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Want to Save at the Pump? Don’t Top Off! by Catherine Magliocchetti - Chemical Engineer, U. S. EPA

Release Date: 7/26/1999
Contact Information: David Sternberg (215) 814-5548

You can save money every time you fill up your car’s gas tank, and help the environment too. Sound too good to be true? It’s easier than you think. Just stop topping off.

Most gasoline stations in the Philadelphia area are equipped with an automatic gasoline shut-off system on every pump. It’s called a stage II vapor recovery control, and it’s an easy way to prevent pollution when gassing up the family car.

Preventing gasoline pollution is important because stray molecules of gasoline are a major contributor to ozone smog, the dreaded brown haze of summer that makes it hard to breathe. These molecules -- called volatile organic compounds -- escape into the air when gasoline evaporates, is spilled, or doesn’t fully burn, like in an inefficient lawn mower engine.

Topping off is a loser three ways.

First, you lose money when you top off because you pay for gasoline that you don’t get. When the gas pump automatically shuts off, a vapor lock blocks more gas from entering your car. After the tank is full, the gas you pump gets sucked back through an outer “vapor-return” hose into the station’s underground storage tank. The meter may be running, but your not getting the gas.

Secondly, you personally pollute the air because topping off clogs the vapor-return hose with liquid gasoline, so it can no longer return excess vapors. It works on the same principle as the water-filled trap on your kitchen sink, except at the pump, you want gasoline vapors to float back down the hose, not get stopped by a liquid-filled trap that you created by topping off.

Even worse, once you plug up the vapor-return hose, it stays plugged up until someone clears it by lifting it overhead to drain all the liquid back into the underground storage tank.

And thirdly, a gasoline-filled vapor-return pretty much guarantees that you and everyone after you will be breathing in a cloud of volatile gasoline molecules -- invisible but harmful -- while you pump gas. Excess molecules under pressure can’t float back down the return hose, so they get forced out around the nozzle and into the air. That’s when you smell gas.

As you stand there filling your tank, you’re getting exposed to some nasty chemicals -- including benzene, toluene and 1,3-butadiene -- that injure your lungs and can even cause cancer over time. As a general rule, if you can smell the gasoline when you’re pumping it, the vapor-return system isn’t working properly, and you should let the attendant know it needs to be serviced.

So the next time you want to top off to the next round dollar, don’t do it. You would be throwing away your money, risking your health, polluting the air, and making sure the next guy pollutes it even more.

If no one topped off, stage II vapor recovery in the Philadelphia area would prevent as many as 17 tons per day of pollutants from Bucks, Chester, Delaware, Montgomery and Philadelphia counties.

And if you’re at a full-serve station in New Jersey, make sure you tell the attendant "not to top off" either. You’ll save some cash -- up to $20 a year -- and help protect the environment at the same time.

Vapor recovery is just one of the innovative pollution control measures that can help you breathe a little easier -- but it only works if you let it.