"John Michael Williams" wrote in message
m...
Claims that people have started fires by using
their cell phone while refueling a car apparently
are false: See
http://www.snopes.com/autos/hazards/gasvapor.asp
and other sites.

However, the first radios transmitted
sparks, so in principle it should be possible to
transmit near a long wire separated by a small gap from
ground or another wire and get a small spark. So, I
decided to try an experiment.

I don't use a cell phone, so I assumed a CB radio
transceiver would be a reasonable substitute: The
power output of a nominal 5 W CB also is consistent
and nonadaptive, so a possible unknown (actual output
power) is avoided. Cell phones are adaptive and
not very consistent in power output, so power
should be monitored during a cell phone experiment.

5 W is considerably more than the 0.2 to 2 W typically
possible from a cell phone; the power should be the
important factor, although maybe someone should repeat this
experiment with a cell phone, which would operate at
a much higher frequency.

I used a Radio Shack TRC-231 handheld (stock #21-1675)
with xmit power on high and set on Channel 40.
The antenna was the one that came with it (about 25 cm
long). I set the volume to max and the squelch at min
to be able to detect anyone else trying to use the
channel; this was just to be sure that my brief, silent
transmissions would not interfere with anyone.

I used the CB indoors, in a mostly metal-shielded
room. Because CB wavelength is around 10 m, everything I
did was in the near field; however, the inverse square law
for power still holds, allowing that the CB antenna is more
of a line than a point source under my conditions below.


The first thing I noticed was that every time I keyed the
transmit button, the CB would switch the
light level of a nearby touch-dimmed lamp, and it
made a Microalert microwave detector scream. I unplugged
the lamp and turned off the Microalert.

Then, I tried to light a 120VAC indicator neon lamp attached
to two solid copper switchback wires totalling about 1 m
long, so the lamp was in the middle effectively of a dipole
antenna. I tested the lamp and found it would light with
10 microamps current. The CB had no effect, even if held
parallel to, and almost touching, the wires. Thus, the near
field of a 5 W CB radio can not supply about 90 V at even
10 uA, under these conditions.

I then attached a 1.2 m monopole antenna to an oscilloscope.
This antenna has a Schottky hot carrier diode and impedance
matching resistors builtin. It's home made, but it's probably
as good as any other wire about that long. I hooked
the antenna coax to an oscilloscope: With the CB transmitting,
and its antenna parallel and 1 m away from the monopole,
the amplitude was about 100 mV p-p, at 27 MHz or so. I could
not get more amplitude no matter how close I held the CB,
or at what angle. Touching the bare monopole wire increased
the amplitude by no more than 10%.

So, first conclusion: To get even a 1 V spark would take a
wire at least 9 m long, all somehow kept within 1 m of the
transmitter. Thus, it appears it is not feasible to create a
hazardous spark with a CB at a gas station.

Just to be sure, I taped a 1 m wire to a table top in the dark
and slowly brought it closer and closer to another wire
plugged into a wall socket 3rd wire ground (yes, I verified
that the socket was wired to ground first!). At each distance, I
briefly keyed the CB. I could not see any spark, even after
dark-adapting my eyes for 10 min and letting the wires touch.
I might have dark-adapted longer, but I don't know whether
I should have been able to see a 50 mV spark or not.

So, I think sliding over on a car seat, and thus generating a
possible static charge, would be more likely to ignite gasoline
vapor than talking on a cell phone while refueling. However, it
would be useful for someone to repeat this kind of test with an
actual cell phone, as opposed to a CB radio. The wires should
be shorter, for one thing . . ..

I'm cross posting to an antenna group, looking for criticism.

John

John Michael Williams

It's a bit of a stretch to think that cell-phones are a problem, whereas the
car driving off next to you, with a set of spark plugs going for their
lives, is not. Hmmmm.

Ken

"Ken Taylor" wrote:
[snip]
It's a bit of a stretch to think that cell-phones are a problem, whereas the
car driving off next to you, with a set of spark plugs going for their
lives, is not. Hmmmm.

Quite. Not only that, but a petrol station I used to live near had an
in-store bakery.


Tim
--
Love is a travelator.

John,
It's also possible to start a fire rubbing two sticks
together, but it isn't as likely to be an accidental thing.
I would tend to doubt any claims about cell phones starting
accidental fires unless there has been some modification
to the phone, or other unusual circumstance. Turning off
cell phones and radios seems like a reasonable precaution
while fueling, I don't have a problem with that. I also
don't understand why anyone else would either. Do I turn off
my two way radio when fueling? Yes, but mainly because of
how it's connected (ignition switch).
If fuel vapor liable to ignite because of RF? Not unless
the RF field is very strong, or the antenna arcs for some
reason. Very likely? Not really. Possible? Sure. So using
a little common sense... what's the problem?
'Doc

PS - Cross posting is a sure way of causing misunderstandings.

I noticed that the appearance of the no cell phone signs came around the
same time that gas stations started running audio commercials through
speakers at the pump.

'Doc wrote in message ...
John,
It's also possible to start a fire rubbing two sticks
together, but it isn't as likely to be an accidental thing.
I would tend to doubt any claims about cell phones starting
accidental fires unless there has been some modification
to the phone, or other unusual circumstance. Turning off
cell phones and radios seems like a reasonable precaution
while fueling, I don't have a problem with that. I also
don't understand why anyone else would either. Do I turn off
my two way radio when fueling? Yes, but mainly because of
how it's connected (ignition switch).
If fuel vapor liable to ignite because of RF? Not unless
the RF field is very strong, or the antenna arcs for some
reason. Very likely? Not really. Possible? Sure. So using
a little common sense... what's the problem?
'Doc

PS - Cross posting is a sure way of causing misunderstandings.


I was just trying to add some factual information to the
link I gave, which was just a lot of rumor--both pro and con
RF hazards. Check it out.

From time to time, I read postings about people complaining
about others gabbing on a cell phone while (self-serve)
refueling.

I don't follow what you say about cross-posting. I'm not a ham
operator, so if I am making some obvious mistake, I thought
adding the antenna group would get a correction. Is that your
interest?

Hopefully, this thread will end up by putting to rest
fears of cell phones around gas stations, at least from the
RF standpoint. Also, if I'm wrong, and there IS danger
from the RF, someone should be able to correct me. Either way,
it's an interesting topic, don't you think?

John

John Michael Williams

(John Michael Williams) wrote in message om...

I was just trying to add some factual information to the
link I gave, which was just a lot of rumor--both pro and con
RF hazards. Check it out.

From time to time, I read postings about people complaining
about others gabbing on a cell phone while (self-serve)
refueling.

I don't follow what you say about cross-posting. I'm not a ham
operator, so if I am making some obvious mistake, I thought
adding the antenna group would get a correction. Is that your
interest?

Hopefully, this thread will end up by putting to rest
fears of cell phones around gas stations, at least from the
RF standpoint. Also, if I'm wrong, and there IS danger
from the RF, someone should be able to correct me. Either way,
it's an interesting topic, don't you think?


You may have missed out one thing: did you try this with any resonant
loads? Resonant loads are not so hard to come by at the higher
frequencies.

Another question concerns spillage of gas: if youre yacking away its
much easier to spill fuel. I cant draw any conclusions but one has to
at least look at these factors.


Regards, NT

N. Thornton says...

Another question concerns spillage of gas: if youre yacking away its
much easier to spill fuel. I cant draw any conclusions but one has to
at least look at these factors.

Considering how many people refuel their cars each year and the
statistics for refueling fires (150 over the last 10 years) I
draw the conclusion that this isn't a significant problem. At
roughly 50,000 traffic fatalities per year, you are in much more
danger driving to and from the gas station.

As far as talking on your cell phone while driving goes, there is this...

|"Simons and Chabris showed participants a film of two basketball
|teams, one wearing black shirts and the other wearing white.
|These displays were created such that all of the actors were
|partially transparent and thus could simultaneously occupy
|the same locations.
|
|The researchers instructed participants to count how many times
|a basketball passed between members of one team, ignoring the
|other team. Just as Neisser had found two decades earlier,
|many participants didn't notice a woman who walked through
|the scene carrying an open umbrella, even though the woman
|was present for several seconds.
|
|Although Neisser's original findings were striking, they
|stimulated little further research - perhaps in part because
|the results were difficult to incorporate into the mainstream
|science of the time, suggests Ron Rensink, PhD, a psychologist
|and computer scientist at the University of British Columbia.
|
|'Back then, there was still a strong belief that we built
|up a visual representation of all the objects around us and
|held it in a big buffer,' Rensink notes. 'Neisser's work
|flew in the face of that -- people didn't quite know what
|to do with it. There seemed to be a general reluctance to
|pursue it.'
|
|Two decades later, Simons and Chabris's replication has
|received a more welcome reception. The team has now extended
|the original findings by showing that inattentional blindness
|also occurs in more natural displays, in which all of the
|actors are fully visible and opaque. Across a range of
|conditions, more than 25 percent of observers missed a fully
|visible and opaque 'umbrella woman.'
|
|In a particularly dramatic demonstration of the inattentional
|blindness effect, half of the observers failed to notice a
|person wearing a gorilla suit who walked into the middle of
|the basketball game, stopped to face the camera, thumped
|its chest and walked off the screen -- spending a total of
|nine seconds on screen."

Source: http://home.att.net/~jeff.dean/blind.htm




--
Guy Macon, Electronics Engineer & Project Manager for hire.
Remember Doc Brown from the _Back to the Future_ movies? Do you
have an "impossible" engineering project that only someone like
Doc Brown can solve? My resume is at http://www.guymacon.com/

John Michael Williams wrote:

SNIP

However, the first radios transmitted
sparks, so in principle it should be possible to
transmit near a long wire separated by a small gap from
ground or another wire and get a small spark. So, I
decided to try an experiment.

SNIP

There is one other potential source for a spark that you did not
investigate.

A make/break contact in a switch causes sparks when opened. The US
Military specifies special shielded switches for their explosive, gas
vapor, etc., environments.

So, it is possible that pressing the PTT or the ON/OFF switch causes the
necessary spark. Remember the Apollo ground fire. A switch/spark caused
an oxygen explosion.

"Dave Shrader" wrote in message
news:Xu36c.33004$po.292953@attbi_s52...
John Michael Williams wrote:

SNIP

However, the first radios transmitted
sparks, so in principle it should be possible to
transmit near a long wire separated by a small gap from
ground or another wire and get a small spark. So, I
decided to try an experiment.

SNIP

There is one other potential source for a spark that you did not
investigate.

A make/break contact in a switch causes sparks when opened. The US
Military specifies special shielded switches for their explosive, gas
vapor, etc., environments.

So, it is possible that pressing the PTT or the ON/OFF switch causes the
necessary spark. Remember the Apollo ground fire. A switch/spark caused
an oxygen explosion.

I wouldn't call it an "oxygen explosion" but a small fire that grew rapidly
due to the pure-oxygen atmosphere.

Better not open your door or have someone else open theirs next to yu then.
That dome light switch might get you.
"Dave Shrader" wrote in message
news:Xu36c.33004$po.292953@attbi_s52...
So, it is possible that pressing the PTT or the ON/OFF switch causes the
necessary spark. Remember the Apollo ground fire. A switch/spark caused
an oxygen explosion.