93 replies to this topic

[PerroneFord]

That said, I did an expedition some time ago with one member of the group using an Ourorobos and that was an exceedingly impressive piece of kit. Obviously a great deal of thought had gone into even the tiniest aspects of design, and the quality of all components was evidently very high. No plastic mouldings here - everything was purpose-machined out of solid brass etc. I can't imagine a better CCR for extreme use.

All that and its still the most likely to give you a caustic cocktail...

[ScubaDadMiami]

• Guess which CCR Tom Mount dives most of the time these days;
• Guess which unit the NSS-CDS Training Director dives almost exclusively;
• Guess which computer manufacturer has been awarded the contract by the U.S. Navy for use in their CCR training program

When I last dived with Tom he was inseparable from his Meg, but that is over three years ago. How come he's deserted it?

One of the things that attracts me to the Optima IS the modularity and use of standard parts.

If you do come down this way I'd be very grateful for a chance to try it out.

One of the many Mount disciples is John P. Jones, Training Director (I forget the new name for that title) of the NSS-CDS. John has more time on the Optima than practically all other users around the world combined. He cave dives with it roughly five days per week, and he has been doing so since about two year prior to release of the Optima to the public (let's say since about 2003). (He lives about ten minutes from Dive Rite's factory.) He had significant input on its design and development by being the Optima official crash test dummy.

John basically won Tom over after they did a number of cave dives together, and Tom got to see how great the Optima performs in the cave environment. There is also another factor: after Tom underwent heart valve replacement in early 2007 (I might be off on the time a little), when he came back to diving, he decided to start using the Optima because it is significantly lighter on the back compared to the Meg. He still dives his other units to keep current on them and for training others, but his primary unit has been the Optima since about May of 2007.

BTW, going along with what Perrone mentioned, the Optima is one of the units out there that is least likely to have a caustic cocktail because of its use of the Extend Air Cartridge from Micropore. In a cave, where going to open circuit can be more than an inconvenience, lessening the issues related to water entering the unit is a big advantage.

[shadragon]

SDM - Assuming your RB (any model) does go fubar, what redundancies are there? Can your buddy share his RB like a recreational octo or are you limited to your own backup tanks? What do they give you for gas? Does the rule of thirds apply? How?

I see guys diving rebreathers in pairs and those questions have always been on my mind. If in a long DECO or cave situation, how is this handled?

Thx...

[netmage]

SDM - Assuming your RB (any model) does go fubar, what redundancies are there? Can your buddy share his RB like a recreational octo or are you limited to your own backup tanks? What do they give you for gas? Does the rule of thirds apply? How?

I see guys diving rebreathers in pairs and those questions have always been on my mind. If in a long DECO or cave situation, how is this handled?

Thx...

The second part is easier..... I'll let SDM tackle failure modes and options.... you have to be prepared to bailout at any time, rb's only have one DSV, so no buddybreathing. Gas planning in RB teams is a debated topic in the community right now. Suffice it to say, the team needs somewhere between 1.5-2x in reserve bailout to get the team back from..... (the difference comes down to planning for multiple catestrophic failures or a single, if multiple - how far down the rathole do you go....)
... furthest point of penetration
... ascent
... and any deco obligation

Now, what form is bailout.... lets talk about gas... we have onboard and offboard. Onboard gas is the two bottles; diluent and oxygen connected up to the unit. Offboard would be additional carried or staged bottles. Depending on the dive, bailout might be entirely onboard (such as using 27cu or larger tanks on a recreational NDL dive), or entirely offboard which is the more common implementation I've seen (and use). In this case, offboard bailout is generally 1 or 2 AL40's or AL80's w/ a 2nd stage and an decent sized inflator hose. Depending on the situation, we might jack the gas into the unit to supliment onboard supplies, or we might totally bailout and go to the 2nd stage directly.

Like any form of technical diving; at first indication of any failure, the dive is called.
Also, sizing bailout comes with the addage; don't skimp...

In the caves, its nothing to take a few more bottles in and drop them along the line, or to dump a bottle or two of O2 in the basin.... in 99.9999% circumstances, your guarenteed to be egressing down the same path. In wrecks; seas, ladders, and other conditions can become hurdles, so it becomes a factor in dive planning... i.e. for our dive tomorrow, do I really want to do 40 minutes at 200'... how much bailout will I need to drag along (2 x 80's, 1x18/45 & 1x50)... or should I limit to 25 minutes (2 x 40's, same mixes)

Now, the planning I covered above, really should be no different than the reserve planning ANY open water diver does for every dive; open, closed, recreational, technical..... Give a read for the concept of 'Rock Bottom' when it comes to gas planning.

Now, to make this even more complicated, there are some people doing exploration that have determined conventional open circuit bailout to be a limiting factor in the dives, and have opted for a BOB.... BailOut reBreather... A 2nd, totally isolated kit that would sustain bailout facilities should the primary rebreather fail. You can see examples of the Hammerhead and Megalodon in these configurations, as well as smalled AL80's sized units meant to be slung like a stage - this is most certainly not the general 'recreational/technical diving public' here. But it's worth mentioning as there is alot of thought working in that direction.

-Tim

[secretsea18]

What is a "DSV"?


Please use English for those of us who have no idea what you are speaking about. Thanks.

Edited by secretsea18, 26 July 2008 - 07:27 PM.

[shadragon]

What is a "DSV"?

Dive Surface Valves I believe... I have no idea what they do, but at least I got that part... hahaha

[PerroneFord]

What is a "DSV"?

Dive Surface Valves I believe... I have no idea what they do, but at least I got that part... hahaha

It allows you to switch from the rebreather to open circuit with a single flip of a switch. Very handy, and potentially life saving.

[secretsea18]

What is a "DSV"?

Dive Surface Valves I believe... I have no idea what they do, but at least I got that part... hahaha

It allows you to switch from the rebreather to open circuit with a single flip of a switch. Very handy, and potentially life saving.

Thank you for the translation.

And good to see you post!

[ScubaDadMiami]

Emergency gas planning depends upon your philosophy. There are different points of view on the subject.

Let's start by comparing to something with which you are already familiar. If you are doing typical open circuit dives when a complete first stage regulator failure happens, you either go to a spare tank that you bring along (most people don't do this) or you rely upon your buddy's additional second stage for your gas source. What would you do if both your gas supply and your buddy's gas delivery failed at the same time? The very last resort would be to perform an emergency swimming ascent.

Now, I'll bet that most people reading that last part would think that it would be highly unlikely that both systems would fail at the same time, right? However, it is theortically possible, isn't it? The same thoughts go into rebreather diving.

Rebreather divers take emergency gas along on their dives in the form of extra tanks with traditional open circuit regulators. For many dives, the diver will take this extra gas in such a way as to get the diver, or even the buddy, back to the surface. However, once a diver starts getting involved in significant deep diving or cave diving, it gets to a point where carrying so many extra tanks can start to cause potential issues that can impact on safety. Here's where the philosophy comes into play.

Just as with open circuit equipment, rebreather equipment is pretty reliable. So, rather than preparing for all divers to have a complete failure at the farthest point on the dive at the same time, the reality is that there won't likely be a failure in the first place. If there is, it will probably happen near the beginning of the dive, not the farthest point. Even if a failure happens at the farthest point, it will be astronomically unlikely that a complete failure will happen to more than one diver simultaneously.

So, under these circumstances, rather than add risk to the dive by carrying a million extra tanks, why not instead carry more than enough gas to get a diver having an equipment failure back from the dive but divide this between the total dive team? This is less risky than it sounds.

On a rebreather, other than having a full flood as the failure, a diver has many options for handling equipment failures. For example, the diver can take an open circuit tank, plug it in, and then can take a single breath's worth of gas from the tank. By putting this into the rebreather instead of exhaling into the water, that single breath can last anywhere from what would be three breaths to over ten breaths. So, a single 80 tank could be worth at least 240 cubic foot or as much as 400 cubic feet of gas or more (rounded off) when compared to using the same amount of gas as an open circuit diver. A little gas can go a long way. (This is why rebreather divers can dive for hours on very small tanks of the rebreathers.)

This means that a diver having a partial rebreather failure during a dive can extend the gas in the open circuit tank way more than enough to get home. Only if there were a complete flood of a unit would the diver have to completely go back to open circuit. So, those of a particular gas planning philosophy think that the risk of carrying a bunch of extra tanks on a dive to prepare for a very remote risk is riskier than planning for the overwhelming likelihood of realistic chance of failure.

On most of my dives, I carry enough gas to get back home without depending on anyone else. However, there are times when it makes better sense to carry "team bailout," emergency gas divided between team members, that provides enough gas for at least 1.5 members of the team to get back from the farthest point of the dive if having to rely completely on open circuit alone to get back home. The benefit outweighs the risk when considering the extremely unlikely chance that more than one team member will have a complete failure at the farthest point in the dive.

In conclusion, many rebreather divers carry enough emergency gas with them to make it home from a dive or to donate to a buddy in an emergency. In some cases, rebreather divers divide up this gas between team members to reduce risk on their dives while preparing for the likely failure scenarios. Some do it one way some of the time, and the other some of the time. Your dive, your risk, your decision.

BTW, the DSV, or Diver Supply Valve, is just a fancy rebreather name for the mouthpiece from which the diver breathes. In most realistic terms, it cannot be donated to an out of gas diver. Unlike open circuit regulators, the diver has to open and close them via a switch in order to use them. Units like mine have an additional regulator attached to them so that we can resort to open circuit diving with just the flip of a switch.

[peterbj7]

SDM - how does the Optima fare in the event of a loop flood? Is there any serious possibility of clearing the loop and carrying on CCR or SCR, or are you pretty certainly on OC?

And Perrone, can you elaborate on the Ouroroboros and caustic cocktails? I hadn't heard that before and I certainly don't know anyone who's ever had one from that machine. The only cocktail I ever had was from a Draeger Dolphin, which I was only diving as my instructor insisted I had more SCR experience before he would sign me up as a CCR instructor. IMO an abominable machine, for many reasons.

And lastly, anyone - is there any CCR currently available that has the Mk5-type canister that is resistant to flooding?

[ScubaDadMiami]

SDM - how does the Optima fare in the event of a loop flood? Is there any serious possibility of clearing the loop and carrying on CCR or SCR, or are you pretty certainly on OC?

Absolutely, you can. You can completely flood the unit, including the canister containing the scrubber, and then you can blow gas through the unit, removing the water, finishing your dive without having to resort to open circuit to get back home.

The great thing that makes the scrubber material very water tolerant in the Optima is its use of the Extend Air Cartridge from Micropore. The EAC is extremely flood tolerant, virtually eliminating the risk of caustic cocktails (unless you leave a completely flooded unit for 30 minutes or more). With standard pellet scrubber material, once it comes into contact with water, it creates an extremely caustic cocktail that, should it come into cotact with the diver's mouth or be swallowed, causes very severe injury.

[PerroneFord]

And Perrone, can you elaborate on the Ouroroboros and caustic cocktails? I hadn't heard that before and I certainly don't know anyone who's ever had one from that machine. The only cocktail I ever had was from a Draeger Dolphin, which I was only diving as my instructor insisted I had more SCR experience before he would sign me up as a CCR instructor. IMO an abominable machine, for many reasons.

If you ever have the chance to pack one, you'll understand.

The Boros' tolerances are miniscule. And due to the design, even a couple pellets of scrubber material on the canister can cause a failure to seal. This can be a HUGE issue. Even with that, the design of the unit has caused some issues. K.G. designed a hydrophobic membrane to try to combat some of the issues, but it actually only holds the water in once the unit is compromised. As for seeing the unit flood and give a caustic. I watched it happen. Twice. To my dive buddy. Months apart. Once before he got the membrane, and once after.

[ScubaDadMiami]

Here is an exerpt from another post. For the full report, click here.

"For most of our hour long dive, we were within inches of a school of feeding squid. It was amazing to watch this action so close up. The squid were darting into our light beams, catching small finds that we illuminated. It was a win-win situation: they got easy meals, and we got the reward of close up interaction for assisting them in making their catches.

What a great night!"


This kind of close up interaction with wildlife is a huge benefit of rebreather diving. Without the bubbles, you are treated like any other fish in the sea: The biologist's and photographer's dream!

[gcbryan]

Here is an exerpt from another post. For the full report, click here.

"For most of our hour long dive, we were within inches of a school of feeding squid. It was amazing to watch this action so close up. The squid were darting into our light beams, catching small finds that we illuminated. It was a win-win situation: they got easy meals, and we got the reward of close up interaction for assisting them in making their catches.

What a great night!"


This kind of close up interaction with wildlife is a huge benefit of rebreather diving. Without the bubbles, you are treated like any other fish in the sea: The biologist's and photographer's dream!

I get your point of course but in this case you can experience this (I have) on scuba as well.

[ScubaDadMiami]

I beg to differ. Yes, it is possible to experience this on both open and closed circuit diving. However, the odds of it happening on closed circuit are vastly greater than the occasional chance that one would have to experience this on open circuit scuba. There is no comparison.