Clark wrote:
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Clark wrote:
wrote in
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On Aug 10, 8:40 am, Clark wrote:
wrote
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On Aug 9, 5:40 pm, "Hilton" wrote:
Hi,

Seems like it is a no-brainer (and easy) for pilots to use LEDs in
various forms. Why then, do miners not use them? Why do those
trapped miners only have a few hours of light available? Heck,
the
mine companies could buy al cheapo LEDs for nothing and spread
them
throughout the mine for little to no cost. These are give away
items now. One single tiny little LED would be invaluable right
about now and last forever.

Some things just don't make sense.

Hilton

Everything that goes into a mine has to pass the explosion proof
test
requirements. LEDs can pass, but it has to be in a tested design.
That adds cost...

With low voltage systems it's fairly easy to meet the requirements
for
hazardous area ops. IIRC anything below 5 volts is considered safe.

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It's not just voltage. The housing has to be able to contain an
explosion inside of it without igniting combustible gases in the
surrounding air...

That requirement goes away on intrinsically safe devices.

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Actually the requirment is that the device be sealed such that explosive
gases can't get inside where any sparks from the switch turning the
device on and off might ignite them.

I don't believe that is correct. Perhaps a mechanical switch might require
a seal but it might not on a low voltage system. In general an
intrinsically safe device does not require a seal for explosion hazard
mitigation. Other factors such as desire to exclude moisture might result
in a sealed case.

The voltage is irrelevant; sparks are sparks.

Have you ever actually seen a flashlight approved for use in explosive
environments?

They are nothing more than a rubber covered flashlight with rubber
seals on everything and a rubber cover over the switch.


--
Jim Pennino

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