Re: On board fires

[shawl@torchlake.com (Jonathan Shawl)]

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.

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