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March 19th 04, 06:23 PM

In article ,
(The Captain) wrote:

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 the electronic portion of the Intrisically Safe Radio is
the same as the regular Radio of the same model. What is different is
the Battery and the Battery Connections. On an Intriscally Safe Radio
the Battery and Battery connections are Specifically Designed so as
to not spark when changed, while the radio is turned on. This design
change isn't really that expensive, but the testing that is required to
receive the "Intrinsically Safe" Lable, is extremely expensive.

me

March 19th 04, 06:43 PM

I read in sci.electronics.design that Me wrote (in Me-
) about 'CB Radios,
Cellphones and Gasoline Vapor Ignition', on Fri, 19 Mar 2004:
This design
change isn't really that expensive, but the testing that is required to
receive the "Intrinsically Safe" Lable, is extremely expensive.

There are strong suspicions in some countries that it is quite
unjustifiably expensive, because only a few facilities offer it. More
competition is required. Or a government investigation.
--
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

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