(The Captain) wrote in message . com...
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.

Actually, anyone who has worked in the offshore oil industry will be
familiar with the concept of intrinsic safety. This requires that no
electronic instrument shall be able to ignite a mixture of air and
inflamable vapour or gas. All handheld radios used on rigs are
intrinsically safe, making them far more expensive than the standard
variety.

I very much doubt that cell phones are buit to intrinsicly safe
standards, and under those circumstances I would certainly not feel
safe near someone yacking while filling.

So, an interesting querstion is; does your phone conform to UL
requirements for intrinsic safety? And if not, why are you using it
in an area where an explosive gas air mixture is possible?

Cap

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.

I have no idea how UL testing would pertain to a battery operated
device incapable, itself, of electrocuting anyone. However, the
battery eliminator which I have (but did not use in the
experiment I described) is UL approved.

On the safety issue, the same engineer also told me he was able
to create visible sparks with a 100 W transmitter, holding
the antenna near a piece of metal. However, for the following
reason, I suspect the sparks were because his transmitter was
earth-grounded:

The handheld CB I used had a completely insulated rubber antenna
and of course had no ground connection. I replaced the rubber
antenna with a telescoping metal one. I then keyed the transmit
button (as above) in the dark, while trying to get a spark by
bringing the tip near a 1 m x 1 m aluminum 1/4 in plate (ungrounded).
I could see nothing, although touching the metal caused the CB's
power out bar to indicate a drop in power. The plate should have
been an effective AC ground at ~27 MHz.

So, neither induction into a wire nor electrical direct contact
seems likely to make a visible spark, with a 5 W CB transmitter.

I would only expect a 100 mV or so spark anyway, which would be
hard to see.

So, I'm not convinced that a cell phone could cause a spark, either.


I agree that key closure sparks might be possible internal to
the device, and that neither it nor a cell phone would be likely
to have been designed to suppress a flash from such a source.

However, the issue I have tried to address here is a spark from
the RF, not from generic electrical causes. I don't doubt that
gasoline vapor is inflammable in a generic sense.

John

John Michael Williams

See my post titled Intrinsic Safety

--
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/

Guy Macon http://www.guymacon.com wrote in message ...
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

John Michael Williams

John Michael Williams says...

Guy Macon http://www.guymacon.com wrote...

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 agree. If Intrinsic Safety rules were applied, automobiles
would be banned from gasoline stations. This would not only
eliminate the 35 refueling fires that occur every year, but
would also eliminate most of the 50,000 traffic accident
fatalities...


--
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 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 a 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 a


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/CrouseHi...afe/insafe.cfm
http://www.ascojoucomatic.com/images...f1/V1005gb.pdf
http://www.mtlnh.com/datashts/sensors/Sen%20Specs.pdf
http://www.msha.gov/S&HINFO/TECHRPT/...ICAL/imisf.pdf
http://www.gexcon.com/index.php?src=...HBcontents.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/