Deep Bailout Gas Choice for ~70M / 230FT

[Peter L]

the only issue I have with those mixes is O2 toxicity on BO. I want my bottom BO to be around 1.0 max

Agreed, they run hot on PPO2 and deep on END, almost like they were thinking about it from an OC perspective which is what most of the 'GUE like' bods tend to do. :sarcy:

 

[Peter L]

Why?

Because the gas mixes are not ideal for Marks points....
You don't want to bail out onto something at or above 1.3 PPO2 if you have a raging CO2 hit lest your next outcome is an oxtox...

Deep bailout has to cope with three major issues:

1: Narcosis under stress asnd possable C02 hit

2: Oxygen toxisity which is possably hightened by high C02 levels in the blood

3: It needs to be as low viscosity gas to reduce the effects of retained Co2 due to WOB issues = loads of low viscosity Helium


So for a 70m dive you dont want to be over 1.2.3PP02 so max 15% 02

I chose 15/65 for this dive

ATB

Mark

 

[matt]

Due to my deep bailout tank doing some wierness on it's calibrations and some suspected heliums make a run for it past the valve since it's last fill 2 years ago I am having to have it serviced and re-filled.

What would people use as a bail out gas at that depth and why?

Note, I am not quall'd to this depth but will be shortly, it seems to be a bit of an issue finding a bail out gas that covers 60-75M cleanly without hitting an ICD warning on bailout somewhere in the steps.

PL

The deeper I dive the more inclined I am to always match my deep bail-out to the diluent. It makes the whole affair very simple - just bail and turn the computer to OC mode. It also (should) give a low PO2 (which is good if you have CO2 or O2 issues).

10/52 gives a 30m narc and PO2 of 0.8 at 70m.

BTW I only dive Air, 10/52 and 6/72.

Matt.

 

[matt]

15/50 is the choice that fits from an OC perspective but at 70M is a bit hot for both dil flushing and breathing viscosity at depth in a crisis bail out?

15% at 70m is too high for CCR in my opinion. You'll never do a dil flush at 1.2...

 

[matt]

I'm in the same boat as you - thinking about the next step. I have been weighing up using 18/45 for deep bailout,

I wouldn't use 18% over 45m.

 

[Mark Chase]

Thanks, this is where my thinking was starting from in concept. The question is how quick would you get off the deep mix, I am almost thinking that the first bottle should be gone pre-deco depths. What would be the next one you add to this?

This depends totaly on the dive profile.

A 70m MUST return to shot dive I'd have a deep 7ltr tin of 15/65 then my 7ltr 18/45 for 50m to 21m then my 50% Al 80

For an imediate ascent possable dive i'd run 15/65 10ltr steel and 50% AL 80


Most of my diving is imediate ascent possable so i carry a steel 10trimix and and AL80 50% both blown to the max 250 and 230 bar respectivly.


If my SAC is OK Ill make it to the shot and the 50% on my 10ltr but if i am having a Co2 hit id just go up imediatly reguardles of wether or not i am suposed to return to the shot. For this reasion i cary an EPERB and a Nautalius life line VHF radio with GPS.

ATB

Mark

 

[erikradstrom]

This depends totaly on the dive profile.

A 70m MUST return to shot dive I'd have a deep 7ltr tin of 15/65 then my 7ltr 18/45 for 50m to 21m then my 50% Al 80

For an imediate ascent possable dive i'd run 15/65 10ltr steel and 50% AL 80


Most of my diving is imediate ascent possable so i carry a steel 10trimix and and AL80 50% both blown to the max 250 and 230 bar respectivly.


If my SAC is OK Ill make it to the shot and the 50% on my 10ltr but if i am having a Co2 hit id just go up imediatly reguardles of wether or not i am suposed to return to the shot. For this reasion i cary an EPERB and a Nautalius life line VHF radio with GPS.

ATB

Mark

Wow Mark, have you ever tried bailing out at that depth? I would never get up to 21m on a 7l bottle. That is to little gas for me, and then we tried in a calm situation just for training.

 

[matt]

Wow Mark, have you ever tried bailing out at that depth? I would never get up to 21m on a 7l bottle. That is to little gas for me, and then we tried in a calm situation just for training.

For me a 70m dive would be 40 mins on the bottom. That's 160 min (untrimmed).

Assuming the shot is in the middle I would swim 10 mins out, 10 mins back and then the same the other way. So 10 mins from the shot.

Then 70->20 is 5 mins to 45m (that's fast).

50RMV is a good number to use. So 10 mins at 70m is 4000L (571 bar, 7L) and then 5x45m is 1375 (196 bar, 7L).

I didn't work out the deco obligation for the 50% but assume a drop O2 and others are coming down?

Matt.

 

[Peter L]

Wow Mark, have you ever tried bailing out at that depth? I would never get up to 21m on a 7l bottle. That is to little gas for me, and then we tried in a calm situation just for training.

Based on conversations this is a 7L of deep mix augmenting his intermediate mix not instead of..... :juggle:

 

[Mark Chase]

Wow Mark, have you ever tried bailing out at that depth? I would never get up to 21m on a 7l bottle. That is to little gas for me, and then we tried in a calm situation just for training.

Did you miss the 7ltr of 18/45?

I have 14ltrs at 250 bar to get to 21m 7ltrs of 15/60 and another seporate 7ltrs of 18/45 then 11.5 ltrs of 50% and the option of pure 02 CCR or a drop tank.

When i dive a single deep gas I have 10ltrs blown to 250 bar.

ATB

Mark

 

[Mark Chase]

For me a 70m dive would be 40 mins on the bottom. That's 160 min (untrimmed).

Assuming the shot is in the middle I would swim 10 mins out, 10 mins back and then the same the other way. So 10 mins from the shot.

Then 70->20 is 5 mins to 45m (that's fast).

50RMV is a good number to use. So 10 mins at 70m is 4000L (571 bar, 7L) and then 5x45m is 1375 (196 bar, 7L).

I didn't work out the deco obligation for the 50% but assume a drop O2 and others are coming down?

Matt.

Is 50RMV a good number to use?

How long could you breath 50lpm without hyperventilating and blacking out?

I reckon id last a couple of mins max

Remember RMV is an average across the tin. So whilst the immediate OH SHIT moment may be 50lpm, you should be able to get your poo together and cut that back drastically.


TDI teach 30lpm as emergency planning. Id say that about the max id ever plan. On longer deeper dives i plan around 25. which is 2.5 X my normal deco SAC


Un controllable C02 hit elevated breathing?

Don't let it get that far.

Bail out as a first response to unexplained elevated breathing. Don't piss about with pointless dill flushing just go on to an easy breath low 02 low viscosity (High helium) gas and get up fast.


Look at the video of Dave Shaw's co2 hit (retained C02 from workload at depth with high viscosity gas and defective scrubber moisture pad assembly)

He had massive RMV for a few mins then blacked out and died.

Sadly i personaly believe gas planning for big C02 events is a bit pointless. There comes a point where carrying too much gas is more likely to hurt you than it is to save you.


ATB

Mark

 

[nickb]

Is 50RMV a good number to use?

How long could you breath 50lpm without hyperventilating and blacking out?

I've heard you say this before Mark and the answer is, quite a long time. I once did a dive with a guy that averaged 100l/minute and didn't even realise he had a problem:

Would you still hold onto your buddy?

 

[matt]

Is 50RMV a good number to use?

Yes. It allows you to use the whole tin in your calculation and it means you don't have to worry about 240 bar versus 232 and all that other nonsense. You could say 60 is better, it certainly isn't too small.

How long could you breath 50lpm without hyperventilating and blacking out?

At 75m with hypercapnia ... I've no idea. From people I listen to who have had this, I'd say it's a very long time indeed.

Remember RMV is an average across the tin.

Yes. But let's be honest, we're talking about 4 minutes on those 7's.

Sadly i personaly believe gas planning for big C02 events is a bit pointless. There comes a point where carrying too much gas is more likely to hurt you than it is to save you.

I agree. It's why my primary plan is not to bailout. If you want to dive deep and bailout as a primary plan, then dive OC, it's make the logistic simpler.

Matt.

 

[Peter L]

Mr Mitchell might be along shortly to put some corrections on this but I think 80 LPM is doable but on a degrading average I suspect 50-60 is a fair measure from beginning to when you get it back down to first awareness again a few minutes later.

I would seriously love to know more however and as you say Mark, most people would probably end up either stroking or cardiac infacting before they know it as this is something you need to be fit to even get back from.

 

[matt]

I would seriously love to know more however and as you say Mark, most people would probably end up either stroking or cardiac infacting before they know it as this is something you need to be fit to even get back from.

I'd like to know what the difference in the control mechanism is. I'd suspect that the breathing rate you get from exercise caused by the need for more O2 is quite different to the reaction you get when the body goes hypercapnic.

I haven't spent much time on this but did a quick google and found:



6.5kPa = 48mmHg
7.5kPa = 56mmHg
8.5kPa = 63mmHg

Yorkshire Divers - Dummies Guide to CO2 - What is end tidal PCO2 and why is it important?

Matt.

 

[GLOC]

Mark,

This report https://www.divingincidents.org/incidents/18 works out at around 80lpm for 6mins at 16m using air/nitrox.

I need to add the numbers in the Analysis Section.

Regards

 

[Mark Chase]

Mark,

This report https://www.divingincidents.org/incidents/18 works out at around 80lpm for 6mins at 16m using air/nitrox.

I need to add the numbers in the Analysis Section.

Regards

Sorry I just dont beleive its possable to maintain that level of SAC for more than a couple of mins. QED they lost gas in another way and it screwed the calculations

In the KISS scrubber test results they summed it up nicley. A diver with the physical conditioning of a Navy Seal could maintain a RMV of 75ltrs for a couple of mins max.

What use is that on a 2 hour bailout deco plan?


You may hit 50 -60 RMV for the first few mins of a bailout but if you dont get that under control very quickly, IMHO your dead reguardless of how much gas you are carrying.


http://www.kissrebreathers.com/images/PDF/scrubberClassic.pdf


ATB

Mark

 

[packeteer]

fwiw, back when I started diving, my RMV/SAC was 45lpm

and it took a long time to get it below 30

so, imo, high rates of breathing for extended periods are very possible

 

[Mark Chase]

Yes. It allows you to use the whole tin in your calculation and it means you don't have to worry about 240 bar versus 232 and all that other nonsense. You could say 60 is better, it certainly isn't too small.

Why not 100? its just as impractical in the real world

At 75m with hypercapnia ... I've no idea. From people I listen to who have had this, I'd say it's a very long time indeed.

Do you know the efect on the body of hyperventilation?

The reason for all the symptoms associated with hyperventilation has nothing to do with breathing in too much oxygen (O2), but due to breathing out too much carbon dioxide. Hyperventilation causes the level of carbon dioxide in the body to drop below the optimal range (hypocapnia). Carbon dioxide (CO2) is an acid; as such a drop in CO2 level changes the PH of the blood, and makes it more alkaline (respiratory alkalosis).

The blood alkalinity leads to a shift in what is known as the ***8220;oxygen-haemoglobin dissociation curve***8221;. This causes O2 to binds more strongly to the haemoglobin within red blood cells. The effect being that blood cells are fully oxygenated, but the O2 is not released when it reaches target tissues, bodily tissue become deprived of O2 (hypoxia). Notably the nervous and musculo-skeletal systems are most affected, muscles receive less O2 and anaerobic metabolism predominates and lactic acid builds up. The reduction in 02 to the nervous system results in a whole host of neurogenic symptoms including pins and needles and dizziness.

Another factor is that alkalosis causes a decrease in calcium ionisation, this is a form of hypocalcaemia and results in constriction of blood vessels and this further deprives the body tissue of O2. Hypocalcaemia also causes muscles cramp and heart palpitations

Yes. But let's be honest, we're talking about 4 minutes on those 7's.

At 30 RMV the time calculation at 70m is very easy. a 7ltr will last 7mins and a 10 ltr will last 10 mins.


It doesn't take a genius to figure out you cant carry enough gas to plan for a 50RMV at 70m

I agree. It's why my primary plan is not to bailout. If you want to dive deep and bailout as a primary plan, then dive OC, it's make the logistic simpler.

Matt.

There is no alternative to bailing out from an elevated SAC that makes any logical sense.


OC deep diving fixes one problem but opens the diver up to a far more likley issue of limited gas / time related stress.


ATB

Mark

 

[Mark Chase]

fwiw, back when I started diving, my RMV/SAC was 45lpm

and it took a long time to get it below 30

so, imo, high rates of breathing for extended periods are very possible

How long was a typical dive on a single 12ltr to say 25m?