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Rebreather Myths


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#1 ScubaDadMiami

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Posted 29 June 2008 - 10:42 PM

Even if you don't want to face it, rebreathers are here, and they are the future of diving. There are new rebreathers coming to market all the time now, and it is getting to the point where they are almost commonplace. Many dive shops and boats that do not cater to rebreather and technical divers are going to lose business. Times change, and it is time to get with the program.

Being a CCR instructor, I sometimes can't believe some of the untrue myths that are circulated about "how dangerous" rebreathers are. So, in the interest of truth, this is your chance to ask any questions you have about these machines, and I will do my best to let you know about the pros and cons.

I'll start off with the first one:

"I keep hearing about people getting killed on rebreathers. There must be something to all of the talk that I hear about how dangerous they are."

Have you ever heard reports of skilled divers that jump into the water with their tanks turned off, no fins on, and they die after sinking like a rock to the bottom? So, does that make standard SCUBA equipment so dangerous that nobody should be allowed to use it? Even one death is too many. However, the cause of the death should be looked at more closely before automatically blaming a CCR accident on rebreather technology.

Back in earlier days of rebreather diving, there were definitely equipment issues that caused accidents. However, these days, the technology has improved to the point where the equipment can actually be safer than traditional open circuit SCUBA when used by a trained rebreather diver. Of course, that also means that the CCR diver must follow the training in order to take advantage of the tremendous safety that CCR diving can bring. Disregarding training can completely negate the safety factors just as it can with other types of diving.

Examples: Divers failing to turn on gas before entering the water. Divers failing to assemble equipment properly. Divers using broken equipment while knowing that there are problems with it. Divers trying to get extra hours out of batteries that cost less than $1.00. Divers abandoning established protocols on "easy" dives because they think that they only have to follow the protocol on challenging technical dives. The list goes on.

So, you have choices here: You can keep diving open circuit: This makes sense for people that only dive a few times a year in shallow water. You can decide to move into the future: It will cost a lot of money and take time to get with the training program. However, if you are a technical, deep, cave or wreck penetration diver, your life is worth it.
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#2 WreckWench

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Posted 29 June 2008 - 11:37 PM

Thank you Howard...this is a great thread.

However without being too heavy/hard on us...can you explain this statement:

However, if you are a technical, deep, cave or wreck penetration diver, your life is worth it.



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#3 secretsea18

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Posted 30 June 2008 - 05:57 AM

I took a semi-CCR course of training about 9 years ago at Cocos (basically for fun and for the promise of closer hammerhead encounters), and have never taken another dive on a semi-CCR since, nor in 9 years seen another CCR diver at any of the worldwide resort or liveaboard locations I have been to since. We all know there are "fewer or No bubbles"on CCR but please let us all know the other great advantages of this technology. Basically why go through the expense, and time to learn and dive on gear that is more expensive, time consuming to maintain and very heavy to lug around?

Thanks

#4 WreckWench

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Posted 30 June 2008 - 06:51 AM

Great questions Robin! Not to mention requires totally retraining yourself to dive again. :respect:

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#5 diverdeb

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Posted 30 June 2008 - 07:57 AM

First, thanks for starting this thread! My extremely limited knowledge about ccr is that one of the main advantages is you are breathing gas at a constant ppo2. Can you verify that this is one of the major advantages and expound on that, as well as the other points already brought up.

My only obstacle really is $$.
As for me, I'm feeling pretty scubalicious. 

#6 ScubaDadMiami

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Posted 30 June 2008 - 10:47 AM

However without being too heavy/hard on us...can you explain this statement:

However, if you are a technical, deep, cave or wreck penetration diver, your life is worth it.


Let's talk about deep dives first. When you start doing dives below 200 to 250 feet, you really start to consume a lot of gas. So, gas planning becomes critical on these types of dives. I used to dive double 120 tanks, and even with this amount of gas, I could still watch the gas gauge needle move quickly toward zero with each breath on the bottom.

Should the diver be forced to stay just three extra minutes at depth, this then requires up to an extra 20 minutes of decompression during the ascent, which consumes much more gas. I never could fully relax and enjoy dives where this kind of time pressure was always hanging over me during the dive. (I thought that this was supposed to be fun, right?)

Closed Circuit Rebreathers pretty much completely remove this time pressure. The body consumes (metabolizes) the same amount of oxygen whether on the surface or at 1,000 feet deep. CCR takes advantage of this since the diver does not send exhaled gas out into the water; it allows the diver to rebreathe the gas until the body uses the oxygen in the loop. Result: My tiny 27 cubic foot tanks can last me ten to twelve hours in the water regardless of depth. This becomes a very big plus for the technical, deep, cave and wreck diver. Running out of gas is almost completely eliminated. (There are still some things that CCR divers have to do regarding gas planning. However, I won't go into this here unless someone has a question about it.)

So, the first big safety advantage of a CCR is the tremendous reduction in the chance of running out of breathing gas.


. . . please let us all know the other great advantages of this technology. Basically why go through the expense, and time to learn and dive on gear that is more expensive, time consuming to maintain and very heavy to lug around?


This second question starts off with an answer that merges into WW's question. So, I'll start off from there.

Expense: No question about it. A better rebreather model will cost some coin as an entrance fee. There's the unit, and then there is the training. For training on my particular unit, I tell students to prepare to spend an approximate figure of $10,000 for everything. (This can be more or less depending on how much existing equipment the student has that can be used for the rebreather. Many people can re-use existing equipment, keeping the expense down somewhat.) If they buy a used model, however, this figure can approach the $6-7,000 range.

For photographers that make their living off of the pictures that they produce, or for deep divers, this can eventually pay for itself and actually involve saving money in the longer term. How?

Well, everytime you take a dive trip, you pay for the boat fee, hotels, meals, travel expenses and the like. If your living depends upon getting that perfect shot, you can spend dive after dive until you get it. Closed Circuit Rebreathers allow an interaction with wildlife unlike even what you have heard from the stories. It can sometimes get to the point where the fish crowd you out, and you want to swat them like gnats that are swarming around your face. It is that big of a difference.

Ever seen a Howard Hall film? All of the big cinematographers and photographers (except for some of the much older school and geriatric divers) are on CCR for a reason: No bubbles and silence completely change diving.

End result: Many more productive photographs per trip because the diver doesn't have to sit for hours in a spot to wait for timid creatures to overcome the bubbles of SCUBA before exiting their dens.

For deep divers, it can cost $150 for a gas fill for a single dive. CCR divers can often make ten dives off of that same amount of gas. If you are a frequent Trimix diver, a CCR gets to a point where the economics make good sense especially when combined with the much more important safety that they bring to your deep diving.

Time: Really, time is not such a big thing as many think. I spend perhaps an additional 20 minute setting up my gear before a dive outing compared to when I was diving open circuit. When I come home from the dive, I invest perhaps 30 minutes or less of my time cleaning the unit. I very much get a great return on my small additional time invested.

I also save some time and effort with the rebreather that open circuit divers don't. For example, between dives, I get to sit and rest while single tank divers are wrestling with their equipment, changing over tanks. If you own your own tanks, you have to drive them to the dive shop for fills after almost every trip. I can go on several trips before my tanks need fills. How much time does driving to your local shop and waiting for tank fills take?

Weight: There are rebreathers out there that weigh 90 pounds or more. However, mine weighs less than 50 pounds, which is not much more than a single tank set. For deep diving, I actually removed about 50 pounds from my back compared to my double steel tanks.

Let's go back to the tank fill thing. My rebreather tanks are incredibly light and easy to carry. So, when I finally do have to go to the dive shop for fills, I'll be that my back is a lot happier than the person's whose back has to lift much larger and heavier tanks into a vehicle for transport to the dive shop!

. . . one of the main advantages is you are breathing gas at a constant ppo2. Can you verify that this is one of the major advantages(?)


This is a big advantage for CCR divers. For example, I can do a 60 foot dive for over three hours before I even have to begin to worry about entering a mandatory decompression stop situation. This is because a CCR is a "constant, best-mix" diving machine.

Electronic Closed Circuit Rebreathers use computer driven technology to measure the oxygen content in the diver's breathing loop. The computers then add oxygen as needed so that the diver is always breathing a constant partial pressure of gas at the optimal level. Nitrox divers, on the other hand, only get to breathe this ideal partial pressure of oxygen when on the bottom section of their dive, and even then only if maintaining the same depth. This also requires filling the tank beforehand with the "best mix" for the dive; just filling with standard Nitrox mixes will often not give this ideal mix for the dive.

An eCCR will adjust the diver's mix throughout the dive, including the ascent, which allows longer dives with shorter mandatory decompression. The difference in dive time can be huge!
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#7 shadragon

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Posted 30 June 2008 - 11:23 AM

OK, easy ones (I hope).

1) When do you know to change out the absorbent? Is it metered or measured somehow or every X hours of dive time?

2) What pre-requisites are there? Do you need the Intro to TEC course first or some other course?
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#8 netmage

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Posted 30 June 2008 - 11:54 AM

OK, easy ones (I hope).

1) When do you know to change out the absorbent? Is it metered or measured somehow or every X hours of dive time?

2) What pre-requisites are there? Do you need the Intro to TEC course first or some other course?


Absorbent is rated for a particular unit for worst case scenerios... Outside of the lab, there are two symptomatic mechanisms to 'gauge' usage, however they are by no means accurate. One as implemented in the AP Valves Vision is the Tempstick, it tries to assertain absorbent usage by tracking the exothermic reaction within the scrubber bed. A second is thru loose fill sorb with a color indicating dye, as the reaction moves throught he scrubber bed, the material changes from white to violet. Again, both of these mechanisms are not accurate, and really look at a byproduct of the CO2 absorbtion process by tracking heat, not accurate CO2 measurements...

So, back to the question. Units and sorb are run through a gauntlet of tests involving worst case conditions in a lab w/ accurate CO2 devices, max CO2 production in very cold water, etc... And scrubber breakthrough is measured. I imagine the manufactures then pad the results a bit for safety, that then becomes the rated duration published as user guidence. Also, post dive, during the dumping of the sorb, you can get a fairly decent indicator of usage based on how the sorb has changed and clumped as a byproduct of the reaction is moisture. Are you dumping flowing granules, or do you need an icepick to empty your scrubber; again, by no means accurate, but an indicator.
So, the 'scrubber' is rated for x hours.

As for #2, other than the new agency trying to start people on CCR's.... AOW, Nitrox, and Adv Nitrox (as your handling pure O2) would be the appropriate pre-req's.

-Tim

Edited by netmage, 30 June 2008 - 01:23 PM.

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#9 netmage

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Posted 30 June 2008 - 12:16 PM

Some additional decision points....

I had a literal fleet of tanks...
4 sets of cave doubles. (130's, 104's, 108's, etc..)
1 set of AL80s
1 set of HP100s
3x AL40's
3x AL80's
1x HP120
2x HP100s

I drove to the dive shop twice a week, sometimes more to get tanks filled. Hauling hundres of lbs of steel to and from the truck; destroyed 2 sets of tires; and sometimes hauling them up to a 2nd floor apartment.

I sold 2/3rd's of the tanks listed above which covered half the cost of a used rebreather. I kept a few tanks full and fill my diluent bottle at home. I go to the dive shop now once every other week filling three small bottles w/ O2.

If your a vacationing diver, rebreathers are probably not for you... if your a every week diver, or addict like me, it can make sense.

On cave trips, my breathing gas bill is almost nothing and my gear takes half the space, time pressure has become a non-issue during dives and the constant pO2 adds a healthy margin of safety to my NDL times w/o having to sling multiple bottles.

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#10 shadragon

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Posted 30 June 2008 - 12:33 PM

As for #2, other than the new agency trying to start people on CCR's.... AOW, Nitrox, and Adv Nitrox (as your handling pure O2) would be the appropriate pre-req's.

The draw of a CCR rebreather is hard to challenge once price is discarded. It is the Adv NITROX which makes me pause. To take this (depending on the agency I am sure) requires 'Intro to TEC' first or GUI fundamentals course, so I thought. That requires doubles, BP/W and probable GUI or DIR config, which I do not use currently. [WHINE]I really don't want to change all my gear again only to have to change it once more to go to a CCR... [/WHINE]

I just hauled 4 tanks to my car. Two steel and two AL plus a pony. So your point about schleping tanks is well taken. :cool1: Thanks for the sorb answers!
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#11 WreckWench

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Posted 30 June 2008 - 12:48 PM

Advanced Nitrox does not require doubles but it does require redundancy. You can achieve that by using an h valve, second reg and carrying a pony/stage bottle. You can use your normal bc/harness/bp&w and not have to buy new equipment.

Several of OTWDiver's students including Fingrabber, Capn Jack and Scubatooth have gone the advanced nitrox and staged deco procedures course but not all went the doubles route.

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#12 georoc01

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Posted 30 June 2008 - 01:20 PM

Advanced Nitrox does not require doubles but it does require redundancy. You can achieve that by using an h valve, second reg and carrying a pony/stage bottle. You can use your normal bc/harness/bp&w and not have to buy new equipment.

Several of OTWDiver's students including Fingrabber, Capn Jack and Scubatooth have gone the advanced nitrox and staged deco procedures course but not all went the doubles route.



The TDI instructor at my LDS basically said the same thing. They don't have that as a requirement for intro to tec. And if you don't want to buy the equipment and still take the class, I noticed that the course at DIVI Flamingo in Bonaire included the equipment rental.

#13 netmage

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Posted 30 June 2008 - 01:35 PM

Advanced Nitrox does not require doubles but it does require redundancy. You can achieve that by using an h valve, second reg and carrying a pony/stage bottle. You can use your normal bc/harness/bp&w and not have to buy new equipment.

Several of OTWDiver's students including Fingrabber, Capn Jack and Scubatooth have gone the advanced nitrox and staged deco procedures course but not all went the doubles route.



The TDI instructor at my LDS basically said the same thing. They don't have that as a requirement for intro to tec. And if you don't want to buy the equipment and still take the class, I noticed that the course at DIVI Flamingo in Bonaire included the equipment rental.


Hmmm, it's a tangled web.... with a known endgame of CCR, it's ludicrous to put you in doubles only to take you out of them in the move to CCR.... A full 130 provides near the amount of gas as a set of AL80's, at least enough to satisfy course requirements... And in reality, i imagine you could bundle the academics and dives into a CCR class in one fell swoop... Adv. Nitrox is the pre-req and is more about the classroom... Decompression Procedures is not a pre-req (tho usually taught together) is more about diving and skills.

In most moves to CCR you will be changing BC setups tho some like the meg can go anywhere a tank can... , I've never see a meg attached to a SubaPro BC, but I suppose you could... BP/W on a STA are the more common implementation.
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#14 finGrabber

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Posted 30 June 2008 - 01:40 PM

Advanced Nitrox does not require doubles but it does require redundancy. You can achieve that by using an h valve, second reg and carrying a pony/stage bottle. You can use your normal bc/harness/bp&w and not have to buy new equipment.

Several of OTWDiver's students including Fingrabber, Capn Jack and Scubatooth have gone the advanced nitrox and staged deco procedures course but not all went the doubles route.



The TDI instructor at my LDS basically said the same thing. They don't have that as a requirement for intro to tec. And if you don't want to buy the equipment and still take the class, I noticed that the course at DIVI Flamingo in Bonaire included the equipment rental.

I did part of my class using an H-valve and the rest in double 100's. And the redundancy is either a double bladder wing ( which is what I use) or a dry suit

anyway, is there a good resource for the differences in CCR's?

#15 shadragon

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Posted 30 June 2008 - 05:49 PM

Advanced Nitrox does not require doubles but it does require redundancy. You can achieve that by using an h valve, second reg and carrying a pony/stage bottle. You can use your normal bc/harness/bp&w and not have to buy new equipment.

I did part of my class using an H-valve and the rest in double 100's. And the redundancy is either a double bladder wing ( which is what I use) or a dry suit

OK, That I have. I am going diving tomorrow evening (Will post details on that little adventure elsewhere), but I will take a few pictures of my current setup when I get it together. I will probably open a new forum to not distract from an otherwise excellent thread. Thanks!

BTW I ran across this while on another board:

"I like ponies on no-stop diving.
They convert "ARGH!! I'M GOING TO DIE" into a mere annoyance."
-Nigel Hewitt

Love it! :lmao:
Remember, email is an inefficient communications forum. You may not read things the way it was intended. Give people the benefit of the doubt before firing back... Especially if it is ME...! ;)

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