One dead, one missing (since found), 300 foot dive - Lake Michigan

[Vicko]

In case of hypercapnea (due to overbreathing, scruber failure...)would it not be easier to dive the unit in SCR mode until you run out of dill and then bailout (at a hopefully safer depth and lower breathing rate)

 

[beester]

You also have to remember that your WOB on a rebreather (specially at that depth) is much higher than on OC, increasing the risk of additional CO² buildup.

A sanity check that I always do (not deep diving yet on the ccr mind you) is to just hold my breath for a second of 5/10 once in a while... if I can do that without feeling winded I'm sure that I'm not building up CO²... if I can't hold my breath it means I need to take measures (slow down, diluent flush, sanity breath... etc)

 

[doctormike]

In case of hypercapnea (due to overbreathing, scruber failure...)would it not be easier to dive the unit in SCR mode until you run out of dill and then bailout (at a hopefully safer depth and lower breathing rate)

SCR mode is to let you stay on the loop in case of electronics failure or if you are out of O2. I don’t think it would be a good choice for hypercapnea since you aren’t really completely exchanging the loop contents and you would be still generating and retaining some CO2. Better to bail out if there is a serious problem with scrubbing. Dil flush is a short term thing for overbreathing...

 

[rddvet]

In case of hypercapnea (due to overbreathing, scruber failure...)would it not be easier to dive the unit in SCR mode until you run out of dill and then bailout (at a hopefully safer depth and lower breathing rate)

Fear of a co2 hit warrants a bail out in my book all the time. Even if it’s for a short moment then back on the loop.

 

[John C. Ratliff]

Well, this discussion has been an education for me about CCRs. But it really confirms my decision not to dive them. I'm getting too ol' to do that (still diving at 73), and my diving is mostly shallow and in rivers. I am more interested in better underwater swimming techniques than in scooters too. It's kinda like the difference between motorcycles and bicycles (my other sport) to me.

If any readers/divers here are thinking about CCR for relatively shallow water, I would invite you to try vintage double hose regulators instead. They are much less expensive than CCRs, relatively trouble free, and open circuit, but with the bubbles behind you, instead of in your face. This scares fish and other subjects for Underwater photography much less than current open circuit Scuba.

You can find some vintage divers at:

http://vintagescuba.proboards.com/board/3/general-discussion

Home | Vintage Double Hose

There is one double hose regulator that you can buy new (maybe more to come). That is the Argonaut Kraken:

Store | Vintage Double Hose
This regulator has all the "bells and whistles" of modern single hose regulators (LP and HP ports for SPG, inflators, octopus, etc.).

The SeawiscopeEY attachment for a mask can be seen here:

Ever Young: a true near vision aid for divers

John

 

[Brad_Horn]

You also have to remember that your WOB on a rebreather (specially at that depth) is much higher than on OC, increasing the risk of additional CO² buildup.

Why is this the case?

 

[Ze Hippo]

There are videos Jim Winn posted online on both the Emba and Thomas Hume wrecks in late May/early June that show the scooters.

I read they had videos of them prepping for the dive. Where did you see these videos? Anyone know their youtube?

 

[Marie13]

I read they had videos of them prepping for the dive. Where did you see these videos? Anyone know their youtube?

I actually originally saw the Hume one on FB as the Winns were friends of a number of people I know.

Where did you read these dives were prepping for the Doty? The Hume is about 150ft to the sand, and I think the EMBA is about 170ish, maybe a bit deeper. Big jump from that to 300ft.

The Thomas Hume video was posted earlier.

EMBA

 

[beester]

Why is this the case?

Let me rephrase the much, because I can't quantify this. However in the context of this scenario/incident (rebreather accident at 300ft), iI think it's clear that WOB and gas density at that depth (J/m) could have an impact.

From my point of view a CCR has a higher WOB than OC, because your lungs act basically as a pump. You are using your lungs to move gas through the exhalation loop, exhalation counter lung, scrubber and back through the head, inhalation counter lung and inhalation loop. This in it self causes a higher WOB than OC. Next you have the position of the counter lungs which can adversely affect your ventilation effort. (static lung load). Finally you have gas density which has a very high impact on WOB, but this seems to be the same for OC and CCR. (simon mitchell published on this a time ago).

 

[BRT]

Let me rephrase the much, because I can't quantify this. However in the context of this scenario/incident (rebreather accident at 300ft), iI think it's clear that WOB and gas density at that depth (J/m) could have an impact.

From my point of view a CCR has a higher WOB than OC, because your lungs act basically as a pump. You are using your lungs to move gas through the exhalation loop, exhalation counter lung, scrubber and back through the head, inhalation counter lung and inhalation loop. This in it self causes a higher WOB than OC. Next you have the position of the counter lungs which can adversely affect your ventilation effort. (static lung load). Finally you have gas density which has a very high impact on WOB, but this seems to be the same for OC and CCR. (simon mitchell published on this a time ago).

Not a rebreather diver but I've often thought that there should be some battery powered way to put a little positive pressure on the upstream side of the mouthpiece. But, one more thing to go wrong.