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Author codes:-
AA> A.Appleyard <a.appleyard@fs*.mt*.um*.ac*.uk*>
CH> Carl G Heinzl <heinzl@wi*.en*.de*.co*> (Tue, 5 Jul 94 11:24:57 EDT)
RP> Richard Pyle <deepreef@bi*.bi*.ha*.or*>
AMRB = "automatic mixture rebreather"
RP> Geez - you don't want much [putting in a reasonably cheap AMRB], do you
:-) My impression is that a unit meeting all of your criteria will not exist
anytime soon....
AA.1> Why not? Why so expensive and difficult? Oxygen rebreathers for
industry and firemen (and later naval frogmen) were inexpensive and mass
produced for ages
CH> I would think that the environment that these rebreathers were built for
is a little different than we're talking about. It is possible for a fireman
to escape should his equipment stop working and, naval frogmen didn't dive to
very great depths so a free swimming ascent was easily do-able. Also, these
were professional people making this their life's work, and conventional
wisdom allows them to accept responsibility for being in a hazardous situation
moreso and someone who is doing this for run (no matter how well Joe Techdiver
may be trained or what he's been doing).
AA.1> before sport diving was much heard of, e.g. the (UK) Siebe Gorman
Salvus (neck type) (incredibly light and handy, about 40 mins duration),
Proto, UBA, SCBA, etc etc. Technology seems to have forgotten how to make
things simple. To make this into an automatic mixture rebreather seems to me
to need:-
CH> More like lawyers have forbidden it to be cheap. The cost of $5k per
unit liability comes up again and again. [and see below]
AA.2> But now the Japanese are making these tiny diving oxygen rebreathers
mentioned in various messages to Techdiver. As I said before, since the
Japanese think that there is a need for a light simple short-duration oxygen
rebreather, bring back (the neck type of) the good old Siebe Gorman Salvus!
AA.1> * Diluent (air usually) cylinder. This would not add much more to the
cost than it costs to give the set its oxygen cylinder.
CH> Less actually since filling an air cylinder is much less expensive than
an O2 cylinder. It also wouldn't require any O2 cleaning/etc as long as there
were one way check valves.
AA.1> * Electrically-actuated oxygen and diluent values. Various writers to
Techdiver (e.g. JOHNCREA@de*.co* on Wed 29 Jun 1994 06:59:03 -0400 (EDT))
have pointed out these don't need much electricity to run and so only need a
small battery of the common type.
CH> Remember, a lot of this has to be 100% O2 rated.
AA.2> How much would this 100% O2 rating affect the price?
AA.1> * Partial pressure of oxygen (= ppO2) sensor.
AA.1> * Depth sensor.
CH> You would probably want *at least* 2 sensors for redundancy and in real
life, there would probably be three with a 2 out of 3 voting scheme.
AA.1> * Sensor to tell if he is sucking at an empty breathing bag.
AA.1> * Some simple electronics (not necessarily a PC-type CPU) to keep the
ppO2 right and to let more gas in if he sucks at an empty bag.
CH> It would also do deco calculations making it slightly more complicated,
but well within current technology.
AA.2> Why? As I wrote before, the decompression meter should be separate, to
cater for the same set being used by different divers, and the same diver
using different sets. The deco meter should be able to be wired to the AMRB's
ppO2 sensor; if the deco meter is used loose, it assumes air (e.g. he is on an
aqualung, or out of water gradually degassing) unless told otherwise.
AA.1> === Useful would be:-
* ppO2 readout external connection for a suitable decompression meter to
read from.
* Separate aqualung-type pillar valve fed from the air (diluent) cylinder,
so he can fit an aqualung regulator to it as a baleout if he wants to.
PLEASE which of those items is so massively expensive or impossible!?!?
AA.1> Is there any need to add to the cost by having the set in a box?
People have used rebreathers with the bag naked from the beginning. With
modern very tough materials like Kevlar there need not be much risk of the bag
getting cut open.
RP> [The box does not cost very much: it is to protect the set from damage
by bumps on rocks etc]
CH> I'm suprised that no one has corrected you on this yet, however... You
have left out one of the most critical parts of the system, and that is the
CO2 scrubber.
AA.2> In AA.1 I wrote "to make this [= the basic oxygen rebreather] into an
AMRB seems to me to need:-", so I did not list as *'ed paragraphs the parts
like the scrubber that are in the basic oxygen rebreather.
AA.2> An odd technical point: the old Siebe Gorman Proto which stood the
test of long use (not intended for diving) had no canister: the absorbent lay
loose in the bottom of the breathing bag!
CH> From what I've heard the CIS-LUNAR unit is able to recover from a full
flood (i.e. no caustic cocktail!). I believe that they have have patents
pending on their technology in this area. I believe it would be possible to
build a unit such as you described fairly inexpensively and the people who
have made home built units in the past have done just that.
AA.2> And likely mass-production would bring the price down a lot more.
CH> however, it would most likely have failure modes that are unacceptable
to many of us (especially the lawyers!). [and see below re lawyers]
AA.1> Richard Pyle described the Cis-Lunar set:
RP> ... available for purchase later this year.... capabilities v. cost. 25
will be built this year, all ...already ... sold. But if it all goes well,
they'll offer more next year. They have just about all of the criteria you ask
for, plus way more than you probably want, and cost around $12,000-$15,000.
CH> Last time I talked to Rich Nordstrom on the phone, he said that this
year's production run was being expanded to 35. I don't remember if he said
that they would consider making even more, but since they've expanded
production once already, I don't think it would be difficult to extrapolate.
AA.1> That is $$$$!! What are the "way more than I probably want" items?
CH> It has been estimated several times that the liability insurance alone
will cost somewhere in the neighborhood of $5000 per unit. ... I don't know if
there is $5000 built into the CIS LUNAR price for liability, but at $7000 -
$10000 that would be a pretty damn attractive unit, and would fit on one of my
credit cards too :^)
CH> I wonder if we could avoid paying this [$5000] if we had the units
shipped and/or manufactured overseas?
AA.2> Indeed could we? As stated in the discussions about using oxygen
rebreathers for decompressing and for photography, there is a need for
rebreathers, and better this need supplied by properly-made frogmen's
rebreathers or the like than people trying to make their own rebreathers out
of diver's lifejackets (which I have heard of happening) or risking with some
old second-hand industrial rebreather that was not built to cope with seawater
corrosion. I weary of hearing of reasonable things that people daren't do
because of fears of lawyers' bills if anything goes wrong. Lawyers are getting
to look like yet another "good servant but bad master" like fire and the car
etc, whose power needs keeping within bounds. People who need rebreathers need
<rebreathers>, not a load of silly sorry-but'ing from officials and lawyers.
AA.1> Please what is Cis-Lunar's postal address for enquiries?
CH> CIS Lunar's address was posted in the aquaCorps journal on C2 as well as
the addresses/phone numbers of all of the other known active rebreather
companies...
AA.2> I heard a time or two about an oxygen rebreather with no cylinder! but
instead its canister was filled with potassium superoxide (KO2) (not K2O). The
chemistry involved is:-
in body in set
2 H2 (food) + O2 -> 2 H2O 2 H2O + 4 KO2 -> 4 KOH + 3 O2
C (food) + O2 -> CO2 CO2 + KOH -> KHCO3, or
2 CO2 + 4 KO2 -> 2 K2CO3 + O2
and he gets more than his original oxygen back. I heard of an oxygen
rebreather called Oxylite that worked like this. It was intended for
industrial use, but some time around 1916 it was used underwater to make the
underwater scenes in the first movie film version of Jules Verne's `10000
Leagues under the Sea'. (The recent Walt Disney version used aqualungs.) In
the Walt Disney version, and in the book, the divers walked on the bottom, so
likely the `Oxylite' version did also, and so nobody would have got the idea
of the free-swimming diver from it.)
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