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On 30 Jun 1994 22:24:30 -1000 (HST) Epic Dive Shop <epic@so*.ha*.ed*>
wrote (Subject: Re: Solo@90*?):-
> 35 years ago (or so) rebreathers hit the market. Due to lack of proper
training and irresponsible divers they quickly got "bad press" and even now
are struggling in their return... *that* is a damn shame. ...
(1) All too true.
(2) How far has research got into finding the exact neuro-cybernetic and
neuro-biochemical etc mechanism that causes oxygen convulsions and other
hyperoxia symptoms? Is or will there be a drug to suppress these symptoms and
allow deeper safe diving with pure oxygen? (As well as to eliminate oxygen
convulsion risk in medical hyperbaric oxygen treatment for such medical
treatments as killing gas gangrene (Clostridium perfringens) infections.)
On Fri 1 Jul 1994 16:47:48 GMT I (A.APPLEYARD@fs*.mt*.um*.ac*.uk*) wrote
(Subject: automatic mixture rebreathers: when oh when?):-
> I am sorry to reiterate, but among all the flaming etc and intricate
technical discussions has anyone any idea when we will see in the diving gear
shops a simple plain reasonably cheap and reliable, not burdened with too much
to go wrong, automatic mixture rebreather with bag, canister, oxygen cylinder,
air (as diluent) cylinder, robust small ppO2 detector, a little simple
electronics to automatically keep the ppO2 at 1.2 ats, and as little as
possible else? (Its air (diluent) cylinder could have a separate high-pressure
outlet that he can put an aqualung-type regulator on as a baleout if he wants
to.) If suitable decompression meters can't be had, he can use one meant for
an air aqualunger: it will err a lot, but on the side of safety, until a
decompression meter is made that can be set to "I am breathing 1.2 ats ppO2
and the rest nitrogen" mode. If fancying them up is what is delaying them,
then just get the basic thing on the market and let the income from selling
them help to aid the continued development!
On Fri 1 Jul 1994 12:00:23 EDT Carl G Heinzl <heinzl@wi*.en*.de*.co*>
replied:-
> You virtually ask for the impossible. When you have a bag, canister, O2
cylinder, diluent, etc, the system becomes complex and as such the failure
modes increase. For this reason, people that own these things must know how to
deal with the various failure modes. [and described the new CIS-Lunar set]
On Fri 1 Jul 1994 10:22:45 +22305714 (HST) Richard Pyle
<deepreef@bi*.bi*.ha*.or*> replied:-
> Geez - you don't want much, do you :-) My impression is that a unit
meeting all of your criteria will not exist anytime soon....
Why not? Why so expensive and difficult? Oxygen rebreathers for industry and
firemen (and later naval frogmen) were inexpensive and mass produced for ages
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:-
* Diluent (air usually) cylinder. This would not add much more to the cost
than it costs to give the set its oxygen cylinder.
* 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.
* Partial pressure of oxygen (= ppO2) sensor.
* Depth sensor.
* Sensor to tell if he is sucking at an empty breathing bag.
* 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.
=== 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!?!?
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.
[CIS-LUNAR]
Richard Pyle described the Cis-Lunar set:
> ... 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.
That is $$$$!! What are the "way more than I probably want" items?
Please what is Cis-Lunar's postal address for enquiries?
[PRISM]
Richard Pyle wrote also: "At the other end of the spectrum is the Prism
built in the U.K. It is supposed to be available this year in the $4,000 -
$5,000 range, but does not have as much sophisticated electronic controling
systems as the Cis-Lunar rig. The Prism will be available for demo at Hal
Watts' 40 Fathom grotto through the month of July.".
On Sat 2 Jul 1994 23:13:10 -0400 (EDT) JOHNCREA@de*.co* replied:-
> ... it is not a "mixing" unit, but is a constant flow system. You only
have one gas supply feeding in ... [it determines] the MOD (max operating
depth) ... about 2-3x the duration of open circuit systems, and CANNOT deliver
a breathing mix higher in oxygen than that of the supply gas. ... [need for
more diluent as he goes deeper can only be met by supplying more gas mixture
and hoping that he will use up the oxygen out of it fast enough] ... the Prism
becomes less and less efficient as the depths increase.
> [If set for] maximum possible oxygen consumption, then at lower metabolic
demands the system is wasting gas. But, if you set it for a lower metabolic
demand, then suddenly [need] to exert yourself [harder], the potential for
becoming hypoxic is real.
i.e. it gets more and more like an old-style constant-flow compressed-air
set with a bag (not rebreathing bag) to store the air until he needs it, and
the efficiency in duration/weight of the rebreather is largely lost. This
method has been used for ages, e.g. by UK naval rebreathers when used in
mixture mode. I learned something of this on a short commercial diving course
that included using a naval frogman rebreather: needed are: oxygen consumption
of diver; depth of dive; arithmetic to work out mixture strength and flow rate
needed beforehand; then the gas flow rate anmd mixture strength must be set
and tested. Not for the sport diver! Having to know what mixture to use
beforehand is too much (but with more risk of fatal consequences) like the bad
old days of single-grade motor oils (thin for cold, thick for warm) when
countless car journeys from the Alps (cold) down to the French Riviera (hot)
(being too busy to change oil on the way) ended up with a burnt-out engine
being towed, until the motor oil suppliers had to design multigrade oil.
> Prism addresses this letting the diver monitor his system PO2 and manually
adjust a needle valve to keep the PO2's within range. This adds tremendously
to the task loading of the diver, and it probably not an ideal solution.
It is very very far from an ideal solution. When diving I want to enjoy the
scenery or get on with a job or whetever, not have to forever keep fiddling
with my breathing set.
[OTHER SETS]
> There are a number of other units which fall somewhere in-between.
Any chance of a very brief list of names and prices, and names and addresses
of their manufacturers / developers?, so people can enquire about them.
On Sun 3 Jul 1994 01:27:31 -0400 (EDT) CMDR_KEENER <PSTONGE@Tr*.ca*>
replied (Subject: Reabreathers - What about the Lynx?):-
> ... how to ensure that the ppO2's stay in the safe ranges (ie. <1.2 ata
O2
or so). There's been talk of having 'puters automatically take this into
account and adjusting the oxy and diluant proportions accordingly. If memory
serves, one of the USN jobbies does just this. However, on a tour of DCIEM I
was introduced to a rebreather used by some of the CF's divers, and its
unusual feature was its simplicity - O2 flow rate was set up prior to the
dive, and the diluant proportion / supply was actually controlled by a
mechanical sensor. Hence, as depth increased, so was the dilution factor. ...
What is DCIEM and CF?
How does it cope with variations in individual oxygen use with exertion, and
with the body burning more energy to keep warm in cold water? I still prefer a
ppO2 sensor, see above.
On Mon 4 Jul 1994 10:27:12 -0500 Terry McCracken <terrym@it*.ns*.co*.au*>
replied that using an aqualung decompression meter with an automatic mixture
rebreather is invalid if the set ever gives higher ppN2 than an air aqualung
would, and "... a higher PN would probably narc you out of your tree.".
ppO2 of air > 1.2 ats when total air pressure > 1.2*5 ats = 6 ats = 175 feet
= 55 meters depth, when, as Terry said, the diver would also be narked beyond
the limit of safety. So, a diver with an automatic mixture rebreather with air
as diluent could use an air diver's decompression meter safely (but perhaps
with unnecessary decompression stops) for all the diving that most people want
to do on air, until someone designs a decompression meter that can be set to
ppO2 = some value or to read off the set's ppO2 sensor.
Richard Pile wrote:-
> My advice is to attend tek 95 in San Francisco (January), where the
horizon on available rebreathers will be much clearer. Aloha, Rich
Please publish full details on `tek 95', times and dates, how to get there,
and hotels etc, and likely total cost in money and time. Will any sort of
Proceedings of `tek 95' be published? I have never been to America. I live in
Manchester in England.
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