A.A.R.G. JOURNAL

ISSUE NO. 3

JOURNAL OF THE AUSTRALIAN AMATEUR REBREATHER GROUP

c/o Tyacona Old Hume Hwy BERRIMA 2577 TELEPHONE:(02) 97596501

Email: diver@chilli.net.au Internet: http://www.chilli.net.au/~diver SEPTEMBER 1998

Editors Message

Well we've made it to our third newsletter and haven't the past 3 months been interesting. We have some new active homebuilders and RB divers in the AARG, a number of deaths have occurred on the Inspiration, and our web site is getting an average of over 9000 hits per month.

This issue we have information on the 'Electrolung' sensors from Walter Stark, some interesting topics raised by Rod Nairne, a profile of the 'Halcyon', articles by Bill Me on 'Oxygen Toxicity' and William Smithers on 'Manual semiclosed operation', also some local homebuilders news and some dive reports . I'd like to thank all those who have either contributed or let me reprint their articles. Without their input this journal would not exist.

I'd also like to thank Barry Hallett of Southern Cross for sponsoring our postage this issue. He'll have to sell a few Inspirations to pay for it if membership keeps building steadily as it has. We now have almost 100 people on the mail list with many from various points on the globe. A large majority are also actively diving a wide range of rebreathers. If you would put some information together or have any articles or information for publication in the journal please send them to the addresses at the top of this page.

Good luck and Safe diving,

Scott Leimroth

Excerpt from Rebreather list posting:

"Electrolung design VI. Final (Reflections

and speculations)" Walter Starck Jul 21 1998

Development of the Electrolung came about through the chance meeting of John Kanwisher and I aboard Ed Link's diving research vessel in the Bahamas in early 1968. Ed was trying out his new diver lock-out submarine Deep Diver and had invited along several researchers with relevant interests. I was there to do some deep biological collecting and John was there to do heart rate/respiration measurements on divers using some new acoustical telemetry equipment he had developed.

Lock-out dives from Deep Diver were done using hose fed OC Kirby Morgan helmets. Gas for this purpose and to pressurize the lock-out chamber was supplied from a large high pressure sphere carried by the sub. The large amount of gas required for a single dive severely limited the number of dives which could be made and involved substantial cost and logistic considerations. The need for more efficient utilization of gas was clearly apparent.

It turned out that John and I had both been considering the feasibility of a mixed gas CCRB using electronic sensors to control PPO2. We both knew in general terms what was needed but John wasn't a diver or a machinist and I didn't know that much about electronics. However, I had been diving for 15 years and had built a wide range of underwater equipment and John, in addition to being a physiologist, had invented the first polariographic oxygen sensor and held a dual appointment at Woods Hole Oceanographic Institute and MIT where he lectured on electronic instrument design.

When we returned to our homes John started putting together the sensors and control circuit and I started getting together the hardware and machining all of the necessary bits. Six weeks later we both had our respective parts together. John sent me the board and sensors, I installed them and it worked. The overall configuration and design was basically as described but there were, of course numerous details to clean up. The electronics for example were wire connected on a breadboard and the solenoid valve I had hand made and actuated with a solenoid scavenged from a battery operated Cuckoo clock.

Although the prototype was put together quite quickly it was far from a "first thing which comes to mind" effort. Quite a few years experience and thought had led up to it so that when actual construction was began we both knew pretty clearly what needed to be done and how to do it.

Later at Beckman I had the opportunity of working with a whole group of specialists on improving the same device. The outcome was some tidying up of details but no fundamental improvement. The biggest problem was to prevent the creation of problems which didn't previously exist but could be introduced through changes made by specialists who were unaware of consequences outside of the narrow area of their expertise. The experience gave me a real appreciation of both the power and the limitations of specialist expertise and the importance of systems analysis in coordinating and integrating the input of specialists.

Although development of the Electrolung was interesting, even exciting, in itself it was just an interesting incident in a bigger, far more interesting and significant picture. Like most historical events, I suppose, what was happening didn't appear to the participants at the time so remarkable as it later does in the broader perspective of hindsight. The larger perspective on what is taking place right now tends to be somewhat obscured by the ordinary events of living. Except for rare instances whatever we are doing, however interesting and exciting it may be, tends to still feel like life, not like history in the making.

Electrolung Design I : Sensors

by Walter Stark 1998

The Electrolung used three polariographic oxygen sensors. The sensors were robust hand made ones we made ourselves. They had a central platinum cathode about 1/4" in diameter surrounded by a concentric silver anode about 3/8" Diam. In between was an annular groove for the KOH electrolyte. A .001" teflon membrane held in place by a thick silicone rubber boot retained the electrolyte. Although the sensors would run for weeks before desiccation of the electrolyte became limiting our SOP was to make them up fresh and calibrate them for each days diving. At the end of the days diving the membranes would be removed and the sensors washed with distilled water. Making up and washing off the sensors only took a few minutes and assured you always had fresh sensors.

Sensors of this type don't wear out so they were hard wired into the circuit. Unlike galvanic sensors they don't use oxygen but rather just respond to its presence. They work equally well submerged so the effect of any condensation is negligible. A drop of water fully covering the end of the sensor would only slow the response time. It practice we never had any condensation in the sensor area as this came immediately after the canister so the gas was at its warmest and driest point in the circuit. Thick plastic walls probably helped too in avoiding condensation on cold surfaces.

The chief advantages of the sensors were that they were always fresh and condensation wasn't a worry. The disadvantage is that in making them up with fresh electrolyte you can screw up by contaminating the sensor via sloppy technique. Any significant change in calibration after a fresh make up would be an indicator and determining why should be mandatory before proceeding further. Still, there are the black box mentalities who will simply crank the trim pots until they get the reading they want and then assume all is well.

There were two trim pots for calibrating each sensor. One for zero. The other for gain. Zero was checked each time before the sensors were made up. Gain was calibrated initially with air then the unit was put together and a check with pure O2 was done. The permeability of teflon to O2 varies with temperature. The sensors were of potted epoxy construction with the electrodes embedded in the epoxy. A thermistor in contact with the underside of the cathode was also embedded. This thermistor had a similar response curve to the teflon and compensated for the temperature effect keeping output linear over the desired range.

Our chosen set point was 0.5 Atm PPO2.

The bottom line was that with proper care the sensors were very reliable. Enough so, that they could be hard wired in and I know of no case where one ever had to be replaced.

Deaths on the Inspiration.

Our condolences go to the families and friends of the divers who died recently. Three fatal incidents so far have occurred at different stages of the dive. One on the bottom, one on the ascent and one on the descent.

On 20 June Bob Forster, 62, from Corby, was lost during the ascent from a mid-afternoon dive on the Windtown, which lies in about 30m of water 7 miles off Trimmingham in Norfolk. His body was not found.

A member of North Sea BSAC of Peterborough, Bob was diving with two other members of the branch from a local charter boat, the Merlin.

It is reported that, having ascended their shotline, the buddies deployed a surface marker buoy at a depth of 15m. When they looked around, Forster had disappeared from view.

Unable to descend again in a building tidal race, the North Sea group issued a Pan Pan call and a major search was instigated by Yarmouth Coastguard involving inshore and offshore lifeboats, an RAF helicopter and a helicopter from HMS Invincible, exercising 50 miles away.

It was calculated that Bob, who was using an Inspiration rebreather, could remain alive under water for several hours. In addition to surface and air searches, divers from HMS Invincible were dropped from a second helicopter during the evening's slack tide to search the Windtown.

A number of diving boats joined the search, including four from East Anglian BSAC. One tied up to the wreck shotline and member Gary

Bowden attempted a dive but had to turn back in a strong current at 20m.

Nic Gotto, Saturday, July 24 1998. Nic ran Sundancer II Charters out of Union Hall in Cork (South coast of Ireland). He was a very experienced diver and skipper. A number of weeks back, Nic purchased the Inspiration and attended a TDI weekend rebreather course. I've been informed that the practical aspects of this course consisted of a 1 hour pool session, a 45 minute dive and 1 change of scrubber sofnolime - this is on top of the usual lectures and theory.

On Saturday, Nic and 3 other divers went to the wreck of the Kowloon Bridge (second largest wreck in the world). Nic was with a buddy and

the other 2 dived together. I do not know if Nic's buddy was using an Inspiration or OC. Whilst diving at a depth of 10m (ppO2 1.3 bar), Nic encountered a down-draught that almost immediately swept him to 25m (assuming same fraction of oxygen ppO2 2.3 bar). An oxygen toxicity hit occurred. (I can only assume that the unit did not respond to the increased ppO2 in time and that Nic expended a lot of effort getting out of the down-draught). His buddy tried to assist and in the struggle lost his weight belt and mask. Buddy came to the surface, alerted the dive boat and was given another mask. He pulled his way down the shotline and found the other 2 divers. The situation was indicated to them and they commenced a search.

Nic's body was found and a rescue commenced. At about 20m, Nic inverted in his drysuit and at about 14m contact was lost with him but he went to the surface. At the surface, these divers cut him out of the harness. As they knew nothing about rebreathers, they didn't close the loop. Subsequently, the loop flooded and the unit sank back down to the seabed. Nic was pulled onto the boat and blood was found foaming in this mouth. Boat crew immediately commenced AV and CPR for 45 minutes at which point the lifeboat arrived. Nic was declared DOA. Army and civilian divers and currently searching for the unit that Nic was diving.

In September 1998 Keith Milburn, age 44, from County Down in Northern Ireland, was diving with five friends when he went missing. He purchased his unit in early January, he was one of the first people to own an Inspiration in northern Ireland. Keith had had his unit since April. He was trained by Dave Thompson and collected his unit from the factory and so received a "hand-over" from one of their people. He was a very active diver, and it is believed that he would have made two or three dives a week until his death.

His unit was rebuilt at the end of August (he'd cracked a handset), putting new handsets on and extended buzzer. His primary bail-out - his Auto Air- was stowed in front of him and was functioning.

He had finished his dive and was about to get back in the boat when someone dropped something in the water. One can assume that he was in the process of turning the unit's cylinders off at this point. In an effort to retrieve the dropped item he commenced to dive for it. He did not return to the surface, and his body was recovered some time later.

He was found with the O2 cylinder valve closed, the rebreather mouthpiece closed and out, his open circuit oxygen reg was in his mouth.

On examination it was discovered that the oxygen cylinder in his unit was turned off. It would be interesting to know how or why he did not hear the "low oxygen" warning before the situation became serious.

Martin Parker will be making a statement shortly which will be sent to all diving magazines and direct by post to all users.

From Martin (16 Sept '98) :

"Please take care. You MUST know what your PO2 is at all times. Look at the displays every minute, be sure you understand how to evaluate what the readings are telling you (not just the displayed values), Practice diluent flushes regularly, practice going to open circuit bail out regularly. We don't want to lose another diver."

It is interesting to note that of the four deaths recently ALL were diving effectively ALONE.

The A.A.R.G. recommends diving with a competent buddy who is familiar with your gear at all times for safety.

Editors note: All this has me wondering if Jason Rogers is correct in his preference for diving CCRs with a full face mask. After all, divers don't die from going hypoxic. This is just the precursor for drowning. With an ffm and a vigilant buddy perhaps unconsciousness from hypoxia is recoverable in some cases.

Manual Semiclosed Operation

by William Smithers 1998

The following algorithm assumes one exhale-through-the-nose, inhale-through-the-mouth cycle, instead of assuming a full loop purge.

The trick here is that you have to know the ratio of a single deep breath to your *total* loop volume, including the volume of hoses, intergranualr space, the whole nine yards. There's two ways to do this, 1) flood your entire loop with water, while scrubber is installed, drain it into a pail, and measure the amount of water, then figure out the volume of a big exhale, or 2) see how much one purge cycle affects a known loop PO2 as measured against a full loop purge.

So the method is:

I = V*B*((((D/33+1)*F)-M)/R)

Where:

I = Inspirations between loop flushes.

F = FO2 of your mix.

R = Max measured O2 metabolic rate in PO2 per minute

B = Breathing rate at R

M = Minimum acceptable PO2 at any point.

D = Depth in feet seawater

V = Ratio of a single breath to total loop volume.

Here's how I calculated V. Using my EANx70 dil, I filled the loop, then breathed it down to a .52. Then I exhaled one breath and squirted in one breath of diluent. The loop recharged to .595 PO2, after quickly hyperventilating a few times to mix the gas.

That's .105 PO2 below what a full flush would have done, which works out to be about 58% of the expected PO2.

In other words, V = (g-a)/(g-d)

where:

V = breath to loop ratio.

g = PO2 of diluent you are using in the test. (.7)

d = How far you breathed the PO2 down before stopping. (.52)

a = actual PO2 in the loop after depleting from g to d and recharging with a single breath dump-and-pump. (.595)

I did this a couple of more times, and the results came out between 58 and 68%, so I called it 60% to be conservative.

So V got set to .6. Obviously, it's best to do this while at rest, so that you're metabolic consumption won't skew the results.

Plugging this in, and setting a .6 PO2 as the minimum acceptable PO2, I calculated that I should get 30 workload-independent breaths between single-breath purges at 1 ATA on EANx70.

The figures looked good, but thinking I might be off on a bit of an intellectual bender by this point, I hit the treadmill for two 30-minute on-the-loop sessions with EANx70 dil. Each session started with slow walking, worked up to full-sweat running, then back to walking again for the last five minutes. I checked the PO2 just before each 30-breath purge, and lowest PO2 I saw in either session was .58, and the highest was about .63 - with the average spot-on the target zone at .61.

Needless to say, two tests at 1 ATA with a .1 PO2 range are nowhere near conclusive, but it's looking pretty good so far.

For comparison, here's the new EANx40 table:

Depth Breaths before single-breath-purge

----- -----------------------------------

10 66

20 72

30 110

40 145

50 182

60 218

70 255

80 290

90 327

100 363

(Editors note: Authors procedures and calculations not checked by the AARG, use at your own risk)

Oxygen Toxicity

by Bill Mee 1998

Most of you are familiar with the well known hemoglobin oxygen buffering system and it's role in the maintenance of tissue Po2s in the 20 to 60 mm Hg range. When the alveolar Po2 rises above 1500 mm Hg (1.5 ata) (Editors note: One ata =760 mm Hg. 1.5 ata = 1140 mm Hg) this system essentially fails and the tissue Po2 can then rise to levels in excess of 1 ata. At this point the amount of oxygen free radicals (superoxide anion and the peroxide radical - hydrogen peroxide) overwhelm the enzyme systems for eliminating them, with serious destructive and lethal consequences at the cellular level. Ordinarily, the bodies system of peroxidases, catalases and superoxide dismutases mops up these radicals. Almost any college text on biochemistry broadly details the mechanism and kinetics of these reaction mechanisms. The vitamin E family (tocopherol isomers) also plays a very important role in this antioxidant management system. You will note that the alveolar tissue component is exposed to the direct effects of high oxygen without the benefit of the buffering system. This is probably why even moderate exposures of o2 at 1 ata and slightly above cause observable functional deficits (Clark and Lambertsen 1971 and Clark 1988).

The first victim to go down, following the collapse of the hemoglobin-oxygen buffering system, are the polyunsaturated fatty acids that are fundamental components of cell membranes and connective tissue.

Many cellular enzymes, both free and membrane embedded are oxidized, challenging many metabolic systems dependent on these enzymes. Neurological tissues are particularly vulnerable given the high lipid content of axonal, soma and dendritic structures in nerve cells. This probably accounts for the extremely acute damaging effects of hyperoxia on brain function such as hyperoxic induced seizures. Other complex neurological tissues such as the eye and its components (retina) suffer observable deficits.

Vitamin E in known to reduce lipid peroxy and superoxide radicals in vitro. Vitamin C supposedly has similar effects. It is reasonable to believe that the use of established antioxidants will have a beneficial in vivo effect especially since the tocopherols are known to have hydrophobic properties which essentially causes them to partition in bimolecular membrane systems. Given this as a background it is not inconsistent to preposition oneself physiologically with a high level of these antioxidants prior to exposure to elevated ppo2s.

Anecdotally, we have observed very beneficial effects following pre dive and post dive administration of antioxidants. These include large dosages of Vitamin E (especially alpha tocopherols), vitamin C, Vitamin A and a variety of other antioxidants such as coenzyme Q and proanthocyanidin. I can say from my experience and that of George, Jarrod Jablonski and others that, at the least, the symptoms of pulmonary challenge appear to be significantly diminished when a regimen of pre dive consumption of antioxidants is followed.

Back on the subject of the Halcyon, I can categorically state that the primary reason for selecting this device is that, among other things, inherent in the design is a built in limitation on the level of oxygen exposure. The o2 partial pressure is limited by the drive gas. At least you can't go any higher then the level of the supply, although as in any rebreather, you can go lower under certain conditions of failure. The Halcyon has the additional benefit of being respiratory minute volume driven, so that when you stop breathing the system stops utilizing and replacing gas from it's external reservoir. The mechanical action of breathing provides the power source for the system and the ingenious depth compensating mechanism automatically diminishes the discharge volume with increasing ambient pressure. The issue of constant flow semi closed is irrelevant since neither I nor any sensible individual would use the Atlantis. With the Halcyon, providing that it is functioning correctly, the device stop supplying you with gas when you run low and this is obvious and occurs in a manageable way so that you can easily go over to open circuit. I fully expect that an oxygen readout coupled with a decompression computer will be available for the Halcyon in the future, despite the fact that false positives on this readout may lead to premature bailouts. Nevertheless, for those with a technological orientation the putative feeling of security that this may bring on may serve to satisfy many instrument inclined individuals.

When confronted with the facts about cigarette smoking I have made an informed decision not to smoke. When confronted with the far more immediately serious facts regarding oxygen poisoning I have decided not to incur the additional physiological risks and hazards a fully closed oxygen additive system presents. Please bear in mind that oxygen is added incrementally in most of these systems via a pulsatile delivery mechanism. While this may be fine at shallow depths you must be aware that at depths exceeding 100 fsw oxygen is added at pulsatile pressure of greater than 4 ata. At 300 ft you are pulsing oxygen into the system at 10 ata or above. Of course I know that the oxygen mixes fairly uniformly under most circumstances; however the inspired oxygen can be spiked under certain conditions and these socalled "spikes" attain levels way beyond the hypertoxic range. All of this has nothing to do with the issue of electronic control, which is subject to reliability constraints imposed by operation within an aqueous environment. Having personally dived with the Halcyon system deep within Wakulla Springs, I can say that focusing my concerns on the tasks associated with the dive rather than constantly worrying about the reliability of my electronics does make the dive much less stressful. I should reiterate that I have no commercial interest in the Halcyon and only use this system because it has been designed to reflect the particular needs of our project. You be the judge.

Comments by Walter Starck:

I don't disagree with Bill on the possible dangers of tissue damage from exposure to high ppO2 however the use of large doses of antioxidants is not without its own risk.

In April a study was published in the British scientific journal Nature indicating that in excess amounts (e.g. > 500mg/day for vitamin C) antioxidants may themselves act as free radicals thus inducing the very damage they are taken to avoid.

Intrigued by this, I did a search on antioxidant studies and found reference to several recent large scale investigations related to the effects of anti-oxidant vitamin supplements on heart disease and cancer. None found any benefit from the supplements and in several instances there were indications of some elevated incidence of these types of diseases associated with high vitamin intake.

All this doesn't conclusively prove anything one way or the other regarding the putative benefits of Vitamin E for exposure to high PPO2 but it does raise a genuine question as to the possibility it may be actually adding to free radical damage rather than preventing it

If you are taking extreme dosages of vitamins for anti-oxidant purposes on the basis of anyone else's advice it might be well to consider whether there is sufficient scientific evidence to support this use, especially when there are studies which are contra indicative.

Rodney's comments:

Bill Mee's article highlights one of the risks involved with closed circuit rebreathers. Oxygen spiking is one area designers must be aware of, and sensible designs place the oxygen addition point as far upsteam from the divers mouth as practically possible.

Evolved designs do NOT have increased oxygen spiking at depth as described by Mee. This is because although the depth has increased, good design will add a constant mass of oxygen not a constant volume. This is usually achieved by use of fixed intermediate pressure regulators or a compensating regulator and reservoir system.

(I can not comment on the level of safety provided by automatic systems which use software controlled oxygen addition, where the amount of oxygen added is determined by how long the solenoid is held open)

Speaking from experience with my own design, oxygen addition is achieved by the reservoir system whereby each manual oxygen addition results in approximately 1ltr of surface equivalent oxygen.

At 300 feet I could even add this oxygen directly to my lungs, but how? If I have a 2ltr tidal volume for example at 10ata I am inspiring 20ltrs of gas, 1 of which would be pure oxygen. This represents 0.5ata of oxygen, which when added to my setpoint of 1.0 ata gives only 1.5ata, even in this extreme example.

In reality the oxygen mixes very well before inhalation due to the addition point being in the exhalation counterlung so the highest "spike" of oxygen I experience is 1.1ata, most often only rising to 1.05ata from 0.9ata before settling back to 1.0ata.

Where Bill's points really hit pay dirt is if the emergency oxygen addition is a based on a manual freeflow system, where the oxygen can be added in unmeasured amounts. Operating a rebreather in this manner at depth is like dancing with the devil, and should really only be an emergency procedure at depth; ascent should be commenced immediately.

First stop too shallow, last stop too long.

ÓRod Nairne 1998

Deco computers are one of the most expensive pieces of dive equipment, and many divers are far better off with them than trying to calculate RNT for the 4th or 5th dive, as is common on live-aboards. Certainly these devices accurately calculate theoretical deco, and theoretical gas loadings over several days of diving.

However I would question their usefulness for deco diving, especially now that recreational divers are using techniques developed by commercial and military divers 30+ years ago, such as nitrox, helium, rebreathers and oxygen.

Fact one: there is a group of regular Sydney divers, who all own, and over time all had their ass bit (i.e. every last one of them got a chamber ride courtesy of Buhlmann and Aladin's) by diving computers exactly. I have been hit numerous times doing the same thing, just too get out of the water fast. Reality check: what we all knew all along, computers don't work for long deco dives. Eventually we all learned to use the computers as simple bottom timers, blowing off huge chunks off deco by doing deeper stops and oxygen stops. Maybe we should have read the manual: it tells you these are not designed for commercial divers, what this really means is the algorithms are tweaked for maximizing repetitive no deco dives.

There is a long list of other reasons these devices should be thrown in the bin. Firstly, they give the wrong deco profile for deeper/longer dives. Remember that it's not just the deco time, but the shape of the deco that is important. Personally, in my wilder days I used to exit the water after only 2/3rds of the time divers around me do, who are using computers, and this is not even using nitrox or oxygen. I managed this by doing more and longer deeper stops, and shorter shallow stops.

The profiles computers calculate is a good example my point. E.g. a 27 minute dive on the S.S. Catterthun (55-57mtrs) gives a 120 runtime, but with a profile that misses about 3 deep stops. Also, an 18 minute dive to 63msw, with a first stop of 9 or 12 meters. Only once have I seen a semi-realistic deep stop on my Aladdin Pro, a 24mtr stop, but this required a 25min stay at 78msw! The first stop on this dive is actually 35-40msw, if using air. The 3msw stop would have been horrendous, and this would only go part way towards getting rid of all the bubbles formed by missing the deep stops. (No better than US Navy tables in this regard).

As a starting point to safer profiles, divers would be well advised to follow Richard Pyles advice: use the straight buhlmann table, with his custom additional deep stops. (If you need safety factors added to a straight buhlmann table other than deeper stops, you should not be diving at this level.)

Pyles procedure is this: Stop for 2 minutes, halfway between the max depth and the 1st scheduled stop. At this point, if the distance to the 1st scheduled stop exceeds 10 msw, again half the distance, and do a another 2 min stop. Continue this until the distance is around 10mtrs. ALWAYS use 10m/min ascent rate FROM THE BOTTOM. You should ascend from 300 to 250 ft at the same rate you ascend from 50 to the surface. Remember: Pyle has done more deep bounces on trimix than anyone I have spoken to, so I would listen to what he has to say.

For example, a 90m dive, 1st scheduled stop at 40m. Ascend to 65m for the first 2 min deep stop.(90-40=50, 50/2=25, 40+25=65.) As there is still more than 10mtrs separating you from the 1st stop, do the same again, a 2 min stop at 52 msw. Then ascend to the 1st scheduled stop, 40mtrs.

Personally, I do not add any shallow deco to account for the increased time at depth these stops give. The risk of O2 toxicity for longer deco outweighs the argument for the extra time, when thermodynamic and bubble models are remembered. (See Lippmans Deeper into Diving, and the work of Brian Hills in the 60's).

By the way, if you believe the new generation computers are improved, think again. For instance, some "compensate" for cold water, but ignore the fact that a diver with the correct amount of thermal protection wills deco just as efficiently in 30 degree or 10 degree water. Additionally, they perform as badly as ever, giving the first stop too shallow, and the last stop too long.

Editors note: The current AARG practice is somewhat changed from the open circuit practices of deep stops above. These procedures aim to capitalize on the inherent advantages of the use of fully closed circuit rebreathers using gas mix and deep stops to reduce incidence of DCI, decompression times and oxygen exposure.

The aim of the procedure is to keep gas in solution right up to the last step. When gas is kept in solution it diffuses more rapidly from tissues. If all bubbling is kept to a minimum until the last step, the bubble size will be least affected by pressure changes, compared to bubbling occurring during the traditional large pressure change upon ascent to the 1st, and deepest stop level.

Lastly, the bubbling we assume occurs with the short untested decompression times is kept to a minimum by using heliox for bottom mix and decompression*, the low solubility of helium reducing the volume of gas liberated by the final step to the surface.

*only feasible in open water with constant PP02 rebreathers.

The basics of the procedure is this:

*All deep dives are conducted with heliox rebreathers running PP02's of 0.7 to 1.0.

*The deep Pyle stops are modified to stops starting 2 atmospheres off the last level (e.g. if wreck is 75msw but last 5 minutes spent at 57msw, 1st stop would be at 40msw) provided the 1st table stop is not violated.

*All deco is on heliox , using the rebreathers to give us oxygen enriched heliox mixes at each stop.

*A partial flushthrough of oxygen is conducted at 10msw.

*On all dives requiring significant deco, nitrox 50 is carried for emergency decompression should the rebreather fail. (also doubles as drysuit inflation gas)

*For safety no open circuit second stage regulators are provided on oxygen cylinders, however oxygen should be staged at 6msw for emergency use.

*Heliox, nitrox 50 and oxygen tables are used as the basis for all decompression profiles.

These tables are then heavily modified. Notice how the 6msw stop is halved and this time is spent between 12msw and 30msw.

*For high workload dives, the time at 6msw is increased to approximately the standard length Buhlmann stop. The PP02 is kept at 1.4 max so hyperoxia is extremely unlikely.

*Should DCI occur post dive rebreathers and open circuit oxygen are available for in water treatment.

Standard table for heliox bottom mix and open circuit. Nitrox 50 and oxygen deco

75m for 20:00 (21) on Heliox

33m for 1:00 (23) on Heliox

30m for 2:00 (25) on Heliox

27m for 2:00 (27) on Heliox

24m for 3:00 (29) on Heliox

21m for 1:00 (30) on Nitrox 50

21m for 2:00 (31) on Nitrox 50

18m for 3:00 (34) on Nitrox 50

15m for 4:00 (38) on Nitrox 50

12m for 5:00 (43) on Nitrox 50

9m for 8:00 (51) on Nitrox 50

6m for 32:00 (83) on 100% Oxygen

Runtime 83 minutes

AARG Modified table, heliox is used for bottom mix and deco with a setpoint PP02 of 0.7 to1.0, a change to 1.3 to 1.4 at 10msw and up.

75m for 20 min

55m for 1 min

50m for 2 min

45m for 2 min

40m for 2 min

35m for 3 min

30m for 4 min

25m for 5 min

20m for 9 min

15m for 10 min

10m for 10 min

6m for 15min

Runtime approx. 85min

At this stage we have only used these procedures for approximately 40 exposures, however these early dives have had very encouraging outcomes.

Dive Report

Rod and Suzies USA trip July 1998.

by Rod Nairne & Suzie Dudas

Our 1st dive was a checkout dive at Dutch Springs, a flooded quarry. Just in case we needed to acclimatize to cold water diving, and check out our trim for out upcoming dives off Montauk on the RMS Republic. Nothing special to note, the water temp was 10 C and we were in the water for 100 minutes.

Having use of the Dudas Diving Duds store made our gas mixing for the Republic trip easy; with the aid of the haskel gas booster we were able to get full pressure heliox 18 fills in our steel 72 cylinders, as well as boosting the pony bottles to 2500psi of oxygen. For the 2 of us then I mixed 2 72's of heliox 18, 2 72's of nitrox 50, and 2 pony bottles of pure oxygen. We also had a 3000psi 80cf tank of oxygen for top ups on the pony's, as well as for emergency in water deco on open circuit.

We had a 6 hour drive to the dock where we met up with the charter vessel Seeker. The Seeker has a long history in NE wreck diving and is run by it's second owners Dan Crowell and Jennifer Samulski. The second captain aboard for the trip was John Chatterton, crew was Pete Wohlleben, and Greg Mossfeldt, divers were John Yurga, Bonnie Merkel, Richie Kohler, William Cleary, Pat Rooney, Peter Hess, Joe Ferrali, Mike Trapani, and Jeff Schwartz.

We arrived at the Republic site later than expected due to strong winds the night before, so only 1 dive was made the 1st day. The Republic is a 570 foot long steam ship, a White Star Line Passenger vessel the victim of a collision in 1908. Of special note was than the Republic was the 1st shipwreck where radio was used to successfully summon assistance. The Smithsonian Institute allegedly offered prior salvors $250 000 for the telegraph key if recovered. Also, the ship is rumored to have been carrying $30 million dollars worth of gold eagles, 1908 value. For this reason the Republic site has been commercially salvaged several times, using saturation diving techniques. No gold and only a small fraction of the ships fittings/cargo has been recovered.

To our knowledge we were only the second or third group of recreational divers to visit the site; being only 7 miles from the popular wreck of the Andrea Doria, and a deeper dive, most divers are drawn to the larger Italian vessel where recovery of china a common place event.

We warmed up our scrubbers for about 10 minutes before the dive, and started out with a PO2 of around 0.4 to avoid any oxygen spikes on the descent to 250 feet with heliox 18. (Normally we run a diluent with 10% oxygen, and start the descent with close to 100% oxygen in the loop). Arriving on the bottom after we tied off our reel and started swimming along the wreckage. Unfortunately we ended up picked into the debris field off to the side of the wreck, a fact only evident when after reeling out about 150 feet of line, the huge ribs of the hull became visible.

Due to either a strong sense of survival or cowardice we decided not to swim around the wreck without the pace hindering reel. According to the saturation divers, the ship lies very flat with only 18 inches between decks, and massive hull plates obscure any hope of navigating along the sides of the vessel. The only artifacts we saw were a few portholes (we managed to recover 1 of these, as did 1 other diver). Suzie also spotted a few nice sized lobsters, one a possible 15 pounder.

That night we had to moor on the Andrea Doria wreck site, and the consensus of the divers was to stay in place the next day and dive the Doria. Although I had a strong urge to go back to the Republic, Suzies mother I knew would be pleased with us diving the Doria. As it turned out, we had a nice tourist dive on this wreck, we swam down from the side of the ship to the bottom in search of the bridge area, the vis at the 255 foot bottom being only about 20 feet. 20 feet is not much on a 700foot wreck! With no luck locating the bridge or the compass stand from which Suzies Dad recovered the compass in 1967, we ascended slowly to the promenade deck, and swam aft to approximately half way along the wreck, on the way passing Gimbals hole. We were lucky today with a good 50 feet of vis at the 180-200 foot level.

Many of the veteran Doria divers returned from 'Gimbals hole' with bags full of China, from a new hole located originally by Gary Gentile this season. Apparently Gary remained tight lipped about where he was recovering the 1st class coffee cups but John Yurga located the same spot, a crack in the central stairwell at 205 feet.

As it turned out, Suzie was the 1st female to dive the Doria on a rebreather, a nice one-two for mother and daughter… Evie Bartram Dudas was the 1st female to dive the Doria with her husband, John Dudas.

For the tech-heads:

We used 72's 1 heliox 18 for diluent for the whole dive (with the breather we do "oxygen enriched heliox" deco's, no gas switches). The purpose of the 18% oxygen is so we can emergency deco out on open circuit bottom mix to 70 feet, where we would switch to our other 72 filled with nitrox 50, in the event of a loop flood. The nitrox also is used for suit and BC inflation. We run a constant partial pressure of oxygen of 1 ata until 30 feet were we bump it up to about 1.3 to 1.4 ata. As it turned out, Suzie had to switch to open circuit nitrox 50 at 30 feet after her loop flooded. The cause of the flood was a pinched 0-ring on the canister.

Helium

ÓRod Nairne 1998

An increasing number of experienced RB divers are discovering the advantages of using heliox diluent, including using the gas for decompression. At the AARG we even use heliox for shallow 50 to 80 foot dives.

Here are a *few* points for helium usage, hopefully to stir up some discussion, and hopefully stop the practice of all the new RB divers which is to dive nitrox down to 50msw because they "don't have the ticket". SCARY!

Helium:

*is easier to breathe at any depth

*is less soluble than nitrogen

*produces no narcosis

*is cheap to use in a breather and in fact breathers in some ways were developed for it's use

*results in no diver fatigue after a deep dive, in fact in our experience produces less fatigue at 250 than nitrox at 100! So at 100 it's got to be incredible.

*can be used for decompression with a fully closed unit

*Saturation divers use heliox deco right to the surface, they are the real pro's

*takes less heat energy out of the scrubber so theoretically extends scrubber life in cold water

*Requires less dive planning for a deep dives than trimix with several gas switches on ascent

Nitrogen:

*is a difficult gas remove from the tissues

*is dense, so is hard to breathe even at 100 feet (by comparison)

*produces longer deco for long dives (which is what breathers can be used for, right!)

*produces narcosis, something you don't want while operating a device nicknamed "death machine"

*Far more nitrogen can be absorbed in your body than helium due to high solubility

*May result in higher incidence of neurological DCI due to high soluability in fatty tissue such as spinal cord

*Due to density theoretically takes more heat energy out of scrubber, could result in premature scrubber failure in cold water

*is really only any good in Guinness

HPNS

Dave Crockford from the UK has been diving his inspiration with heliox to 93m and reported that HPNS or Helium willies were not a problem for him. One of the team did suffer slightly with compression arthalgia but it soon passed off once stable at 93 metres. (He is in his 60's) It manifested as shakes, evident in the hands.

PARTIAL PRESSURES OF OXYGEN SELECTION IN CLOSED CIRCUIT REBREATHERS.

Copyright Rod Nairne. 1998

The recent advent of closed circuit rebreathers for recreational diving has been accompanied by a change in the P02 setpoints commonly used in these devices. Historically setpoints from 0.5 to 0.7 were used however now it is rare to find divers running a setpoint below 1.2

It may be instructive to investigate some possible reasons why a 30 year tradition in military and commercial/scientific diving has been broken in such a short period. Have we learned something new? Has human physiology changed? Has there been a change in the operating reliability of the oxygen control systems of current models?

These and other questions will have to remain a mystery, I guess it all adds to the "mystique" surrounding closed circuit rebreathers, a mystique only increased by fatalities and near misses.

I have decided to put together some points to help in the choice of the best setpoint for your application. Some of these points will be controversial to many, especially recreational/technical divers, however I believe most of it is accurate and to the best of my knowledge reflects the cumulative and hard won experience and operating procedures of the professional diving community. I make no excuses for being biased, I run and recommend a setpoint between 0.7 and 1.0.

Note: Common practice is to always flush-through with pure oxygen at 6msw for decompression, to give a po2 between 1.3 and 1.6 depending upon efficiency of the flush.

POINTS AGAINST :

Low partial pressures. (0.5 to 1.0)

*May lead to early hypoxia in the event of 02 add failure in closed position

*May cause problems on rapid ascents from depth due to falling PPO2

*According to theory will give longer decompressions (I say theory because I believe more trust is placed in the Buhlmann system that it deserves, based upon the number of DCI incidents I have observed)

High partial pressures. (above 1.0)

*In the event of solenoid failure in the open position gives less time to detect and shut offcompared to a low setpoint, before dangerous PP02's are reached.

*Causes real operational problems on descent due to oxygen spiking,

*All the procedures used to reduce 02 spiking on descent, rate on the scale from inconvenient to dangerous, such as shutting electronics down, 02 valves off etc.

*depletes the body's natural defence (see Bill Mee's article this issue) to high PPO2's so that if a oxygen spike occurs late in the dive the chance of a convulsion is much higher (a fact borne out by combat swimmer experience)

*loads the body's oxygen clock during the high work load portion of the dive giving less of a safety factor for shallow water pure oxygen decompression.

*requires special procedures for sensor calibration/verification due to the setpoint being above 1 ata.

*leaves little margin for sensor inaccuracies on the high end of the scale, i.e. a 20-30% low reading will result in PPO2's exceeding 1.6

*there is limited data on the safety of high PP02's in closed circuit rebreathers, (what there is all bad) so qualifies as experimental diving, thereby increasing the risk where risk is already a significant operational factor.

*almost all reduced inert gas loading is lost at depth, the difference between a setpoint of 1.0 and 1.4 at 75msw is only 4.7% inert gas.

*high PP02's trade off the risk of hyperoxia against a perceived reduced risk of decompression illness, where hyperoxia will more likely lead to mortality, this is indeed mystical.

Additional Comments from Walter Starck:

Under normal circumstances some degree of spiking upon descent is unavoidable unless you choose to have 0.0 % O2 in your dilutent supply. Descent also often entails some vigorous swimming if a current is present. With a high setpoint you can easily enter the zone of possible oxygen toxicity. Falling PPO2 during rapid ascent is not normally a problem as it is automatically detected and O2 added by the control system.

Increase in PPO2 can take place quite rapidly. Decrease is limited by the rate of metabolic use and takes place slowly providing time to detect and take appropriate action. With low PPO2 remedial action only involves manually introducing more gas. High PPO2 requires shutting off the O2 supply, flushing the loop and introducing new gas.

The effect of frequent and prolonged exposure to PPO2 > 1.0 ATA is unknown but both theory and clinical evidence suggest the possibility of cumulative long term tissue damage.

Though running a high setpoint does result in less decompression as required by tables any decrease in risk of DCS is problematic. In other words the increase in inert gas absorption accompanying a lower setpoint is compensated for by longer decompression. The risk isn't increased so long as the required decompression is adhered to.

Modes of sensor malfunction tend to be in the direction of less sensitivity to O2 rather than more. This leads to a greater likelihood of PPO2 being higher than reported by the sensors rather than being lower.

The exposure/response pattern for oxygen convulsions is chaotic. The pattern for hypoxia is much more regular and consistent.

Everything considered, the upper limit of PPO2 is more dangerous than the lower. A setpoint of around 0.5 to 0.7 provides a comfortable buffer against hypoxia and stays well away from the multiple dangers toward the upper end. The only real advantage of a high setpoint is less decompression. The convenience is outweighed by the risks. I suspect the only real reason why higher set points have been chosen recently is that for the kind of dive profiles most users are doing they can save significantly on decompression and the divers involved are free to make their own choice. In the military and commercial worlds diving medics have a lot to say about such things and the divers themselves are required to follow the rules.

Rebreather News

This past season, John Chatterton and Danny Crowell of the charter vessel Seeker have been using rebreathers for deep wreck dives off the New Jersey and New York coastline. Danny has been using an essentially unmodified Drager Atlantis to dive wrecks in the 50-75msw range including the Andrea Doria.

Danny has been running trimix and using standard jets with proprietary gas flow calculations based on testing with different gas mixtures. According to Danny, the helium in the mix allows hypoxic trimix to be run with acceptable loop PP02's. A switch to OC nitrox is made on decompression. The only modifications that have been made are the use of larger tanks for the drive gas, up to 50cf.

John Chatterton has spent the season sorting the bugs out of his AURA 2000 fully closed circuit rig, and has had many teething problems requiring bailout to open circuit during the dives. According to Danny, he turned up with a bigger bailout cylinder every week ;) Unfortunately I missed the chance to observe the AURA during our days on the Seeker, the unit was out of action.

However John is at the time of this writing sucessfully diving the Britannic, depth 120msw, with his AURA unit. He has special permission to enter the wreck from the owner based upon the bubbleless nature of his breathing system. OC divers are restricted to the exterior of the wreck.

Danny Crowell is also on the expedition, along with Greg Mossfeldt, as deep support divers. They are both using Drager Atlantis units for deep support at 65msw, and get to dive the wreck during the 2nd week of the expedition. Presumably they will be using Drager Atlantis units.

We hope to have a full report on the performance of the rebreathers on the expedition next issue.

Dive reports are available at http://website.lineone.net/~britannic98/

CIS LUNAR rebreathers are being used for Bill Stones 'Wakulla 2' project. While Wakulla Springs has just about been 'Walled Out' by the WKPP on OC, and now with Halcyons, the Wakulla 2 project will try to map the system using a million dollar mapper attached to scooters. Two divers from Australia, Andrew Poole & John Vanderleest, are going to the US to join the team.

It was recently reported by Rich Pyle that one of the divers he was training on the CIS had a hypoxic episode after a number of events compounded into a problem. Some of the errors were:

1) Not telling all the divers to manually bring the loop PO2 back to setpoint after a loop flush.

2) Using heliox 14 as a diluent in shallow water.

3) Allowing a diver to enter the water with improperly calibrated O2 sensors.

4) Possibly allowing a diver to enter the water with improperly changed batteries.

A.A.R.G. Member News

Errol Harding of South Australia has been busily working on his homebuilt for the last few months. He has machined a very professional looking mouthpiece and a variable capacity scrubber. Errol also got his hands on a O2 booster pump and should have it repaired in no time considering his workshop. Errol currently dives his Atlantis and can't wait to get his CCR up and running.

Jason McHatton has modified his FGG by fitting two 3ltr pony bottles and a custom made scrubber and O2 sensor. He intends adding more sensors and diving it fully closed in the near future.

He recently dived the Coolooli in 40m using Nitrox 32 and a flow rate of 10.6 litres/min. During the dive, the bag contents were measured at Nitrox 23 to Nitrox 26 throughout the dive. This means O2 consumption was between about 0.8 to 1.0 litres/min.

Jason has added a set of wings to his unit and carried a 7 litre steel of air for suit/wings inflation and bailout.

Rebreather Profile

The HALCYON PVR-BASC

The Halcyon is a semiclosed unit but works on a Passive Variable Ratio GAS Addition Semi-Closed Circuit (PVR-BASC) principle. Basically it is a bellows system with a smaller bellows inside the large one. The smaller bellows expels 25% of every breath at the surface and proportionately less with depth as a result of the depth compensated discharge control device which optimizes gas efficiency.

In semi-closed circuit rebreathers, passive addition is achieved by controlling the diver's exhalation. There is a French unit that was designed for military use that expels 20% of every breath into the water with a double bellows arrangement. There is a Canadian unit that was designed for pipe penetration bailouts that expels 25% of every breath with a spring-loaded proportional discharge valve.

None of these units will cause hypoxia as a result of ascents. All of these units are keyed to the diver's respiratory minute volume to tighten oxygen partial pressure control. All of these units will warn the diver through successive shortness of breath if a GAS addition failure has occurred, similar an intuitive warning, close to OC scuba.

The HALCYON has water traps designed into every circuit zone. A primary trap just prior to the scrubber has a significant reservoir area along with an over board pump system.

It also has a variable volume scrubber so you can adjust the amount of absorbent depending on your expected dive time.

For open circuit bailout it uses a drum mechanism in the mouthpiece which is rotated with a 'window winder' attachment on the front of the mouthpiece. This is quick and easy to use and means you don't have to remove the mouthpiece to bailout.

Gas supplies are plugged in to the unit via connectors which are easily accessible on hoses on the right side, the overboard pump is also attached here.

Although the Halcyon is only presently owned and used by about 20 people it has been used to make a number of record breaking cave dives in Wakulla springs in the USA and also on cave dives in France as well as deep ocean dives in Hawaii.

Halcyon 800-327-0412 954-462-5570

Voice 954-462-6115 Fax 940 NW First Street, Ft Lauderdale, FL 33311

email: brownies@netrunner.net

website: http://www.halcyon.net

Contact: Robert Carmichael

Type: Semi-closed, constant fraction

Model: Halcyon, Approx. $13000.00 USD

AARG visits FLORIDA CAVES

by Rodney Nairne and Suzanne Dudas.

Suzanne Dudas and I spent a few days in Florida and managed 3 150minute dives, the 1st in Ginnie Springs, where we swam to the dome room, the second and 3rd at Madison Blue.

On our 1st dive in Madison, we swam up the Gold line to about 2000 or so feet, and on the way back did the tourist Godzilla room. The 2nd dive here we had a great dive, up the gold line, past 2 double staging divers exiting the cave, through Potters Delight, Rocky Horror and upstream in the courtyard to about 3200 or 3500 feet. This dive was incredible, and the locals say the best cave this side of 250 feet depth in Florida. The depth in the cave is only 70 or 80 feet, once in the courtyard the depth varies from 80 to 110 feet, so there is not much deco.

The only problem we had with diving the rebreathers in the caves was I rolled off a valve in Rocky Horror, and Suzie needs thinsulate. I was only a little chilly on the last dive, with polyprop undergarment, despite being completely wet for 2 hours.

Our setup was identical to the Northeast wreck dives, except we had a long hose on 1 of our steel 72's and the reels/lights needed for safe cave diving. I just topped off our tanks so we had 60% and 70% helium bottom mix, and nitrox 32 in the other tank. After the fourth dive we would need to top off our steel 72's, that is after 10 hours of diving. We averaged 1000psi oxygen usage every 150 minutes including 02 flushthrus for deco. I switched to a 20 watt bulb for the extra duration, and found I could see even better than with the 50 watt, because my dark vision was not as effected by the intense 50watt beam, so I had excellent peripheral vision. However the 50 watt globe would be essential when scootering for signaling.

Please Note

The A.A.R.G. is dedicated to the dissemination of information about rebreathers and rebreather diving, particularly in Australia and the South Pacific region. Our aim is to increase the general diving publics' awareness about rebreathers and related issues and to provide you with the stimulus to make your rebreather diving safer. However NO responsibility is taken for the accuracy of any information presented in this newsletter. You should always seek out verification of any information you acquire about rebreathers and use your own judgment as to it's validity to your context. Be safe, be conservative and dive safe. Remember, this is not diving equipment, this is life support equipment and your life may depend on it.