Debunking the Gas Email
Yesterday a good friend forwarded to me (and at least a dozen other buddies) an email with this subject line "Interesting news on pumping gas". Purported to be from a pipeline company worker, it presents, in pseudo industry jargon, four seemingly compelling reasons to squeeze the maximum value out of each dollar spent for gasoline (backed up with a semi-rant on what companies are buying Saudi or Venezuelan oil).
Item 1: We've probably all aware of root cellars and wine cellars - they're used for their year round constant temperature - and that comes from being underground. In the San Francisco Bay Area the average average annual underground temperature is 60° - coincidentally the temperature at which the gasoline is measured and loaded. The ground surface temperature may vary over the course of the day, but the underground temperature does not fluctuate daily. So if there is an change in the fuel's temperature, it can only occur during transportation, and should stabilize when dumped into storage tanks.
Item 2. The idea here is that delivering gas on the maximum discharge setting creates more vapor that is then recycled back into the station's tank on condensation. Perhaps, but we're talking just a few drops at best. Is it worth hanging around the pump another 5 minutes?
Item 3. First I'm in a quandary as what actually comes first: half-empty or half-full - I guess it's a chicken and egg thing. Perhaps the author of these tips is really trying to speak to both optimists AND pessimists simultaneously. Whatever - the real (specious) point this bonehead is trying to make is that the lower the fuel level, the greater the propensity is for evaporation. This is LOL funny - unless your gas tank is a pyramid, the surface area for evaporation is probably the same no matter what the fuel level (granted gas tanks shapes have gotten creative since they've become molded out of plastic, but you get the point). Plus, since evaporating hydrocarbons are a pollution source, every vehicle sold in the US since 1968 has a sealed fuel system with a mandatory vapor recovery system built in. Most vehicles won't even run with the gas cap loose. Besides who wants waste twice as much time in a gas station? On second thought there is merit to this claim - it'll only cost you half as much to fill the tank! That'll feel good, won't it?
Item 4. This is only one of the four with some merit - that the ingress of thousands of gallons of fuel will stir up sediment in the storage tanks that in turn could end up in your tank. It may have been true in 1966 but hey, we're living in modern times; with the advent of fuel injection sophisticated filtration systems are the norm, both on your vehicle and in the stations plumbing. Nothing to worry about here - except perhaps if it's 6 AM . . . has that tanker driver had his coffee? Is that diesel or regular that he just put in the premium port?
The lesson is that we should all be a bit more more skeptical before we hit that forward button.
For more details on this urban myth (and make it the first place to visit when you get the next forwarded email warning), be sure to check out Urban Legends.
- Only buy or fill up your car or truck in the early morning when the ground temperature is still cold.
- When you're filling up do not squeeze the trigger of the nozzle to a fast mode, always use the slow setting.
- One of the most important tips is to fill up when your gas tank is HALF FULL or HALF EMPTY.
- If there is a gasoline truck pumping into the storage tanks when you stop to buy gas, DO NOT fill up!
Item 1: We've probably all aware of root cellars and wine cellars - they're used for their year round constant temperature - and that comes from being underground. In the San Francisco Bay Area the average average annual underground temperature is 60° - coincidentally the temperature at which the gasoline is measured and loaded. The ground surface temperature may vary over the course of the day, but the underground temperature does not fluctuate daily. So if there is an change in the fuel's temperature, it can only occur during transportation, and should stabilize when dumped into storage tanks.
Item 2. The idea here is that delivering gas on the maximum discharge setting creates more vapor that is then recycled back into the station's tank on condensation. Perhaps, but we're talking just a few drops at best. Is it worth hanging around the pump another 5 minutes?
Item 3. First I'm in a quandary as what actually comes first: half-empty or half-full - I guess it's a chicken and egg thing. Perhaps the author of these tips is really trying to speak to both optimists AND pessimists simultaneously. Whatever - the real (specious) point this bonehead is trying to make is that the lower the fuel level, the greater the propensity is for evaporation. This is LOL funny - unless your gas tank is a pyramid, the surface area for evaporation is probably the same no matter what the fuel level (granted gas tanks shapes have gotten creative since they've become molded out of plastic, but you get the point). Plus, since evaporating hydrocarbons are a pollution source, every vehicle sold in the US since 1968 has a sealed fuel system with a mandatory vapor recovery system built in. Most vehicles won't even run with the gas cap loose. Besides who wants waste twice as much time in a gas station? On second thought there is merit to this claim - it'll only cost you half as much to fill the tank! That'll feel good, won't it?
Item 4. This is only one of the four with some merit - that the ingress of thousands of gallons of fuel will stir up sediment in the storage tanks that in turn could end up in your tank. It may have been true in 1966 but hey, we're living in modern times; with the advent of fuel injection sophisticated filtration systems are the norm, both on your vehicle and in the stations plumbing. Nothing to worry about here - except perhaps if it's 6 AM . . . has that tanker driver had his coffee? Is that diesel or regular that he just put in the premium port?
The lesson is that we should all be a bit more more skeptical before we hit that forward button.
For more details on this urban myth (and make it the first place to visit when you get the next forwarded email warning), be sure to check out Urban Legends.
Labels: Gastips, Urban myths
posted by Chasmo at
8:25 AM
3 Comments:
Good post with objective analysis regarding refueling myth’s vs. facts. I’d like to expand on this by briefly describing a source of gasoline vapor emissions at gas stations which are significant, but have been largely overlooked. These hydrocarbon emissions come from gasoline storage tank evaporative losses, and they represent significant quantities of VOC (Volatile Organic Compound) and HAP (Hazardous Air Pollutant) emissions.
Here’s how: Stage II vapor recovery systems are great for capturing the hydrocarbons emitted from the vehicle fuel tank as the motorist refuels his/her car; however, these systems are incompatible with the vapor collection system used within newer cars. These vehicle based systems are called ORVR; On-Board Refueling Vapor Recovery systems, and they use a small carbon canister connected to the top of the vehicle fuel tank. What happens is this: while refueling an ORVR equipped vehicle at a Stage II site, the vapors displaced by the incoming fuel are routed to the ORVR canister. At the same time, the vacuum pump located within the fuel dispenser is drawing back a mixture of air and gasoline vapor to the underground storage tanks. Since the majority of the hydrocarbon (HC) vapors are directed to the ORVR system, the Stage II system will return mostly air (with a small percentage of HC vapors) to the vapor space of the underground storage tanks.
All is fine at the refueling island as HC vapors displaced during the refueling process are either directed to the ORVR system or returned, along with a lot of air, to the underground storage tank. However, the air which is returned to the vapor space of the underground storage tanks “leans-out”, or reduces the HC concentration below a naturally occurring level called the “equilibrium level”. To re-establish this natural vapor phase equilibrium level of HC concentration, liquid gasoline will begin to evaporate. The expansion of liquid phase gasoline to vapor phase gasoline is very large, one gallon of liquid gasoline will form 520 gallons of vapor phase gasoline at typical equilibrium concentration levels. The storage tanks are equipped with pressure –vacuum relief valves located on the tank vent lines; typically these vertical vents are located along the boundary of the fueling station property. As the liquid evaporates, the vapor volume and pressure begins to build in the storage tank, eventually causing the pressure relief valve to open (certain valves can be heard chattering like a boiling tea kettle). The open valve will then release concentrated hydrocarbon vapors directly to the atmosphere.
The loss rate is typically about 2 gallons of liquid gasoline per 1,000 gallons of fuel dispensed. For busy stations, this loss equates to 1,000 gallons of liquid fuel per month, with associated tonnage quantities of VOC’s and HAPS’s emitted up the vent pipe on an annual basis. In addition, since the storage tanks are subjected to a constant, high back-pressure, small breaches in the fittings, connections or underground piping (called below-grade piping) will experience continuous leakage of HC vapors (these are called “fugitive emissions”). What’s particularly bad about below-grade fugitive emissions is that they will condense, mix with water and cause groundwater contamination.
So, the root cause of the air emissions and potential groundwater contamination is the pressurization of the storage tank. In-turn, the pressurization of the storage tank is caused by the ingestion of excess air due to the overlapping use of Stage II systems and ORVR systems. The Stage II systems are installed at gas stations, and the ORVR systems are installed on newly built vehicles. What is the solution to such a problem? Is the answer to turn-off the Stage II systems and rely solely on the ORVR systems to capture the refueling emissions? No; here’s why. If the Stage II systems were to be shut down and discontinued, during refueling of vehicles, the motorist whose car is not equipped with the ORVR system would be directly exposed to a high concentration of HC vapors. The ORVR systems are not in use throughout 100% of on-road vehicles, as a phase-in approach to newly built vehicles has been adopted.
Should ORVR systems be discontinued, with sole reliance on Stage II systems to recapture the refueling vapors? No; that’s not the answer either, here’s why. If the ORVR systems were stopped being installed within vehicles, many states would need to mandate the need for use of Stage II vapor recovery systems. To retrofit the hardware and piping into existing stations, which were not pre-plumbed for this gear, would be a very expensive and intrusive proposition. In addition, even without ORVR systems, stand-alone Stage II systems tend to ingest excess air which again pressurizes the storage tanks.
So; what’s the solution? A viable solution would be to allow each system to remain; the Stage II hardware at the fueling station and the ORVR canister within the vehicle. However, to combat the tank pressurization caused by the fundamental incompatibility of the two systems operating simultaneously, some sort of vapor processing technology can be used monitor and control the storage tank pressure. Ideally, this gear could be further designed to yield recovered product as part of its operation. In addition, such a system should be robust and maintenance free. Ok; does such a system exist? Yes. Please google PERMEATOR or ARID Technologies
tpt- Thanks for the insightful response - obviously you have some experience in hydrocarbon evaporation. I literally had no idea and I'm sure few people do that this kind of problem existed. I also appreciate your summary of the solution, however if this is really a serious health issue, how do we take it step further and implement the solution? Lobby the EPA or California Air Resources Board? Congress? Is there a point organization that needs support to make it happen? How can one succinctly summarize this issue in one or two short paragraphs if an email to a representative?
Chasmo & tpt, great posts, sharing more than I ever thought of on the topics. I particularly loved the listing of reasons from the original e-mail Chasmo got. Of those, I try and follow item #3 - although for reasons completely unrelated to saving gas (and I am not referring to how my gas gage drops more quickly after 1/2 a tank for one car).
The impetus for not letting my tank get to empty (or fumes) is more a disaster preparedness issue. It's particularly applicable in the Bay Area with the earthquake danger (although people near the New Madrid fault in the mid-west are not free from the risk). Earthquakes are sudden and a major one can knock out power in wide areas. If in the event of an issue, power is out, pumps at gas stations will not be able to pump gas.
I'd sum it up as good practice, just to be able to deal with the unexpected - but at no point would I consider it a cost/gas saving measure. It is also not something I'm draconian about. If it's running errands or other things or a day trip and I have enough gas to get home (especially if car #2 has at least 1/2 a tank in it) I'll let things get down much less than 1/2 full.
Chasmo, thanks again for the entertaining and educational post. If you ever want to check out other gas saving myths, the Discovery Channel show Mythbusters did an episode on gas saving myths a season or two ago. The website probably has some of those details too.
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