Studies on outcomes of omitted decompression - how badly do you get bent for x minutes of skipped deco, aka how risky is a dive?

[scubadada]

@DiveLikeAMuppet

This kind of information is difficult to come by. A simple example, a dive to 100 feet on EAN32. My Teric is set at 80/95. Using the NDL and Deco planner, the NDL is 26 min, a bottom time of 42 min gives 9 min of deco and a dive of 50 min gives 17 min of deco. The probability of DCS, if skipping the deco, can be calculated using the SAUL Recreational Dive Planner, a probabilistic decompression algorithm. Fifty min is the longest time that will be calculated at 100 ft/EAN32. This is a single, clean dive. The type of DCS is not designated.

 

[DiveLikeAMuppet]

Is the original question for your own understanding or something more official? It might help,

It's purely a personal sense check to give some meaning to what's otherwise "just a number". I want to visualise how "hard" some of the deco ceilings might be because I feel that some of my diving that I would consider absolutely routine might be way more dangerous than I think it is.

I'm getting closer to the point where I too would describe 75 minutes runtime (40ish mins bottom, 35ish mins deco?) as only 75 minutes and I'm not sure it's the right mindset .

 

[crofrog]

It's purely a personal sense check to give some meaning to what's otherwise "just a number". I want to visualise how "hard" some of the deco ceilings might be because I feel that some of my diving that I would consider absolutely routine might be way more dangerous than I think it is.

I'm getting closer to the point where I too would describe 75 minutes runtime (40ish mins bottom, 35ish mins deco?) as only 75 minutes and I'm not sure it's the right mindset .

Risk homeostasis and risk normalization.

Not that many years ago a 75 minute dive was considered "a big dive"

 

[crofrog]

It's purely a personal sense check to give some meaning to what's otherwise "just a number". I want to visualise how "hard" some of the deco ceilings might be because I feel that some of my diving that I would consider absolutely routine might be way more dangerous than I think it is.

Search out "pressure-root-time" as a way of comparing exposure.

Decompression – The Theoretical Diver

thetheoreticaldiver.org

 

[Duke Dive Medicine]

It's purely a personal sense check to give some meaning to what's otherwise "just a number". I want to visualise how "hard" some of the deco ceilings might be because I feel that some of my diving that I would consider absolutely routine might be way more dangerous than I think it is.

I'm getting closer to the point where I too would describe 75 minutes runtime (40ish mins bottom, 35ish mins deco?) as only 75 minutes and I'm not sure it's the right mindset .

That's a really interesting insight. It seems like you're recognizing the possibility of becoming complacent, which could lead to drift from a good safety mindset and safe diving procedures. And, I basically just said the same thing that @crofrog wrote while I was typing this

 

[Alex Ouroboros]

It's purely a personal sense check to give some meaning to what's otherwise "just a number". I want to visualise how "hard" some of the deco ceilings might be because I feel that some of my diving that I would consider absolutely routine might be way more dangerous than I think it is.

I'm getting closer to the point where I too would describe 75 minutes runtime (40ish mins bottom, 35ish mins deco?) as only 75 minutes and I'm not sure it's the right mindset .

Ok, well am glad your getting in to the deco thing with a questioning attitude, I’d recommend “deco for divers” by mark Powell and “diving fundimentals” GUE, certainly will give you good reading all round, I also think “the last dive” Bernie chowdury and “caverns measureless to man” sheck exley,, fantastic reads and will appeal to your enquisitive nature.
What I will say is that there is absolutely no shame in deciding to make some of the shallow stops longer, ie, I very frequently look about at the 6m stop and ask others how long they have left , if people have an extra 15-20mins on me I’m sometimes inclined to do an extra 10mins on the basis of, on a ccr the amount of extra O2 is nothing in the scheme of things, the boat is going nowhere before the others get out, there’s an extra set of hands in the water if something unforeseen happens, I can get on the boat with confidence and say next diver in 5mins, etc etc, some people seem to race to exit with no pressure to do so and I think the pro,s are ignored for no cons, I also make a point of leaving each shallow stop and monitoring how I feel while also ascending very slowly to the next from the 18-20m depth.. especially final ascent to surface while keeping exertion to a minimum. Best of luck. (Mind and ears open )

 

[Kendall Raine]

@DiveLikeAMuppet

This kind of information is difficult to come by. A simple example, a dive to 100 feet on EAN32. My Teric is set at 80/95. Using the NDL and Deco planner, the NDL is 26 min, a bottom time of 42 min gives 9 min of deco and a dive of 50 min gives 17 min of deco. The probability of DCS, if skipping the deco, can be calculated using the SAUL Recreational Dive Planner, a probabilistic decompression algorithm. Fifty min is the longest time that will be calculated at 100 ft/EAN32. This is a single, clean dive. The type of DCS is not designated.

View attachment 828827

I'm a bit confused by this. It appears that the schedule attached computes Pdcs assuming stops as described. In other words, the Pdcs for 100x50 on 32 is 1.185% assuming stops 20x2 and 10x15. If so, Pdcs if those stops were skipped would be higher. Am I missing something?

I looked for SAUL but the link is broken and I can't find it. Do you have a link?

Thanks,

 

[inquis]

It appears that the schedule attached computes Pdcs assuming stops as described.

I believe the table was manually compiled, not a direct output from the Saul Planner. The deco schedule is from the Teric (providing an indication of "recommended" deco time that would be skipped) and Pdcs is computed by the SP for a no-stop ascent.

 

[DiveLikeAMuppet]

Search out "pressure-root-time" as a way of comparing exposure.

Decompression – The Theoretical Diver

thetheoreticaldiver.org

That's a good approach - I know the blog but missed this.

Risk homeostasis and risk normalization.

Not that many years ago a 75 minute dive was considered "a big dive"

That's a really interesting insight. It seems like you're recognizing the possibility of becoming complacent, which could lead to drift from a good safety mindset and safe diving procedures. And, I basically just said the same thing that @crofrog wrote while I was typing this

The problem is when everybody around you happens to be obsessed with diving. Things will start to appear much more normal - more so when you see everyone online diving much more extreme dives seemingly every day.

Decompression is also really difficult to visualise. You can get a perception of being very far away from home when at depth (ascent will be long and I do feel far away from home) or when inside a cave (duh). You can experience how far can you swim with couple stages while holding your breath. You can try a bit of zero viz - no mask - 5 degrees stress. You can "enjoy" cold or a leaking drysuit.

You can't try deco ceilings, it's a something a computer tells you to do. On OC I used a mental exercise to compare how long would the deco plan take on back gas (assuming it's unlimited) - it's sobering to see especially when carrying 2 deco gases. I haven't found such model yet on CCR, outside of needing lots of bailout.

Ok, well am glad your getting in to the deco thing with a questioning attitude, I’d recommend “deco for divers” by mark Powell and “diving fundimentals” GUE, certainly will give you good reading all round, I also think “the last dive” Bernie chowdury and “caverns measureless to man” sheck exley,, fantastic reads and will appeal to your enquisitive nature.

Are you raiding my bookshelf ? I found Under Pressure by Gareth Lock to be really interesting too, and Breakthrough by John Clarke, to keep the list complete.

 

[scubadada]

I'm a bit confused by this. It appears that the schedule attached computes Pdcs assuming stops as described. In other words, the Pdcs for 100x50 on 32 is 1.185% assuming stops 20x2 and 10x15. If so, Pdcs if those stops were skipped would be higher. Am I missing something?

I looked for SAUL but the link is broken and I can't find it. Do you have a link?

Thanks,

I believe the table was manually compiled, not a direct output from the Saul Planner. The deco schedule is from the Teric (providing an indication of "recommended" deco time that would be skipped) and Pdcs is computed by the SP for a no-stop ascent.

Hi @Kendall Raine

@inquis is absolutely correct. The deco schedule is from my Teric. The P(DCS) is output from the SAUL planner with a direct ascent from the bottom time, 26, 42, or 50 min. It should be noted that the SAUL planner includes a 3 min safety stop. The risk of DCS is a bit higher than calculated.

The Modern Decompression website and the SAUL planner has been "broken" for a while. @tursiops suppled a link to the planner in a previous thread, Diving with gradient factors for a new recreational diver

The Saul probabilistic decompression algorithm has been discussed several times in The Theoretical Diver cited by @crofrog