SCR vs. CCR

[Narced]

Let me preface by saying I have ALOT of learning to do about rebreathers.

I am, however, very interested in them (aren't we all?). I think I have a decent grasp on the fundamental operative differences in the two, but would like to hear from those of you who have dove with both closed and semi-closed as to what the real difference is in diving recreational depths and wreck penetrations (easy wreck penetrations, no Andrea Doria adventures)?

My hope is to ascertain what differences I would experience between SCR and CCR with the type of diving I do.

thx all.

 

[VTWarrenG]

CCR - maximum operating depth is not limited by oxygen partial pressure, it's limited only by the narcotic potency of your diluent gas.

SCR - depth is limited by diluent AND oxygen partial pressure (which is in turn dictated by the mass flow of oxygen). Depending on the model, you can typically select an orifice sized appropriately to get whatever depth you want.

I should note that there is no such thing as "recreational rebreather diving." Rebreathers (specifically CCRs) are still at the very forefront of diving technology, and their use should not be taken lightly. All appropriate precautions (there are hundreds) should be taken. Many more folks than you and I have died using 'breathers. Most of the fatalities, unfortunately, were caused by user error.

Since you're looking mainly at shallow dives, the only significant difference for you between SCR and CCR will be the impact on your wallet. SCRs are also often considered "less safe" than CCRs, mainly because they tend to have inferior electronics.

I should also note that penetration depth is not really a factor in choosing a rebreather -- the fundamental worry of 'breathers is hypoxia, not gas supply. It doesn't matter whether you're in an overhead or in open-water, a 'breather can kill you the same way.

Dive safe -- and please get some very thorough training in using a 'breather before you get much further along the selection process.

- Warren

 

[padiscubapro]

actually many people consider SCR rebreathers more safe because they don't generally have any electronics to fail.. they have a mechanical gas flow which keeps the FO2 more or less consitent.. Many people add monitoring to SCRs because, if your work load changes dramaticly your FO2 will change.. at high work loads you will have less o2 than expected when doing nothing you will have a higher o2.

I feel a properly trained CCR diver is safer, if he knows the proper bail out procedures, because you can run a CCR as a MANUAL SCR if the electronics fail.

SCRs are better than OC for shallow dives (less than 130 - some have a max working depth considerably less). CCRs are the best way to dive for ALL depths. CCRs are more complex and require more training than an SCR but in the long run its a better option since you will ALWAYS be breathing the optimum mix for whatever depth you will be diving. There are some people using SCRs at much deeper depths but it requires using multiple mixes (modifying the rebreather to be able to switch gases) or using oc to get to depth and switch back for ascent.

SCR maintains constant FO2 so PO2 varies based on depth.

CCR maintains constant PO2 so the FO2 varies by depth, as one goes shallower the FO2 rises enhancing your offgassing..

 

[Narced]

for the information so far, this is the kind of thing I am curious about. What difference in maintenance time and cost is ther between the two as well? With a rebreather there is obviously going to be more time that needs to be apportioned to maintenance, but is there a significant cost and time difference between the closed and semi-closed as well?

thanks guys-and VTWarrenG, don't worry, I am no where near touching a re-breather yet. I am at this point trying to weigh the differences in the two types and decide what would be the better choice for what I would plan to do with it. Based on that I want to figure out the cost and maintenance (something I have not been able to find much info on), for whichever seems the better choice. With some of this ground work I feel I can make a better choice as to whether to pursue the rebreather option or not. Usually I would just want to get the training and then decide what to do, but in this case the training seems so proprietary I don't see the point in it unless I intend to pursue uising the rebreather.

Please feel free to yell at me for the training comment as well. When investigating NITROX I figured take the course and then decide, no harm in extra knowledge. In this case it is just a larger commitment of both time and money. I need to weigh that commitment against the advantages to make a good decision here.

thx again, i look foreard to the maintenance input as well.

 

[padiscubapro]

Training is VERY unit specific. My after dive maintanance on an inspiration is only about 15 mins or so.. I give the whole unit a good rinsing, put some buddy clean or listerine in the counter lungs and loop, drain that into the scrubber canister the flush it out.. the scrubber lid is dried with some paper towels and compressed ait, then everything is sealed up until preparation for the next dive.. if I'm diving the next day, I'll repack my scrubber and seal unit, do a neg pressure test, the inflate the loop for a pos pressure test and I'm done.. The testing the night before adds about 15 mins... most of which is waiting time.

Its a very easy unit to clean and maintain.. sensors are usually changed every 1.5 years (batteries every 20hrs of dive time or so).. I change mine once a year since the sensors are only $70 or so a piece.


figure on spending 7k or more for an inspiration and training.

 

[Narced]

Thanks. What can a person diving four-five weeks out of the year (with a couple trips interspersed as well) expect to spend on maintenance? (For the media and all as well, 70 bucks for batteries sounds pretty reasonable so far, just wondering how much all the "little" stuff adds up.

 

[VTWarrenG]

The only consumables in rebreathers are:

1) Diluent gas. It doesn't cost anymore than any other nitrox or trimix fill.

2) Oxygen fills. This cost is not as standardized as diluent fills.

3) Scrubber material. It's pretty cheap -- your tank rental or air fill fee for open-circuit scuba is probably more.

4) Sensors. Most units use medical-quality Teledyne sensors, which are pretty expensive -- but $70 a year isn't really that bad.

5) Batteries. You've got bigger things to worry about.

The following is just my opinion:

CCRs are too expensive for me. Unfortunately, current off-the-shelf SCRs are still too primitive and, IMHO, carry too much risk for me to consider them as alternatives to OC scuba. The good news is that there's a tremendous amount of evolution going into commerically manufactured SCRs, and I intend to wait until the industry has reached the 95% mark before jumping in. I'm looking forward to the fine day when I can say with confidence: "rebreathers are as safe, or safer, than OC scuba."

Keep in mind, narced, that rebreathers require a lot of time to maintain, not necessarily a lot of money. Both SCRs and CCRs have a lengthy list of required pre-dive and post-dive checks and procedures. CCRs, because of their complexity, can have up to an hour or two of pre-dive checks to ensure complete functionality. Several folks have died because they simply didn't fully pre-dive their rig.

And, btw, the reason I consider SCRs to be more dangerous than CCRs is simply because they tend to come with unreliable monitoring electronics (or none at all) -- and by the time you feel hypoxic, it's usually too late to get out the bailout reg.

- Warren

 

[Narced]

whether it is what i want to hear or not, great information. Your input seems to mostly agree with the dilemna I have come upon during my own research. If cost and time were simply no object, then I would embrace several of the CCRs with open arms. The diligent maintenance does not put me off, but the long pre and post dive checks on the CCRs seem to make tham almost not worth the trouble, particularly on a vacation where divng may not be the only activity.

The SCRs seem to be changing for the better and due to the price and seemingly less maintenance (at least pre and post dive) these tend to be more attractive right now. Also, I am not planning deep or technical diving with it either.

I guess you just made another question for me as well;
Is the difference in price, maintenance, and of course safety when talking about the type of diving I would want it for make the CCR the choice over the SCR or not?

Also, thx again for the breakdown on maintenance costs, those are plenty reasonable in my book.

 

[padiscubapro]

Originally posted by VTWarrenG
The only consumables in rebreathers are:

1) Diluent gas. It doesn't cost anymore than any other nitrox or trimix fill.

2) Oxygen fills. This cost is not as standardized as diluent fills.

3) Scrubber material. It's pretty cheap -- your tank rental or air fill fee for open-circuit scuba is probably more.

4) Sensors. Most units use medical-quality Teledyne sensors, which are pretty expensive -- but $70 a year isn't really that bad.

5) Batteries. You've got bigger things to worry about.

The following is just my opinion:

CCRs are too expensive for me. Unfortunately, current off-the-shelf SCRs are still too primitive and, IMHO, carry too much risk for me to consider them as alternatives to OC scuba. The good news is that there's a tremendous amount of evolution going into commerically manufactured SCRs, and I intend to wait until the industry has reached the 95% mark before jumping in. I'm looking forward to the fine day when I can say with confidence: "rebreathers are as safe, or safer, than OC scuba."

Keep in mind, narced, that rebreathers require a lot of time to maintain, not necessarily a lot of money. Both SCRs and CCRs have a lengthy list of required pre-dive and post-dive checks and procedures. CCRs, because of their complexity, can have up to an hour or two of pre-dive checks to ensure complete functionality. Several folks have died because they simply didn't fully pre-dive their rig.

And, btw, the reason I consider SCRs to be more dangerous than CCRs is simply because they tend to come with unreliable monitoring electronics (or none at all) -- and by the time you feel hypoxic, it's usually too late to get out the bailout reg.

- Warren

It seems my post wasn't as clear as I expected..

there are 3 sensors about $70 each retail...
batteries are 6-$10 each you need 2 they last at least 20 hours of run timw, there are ways to optimize the battery life.. but worst case is chaning both each time.. I always run a specific contoleer as the master that gets eaten up in about 20 hours the slave does very little unless it becomes the master so it lasts about 40 hours.. so I change the master 2 times to each slave change..

the scrubber price varies.. for someone who is buying a keg at a time its around $200 a keg and it is about 9 fills... I but a few kegs at a time so my cost is around $140

you are using 3 liter cylinders(about 20cft) it gives around 10 hours of bottom time--- figure $10-20 for a fill

you diluent is an air fill for a another 3 liter (20cuft) about $3 I get about a week of diving on it (2 to 4 dives a day depends only on max depth for initial loop fill)


for someone doing air based diluent dives it works out about the same as someone using nitrox but having better confort, no dry mouth and breathing warm gas and a always the optimum mix..
If you are into deep trimix diving like I am it savbves you a fortune.. a typical trimix fill for a single set of double 95s is between $75 and $100 a fill in many places plus all your deco gasses.. I get about a $10 fill and I'll get at least 10 dives usually much more out of it..
so at worst it costs $25 per fill (typical cost around $15)of scrubber for 3-4 hours conservatively and $20 for gas fills for at least 10 hours of diving

so for a single day of trimix rebreather diving its $70 plus gas left over for the next couple of dives where someone on open ckt is $150-$200 plus deco gasses at least another $50 bucks.

 

[padiscubapro]

Originally posted by VTWarrenG
The only consumables in rebreathers are:

1) Diluent gas. It doesn't cost anymore than any other nitrox or trimix fill.

2) Oxygen fills. This cost is not as standardized as diluent fills.

3) Scrubber material. It's pretty cheap -- your tank rental or air fill fee for open-circuit scuba is probably more.

4) Sensors. Most units use medical-quality Teledyne sensors, which are pretty expensive -- but $70 a year isn't really that bad.

5) Batteries. You've got bigger things to worry about.

The following is just my opinion:

CCRs are too expensive for me. Unfortunately, current off-the-shelf SCRs are still too primitive and, IMHO, carry too much risk for me to consider them as alternatives to OC scuba. The good news is that there's a tremendous amount of evolution going into commerically manufactured SCRs, and I intend to wait until the industry has reached the 95% mark before jumping in. I'm looking forward to the fine day when I can say with confidence: "rebreathers are as safe, or safer, than OC scuba."

Keep in mind, narced, that rebreathers require a lot of time to maintain, not necessarily a lot of money. Both SCRs and CCRs have a lengthy list of required pre-dive and post-dive checks and procedures. CCRs, because of their complexity, can have up to an hour or two of pre-dive checks to ensure complete functionality. Several folks have died because they simply didn't fully pre-dive their rig.

And, btw, the reason I consider SCRs to be more dangerous than CCRs is simply because they tend to come with unreliable monitoring electronics (or none at all) -- and by the time you feel hypoxic, it's usually too late to get out the bailout reg.

- Warren

predive checks don;t take long.. if they are done correctly they take about the same time as someone doing a reasonable OC check..

The POS and NEG checks don't take long.. in fact if on sets up the gear the night before or well before you are ready to dibve its a non issue.. fill up the lungs until the pressure relief valve vents.. the lungs are nice and firm, check before you get ready to don gear if they are still firm no leaks..

the calibration procedure on an inspiration only takes about 1 minute.. after you don your gear you prebreath the loop for 3 minutes.. I usually can get in the water before any of the OC divers are ready, and between dives I don;t have to worry about rigging up for the second dive..


Most of the accidents were do to lack of proper training, failure to follow proper pre dive procedures and most of all exceding ones training on the unit.. just because you were doing 300ft dives on OC doesn't qualify one to do a 200ft dive on a rebreather.


On an SCR monitoring really isn't a big issue.. If you chose the right orafice for the gas and depths you will be diving you mix will be fine.. if you find your self working harder than you excpected, take some additional deep breaths to get more fresh gas into the loop.. if its a RB based on RMV then as long as you are using the right gas you wount have a hypoxic mix