Re: Air Use Calculations

[protek@shreve.net]

    I had mixed thoughts when I wrote that scrubber letter.  Ultimate
safety would be better realized with the ability to scrub sub air.  There
may be times in certain emergency conditions where a person might have to
stay down for a long time and have to have O2 or at least the removal of
CO2.  I can see where safety would be much better served by having one on
board.  But, if I personally had one, I would not use it for short dives
and that is all I have ever made in my sub.  I have my compressed air
inside with me in the form of two scuba tanks plus I carry a pony bottle
with regulator.  I can connect to all three in case of an emergency so I
have air to breath if necessary.  I also have a way to vent this buildup of
air pressure to the outside safely to keep the inside pressure from
exceeding the outside pressure.  If one is going deep and uses this type of
emergency breating it is possible to get the bends on ascent.  There are
some dangers, but as a whole and for my uses, I decided to just use SAR for
the time being.

Gary Boucher


At 09:03 AM 10/31/99 -0800, you wrote:
>      I have to agree with you, Gary.  I don't think
>it's worth the trouble or the money to build in a
>scrubber when I'm only down for about an hour at a
>time.  If I were to get stuck on the bottom for longer
>than that, I'm probably not coming back up again
>anyways unless I flood the cabin n swim out.  As far
>as the "surface and replenish" thing goes, it seemed
>pretty easy to just design in a couple of fans and
>some ducts to circulate some fresh air in while on the
>surface.  
>
>--- protek@shreve.net wrote:
>>     I find it unusual that so many people who plan
>> to build small subs want
>> to design the air rebreather system first.  It seems
>> like this is their
>> first priority.  The thought of diving without O2 is
>> unthinkable to so
>> many.  But, depending on the volume of the air
>> inside the hull, there is a
>> time interval where one can breath the inside air
>> only with no problems.
>> Many subbers do this continuously with no use of 02.
>>  The SAR (surface and
>> replenish) method has worked for me in my sub, but I
>> don't go for long
>> duration dives where more is needed.  The cost of
>> the materials for
>> scrubbing for me would not warrant their use on
>> short dives.  In other
>> words, for me personally, I would not even turn it
>> on till I had been down
>> long enough to need it.
>>     A no-scrubber time limit needs to be established
>> though and adhered to.
>>  Also, one must realize that emergency situations
>> may extend down time to
>> greater duration than the SAR method can handle.  In
>> my case I have
>> compressed air on board.  This does raise the inside
>> pressure if used and
>> that is another problem I will admit.
>>     Scrubber systems do not take up much space in
>> most cases.  The main
>> weight is the O2 bottle itself.  If I were designing
>> a sub again, I would
>> leave space for the system and allow for the
>> estimated weight but not
>> concentrate on this systems fine details till I had
>> a workable sub.  Then
>> if you choose to use a scrubber it can be installed.
>>     Once again, if you don't have a scrubber there
>> is less safety built
>> into your system.  So I am not saying to not use
>> one.  I am saying that I
>> don't in my sub.  And IF (and that can be a big IF),
>> I never have to sit on
>> the bottom without the ability to surface, I will
>> probably never need one
>> because of the duration of my dives.  Scrubber or no
>> scrubber, if you do
>> use the SAR method for a particular dive you should
>> have an efficient
>> method of purging the old air from the subs hull. 
>> Opening the hatch for a
>> couple of minutes is not enough as the air does not
>> have time to exchange.
>> 
>> Gary Boucher
>> 
>
>
>=====
>"Noisy outside, empty inside." - Confucius
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