Contradictions in conservatism (or safety)?

[woodcarver]

One thing to remember is that the people who participate in ScubaBoard are on average not representative of the scuba community as a whole.

This is exactly why I thought this was the right place to ask. It has not taken long to see a majority of those posting here were not average divers. I don't think the typical vacation diver would understand the question.

The answer is, we're not. We're trying to conduct ourselves in a manner that's sufficiently safe for everyone's risk perception to be within their risk tolerance.

This is kind of what I have surmised. But trying to get a better understanding of the logic people use.

Like many activities in life it comes down to a personal choice in risk tolerance. There is no absolutely safe line. As divers and researchers have progressed in their understanding of DCS that fuzzy line has shifted a bit and new algorithms are develpoed and then implemented by the manufactures. The informed diver has the option to select the algorithm that they believe best matches their personal diving factors and risk tolerence. Since few of us know all the variables and many of the dive computer manufacturers use proprietary versions of the algorithms, the choice is still somewhat arbitrary.

This is what my impression has been and what prompted my questions. Your 4th sentence is directly aimed at what I'm trying to get a better understanding of. @RainPilot helped a bunch in his explanation of how he arrived at his choice.

It would also be a mistake to assume that this attitude contradicts an attitude toward having lots of gas

Agreed. My observation was in this aspect of diving, almost everyone was in agreement-take plenty of gas and plan some reserve. A safe practice in everyone's eyes.
But the separation of viewpoints in choice of what algorithm to follow and whether a more liberal one would put somebody closer to what seems to me to be an inexact line, is the contradiction(?) I refer to.
With numerous examples of people getting bent following their computers, some considered to be conservative, why/how does somebody decide that a more liberal setting is a better option for the individual? I do fully understand that some people are more risk averse than others, and suspect this is possibly the driving factor for most. I'm trying to figure out if this is where I'm at-

My solution was to do deco training so that I don’t have to decide between bottom times and safety factor anymore.

-and how to determine where I might fit in his explanation.
Appreciate all the feedback.

 

[boulderjohn]

With numerous examples of people getting bent following their computers, some considered to be conservative, why/how does somebody decide that a more liberal setting is a better option for the individual?

I do not remember seeing numerous examples of people getting bent following their computers. It is statistically extremely rare.

What you may be thinking of is the many times people post saying that lots of people get bent following their computers. There is a big difference between reading posts in which people say it happens a lot and reading actual examples in which it happens.

 

[woodcarver]

There is a big difference between reading posts in which people say it happens a lot and reading actual examples in which it happens

This is actually from reading a lot of DAN articles and other related incidents. A number of which indicate the divers didn't exceed NDLs, yet the divers still suffered a variety of symptoms. Not so much from anecdotes that have been related here, although there have been some in the A&I forum that would apply.
I realize there are a lot of factors that can influence an individual's risk on any given dive, and that the same dive done on a different day can result in DCS. How might someone adjust for that day to day or dive to dive? Or is it even realistic to try with the number of potential variables? Do you guys that have been diving for a long time evaluate yourselves and adjust on every dive? How, or why, did you decide to use the algorithm you use? It seems that some use much more conservative settings than others, or at least that's my understanding.
Part of the reason I asked this here is I know a lot of you are experienced tech divers and have a much better understanding of what's involved in keeping yourself from harm while trying to get the most (whatever the goal is) from every dive. I'm trying to get a better understanding of the thought process that you go through in making your decisions.
I am relatively new to diving. Trying to speed up my learning curve by asking, and listening (reading), questions of you folks that have been doing it awhile. And, in my ignorance, perhaps not asking the question very well.

 

[RainPilot]

I think you posed the question well. It’s something that’s always confused me as well, especially on this board. It helps to realise, as @boulderjohn has said, that SB by no means represents the vast majority of divers out there.

It’s important to listen to your body as well, easier if you are diving regularly. For me a fairly small change in GF makes a noticeable difference in post dive fatigue etc, I believe a lot of us have sub clinical DCS and attribute it to lugging heavy gear and feeling a bit off. Try to correlate your post dive wellbeing with your profile and you should soon get a handle on how various profiles will affect you.

 

[KenGordon]

I do not remember seeing numerous examples of people getting bent following their computers. It is statistically extremely rare.

What you may be thinking of is the many times people post saying that lots of people get bent following their computers. There is a big difference between reading posts in which people say it happens a lot and reading actual examples in which it happens.

We don’t know, except by talking to the people who treated them, whether they were within tables or not, but we know that being bent is not extremely rare.

From Specialised Services clinical commissioning policy: Hyperbaric Oxygen Therapy for Decompression Illness/Gas Embolism - NHS England - Citizen Space

A1.1 Prevalence of the disease/condition.
Between 2011/12 and 2013/14, there was an average of 293 divers and 2 cases of gas embolism who were treated with hyperbaric oxygen per year (NHS England, 2015).

BSAC do split out within limit so for DCI. 22% (maybe more, the categories are not really mutually exclusive) of the 56 cases in the 2017 Incident Report https://www.bsac.com/document/diving-incident-report-2017/bsac-diving-incident-report-2017.pdf are within limits,

 

[boulderjohn]

This is actually from reading a lot of DAN articles and other related incidents.

Could you provide some links? I just did a search of the DAN site and found one article about one diver who got DCS while supposedly diving within computer limits. The thrust of that article is that however rare it might be that one can get DCS while staying within limits, it is possible.

And it is possible--but how likely?

The total incidence of DCS for all divers is extremely low. No one can say for sure what that total is, but I have seen estimates of 0.002% of all dives resulting in DCS. You have to figure that a large part of that group were diving beyond NDLs. A large percentage of those were technical divers who are pushing limits. Every case I know personally was technical divers using an algorithm I consider to be on the outer edge of safety. That leaves a small percentage of that small percentage to be people diving within computer limits.

We also know that some people seem to be more prone to DCS than others, for a variety of reasons, many of which are not understood.

Yes, it does happen, but it is a mistake to assume it is happening in numbers that should lead us to a state of constant panic.

 

[boulderjohn]

BSAC do split out within limit so for DCI. 22% (maybe more, the categories are not really mutually exclusive) of the 56 cases in the 2017 Incident Report https://www.bsac.com/document/diving-incident-report-2017/bsac-diving-incident-report-2017.pdf are within limits,

So they estimate that 22% of all cases of DCS were to divers diving within limits. What is the percentage of total dives resulting in DCS (and not the more general category of DCI)?

 

[scubadada]

Hi @woodcarver

So, what you are asking about is what used to be called undeserved DCS, now called unexplained DCS. Statistically, there are always going to be episodes of DCS that are unexpected. Some will eventually have a tentative explanation, PFO, dehydration... Some episodes will have no explanation. Currently, there is no evidence that one decompression algorithm is of greater risk than another. There will probably never be this evidence. If I were to hazard a guess, I would bet that the episodes are related to the frequency with which that computer or deco algorithm is used.

There have been many discussions on SB around choice of deco algorithm for rec diving. Do your best to make sense of them. Choose the deco algorithm that best meets your needs.

 

[KenGordon]

About 99% according to the NHS, 2 cases of gas embolism and 293 deco incidents. The BSAC report has another category of ‘illness’ which has a lot of what are obviously bent divers but who never went to a chamber.

By the way it is 41% of the bent divers within limits, they clear that up earlier in the text. You ought to read the description of the sorts of dives that fall into this category.

In the discussion in the link above:

Decompression incidents
The BSAC database contains 56 reports of ‘DCI’ incidents in the 2017 incident year, some of which involved more than one casualty. An analysis of the causal factors associated with the 56 incidents reported in 2017 indicates the following major features:-
45% involveddivingtodeeperthan30m
41% were within the limits of tables or computers
41% involvedrepeatdiving
11% involvedrapidascents
7% involved missed decompression stops
Some cases involved more than one of these factors.
Given that 41% of DCI cases arose from dives reported to be within decompression limits, divers should be alert for DCI symptoms arising from any dive.

 

[woodcarver]

I'm sorry I cannot provide any links. I have been reading a lot, for a while, about numerous things diving related. I have not kept track of where I read what. But I have been reading a lot of DAN articles and incidents and have gone to a number of links about accidents all over. Many are news articles, which I know often have poor reporting.
I'm not inferring that it is something that occurs often or even enough to cause any panic. If I thought it was that prevalent, I would content myself with snorkeling.

We also know that some people seem to be more prone to DCS than others, for a variety of reasons, many of which are not understood.

This is what I'm trying to figure out how to potentially minimize. I understand that statistically it occurs in a small percentage of divers. How do I best stay out of that small percentage? And how does the choice of algorithm/DC impact the possibility?

So, what you are asking about is what used to be called undeserved DCS, now called unexplained DCS. Statistically, there are always going to be episodes of DCS that are unexpected. Some will eventually have a tentative explanation, PFO, dehydration... Some episodes will have no explanation. Currently, there is no evidence that one decompression algorithm is of greater risk than another. There will probably never be this evidence. If I were to hazard a guess, I would bet that the episodes are related to the frequency with which that computer or deco algorithm is used.

There have been many discussions on SB around choice of deco algorithm for rec diving. Do your best to make sense of them.

Yes, this is what I'm asking about. And this thread is an attempt to make sense of them for me. I thought if you all could explain how you decided which DC to use based on it's algorithm, it would help me understand the differences. Your sentence indicating no evidence of one having greater risk than another would indicate to me that it wouldn't make any difference which was chosen. That's sort of what I'm trying to determine in regards to me. It is confusing. Thanks