Re: [Texascavers] Static Electricity and Gas Pump Fires

[Rod Goke]

I think that a properly working (or even improperly working) cell phone is unlikely to start a fuel pump fire, but I would not say that it is impossible if the phone is actually in contact with the explosive vapor. You don't have to have a high voltage power supply to produce sparks. For example, whenever a mechanical switch turns off and breaks an electrical circuit with an inductive load, a high voltage spike can occur momentarily across the switch contacts, producing a small spark. Similarly, the commutator and brushes inside a typical DC motor continually make and break electrical connections with inductive loads (the windings in the armature) whenever the motor runs. This often causes small sparks to occur between the commutator and brushes, even if the motor operates on low voltage from a battery. Many cell phones have vibrator options for ringing. I suspect that the vibrations are produced by a small DC motor, although I haven't opened one to be certain of this. If this is the case, and if enough vapors happened to seep into the phone to form an explosive fuel/air mixture, then it is conceivable that an incoming call would run the vibrator motor and ignite the vapors. Even the switch on a flashlight or headlamp possibly could produce enough of a spark to ignite explosive vapors if the switch is not separated from the vapors by an air tight seal. I believe this is an issue in the design of certain lights intended for use in mines and other environments where explosive gasses or vapors might be encountered, but I never investigated the issue in detail. I believe that this issue influenced the design of certain mining oriented headlamps that some of us used to use for caving. There is also the issue of what happens when the cell phone transmits a radio signal. In principle, any nearby metal object will act as a receiving antenna and will have a small voltage induced in it by the radio signal. I doubt that this effect is strong enough to have any significance in the case of cell phones and gas pump fires, but concern about it in some people's minds might be rooted in the old idea that signals from strong radio transmitters could induce strong enough electrical signals in nearby wiring to set off electrically triggered blasting caps. Sometimes in areas where people were using explosives with electrically controlled blasting caps, I recall seeing signs warning people not to use radio transmitters, so I suspect that this might be what influenced some people to think that cell phones could trigger gas pump explosions. Rod -----Original Message----- From: James Edwards Sent: Jul 9, 2011 10:45 AM To: Rod Goke Subject: Re: [Texascavers] Static Electricity and Gas Pump Fires Yeah, it was obvious in the second two videos that the customers picked up static electricity when they rubbed their clothing. I don't see how a properly working cell phone could generate static electricity or a high enough voltage to spark, do you? -Andy On Sat, Jul 9, 2011 at 10:38 AM, Rod Goke wrote: > > 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: texascavers@texascavers.com > > 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: texascavers@texascavers.com > > > 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: > texascavers-unsubscr...@texascavers.com For additional commands, e-mail: > texascavers-h...@texascavers.com --------------------------------------------------------------------- Visit our website: http://texascavers.com To unsubscribe, e-mail: texascavers-unsubscr...@texascavers.com For additional commands, e-mail: texascavers-h...@texascavers.com