Re: On board fires

[DaveIrons@aol.com]

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