Can you do too much deco?

[RedSeaDiver2]

We are going to be doing a lot of archaeological dives on CCR on a wreck in 65 metres/213 feet - daily diving for weeks on end. We are fortunate that the water is warm but the location means that we need to be extra cautious about DCS.

We are looking at various profiles in MultiDeco, and the question has become - is there such a thing as too much deco? (provided that you are comfortable, warm, and stay within OTU and CNS limits). Is too much deco bad?

Most profiles/run times give us a working time on the bottom of around 23 minutes which we are fine with, something that has been considered is using a GF of 30/60 which should build in a pretty good safety margin.

Thoughts?

 

[Dr Simon Mitchell]

Hello,

Short answer is no, and yes!, but I think its no for your plan.

The answer needs some qualification. It really depends on what risk you are focusing on. If your focus is primarily on DCS as you imply, you can't really do too much deco, unless you distribute your stops stupidly. As you are probably aware, there is probably a disadvantage in over-emphasising deep stops. Your chosen gradient factors will place most of the emphasis on long shallow stops, so no, from a DCS risk perspective more is probably better.

However, you need to bear in mind that long decompressions on oxygen increase the risk of oxygen toxicity in its multiple forms, including pulmonary (rarely a problem), CNS (potentially a big problem), and hyperoxic myopia if you do lots of diving. I suspect that in dives to 60m you will be fine, especially if you intend staying within oxygen clock limits.

Simon M

 

[SlugLife]

Are you asking:

1. Can you spend too much time on a deco-stop?
2. Can you have too much "deco" by doing a bunch of frequent deco-dives?

 

[RedSeaDiver2]

Hello,

Short answer is no, and yes!, but I think its no for your plan.

The answer needs some qualification. It really depends on what risk you are focusing on. If your focus is primarily on DCS as you imply, you can't really do too much deco, unless you distribute your stops stupidly. As you are probably aware, there is probably a disadvantage in over-emphasising deep stops. Your chosen gradient factors will place most of the emphasis on long shallow stops, so no, from a DCS risk perspective more is probably better.

However, you need to bear in mind that long decompressions on oxygen increase the risk of oxygen toxicity in its multiple forms, including pulmonary (rarely a problem), CNS (potentially a big problem), and hyperoxic myopia if you do lots of diving. I suspect that in dives to 60m you will be fine, especially if you intend staying within oxygen clock limits.

Simon M

Hi Simon,

I was hoping that you would chime in - I was thinking that the short answer was No but wanted to make sure that I hadn't missed anything! Using MultiDeco the plan with 23 minutes of working time and GF of 30/60 gives a total run time of 148 minutes, and a CNS 80.2%. The planning at this stage is three teams, with every team doing one dive per day and using a rotation system where each day one team does a morning dive, one team does an afternoon dive and the third team is having a dry/standby day, then the next day the dry team moves to the morning dive slot, the morning team from the previous day moves to the afternoon slot and the afternoon team becomes the dry/standby team. Should be an interesting project.

 

[RedSeaDiver2]

Hello,

Short answer is no, and yes!, but I think its no for your plan.

The answer needs some qualification. It really depends on what risk you are focusing on. If your focus is primarily on DCS as you imply, you can't really do too much deco, unless you distribute your stops stupidly. As you are probably aware, there is probably a disadvantage in over-emphasising deep stops. Your chosen gradient factors will place most of the emphasis on long shallow stops, so no, from a DCS risk perspective more is probably better.

However, you need to bear in mind that long decompressions on oxygen increase the risk of oxygen toxicity in its multiple forms, including pulmonary (rarely a problem), CNS (potentially a big problem), and hyperoxic myopia if you do lots of diving. I suspect that in dives to 60m you will be fine, especially if you intend staying within oxygen clock limits.

Simon M

Hi Simon,

I was hoping that you would chime in - I was thinking that the short answer was No but wanted to make sure that I hadn't missed anything! Using MultiDeco the plan with 23 minutes of working time and GF of 30/60 gives a total run time of 148 minutes, and a CNS 80.2%. The planning at this stage is three teams, with every team doing one dive per day and using a rotation system where each day one team does a morning dive, one team does an afternoon dive and the third team is having a dry/standby day, then the next day the dry team moves to the morning dive slot, the morning team from the previous day moves to the afternoon slot and the afternoon team becomes the dry/standby team. Should be an interesting project.

Are you asking:

1. Can you spend too much time on a deco-stop?
2. Can you have too much "deco" by doing a bunch of frequent deco-dives?

More Q1 - but on deco-stops.

 

[GF99/99]

Back during Corona season when there was nothing to do but dive. My dive buddy and I use to do 180min scooter shore dives 5-6 time a week for weeks in a row with only the occasional rest day here and there. We were diving same depth but little bit longer bottom time and more aggressive GF and never had any issue.

As mentioned its the OTU's you will start racking up after several days

This what we were diving

 

[Johnoly]

.. using a rotation system

How many total dive days are planned?

 

[RedSeaDiver2]

How many total dive days are planned?

Months

 

[RedSeaDiver2]

Back during Corona season when there was nothing to do but dive. My dive buddy and I use to do 180min scooter shore dives 5-6 time a week for weeks in a row with only the occasional rest day here and there. We were diving same depth but little bit longer bottom time and more aggressive GF and never had any issue.

As mentioned its the OTU's you will start racking up after several days

This what we were diving

View attachment 749196

You was fine running CNS% that high?

 

[tbone1004]

We are going to be doing a lot of archaeological dives on CCR on a wreck in 65 metres/213 feet - daily diving for weeks on end. We are fortunate that the water is warm but the location means that we need to be extra cautious about DCS.

We are looking at various profiles in MultiDeco, and the question has become - is there such a thing as too much deco? (provided that you are comfortable, warm, and stay within OTU and CNS limits). Is too much deco bad?

Most profiles/run times give us a working time on the bottom of around 23 minutes which we are fine with, something that has been considered is using a GF of 30/60 which should build in a pretty good safety margin.

Thoughts?

As said above, short answer is no however I would seriously re-evaluate your GF's as they are out of whack with currently accepted balance of GF. If you want a high of 60 then I would have a low of around 50 not 30. 45 at the lowest. The balance between low and high is coming into higher prominence in discussions with many diving a low somewhere around 80% of the high after several studies over the last few years.

What many of us personally do/recommend is choose our profile that we are happy with, for me on a 60m warm dive that would probably be 70/85 or 60/80 depending on how much fun we had the night before and once I got up to 30-20-10ft range, then hang out for a while. If I'm on a line just hanging in the middle of the ocean I have to admit that that probably wouldn't be a very long time but if there was something to do or look at then I am prone to nearly draining my tanks before I get out of the water. Don't forget low ppO2 gas breaks *air breaks but no one I know actually carries air anymore so it's some sort of a low ppO2 break*, and if you finish your deco on the "normal" gf's and are just hanging out for good measure then you can switch to a less harsh gas for the remainder of your time in the water that will still have you offgas but less likely to cook your lungs. A 60m dive should have 50% on there so you can stay on that until it is empty without having to worry about switching again.

If you have a Shearwater the surfGF function is quite convenient and if you want to get out at a gfHi of 60, just chill out until the surfGF is 60 *which will take a hot minute* but no need to set the actual ascent profile that low because it will give you a weird profile and if something goes sideways you may be in more trouble than you're attempting to save.