Rosalie,

You misunderstand a lot when it comes to the science you teach and it's
real world applications.

An explosion proof switch is simply a switch that is totally sealed from
the environment it is in. There are many ways to do this and certainly
a mercury switch is one of the most reliable in a low shock application.
Your explanation is simply not correct.

Regards, Ron

On Sun, 26 Oct 2003 17:22:32 -0500 (EST), (Ron
Thornton) wrote:

Rosalie,

You misunderstand a lot when it comes to the science you teach and it's
real world applications.

An explosion proof switch is simply a switch that is totally sealed from
the environment it is in. There are many ways to do this and certainly
a mercury switch is one of the most reliable in a low shock application.
Your explanation is simply not correct.

Regards, Ron

You may be right Ron. Then again, you may be wrong.
Ex-cathedra statements just don't cut it.

For example, Here's the Honeywell take on an "explosion-proof"
definition:

"Explosion-Proof Switch-a UL listed switch capable of withstanding an
internal explosion of a specified gas without ignition of surrounding
gases. "

This seems to agree with Rosalie's offering. So where are you coming
from, evidentially speaking?

Brian W

Brian,

No I do not believe it doesn't agree. Honeywells definition differs in
that it does not infer that the gas internal to the switch is the same
gas that is in the outside environment. Her inference was that the
external gas could migrate into the switch, explode and not ignite the
outside gas. This is like saying that in all instances a gasoline
engine with a flame arrestor will not ignite gas fumes in a boat when in
fact on rare occasions they do. Not a design I would stake my life on.
I remember testing switches that would shoot a flame out when turned off
at elevated temperatures because they would ignite flammable gases that
outgased from the materials inside. I believe your interpretation of
the Honeywell definition is incorrect but it has been a long time since
I have dealt with these things so as always I stand to be corrected.

Regards, Ron

Humphrey Davy invented what may have been the first explosion proof
device, as you may possibly agree. His miner's lamp, which was a wick
lamp, was fitted with a surprizing novelty: two cylinders of copper
gauze cloth. This offered certain advantages over the miner's
traditional canary. It indicated firedamp with its flame color, and
if the mixture became explosive, the flame quenched on the copper
gauze before escaping. The gauze took just too much heat out of the
flame front in that small space.

School kids used to be shown a chemistry lab demo of a bunsen
burner, with a copper gauze held over it. The flame could be ignited
above or below, with the other side unlit.

Brian Whatcott Altus OK


On Mon, 27 Oct 2003 19:14:38 -0500 (EST), (Ron
Thornton) wrote:

Brian,

No I do not believe it doesn't agree. Honeywells definition differs in
that it does not infer that the gas internal to the switch is the same
gas that is in the outside environment. Her inference was that the
external gas could migrate into the switch, explode and not ignite the
outside gas. This is like saying that in all instances a gasoline
engine with a flame arrestor will not ignite gas fumes in a boat when in
fact on rare occasions they do. Not a design I would stake my life on.
I remember testing switches that would shoot a flame out when turned off
at elevated temperatures because they would ignite flammable gases that
outgased from the materials inside. I believe your interpretation of
the Honeywell definition is incorrect but it has been a long time since
I have dealt with these things so as always I stand to be corrected.

Regards, Ron