Is this IT?!

[silent running]

Forcing cal with 100% isn't necessarily a bad thing, and with a few home made add ons, it can be gotten around.. MY HH requires 100%, yet I have yet to have a problem calibrating in far away places... Last trip to truk I had 92%

and BTW a PERFECTLY functioning PSA system without an extra argon removal stage generates 95.4% o2. 4.5% argon, .1% trace gases

OK Joe, spill the beans, how do you get 92% O2 to register as 100% in the electronics? By pressurizing the head past 1 ata?

And how could I have gotten higher than 95% in places like Ambon Indonesia, where I'm pretty sure they only had a PSA system? My sensors were calibrated to good O2 back home and came back down to 20+% in air after cal with the O2 in Ambon, and the O2 there looked like about 97% on my 2dry at sea level. How common is an extra argon removal stage on PSA systems?

 

[Gill Envy]

Hi Gil, FYI during the Prism course, you must learn to fly the unit with manual inject only for the first few days. The electronics don't get turned on until the last day, if you get that far.

I did not know that, that seems very wise! Curious to see the new generation Prism and the philosophy tweeks. I hope they stick to their guns!

You know what I'm going to say, don't you? The Prism and MK 15, 15.5 all have SP only controllers and a passive 2dry which allows the user to fly manually. In fact, as I've mentioned above, those units emphasize the capability of unit to be flown without power as a safety feature which thereby familiarizes the diver with manual injection, including the mindset necessary to use it and rely only on yourself to maintain PO2.

Ever since you gave me a serious rundown of the prism, i've been very intrigued with that passive secondary... it's brilliant IMHO, not to mention that radial scrubber...wow does that give you a long burn time. There is a lot about the prism that is a nice fine balance between automation and diver engagement... there's no good reason why it hasn't become more popular. I guess it goes to show that once you figure this stuff out on such a deep level, you've probably already committed yourself to a particular rebreather and all the training. My comparison article attempts to flesh out some of this kind of stuff so that people have a better chance of understanding some the deeper issues before making the plunge. maybe you could do a write up on the prism... add to the short blurb i've done on it.

There have been, very, very few fatalities on these types of system, especially considering the huge number of man hours from military training, research and operational use. It's certainly amounts to many more hrs of safe CCR diving than has currently been wracked up by all the recreational MCCR users out there to date.

I sure do wish we could do a real numbers comparison on number of units/types and hours used. It's impressive that the Prism has such a low fatality rate as well.

Just because I have a solenoid, doesn't mean I'm lazy. My HUD tells me all the info I need-SP, power, sensor voted out-and I use the 2dry to cross check it and to check the sensors directly, with power off.

"Trust, but verify". Now why does that sound so appealing, and where did I hear it before?

from what I can tell you have a very good and balanced approach to diving your rebreather.

All the mCCR is safer theory aside, the real deal breaker is weather or not you can safely continue to dive on a trip in the event of a system malfunction... I guess E and I are about to see how that theory stands up, aren't we?!

Only 15 days to go till our Bali/Alor trip!!! 5-6 hours of bliss a day! very much looking forward to it!

 

[silent running]

I did not know that, that seems very wise! Curious to see the new generation Prism and the philosophy tweeks. I hope they stick to their guns!



Ever since you gave me a serious rundown of the prism, i've been very intrigued with that passive secondary... it's brilliant IMHO, not to mention that radial scrubber...wow does that give you a long burn time. There is a lot about the prism that is a nice fine balance between automation and diver engagement... there's no good reason why it hasn't become more popular. I guess it goes to show that once you figure this stuff out on such a deep level, you've probably already committed yourself to a particular rebreather and all the training. My comparison article attempts to flesh out some of this kind of stuff so that people have a better chance of understanding some the deeper issues before making the plunge. maybe you could do a write up on the prism... add to the short blurb i've done on it.




I sure do wish we could do a real numbers comparison on number of units/types and hours used. It's impressive that the Prism has such a low fatality rate as well.



from what I can tell you have a very good and balanced approach to diving your rebreather.

All the mCCR is safer theory aside, the real deal breaker is weather or not you can safely continue to dive on a trip in the event of a system malfunction... I guess E and I are about to see how that theory stands up, aren't we?!

Only 15 days to go till our Bali/Alor trip!!! 5-6 hours of bliss a day! very much looking forward to it!

Yahoo! Can't wait, hating the job more than ever!

Thanks for the thoughtful post Gill, -Andy

 

[caveseeker7]

Yes.

What about malfunctions?

You twist the BOV lever to OC and bailout. That's it.

There are no gauges to cross check, no broad variety of problem-based protocols to follow,
not even alternate displays or manual controls available.

You bail out.


If for some reason the electronics fail to notify the diver to bailout,
you're in the same situation as with any and all other rebreathers
that fail to signal the need to bailout: You're screwed.
May it be because they lack them in the first place or because the signal fails.

Not unlike being OOG on OC without notification of it.

 

[caveseeker7]

It strikes me that there's a much bigger problem with the MK6, as thrashed out on the RBW forums: It has no manual inject.

It doesn't need manual O2 injection, if you can't stay on the loop you bail out.

You can add diluent via the BOV manually (as KISS divers do) or automatically by dumping gas
from the loop and using the BOV's automatic diluent addition.

With proper training you'll be able to stretch your gas supply accordingly.

It also means, because of the small size of dil tanks, that you really can't do a deco dive with the unit, because then you'd have no route to safety if the electronics fail unless you brought a bailout tank.

1. The unit is build and marketed for recreational diving. 40m max depth, no deco.
2. Most recreational diving happens in the 20-30m range.
3. The constant pO2 will increase your NDL, especially in the range down to 30 m.
4. If you push the limits, even recreational ones, be properly prepared for it.

If you brought a bailout OC tank, then you've lost the benefit of the small, easy to use, convenient MK6.

That's the same with any RB, independent of the units size, weight or convenience.
The MK6 just happens to be smaller, lighter and more convenient than anything else I've seen.

And if you can't do a deco dive with a rebreather, then what's the point?

You can do deco dives (within Nitrox limits), but need to be prepared for it.
With the proper skills, proficiency and equipment. Same as any other RB.

 

[caveseeker7]

I agree lack of manual O2 inject is not a good thing, but it can be worked around-it would be very easy to add a button to the exhale lung.

The lack of manual controls and alternate monitoring is only a bad thing for divers who have the knowledge, the skills and the proficiency to use it properly. For anyone else they may well be a liability.

Just look at the long list of fatalities, look at all the features the units and options the divers had. Setting aside the initial cause of problems (unit, diver or both), the outcome seems to support the idea of bailing out rather than fiddling and fixing UW. Now consider the target market, recreational divers, that usually don't even fiddle and fix on surface, are accustomed to and enjoying the ease and simplicity of OC.

There are plenty of RB divers that live by the mantra "If in doubt, bailout!"
They're usually the ones alive. Obviously there's a depth/time range were bailout isn't the best option, but the MK6 hasn't been developed for that.

I know, it's not easy to wrap your (well-trained, CCR trimix experienced) head around it. It sure took me a while.

 

[caveseeker7]

Hi Gil, FYI during the Prism course, you must learn to fly the unit with manual inject only for the first few days. The electronics don't get turned on until the last day, if you get that far.

Or the entire course, if they crapped out ...
Great prep for mCCR training, though.

The Prism and MK 15, 15.5 ... the huge number of man hours from military training, research and operational use.

You're quite right regarding simplicity and features of PRISM/MK series. But you can only reap their advantages if you're disciplined, skilled and proficient, some things many "civilian" divers lack, on any system.

The military especially keeps a very high level of both discipline and proficiency. In addition to a much more elaborate dive protocol when it comes to mixed-gas CCRs. And I'm absolutely sure there would have been less military fatalities than civilian had they chosen either AP or ISC units. Aside from units being grounded after a couple of incidents/accidents until causes are found and problems fixed. Something we civilian divers don't seem to bother with either.

 

[silent running]

The lack of manual controls and alternate monitoring is only a bad thing for divers who have the knowledge, the skills and the proficiency to use it properly. For anyone else they may well be a liability.

Just look at the long list of fatalities, look at all the features the units and options the divers had. Setting aside the initial cause of problems (unit, diver or both), the outcome seems to support the idea of bailing out rather than fiddling and fixing UW. Now consider the target market, recreational divers, that usually don't even fiddle and fix on surface, are accustomed to and enjoying the ease and simplicity of OC.

There are plenty of RB divers that live by the mantra "If in doubt, bailout!"
They're usually the ones alive. Obviously there's a depth/time range were bailout isn't the best option, but the MK6 hasn't been developed for that.

I know, it's not easy to wrap your (well-trained, CCR trimix experienced) head around it. It sure took me a while.

Yes Stefan, I understand the unit is set up for when-in-doubt-BO, complete with BOV. I was lamenting the lack of a man add button not only for the ability to manually control the PO2 in an electronics failure-which would also require some kind of inline after market cell and computer, but also to boost PO2 at 6M for added safety/speed of off-gassing. The MK6 has been well thought out for recreational, strictly non deco diving and is probably more than adequate for it.

Your point about the additional features of more tech oriented ECCRs used by most of the experienced deceased CCR divers not being of much help, is indisputable. I'm not a big fan of added complexity in CCR as very few people function reliably during high stress/emergencies. But I don't think that a few simple, redundant features need be complicated, nor hard to use eg: Prism and MKs. If a scattered, avant-garde guitar playing boho like myself can learn how to use one, I'd bet anybody who loves diving as much as I do can as well.

It would be easy to fit the manual add button and comp/sensor if one liked all the other MK6 features and wanted to use it for longer nitrox deco dives. And frankly, once newbie CCR divers realize that they can rack up 20 minutes of deco at 130ft watching some hammerheads and get rid of it during their multi level ascent and still be out of the water in less than 90 minutes, they will want to do those dives. Which means people will likely start looking for ways to do that more safely by rigging the unit to enable bringing more BO and or a 2ndry PO2 monitor/comp and man add. The benefits of CCR multi-level nitrox deco diving are significant enough that I think it's not IF people will use the MK6 for longer deco dives, but when. And I for one think the mfg should plan for this as a type of module 2 and not leave the necessary modifications up to the users... -Andy

 

[peterbj7]

One general point - I never dive my CCR without a separate bail-out tank. And I can think of a few fatalities that probably wouldn't have happened of those divers had adopted that practice.

The RB in question is strictly for rec depths, but even so you might be surprised how quickly your small on-board diluent tank will drain if you're breathing it OC. I remember a manual injector oxygen valve on my Inspiration sticking open at 91m. I switched to a side slung tank for a few moments of OC while I sorted out the problem, and more than half drained it in 9 or 10 breaths.

Can't this machine be flown SCR?

Hi Stefan! Long time no speak.

 

[caveseeker7]

Hi Peter, good to hear from you.

I agree, diving without Redundant Breathing System is not very smart. Never really, if think about it. Even a small 2 ltr bailout (or pony on OC) tank can make a difference in an emergency.

Down to 20m the onboard should be fine, but considering the RMV increase under stress in an emergency still doesn't seem to be the way to go IMHO.

Anyway, the MK-6 has a BOV, simple quarter turn on a lever gets you onto OC air (computer switches to fO2, too, nifty). Even in CC position, the BOV acts as the ADV, so you get diluent whenever there isn't enough gas in the loop to draw a breath. Dive with minimal loop volume like any other RB, and fresh gas is close by, CC or OC. Hence I doubt using the unit SC would be a problem at all.

Hope things are looking up in Belize, keep my fingers crossed for you. Take care.