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Because that is to avoid igniting the vapor of petroleum by cellular phones, you know the battery contacts of the cellular phones might create a spark when somebody is calling you or when you are talking with someone, even when receiving or sending sms, the power being drained by the cellphone is dependent on the cellsite nearest to your phone or covering your phone, the sudden increase in power drain of cellphone might cause a spark.
Sorry glenjoy, but during normal operation there are no sparks. That was 100 years ago ;-) . The problem is if the phone is falling off: this can cause sparks (short-circuits etc) and ignite the vapor.
That is one thing I really do not know also if falling off also, as I recall, it was the spark at the contacts of the battery that they said causes the sparks at the instance that the phone drains high current, I do not know, I did not experimented on it.
I think sparks due to the battery and contacts is one reason.
The other is the ionization of air arround, close to the aerial due to High frequency radiation. This causes a glow (simillar to the spark effect) arround any sharp edges of the antenna which can ignite any fuel vapours.
One of my friends told me few days ago an interesting thing. He was talking at his GSM phone, outside a building, and it was a very wet day. While he was talking, he touched the metal of a car. He told me he felt the GSM transmissions pulses quite seriously, it was a quite strong sensation. Perhaps in some very rare conditions, sparks can be generated.
This could easily be a regulation made by a government official with very little technical skills. Many years ago the only mobile radios were HF and ran about 100 W output. At the same time, explosives that were used in road construction were detonated by small modules that were electrically triggered. (You may remember cinema scenes with the person pushing down the plunger of a box.) The length of wire was very large and there was the possibility of the 100 W of HF RF getting into the cable and detonating the explosives prematurely.
People with military training can remember another safety precaution where you carry the detonation control box and the roll of cable with you when you set up the explosives and connect the cable to the explosives. Then you walk away to a safe location while unreeling the cable and only then connect the cable to the detonation control box.
flatulent, I guess you use the example with the mil detonators just to stress out that you need enourmus power to detonate explosives. Because I can't see any connections with possible detonation from the power emmited near the cellphone antenna.
As I remember some cases in gas stations ( very few ) cars were blown up due to cellphones.
One must check the physics of detonating a fuel vapor by EM field. I don't know if it is possible to detonate fuel using the frequency of a cellphone - that is 900MHz- 1.8GHz if I am correct.
HF is much-much lower than satelite frequencies and as I recall from my mil duty we had no problem with HF near gas stations.
Think of it as we have a microwave oven - let's call it a satelite freq oven : Which element ( water?, gas? oil?, alchool? other?) would absorb the most power emmited by the satelite frequency of the oven?
In a mw oven water does so.
I may be a physist but I don't remember power absorbtion lists. So just check a similar list and you 'll get the answer.
It seems that a detonation due to the interaction of vapor of petroleum and cellular phones is a rare event.
But it is not an intrinsically safe situation. If an amount of detonable gas is located close to a device with enough energy stored then a rare event could happen.
May be that the detonation will not be produced by a normal phone call but perhaps for a failure in the circuit or a catastrophic destruction of the phone by accident. So, it is not an impossible event, just an event with an extremely low likelihood.
A cellphone will not and cannot cause an explosion at a petrol(eum) station.
I watched an episode of Mythbusters on Discovery Channel (DStv) once. They made a plexiglass box, filled it with petrol fumes and put a cellphone inside. They proceeded to phone the cellphone, it rang and there was no explosion. They then stripped the antenna of its plastic coating, exposing the bear metal, yet again there was no explosion when the phone was called. They removed the battery and shorted the contacts and the there were no sparks (or not powerful enough sparks). They removed the internal current limit of the battery and again shorted the battery, still no explosion. The conclusion, a cellphone cannot cause petrol fumes to ignite.
Cellphones are in the range of 3 - 5 Watts transmitting power (if I remember correctly).
It is the electroststic discharge from you to your car that causes the fumes to ignite.
The chances may be very small, but not 0.
It may be a 'mith' as someone called it, but would you bet your life (and other peoples lives) on it??
Its not going to be easy saying that mobile phones can never ignite vapour when your 400 feet in the air with 3rd degree burns.
I think people have given good explainations. Also, what if there was a 'coil' or strip of wire that happened to be the wavelength of the frequency transmitted? and many phones using frequencies close to eachother? A radio transmitter can cause a spark in the reciever if both are perfectly tuned, even at 1 watt. I'm sure we've all seen 'St.Elmos fire' on GSM basestations (although they run at minimum 30watts)
One more thing, it may not have anything to do with electronics at all. In the UK people have been banned from using their mobile phones when driving, why? because the distraction causes accidents. You hold you phone in one hand, pump in the other, the risk of dropping either and dowsing yourself in petrol goes up.
This is probably a pointless post for me, but its just ideas.
This can be the most feasible answer to this thread, talk about economic losses. Btw, why in banks also it prohibited to use cellphones, there are no explosive materials or gas in banks, and don't tell me for the security of depositors and clients withdrawing moneys.
Apparently not only can the storage registers change but also the billing at the time of delivery / sale can be corrupted for example 1000 litres to fill a motor bike in either case the petrol stations have to call out a member of staff to sort out the problem thus loosing income.