Although the danger of igniting a gasoline pump fire with a cell phone has been greatly exaggerated in Internet rumors, the danger of starting such fires with electrical sparks is quite real, and, by far, the most common cause of dangerous sparks near gasoline vapors is static electricity. Wherever gasoline vapor mixes with air in the right concentration, it forms an explosive mixture, which can easily be ignited by even a tiny electrical spark. This critical fuel/air mixture can easily exist near where a fuel pump nozzle enters the gas tank filler pipe of an automobile, especially while fuel is actually being pumped into the tank, since fuel entering the tank forces vapors to flow out the filler pipe. Care should always be taken to prevent sparks near this area. Small sparks can be produced accidentally in a variety of ways, such as inside an electrical switch whenever a typical electrical device is turned on or off (especially when turning off) or inside a typical DC motor whenever it is running. Tiny sparks of this type can occur inside even low voltage battery operated devices, especially when the device involves an inductive load, such as a motor or electromagnet. These sparks, however, should not ignite gasoline vapors unless they are actually in contact with fuel vapors of appropriate concentration. It generally is wise not operate electrical gadgets where they might come in contact with concentrated gasoline fumes, but, frankly, I suspect that very few fuel pump fires actually start this way. A much more common source of dangerous sparks while fueling a vehicle is static electricity, especially when there is low humidity in the air. If you've ever lived in a low humidity environment, you've probably noticed how quickly and easily you can build up enough of a static charge to produce a painful shock whenever you touch a grounded metal object. Sometimes you can do it merely by walking a few steps or by accidentally brushing your clothing against some surface of the right material. If this happens while you are trying to fill your car's gas tank, you can easily produce a spark between your hand and the pump nozzle when you touch it or between the pump nozzle and the filler pipe when you try to insert the nozzle into the filler pipe or between your hand and the car if you touch it after having temporarily stepped away. In the videos Simon referenced, it appears to me that the cell phones did not ignite the fires directly, but, instead, they distracted the accident victims, who then behaved in ways that easily could have produced static electricity sparks. Notice that in each of the first two videos, the victim (probably distracted by the cell phone) lets go of the nozzle, moves away, and then returns and touches the nozzle without first grounding himself or herself by touching a grounded metal surface safely away from concentrated fumes near the filler pipe. The resulting spark near the nozzle and filler pipe is what most likely started these fires. In the last video, involving a workman on a large tanker truck, it is difficult to see exactly what happened, but a similar static electricity discharge would be a likely candidate in my opinion. The most effective way to protect yourself from this kind of accident (aside from getting someone else to do the job for you) is to think about static electricity during the fueling process and to cultivate good habits to avoid any static discharge close to the filler pipe, or anywhere else that concentrated gasoline vapors are likely to exist. For example, when you first walk up to the pump, initially discharge any static electricity that might have built up on your body by first touching a grounded metal object away from any liquid gasoline or concentrated vapors. Typically, touching some portion of the metal pump housing away from the nozzle will suffice for this. Then before touching the nozzle to the automobile filler pipe, you want to make sure that no spark will occur at this worst possible location, so while holding the nozzle in one hand, you first touch the metal automobile body with your other hand in a location somewhat away from the filler pipe, so if any spark occurs, it will happen safely away from any concentrated vapors in the pipe. Then while pumping the gasoline, it's best to stand there with your hand on the nozzle, so that you body will remain grounded and will not build up any new static electricity charge during the process. If you have to let go and leave for any reason, even a few steps away, be aware that this short movement might have caused a new static electricity charge to have built up on your body, so don't touch the filler pipe or nozzle or anything else in that vicinity without first discharging any possible static charge by touching a grounded metal object away from the fuel vapors. Similarly, when you've finished filling the tank and are ready to put the gas cap back on the filler pipe, first touch the metal car body in a safe place before you touch the filler pipe area, so if any spark occurs, it will happen safely away from any concentrated vapors near the pipe. If the victims in the videos had thought and acted this way instead of focusing on their cell phone distractions, the fires most likely would not have occurred. Anti-static precautions of this type might seem like an annoying hassle when you first hear about them, but after you've done them a while, they become routine habits that take negligible time or effort. In principle, they are the same kinds anti-static precautions that people learn to practice when working with sensitive electronic components that can be damaged by accidental static discharge. As a retired computer engineer with several decades of experience with electronic hardware, I became familiar with static electricity issues long ago. Sometimes, people wear wrist straps with ground wires to prevent static charges from building up on their bodies while working with static sensitive electronics, but in most cases, the same effect can be achieved simply by cultivating good anti-static habits and knowing what to touch when to prevent static discharges from occurring where they can do damage. In all of this discussion about touching grounded metal objects to discharge static electricity, remember that the idea is to make electrical contact between your body and the metal object, so it won't work if your hand is covered by a glove that doesn't conduct electricity. Hence, it's probably best not to wear gloves during this process. Similarly, it works most effectively if you can touch an unpainted metal surface, since paint might act as a thin insulator and interfere with electrical contact. Rod -----Original Message----- From: Simon Newton Sent: Jul 8, 2011 2:25 PM To: [email protected] Subject: [Texascavers] Re: [texascavers] cell phone at the gas pump rumors disproved??? How do snopes explain this? http://www.youtube.com/watch?v=gct1BmKNvU0 And this? http://www.youtube.com/watch?v=oUf8vc7I6bc And this? http://www.youtube.com/watch?v=2aW-Qaio6Uw& Simple point here, be safe and use your head around flammables. Why take unnecessary risk? Try an minimize ignition sources, including static electricity, electronics, smoking, etc. On Fri, Jul 8, 2011 at 2:06 PM, wrote: > > ---------- Forwarded message ---------- > From: James Edwards > To: [email protected] > Date: Fri, 8 Jul 2011 14:04:53 -0500 > Subject: cell phone at the gas pump rumors disproved > http://www.snopes.com/autos/hazards/gasvapor.asp > > I've never seen any "news" spread by e-mail that's true. If you hear about > something via e-mail before you hear about it in the news, you should > immediately suspect it. Check it on Snopes. This story is no exception. > > -Andy > > > > --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected] |
- [Texascavers] Static Electricity and Gas Pump Fires Rod Goke
