CB Radios, Cellphones and Gasoline Vapor Ignition

[KLM]

On Fri, 19 Mar 2004 07:29:27 -0500, Active8 <reply2group@ndbbm.net>
wrote:

We also don't want the thing detonating from the interrogation with
people around and that's the biggest prob. You have to admit only
one person at a time into the area. That's not too bad. It's common
courtesy to stand back from someone using an ATM so maybe a few feet
will do. Like in a bank line.

I did consider this objection. The interrogation will be done going
into a designated area (eg. sports stadium, train station where other
waiting to go in can wait some distance away. If I recall this
(checks going in) was done for the Superbowl and were not backpacks
and other bags banned? So have them enter a blast cage (to catch the
sharpnel mostly) or something like that for RFID interrogation. The
idea is not unlike the airport metal detector gate check. Once they
are in they are presumed to be safe.

So perhaps have similar "interrogation gates" for people entering a
pedestrians only shopping area, or to Times Square for the New Year
bash.

We are dealing with only one threat - CP triggered bombs. Therefore,
please think small and figure if it is worth doing. I am not trying
to protect the whole world.

 

[Active8]

On Sat, 20 Mar 2004 02:28:56 GMT, KLM wrote:

On Fri, 19 Mar 2004 07:29:27 -0500, Active8 <reply2group@ndbbm.net
wrote:



We also don't want the thing detonating from the interrogation with
people around and that's the biggest prob. You have to admit only
one person at a time into the area. That's not too bad. It's common
courtesy to stand back from someone using an ATM so maybe a few feet
will do. Like in a bank line.

I did consider this objection. The interrogation will be done going
into a designated area (eg. sports stadium, train station where other
waiting to go in can wait some distance away. If I recall this
(checks going in) was done for the Superbowl and were not backpacks
and other bags banned? So have them enter a blast cage (to catch the
sharpnel mostly) or something like that for RFID interrogation. The
idea is not unlike the airport metal detector gate check. Once they
are in they are presumed to be safe.

So perhaps have similar "interrogation gates" for people entering a
pedestrians only shopping area, or to Times Square for the New Year
bash.

Simple. Drop precast, steel reinforced entryways in the street.

We are dealing with only one threat - CP triggered bombs. Therefore,
please think small and figure if it is worth doing. I am not trying
to protect the whole world.

--
Best Regards,
Mike

 

[Ed Price]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:eRbCCRJiMhWAFwYo@jmwa.demon.co.uk...

I read in sci.electronics.design that CW <clinton.magers@comcast.net
wrote (in <UtKdnXVNibo6kMfdRVn-uA@comcast.com&gt about 'Cellphones and
Bombs', on Thu, 18 Mar 2004:
You can try to ratioanlize it as much as you want. The willfull
electronic interference of a radio service is a crime. Did you read the
part of my post about signal blocking? I thought not. Go back and try
again. If a terorist is going to strike, he is going to strike. The
Department of Homeland Paranoia is not going to be able to do anything
about it.

I am ALMOST old enough to remember a similar idea held in UK and Europe
before WW2, that 'the bomber (aircraft) will always get through'. The
RAF pretty well disproved it.

OTOH, the Eighth Air Force did pretty much prove it. Unfortunately, they
didn't always come back.

Ed
wb6wsn

 

[Ed Price]

"Roger Gt" <not@here.net> wrote in message
news:_ka6c.25584$D82.1569@newssvr29.news.prodigy.com...

"Active8" wrote
: Roger Gt wrote:
: > "Paul Burridge" wrote
: >: Jim Thompson wrote:
: >:
: >:>I was struck by a thought when I heard the latest Palestinian
: >:>terrorist trick is to send a kid through the border with a
: > back-pack
: >:>bomb triggered by a cell phone....
: >:
: >:>The Israelis should get a telemarketer's speed dialer and
: > constantly
: >:>dial away... boom... boom... boom...
: >:
: >:>ROTFLMAO!
: >:
: >: Yes, I'm rolling on the floor laughing at all these deaths,
too,
: > as
: >: I'm sure we all are.
:
: > Huh?
: > He seemed to be laughing at the lame Idea! I also thought it
: > funny that anyone would try something which would almost
totally
: > wipe out the cellular phone service for the entire country...
:
: does a 200 station phone room with auto-dialers all calling one
: state wipe out POTs? WTH are *you* talking about?

Gee - Primitive! Not a Telephone guy I guess......
The last autodialer I worked on was a Dual DS3 line unit with a
router.
2 times 864 lines wide. A few of those would really choke a
network!

So YOU are one of the SOB's who create those things?

Ed
wb6wsn

 

[Ed Price]

"Ben Bradley" <ben_nospam_bradley@mindspring.example.com> wrote in message
news:572i50l3vv3l6t933e5u4bjq7k2rq3hq7r@4ax.com...

In rec.radio.amateur.antenna,

( I suppose this is on RRAA because cell phones have antennas )

sci.electronics.design,sci.electronics.basics, Jim Thompson
thegreatone@example.com> wrote:

Of course, in the USA, one could put the cell number on the
national DO-NOT-CALL list, then only an "illegal" telemarketer would
trigger the bomb.

Bombers might figure ways around this (especially if they search
Usenet), such as a cellphone answering circuit and a "dee tee em eff"
decoding circuit. I wouldn't want to spell it out for them...

...Jim Thompson

They may not be as illiterate as you suggest; perhaps Pig Latin could offer
sufficient encryption: Eeday eetay emyay effyay.

Ed
wb6wsn

 

[Guy Macon]

John Michael Williams <jwill@AstraGate.net> says...

Actually, a former maritime safety engineer Emailed me
about this. However, he could not locate the law or regulation
which defines "intrinsic safety". If you can find a law
or regulation governing operation of a transmitter around
a gas pump, please post it.

The National Fire Protection Association’s (NFPA) National Electrical
Code (Article 500, NFPA 70) defines Hazardous Locations as those areas
"where fire or explosion hazards may exist due to flammable gases or
vapors, flammable liquids, combustible dust, or ignitable fibers or
flyings."

NFPA-NEC Intrinsic Safety ratings detail the specific Hazardous
Location in which an electrical device can be used without fear
of electrostatic discharge that may cause an explosion. The
classification that applies to auto fuels are: Class I: Gases,
vapors and liquids - Group D: Hydrocarbons, fuels, solvents,
etc. - Division II: Not normally present in explosive concentrations
(but may accidentally exist).

Other standards that apply to Intrinsic Safety are:


ANSI/UL 913 Intrinsically Safe Apparatus and
Associated Apparatus for Use in Class I, II, and III,
Division 1, Hazardous (Classified) Locations

US Mine Safety and Health Administration (MSHA)
Mine Wide Monitoring Systems (MWMS) Program:
MSHA ACRI2001 - 30 CFR Part 18, Part 23

CENELEC/EN European Standards for electrical
apparatus for potential explosive atmosphere
General requirements EN 500 14 [IEC 60079-0]
Increased safety "e" EN 500 19
Intrinsic safety "i" EN 500 20 [IEC 60079-11] [BS 5501 part 7]

Canadian Standards Association (CSA) C22.2 No. 157-92

ANSI/ISA RP 12.6 Wiring Practices for Hazardous (Classified)
Locations Instrumentation - Part 1: Intrinsic Safety

Factory Mutual Research Corporation (FMRC)?

American Society for Testing and Materials (ASTM)?


Also see:

http://www.crouse-hinds.com/CrouseHinds/resources/intrinsically_safe/insafe.cfm
http://www.ascojoucomatic.com/images/site/upload/_en/pdf1/V1005gb.pdf
http://www.mtlnh.com/datashts/sensors/Sen%20Specs.pdf
http://www.msha.gov/S&HINFO/TECHRPT/ELECTRICAL/imisf.pdf
http://www.gexcon.com/index.php?src=handbook/GEXHBcontents.htm
http://www.electrona.se/pdf/tp_1110_3.pdf
http://www.ieee-pcic.org/archive/pcic98.pdf





--
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 Woodgate]

I read in sci.electronics.design that Ed Price <edprice@cox.net> wrote
(in <12W6c.19644$uh.12711@fed1read02&gt about 'Cellphones and Bombs', on
Sat, 20 Mar 2004:

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:eRbCCRJiMhWAFwYo@jmwa.demon.co.uk...
I read in sci.electronics.design that CW <clinton.magers@comcast.net
wrote (in <UtKdnXVNibo6kMfdRVn-uA@comcast.com&gt about 'Cellphones and
Bombs', on Thu, 18 Mar 2004:
You can try to ratioanlize it as much as you want. The willfull
electronic interference of a radio service is a crime. Did you read the
part of my post about signal blocking? I thought not. Go back and try
again. If a terorist is going to strike, he is going to strike. The
Department of Homeland Paranoia is not going to be able to do anything
about it.

I am ALMOST old enough to remember a similar idea held in UK and Europe
before WW2, that 'the bomber (aircraft) will always get through'. The
RAF pretty well disproved it.


OTOH, the Eighth Air Force did pretty much prove it. Unfortunately, they
didn't always come back.

The idea was that there was *no effective defence** against bomber

aircraft, and it is that which is false. OTOH, there was no effective
defence against V2 rockets at the time. Luckily, they were developed too
late to prevail.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Jeff Liebermann]

On 17 Mar 2004 12:02:15 -0800, jwill@AstraGate.net (John Michael
Williams) wrote:

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.

There were few spark transmitters mounted in automobiles. They were
just too inefficient, big, and clumsy to be functional. Transmitters
in vehicles really didn't start until tube type transmitters became
popular. The problem was that the typical mobile radio used a
dynamotor (motor-generator) combination to generate the necessary high
voltages. With the radio and dynamotor mounted in the trunk of the
vehicle, there was a good chance that gasoline fumes would accumulate
in the trunk of the vehicle and be ignited by the spark from the
dynamotor commutator. See the photo of the 80D at:
http://www.telmore.com/ka1nvz/old_two-way/motorola/49-59.html
The dynamotor is the black cylinder near the handle. The 140D was
twice as big and heavy.

Back in the 1960's, my 1960 Ford Falcon had an assortment of Motorola
80D and 140D radios in the trunk. I experienced a small explosion in
the trunk ignited by the dynamotor. I had filled up the gas tank at
the local gas stop (for 19 cents per gallon). Warm weather caused it
to expand and leak vapour into the trunk. Key the transmitter, the
dynamotor starts, sparks, and boom.

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.

Lovely. A harmonic generator. Any reason you want lots of harmonics?
Shottky diodes or any other non-linear device, do not belong in
antenna matching circuits.

It's home made, but it's probably
as good as any other wire about that long.

Wrong. Optimum for CB is either a 1/4 wave monopole (102 inches) or
two of them to form a half wave dipole.

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.

Find a 4 watt flourescent light. Attach a 1/4 wave antenna to your 5
watt CB radio. Transmit. Hold lamp in hand and touch the end of the
102" antenna. It will light when you talk. (Note: With AM
modulation, you only get 5 watts when you yell into the microphone.
Without modulation, you only get about 2.5 watts of RF). Now, ask
yourself what voltage is required to light the flourescent lamp.

In order to get a spark, you need to generate enough voltage to ionize
the air between the contacts. That's about 20KV/inch. If we
eliminate the antenna, 5 watts of RF into 50 ohms will generate:
P = E^2 / R
E = 16v rms
E(peak) = 1.4 * 16 = 22 volts
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches
Kinda small, but given a microscope, a 1 mil spark gap will arc. Of
course the VSWR protection circuity in the transmitter will instantly
shut down the transmitter when it arcs, but that takes a few millisec.

Notice that this is a voltage phenomenon, and is not dependent upon
the power level. Therefore, an antenna that offers a voltage step-up
will generate a higher voltage. However as the antenna is in the air
and nowhere near a close enough ground to arc, it doesn't matter. If
there's gonna be any arcing, it will be between the xmitter output and
the base of the antenna.

The typical mobile FM transmitter of the day (1960's) cranked out
between 15 and 150 watts. Most were around 75 watts. Run the calcs
again for 75 watts and see if the gap is more reasonable (I'm lazy).

The next question is how much heat is necessary from the arc to ignite
the gasoline vapour. I'll leave that as an exercise for when I have
more time to burn. Gotta get back to lying and cheating on my taxes.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS

 

[John Michael Williams]

Guy Macon <http://www.guymacon.com> wrote in message news:<7rednfdoKtWg3sHd4p2dnA@speakeasy.net>...

See my post titled Intrinsic Safety

I did. Thanks.

It appears that the laws involved pertain to manufacturers
and commercial operations. So, I think none would
govern use of a cell phone while gassing up.

I once wired a farm house, but that was before the NEC
included the concept, I think.

John
jwill@AstraGate.net
John Michael Williams

 

[John Michael Williams]

Hi Jeff.

Thanks. Comments below.

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in message news:<mppp50ho4dr08ahkb3dlbqkcfkp0ihjn52@4ax.com>...

On 17 Mar 2004 12:02:15 -0800, jwill@AstraGate.net (John Michael
Williams) wrote:

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.

There were few spark transmitters mounted in automobiles. They were
just too inefficient, big, and clumsy to be functional. Transmitters
in vehicles really didn't start until tube type transmitters became
popular. The problem was that the typical mobile radio used a
dynamotor (motor-generator) combination to generate the necessary high
voltages. With the radio and dynamotor mounted in the trunk of the
vehicle, there was a good chance that gasoline fumes would accumulate
in the trunk of the vehicle and be ignited by the spark from the
dynamotor commutator. See the photo of the 80D at:
http://www.telmore.com/ka1nvz/old_two-way/motorola/49-59.html
The dynamotor is the black cylinder near the handle. The 140D was
twice as big and heavy.

Ships around the turn of the 20th century transmitted morse code by
spark, I think.

Back in the 1960's, my 1960 Ford Falcon had an assortment of Motorola
80D and 140D radios in the trunk. I experienced a small explosion in
the trunk ignited by the dynamotor. I had filled up the gas tank at
the local gas stop (for 19 cents per gallon). Warm weather caused it
to expand and leak vapour into the trunk. Key the transmitter, the
dynamotor starts, sparks, and boom.

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.

Lovely. A harmonic generator. Any reason you want lots of harmonics?
Shottky diodes or any other non-linear device, do not belong in
antenna matching circuits.

It's home made, but it's probably
as good as any other wire about that long.

Wrong. Optimum for CB is either a 1/4 wave monopole (102 inches) or
two of them to form a half wave dipole.

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.

Find a 4 watt flourescent light. Attach a 1/4 wave antenna to your 5
watt CB radio. Transmit. Hold lamp in hand and touch the end of the
102" antenna. It will light when you talk. (Note: With AM
modulation, you only get 5 watts when you yell into the microphone.
Without modulation, you only get about 2.5 watts of RF).

Interesting idea. I would have thought that a tube would require
more V than a neon lamp to get started. I'll try it if I can
find a lamp.

What you seem to be suggesting is that I simply connect the
lamp to the 1/4 wave receiving antenna, right? Why introduce
my hand? For ground on the other lamp contact?

I don't see the point of attaching a long
wire to the CB, because they don't come with long bare wires.
Clearly, I could get a good spark by attaching a wire to the
CB batteries, and avoid all the RF stuff!

Now, ask
yourself what voltage is required to light the flourescent lamp.

In order to get a spark, you need to generate enough voltage to ionize
the air between the contacts. That's about 20KV/inch. If we
eliminate the antenna, 5 watts of RF into 50 ohms will generate:
P = E^2 / R
E = 16v rms
E(peak) = 1.4 * 16 = 22 volts
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches
Kinda small, but given a microscope, a 1 mil spark gap will arc. Of
course the VSWR protection circuity in the transmitter will instantly
shut down the transmitter when it arcs, but that takes a few millisec.

22 V is a lot more than I could get with a 1 m monopole: I only
got 100 mV peak to peak. It appears my 1 m wires
were too short; but, if I use a long wire, the distance from the
transmitter will lower the power transfer to some
of the wire, won't it? Or, I'll have to move away, into the
far field--but that will also lower the power.

There's no question 5 W is enough to make a spark of arbitrary
size, given an inductor somewhere around, but I don't see where
the 50 ohms comes from, if I'm looking for a spark caused by the RF?

Notice that this is a voltage phenomenon, and is not dependent upon
the power level. Therefore, an antenna that offers a voltage step-up
will generate a higher voltage. However as the antenna is in the air
and nowhere near a close enough ground to arc, it doesn't matter. If
there's gonna be any arcing, it will be between the xmitter output and
the base of the antenna.

The transmitter antenna is coated with about 3 mm of rubber; I think
cell phones are the same way. A spark has to come from the RF,
I think. There is a BNC connector, but that implies complete
shielding (even flame suppression!) at the antenna base.

I have a telescoping antenna intended for a receiver that is bare
metal, though. I could substitute it.

The typical mobile FM transmitter of the day (1960's) cranked out
between 15 and 150 watts. Most were around 75 watts. Run the calcs
again for 75 watts and see if the gap is more reasonable (I'm lazy).

The next question is how much heat is necessary from the arc to ignite
the gasoline vapour. I'll leave that as an exercise for when I have
more time to burn. Gotta get back to lying and cheating on my taxes.

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

John
jwill@AstraGate.net
John Michael Williams

 

[Jeff Liebermann]

On 20 Mar 2004 23:28:38 -0800, jwill@AstraGate.net (John Michael
Williams) wrote:

Ships around the turn of the 20th century transmitted morse code by
spark, I think.

The Lusitania, Mauritania, Titanic, and Olypic all ran on coal. No
gasoline in sight. Later vessels ran on bunker C fuel oil, which is
more like tar than gasoline. I don't think one has to worry about
sparks on such a vessel unless it's finely devided coal dust, which
finished off the Lusitania in a secondary explosion after the torpedo.

Interesting idea. I would have thought that a tube would require
more V than a neon lamp to get started. I'll try it if I can
find a lamp.

Neon lamp needs about 60 volts to light and 40 volts to stay lit. The
4 watt flourescent tube wants at least 90 volts to start, and I think
(i.e. guess) about 50 volts to stay lit.

What you seem to be suggesting is that I simply connect the
lamp to the 1/4 wave receiving antenna, right? Why introduce
my hand? For ground on the other lamp contact?

Yep. You're the ground. You should be fine with a 5 watt CB and a 1/4
wave whip. The high voltage point is near the tip. However, don't
try it with an illegal CB linear. You'll get an RF burn for your
troubles.

Incidentally, there are cell phone antennas with lights in them.
http://cellphones-accessories.com/12stobligcel.html
They're LED's which require much less power to light than a 4 watt
flourescent bulb. Still, it's kinda interesting.

I don't see the point of attaching a long
wire to the CB, because they don't come with long bare wires.
Clearly, I could get a good spark by attaching a wire to the
CB batteries, and avoid all the RF stuff!

Exactly. Same with an open relay contact or toggle switch. However,
don't foget that you need containment to create an explosion.
Sparking the DC inside the trunk is the mostly likely location.

22 V is a lot more than I could get with a 1 m monopole: I only
got 100 mV peak to peak.

The 22 volts peak is at the RF connector. I'm assuming that if there
is a spark gap, it will be in the coax cable or associated antenna
connectors.

It appears my 1 m wires
were too short; but, if I use a long wire, the distance from the
transmitter will lower the power transfer to some
of the wire, won't it? Or, I'll have to move away, into the
far field--but that will also lower the power.

Inverse square law. Double the distance, and you get 1/4 the power.
For a fix load resistance, 1/4 the power is 1/2 the voltage. However,
you'll get vary bad coupling efficiency with such an arrangement. I
could grind the near field equations but you'll never get ALL the
power (5 watts) delived to your random wire pickup. Think resonance
and close coupling if you want to do better.

There's no question 5 W is enough to make a spark of arbitrary
size, given an inductor somewhere around, but I don't see where
the 50 ohms comes from, if I'm looking for a spark caused by the RF?

That's the approximate impedance of the antenna as found on a typical
mobile installation. Again, I'm assuming that if there is a spark to
be found, it will be at the coax ends or connectors. They're all 50
ohms.

The transmitter antenna is coated with about 3 mm of rubber; I think
cell phones are the same way. A spark has to come from the RF,
I think. There is a BNC connector, but that implies complete
shielding (even flame suppression!) at the antenna base.

A BNC connector is quite open but is good for maybe 150 volts of RF.
However, all it takes is a sloppy coax connection, with some of the
braid wires slopped around near the center pin of the BNC, and you
have a potential spark gap.

I have a telescoping antenna intended for a receiver that is bare
metal, though. I could substitute it.

Won't make much differnce. At 0.001" gap necessary for a spark with 5
watts can only happen with a defective installation.

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

I beg to differ. The ignition of a gasoline oxygen mixture requires a
specific amount of energy to ignite. Anything less will not produce
the requiste chemical reaction. Think spark plug heat ranges and glow
plugs in model airplanes. I'll grind the numbers if you want, but
it's now midnight, I'm tired of waiting for Windoze update, and I'm
going home.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831.336.2558 voice http://www.LearnByDestroying.com
# jeffl@comix.santa-cruz.ca.us
# 831.421.6491 digital_pager jeffl@cruzio.com AE6KS

 

[John Woodgate]

I read in sci.electronics.design that Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote (in <mppp50ho4dr08ahkb3dlbqkcfkp0ih
jn52@4ax.com&gt about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:

The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Bill Sloman]

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> wrote in message news:<ofhq50dfqlmeto169hrsj8f3e0n8eaab09@4ax.com>...

On 20 Mar 2004 23:28:38 -0800, jwill@AstraGate.net (John Michael
Williams) wrote:

<snipped lots of good stuff>

I think if I can see the spark, it can ignite gas vapor,
provided the flame had a path out of the gap.

I beg to differ. The ignition of a gasoline oxygen mixture requires a
specific amount of energy to ignite. Anything less will not produce
the requiste chemical reaction. Think spark plug heat ranges and glow
plugs in model airplanes. I'll grind the numbers if you want, but
it's now midnight, I'm tired of waiting for Windoze update, and I'm
going home.

The ignition of a gaseous oxygen-gasoline mixture, or a (potentially
more sensitive) hydrogen-oxygen mixture does require a specific
minimum amount of energy, which depends on the partial pressures of
the oxygen and the fuel, and - IIRR - the partial pressures of any
inert diluent gases around.

Lesser amounts of energy can induce the requisite chemical reaction,
but the reaction will fizzle out, rather than providing enough energy
to ingnite the surrounding shell of a gas mixture and produce a
self-propagating flame front.

The controlling relationship is between the volume of the sphere in
which the reaction is first initiated, and the surface area of that
sphere - if the intial volume is too small, not enough energy is
released to heat the surrounding shell of gas to the ignition
temperature.

Once you've got the basic idea,the thermodynamics is pretty
straightforward.

I had to work through the equations many years ago for an experiment
intended to monitor the process in which one of the "Dewar benzenes"
converted itself to normal - Kekule's - benzene, which is an
enormously energetic process, involving about an order of magnitude
more energy per molecule than you get out of TNT and PETN. I really
didn't want to blast my experimental apparatus to smithereens.

When I went through the calculations with my supervisor, he pulled a
very long face - the motivation for the experiment had been some
unexpected flashes of light seen when a dumb organic chemist had
released small drops of liquid "Dewar benzene" into a hot cell, and my
calculations made it clear that the flashes of light were just thermal
radiation from a hot plasma, rather than fluorsecence from from an
electronically excited state of Kekule benezene, which is what my
supervisor had been hoping for ...

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/entries/2001/robson/benzenering.htm

-------
Bill Sloman, Nijmegen

 

[John Woodgate]

I read in sci.electronics.design that Bill Sloman <bill.sloman@ieee.org>
wrote (in <7c584d27.0403210545.76dad16b@posting.google.com&gt about 'CB
Radios, Cellphones and Gasoline Vapor Ignition', on Sun, 21 Mar 2004:

For the difference between Dewar benzene and Kekule benzene see

http://www.chemsoc.org/exemplarchem/entries/2001/robson/benzenering.htm

Dewar benzene can actually be made? Do you know when it was discovered?
What about the prismatic form? I would have thought that was a lot
easier to make, if I didn't have a suspicion that that is where simple
bonding ideas break down.

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Michael Williams]

bill.sloman@ieee.org (Bill Sloman) wrote in message news:<7c584d27.0403210545.76dad16b@posting.google.com>...

...

The controlling relationship is between the volume of the sphere in
which the reaction is first initiated, and the surface area of that
sphere - if the intial volume is too small, not enough energy is
released to heat the surrounding shell of gas to the ignition
temperature.

...
-------
Bill Sloman, Nijmegen

This makes sense. I think I can see a spark 0.1 mm in
radius, at say 4000 K. That's about 4 cubic picometers
in volume and about 0.1 square micron in surface area (assuming
sparks have smooth surfaces). But, I'm not sure how to relate
that to the threshold of flame propagation.

If energy is a factor, rather than power, the duration of
the spark would seem to be relevant, too.

John
jwill@AstraGate.net
John Michael Williams

 

[Jeff Liebermann]

On Sun, 21 Mar 2004 08:47:34 +0000, John Woodgate
<jmw@jmwa.demon.contraspam.yuk> wrote:

I read in sci.electronics.design that Jeff Liebermann
jeffl@comix.santa-cruz.ca.us> wrote (in <mppp50ho4dr08ahkb3dlbqkcfkp0ih
jn52@4ax.com&gt about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.

I didn't know that it wasn't linear. I just assumed that it takes the
same amount of energy to peel electrons off of a single atom (ionize)
regardless of gap seperation. A wider gap requires more voltage to
ionize more atoms to create a longer conduction path, but the energy
per atom is the same. I also couldn't find (Google) any useful
references that showed this non-linearity. Unless the heat generated
by the ionization contributes to assisting furthur ionization, my
seat-o-de-pants physics says it should be linear (for DC).

There's also the minor detail of RF excitation versus DC. As I
vaguely remember from my 35 years ago college welding classes, TIG
welding uses RF to strike the arc because it takes less
power/energy/whatever to start the arc. We're allegedly talking about
striking an arc across 0.001" with a 5 watt, 27MHz transmitter
terminated with a 50 ohm load. If it's non-linear in the opposite
direction, the calcs are gonna be no fun.

I have everything it takes to test this. Microscope slide, with two
sewing pins glued with hotmelt goo and seperated by 0.001". Apply RF
and watch through the microscope. I'll see if I can throw something
together and post photos (time permitting).

Also, I've always been tempted to build a low power, QRP spark gap
transmitter. Although the mode is illegal, I suspect that operating
spark at below Part 15 incidental emission standards, would be
tolerated. Getting the arc to start at such low power levels might
require some exotics (i.e. piezoelectrics). This could be the start
of something interesting (or disgusting).


--
Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
(831)421-6491 pgr (831)336-2558 home
http://www.LearnByDestroying.com AE6KS
jeffl@comix.santa-cruz.ca.us jeffl@cruzio.com

 

[Bill Sloman]

John Woodgate <jmw@jmwa.demon.contraspam.yuk> wrote in message news:<9nrqPFCmaVXAFwWE@jmwa.demon.co.uk>...

I read in sci.electronics.design that Jeff Liebermann
jeffl@comix.santa-cruz.ca.us> wrote (in <mppp50ho4dr08ahkb3dlbqkcfkp0ih
jn52@4ax.com&gt about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:
The gap necessary to create an arc with 22 volts is:
22V / 20,000V/in = 0.001 inches Kinda small, but given a microscope,
a 1 mil spark gap will arc.

But it takes about 350 V to do so. The relationship between voltage and
gap length is very non-linear below about 500 V.

In fact the Paschen curve - breakdown voltage plotted against gap -
has a minimum at around a couple of hundred volts, and the breakdown
voltage starts rising again for very small gaps. The linear right-hand
branch of the graph where you might see a slope of 20,000V per inch
doesn't extend down to 22V.

The theory explaining the conductivity of electricity through gases
was worked out around the turn of the last century, and doesn't seem
to be all that well known any more. Pity.

-------
Bill Sloman, Nijmegen

 

[Nico Coesel]

KLM <klmok88@yahoo.com> wrote:

On Thu, 18 Mar 2004 05:39:21 +0000, Tim Auton
tim.auton@uton.[groupSexWithoutTheY]> wrote:


Do you all think that tangos are dumb enough to trigger the bomb
with the ringer or would the detonator answer first and listen for a
DTMF sequence. Hmmm? Achmed the bomb maker gets a wrong number just
as he's connecting the thing.

I very much doubt they bother with DTMF decoders. I mean, how often do
you get a wrong number? I've had about 4 in my life. They'll just
connect the ringer (or vibrate function) to the detonator (with
whatever minimal circuitry in between is required - I've never used a
detonator!) and then only turn the phone on at the last minute.

It's not dumb to design a remote detonation system that requires the
absolute minimum of specialist knowledge and equipment to construct.



To use the unique cellphone ID to detonate a remote bomb is actually
a very ingenious innovation. No timers to mess with. The terrorist
has full and instant control of the time and place to set off the
bomb.

As Tim says its relatively easy to connect the ringer wires to a
simple circuit to output enough juice to trigger the detonator. Frist
year student project - like using a battery to keep a capacitor
charged and the ringer closes the discharge switch. Boom.

I'm pretty sure that it won't work that simple. There are other
factors at play that make controlling things with a telephone a lot
harder to achieve than you think... For everyone's safety I'm not
going into the details.

--
Reply to nico@nctdevpuntnl (punt=.)
Bedrijven en winkels vindt U op www.adresboekje.nl

 

[CW]

If you think it is that hard, it's obvious the reason you won't go into the
details. You don't know.
It is rather easily done.

"Nico Coesel" <nico@puntnl.niks> wrote in message
news:405e167b.32890183@news.planet.nl...

I'm pretty sure that it won't work that simple. There are other
factors at play that make controlling things with a telephone a lot
harder to achieve than you think... For everyone's safety I'm not
going into the details.

 

[John Woodgate]

I read in sci.electronics.design that Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote (in <c1tr509eqipks7lt08ttt5cvnpkumu
89u3@4ax.com&gt about 'CB Radios, Cellphones and Gasoline Vapor
Ignition', on Sun, 21 Mar 2004:

I didn't know that it wasn't linear.


Google for Paschen's Law. For high voltages it is linear enough for

calibrated spark gaps to be used as voltmeters in the past. The high-
voltage terminals were open and accessible, giving a whole new meaning
to the phrase 'Paschen killers'.(;-)
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk