Re: On board fires

[shawl@torchlake.com (Jonathan Shawl)]

Dave,
Just one more thought on this, maybe a all plastic type squirt bottle should be
used to help avoid the dangers of a low voltage DC shock.
Jon


DaveIrons@aol.com wrote:

> Jon and Rick you have made some good points.
>
> Pure water does not conduct electricity.  The reason water is commonly
> considered a
> conductor, is because pure water does not exist in nature.  In fact pure
> water may be a
> good insulator.  The problem is that water, the universal solvent, quickly
> picks up ions.
> Distilled water will aggressively dissolve metal and minerals.  Some
> municipal water
> systems add about 150 PPM.  Calcium Carbonate to the water supply.  If they
> delivered soft
> water it would dissolve the lead from the pipes and contaminate the drinking
> water.  The
> well water in Jon's house will contain some ions and is probably only
> slightly conductive.
> Salt water is a very conductive.  Distilled water, reverse osmoses water and
> purified water
> are all generically referred to as deionized water.  Reverse osmoses units
> often have a
> light that indicates any conductivity in the water.  When the light is off
> the filter is
> working properly.
>
> Distilled water may not be the best choice as a primary fire extinguisher.
> However, most
> fires could be extinguished by a tiny squirt directed in the exact location
> of the hot spot.
> A little water bottle would also make a dandy thirst quencher at the end of a
> dive.  Water
> may be the only fire extinguishing substance that is completely nontoxic.
>
> If any water that does puddle on the floor of the sub, I would think that
> good boat design
> would provide for some accumulation of water.
>
> For the primary fire suppression system, I would think, dry chemical would be
> used only
> as a last resort.  Nitrogen may be safer than Carbon Dioxide (CO2).  Air is
> 79% Nitrogen.
> Some advanced divers are using Nitrox mix for very deep dives.  Nitrogen can
> extinguish
> a flame by depriving it of Oxygen the same as CO2.  Water cools the flame.
> Water is
> generally considered the method of choice by fire departments when
> extinguishing fire in
> porous material like wood or paper.
>
> David Irons
>
> Rick Lucertini wrote:
>
> > [snip]
> >
> > >Since subs have low voltage electrical systems, what about a water spray
> type fire
> > extinguisher?
> >
> > Water should never be used around electrical fires, low voltage or
> otherwise.  Since
> > water conducts so well, it could lead to other problems in other
> electrically
> > sensitive systems.
>
> Jonathan Shawl Wrote:
> >That is a good rule to follow in general, and it is true that water
> sometimes can conduct
> electricity. Most everybody thinks water is a good conductor of electricity,
> BUT clean
> fresh water with a low mineral content is NOT a good conductor at all.  Where
> I worked
> we used water cooled power cables for power to the heater elements, 24 to 100
> volts. The
> same
> water ran through the cables and the entire furnace, the only insulator to
> stop it from
> shorting out was the water itself. I don't remember exactly the distance
> needed per volt
> to isolate the power but it wasn't much. I did the following experiment. Kids
> don't try
> this at home! I took a power cord and stripped the wires back a 1/2 inch and
> taped the
> wire so the bare ends stayed about 1/2 inch apart. I carefully plugged in the
> cord to a
> 120 volt outlet and stuck the other end in a glass of our well water and....
> nothing
> happened, no bubbles or anything. So I added (with a salt shaker) a very
> little salt to
> the water and it started to sizzled and bubbled right away. This showed me
> that it is not
> the water that conducts but the minerals in it that can conduct. As far a
> short circuits
> go I don't think putting some fresh water spray on a burning LOW VOLTAGE
> (under 24
> volts)
> wire would do much other than cool the wire and put out the fire. That is not
> the same as
> saying it is a good idea, I'm not saying that. But I would have to question
> the use of
> anything else in a fire extinguisher as being safe at all to breath being in
> a closed
> space. Vance, what kind do they use on the "real" subs?
> I like the idea of the BIBBS or something like it!
> Jon