cant ignite gasoline then why is it illegal to smoke at the pumps?
The answer to this is quite simple.
The environment at a gas station is specifically designed to vent gas vapors so that they don’t build up to the required fuel to air ratio. Therefore merely smoking a cigarette at a gas station is NOT dangerous.
Then why is it illegal. The answer is because though the burning cigarette may not ignite the vapors, if someone were to light the cigarette at the pump there would be an open flame from the lighter and this is enough to ignite vapors. Not only the flame but the initial spark from the lighter is actually molten metal, in most cases, flint. This spark has a higher temperature than a burning cigarette so that adds to the probability of igniting fumes. While we’re at it, lets look at a circumstance. The gasoline coming out of a pump is under pressure. Pressure creates more fumes when the pressure is released as it exits the spout of the pump. Let’s say it’s a windy day, you bend over behind your car to light your cigarette out of the wind. Now, youre applying the heat right where there is a higher concentration of fumes. The government cannot account for every circumstance so to play it safe they just made it illegal. Don’t smoke at the pump is the easy solution, regardless of the act itself really is dangerous.
So theoretically, if you want to smoke an already lit cigarette at the pump, go for it, but do not light the cigarette while you are at the pump.
and to the smartass who commented about my brief notation from wikipedia. this was written in anger as a response to the ignorance of another person. This is not used for any purpose other than me venting, so yes if i copy and paste one section that describes the technical portion in a way that I dont feel like taking the time to try and word, then yes, its my poetic license to do so.