Why are cell phones not safe near petrol or in hospitals?

Two questions about the safe use of mobile/cell phones.

Their use is prohibited in petrol stations. What physical process could ignite the petrol?

They are also prohibited in hospitals because it is claimed that they could interfere with hospital equipment. If I was to stand outside the hospital on the far side of the hospital to the phone mast, wouldn’t the signal pass through the hospital and cause the problems with the equipment? And all the other users whose signals pass through the hospital must also cause problems?

Or is it something else altogether?

According to Snopes Is Cell Phone Use at Gas Pumps Dangerous? | Snopes.com it’s a myth that they’re dangerous to use at gas stations. Mythbusters did an episode on it as well.

Cellphone use is (was) banned in the US while pumping gas because of an urban legend.

The reasoning behind cellphone bans at hospitals is more reasonable:

  1. The RF emissions from a phone might be strong enough to interfere with sensative monitoring equipment (unlikely, but why risk it).
  2. They are annoying to other patients.

With gas stations, I believe that there is a fear that static discharge could ignite gasoline vapors. I saw something recently that suggested that that fear was overblown. With hospital telemetry (IANAEE, so caveat emptor), interference may be possible when the transmitter (your phone in this case) is close to the equipment. Transmission strength drops off as the square of the distance. The location of the receiver has nothing to do with it.


You forgot the even bigger reason:

They are annoying to the hospital staff–doctors, nurses, aids, etc.

I’ve heard the real reason why they were banned in Petrol stations is to prevent the electronic equipment mis-reading the amount of petrol.

That could easily be another urban legend of course.

Yes, I’m sure you’re right. But I am always slightly surprised at how irritating mobile phone conversations can be. After all, if it was two people, side by side, talking to each other we wouldn’t mind. Is it the volume, or the tone, or the sheer inanity of only hearing one side of a conversation?

Despite what is generally believed it has been found that there is a small possibility that mobile phones can cause clinically significant interference, and it therefore would be prudent to limit usage to areas without sensitive equipment. Cite

Doctors and nurses, and some other staff at my hospital, are given DECT phones so that they can make and recieve calls on the move inside the hospital. I find it amusing when I’m stopped by a well meaning visitor or volunteer and told off for using the authorised mobiles, I then have to explain that it’s hospital issue.

Some hospitals in London allow certain areas for members of the public to use their mobiles, others have a more liberal policy where they’ll only stop you when you’re making a nuisance of yourself (on wards or in clinics), others are completely intolerant of mobiles.

There are some hospitals in the Boston area that allow cell phone use anywhere inside. The one I go to most often does. I still believe the reason is it pisses people off and there are a lot of people that talk loudly and can’t pay attention to the world around them when a cell phone is glued to their ear. It can irritate other patients and staff and interfere with instructions either to the patient or visitors.

My retina guy bans cell phones from his examination and procedure rooms. It makes sense to me, if you’ve got someone rooting around inside your eyeball the last thing you want is an unexpected loud noise. Some cell phone ring tones are earsplitting, and a flinch on the part of the doctor or patient is an undesireable event.

Doctor: “Nurse?”

Nurse: “Yes?”

Doctor: “Please hand me that chart.”

Nurse: “It’s fine, doctor.”

Doctor: “What?”

Nurse: “I said it’s fine.”

Doctor: “What’s fine?”

Nurse: “My heart.”

Doctor: “I said chart. Hand me that chart.”

Nurse: “What?”

Doctor: “Chart. Chart.”

Nurse: “Are you there?”

Doctor: “Can you hear me?”

Nurse: “You’re breaking up a bit. What did you say?”

Doctor: “Hello?”

Nurse: “Okay, I can sort of hear you.”

Doctor: “What?”

Nurse: “Hang on. Let’s go talk over by the window.”

For a pump to be capable of mis-reading based on nearby mobile phone transmissions would seem to require that the pump designers made a point of building in this feature. (Among other considerations is the point that there is little reason for a pump to use any sort of wireless signal transmission.) That would be even more true if the mis-reading is to reliably be under, and by a plausible amount.

And of course if the word got out that it was magically possible to cause the pump to charge less than what was correct, it would be incredibly easy for customer to surreptitiously use their mobile phone to do so. Which means that stations would need sophisticated equipment to monitor compliance, rather than simply a sign that says (in effect) “Please turn off your mobile phone so that you don’t get undercharged.”

So while I certainly can’t say this is impossible, it does seem very far-fetched.

Right–my intent was not so much to deny that risk of interference with equipment is a real concern, but to suggest that not irritating other patients takes a lower priority than avoiding situations where someone on a cell phone is obstructing hospital staff.

It’s the volume.You speak more loudly into a phone than you do in a conversation with a person. This isn’t just true for cell phones–it was true in the days of landline phones, too.
But we never complained about it in the old days, because when somebody was on the phone, he was physically tethered to the wall; that means that you remain in control of the situation, not him. He couldn’t move much, and you could just step away from him and not hear his talking.

When we complain about cell phone users , it isn’t just the loudness that bothers us—it’s the fact the we lose control of our personal space, and feel our privacy being invaded .

Distance makes a big difference. Your phone’s signal is over 1000 times stronger at 3 feet distance than at 100 feet. Even if the frequency is different, a close, strong signal can “swamp” a receiver’s input circuit, rendering it deaf, while the same signal a few feet farther away might have no effect at all.

That said, I think the problem may have been greater with older technologies.

The annoyance factor remains, for reasons that others have covered.

If one were to follow the conspiratorial bent of the theory we could assume the pumps were quickly redesigned to avoid the problem.
However they would be unable to withdraw the cover story without revealing the truth.
If one were to believe in such things.

I have to agree with your assessment though. Having read your post and thought about it for a minute the whole thing sounds a bit ‘Fox Mulder’

As a general rule, it’s not safe to use electrical equipment around flammable vapors or gases unless it has been designed and certified for operation in that environment. The concern is that a spark may ignite the vapors.

The problem in hospitals is that they have equipment like EKG machines that have unshielded leads that are used to pick up very weak signals from the patient. This makes them vulnerable to electromagnetic interference. GSM cell phones are noted for their ability to cause interference to poorly shielded electronic devices. Two-way radios can also produce strong electrical fields.

Medical EMC: RFI Requirements for Medical Electronic Equipment

I have several hand-held two-way VHF/UHF radios that can produce 5+ watts when in high-power mode. They can cause severe interference and malfunctions when used near electronic equipment that isn’t properly shielded, which includes most consumer-grade hardware. I’ve seen them cause PCs to crash and displays to go berserk.

Ok, we’re all agreed that the petrol station ban probably started due to urban legend but according to the snopes link both Nokia and Ericsson have confimed there is a risk, albeit small. The article doesn’t have any idea what that risk is though.

Any theories? There must be a reason Nokia and Ericsson have acknowledged there is something to it.

My understanding is that if a cellphone is dropped, the battery can make a minute spark as it disconnects. It’s a pretty slim chance, but better to inconvenience billions of customers rather than risk a 1:1,000,000,000,000 chance of starting a fire :rolleyes:

I always found it funny that people in many parts of the US are paranoid about this. I mean, folks smoke cigarettes on gas station forecourts quite happily, but a cellphone might cause an explosion?