Assessing DCI risk factors and adjusting dive plans

This is in response to the thread http://www.scubaboard.com/forums/accidents-incidents/464715-bent-i-guess-really-can-happen-me.html - instead of attempting a derail, I felt the topic deserved it's own separate discussion.


It's well known that a variety of factors prior to, during, and after each dive contribute to the relative probability of taking a DCS hit. Generally speaking - we're taught to stay hydrated, sleep well the night before, use proper exposure protection, exercise/eat right, etc... However, it appears there is very little empirical evidence to suggest exactly how much these factors affect an NDL and thus, we have very few objective means of applying conservatism to our dive profiles.

While we can argue the various facets of a DCS occurrence down to whether the diver's breakfast contained egg yolks or not, this is not the point of this thread. Rather, I'd like to know how each of us assesses our relative DCS risk factors and how we incorporate those assessments into our own dive planning.

For instance, I work mostly 2nd shift and occasionally have a hard time getting a good night's rest for an early dive departure. When this happens, I'll often cut a few minutes off of my planned ascent time for each dive, and generally shoot for slightly longer surface intervals. Conversely, I will generally not alter my dive plan if I had a bacon McMuffin for breakfast as opposed to fruit and yogurt.

In addition to the "day of" assessments, I have been bent once before and do not have a regular cardio routine. Since my incident, I am a stickler about ascent rates (the reason for my hit), and typically extend my safety stops to 5-7 minutes and wear more exposure protection than is typically needed (granted, I am a wuss). I likely would not alter my dive plans based on personal fitness alone, unless the dive is to be highly physical in nature (although changes in one's cardiopulmonary efficiency may extend allowable air time, and thus the dive - but we are referencing DCS here, not RMV/SAC).


So how do you personally identify, assess, quantify, and implement these individual risk factors into your diving routines?

Instructors - please feel free to chime in on how you explain these factors to your students.

This is a really good question.

I follow the GUE minimum deco ascent strategy for my NDL dives. If I have any questions about how I feel . . . if we've done a couple of dives, or the water is really cold, or I had to swim against current -- I'll do the "double the shallow stops" routine. That means 2 minutes at 30, 20 and 10, in addition to whatever stops were called for deeper.

Early on, I did a full NDL dive at 95 feet and just minimum deco, and had some funny marks on my shoulders that might have been harness bites and might have been skin bends where I had harness pressure. I wasn't sure. I've been more conservative since then, and I dislike square profiles and almost ALWAYS request the 2 minute stops for any deep, square profile dive.

TS&M, did you have pain with those marks? I mean deep painful pain? I've had skin bends twice, in my fatty tissue lower tummy, hip areas with deep deep tissue pain and excruciating lower back pain. The first time, I discounted the whole situation believing myself to have been bruised from backrolls etc due to my butt being built so near to the ground but the boat gunnels are quite high. I took a couple of days out of the water thinking I needed to give my back a rest. Went back diving for the rest of the trip day after day, dive after dive with no further instance.

Upon returning home decided to do a liitle research and got quite the shock to realize that bruises were the classic skin marbling of skin bends. After I quit shaking from the revelation, lost weight and dove many more dives over the course of a few more years, only to have it happen again though not as severe (diving off of same boat as is quite common for me).

Same cure, stayed out of the water for a few days, got home and lost a bit more weight. Another couple of years have gone by along with an approximately equal number of dives in between and since.

I'm aware of time passing (aging factor), still struggling with the weight but mostly, I'm trying to ensure more disciplined ascents, with extra time at safety stops and cussing myself out for not putting my computer log up to take a good look at what was similar about those two days that were so far apart.

My local dive sites are well suited for dive plans that allow me to do multilevel dives that allow me to slowly come out of pressure. Drop down to 80' for 15 minutes, come up to 60' for 15, turn around and 40' for 15 followed by 20' for 10 and 10' for 5.

I'm going on a trip soon that will have deeper dives where this may not be as possible so I'll have to carefully consider my dive plan and not just run on autopilot.

If I know I have a big sea dive coming up (by big, I mean anything between 20-30m), I always at least double my water intake and try to cut down on my caffeine intake (which i generally fail miserably at). I try to get a good night's sleep the night before, and on dive day I actually have a proper breakfast as opposed to just some toast or cereal bar. I follow a minimum deco ascent strategy, plus add in a 3 minute stop at 6m, followed by a 1m/minute ascent to the surface.
Most of my dives are fairly square profiles, and this strategy seems to work for me.

This is another issue as well -not at all addressed by any of the Tech cert agencies including GUE & UTD- which IMO/IME warrants the use of a computer: two or more deep deco dives per day over a week or more, especially on deep air -you will start to N2 load your slow tissues over the course of several days such that they will not clear or perhaps even accumulate unless you elect to take a day-off or two.

Even if you use a bottom timer & Ratio Deco exclusively, a Shearwater Petrel computer helps by keeping a continuous record of your tissues' loading/saturation/off-gassing/residual tensions and provides info data you might have to use to start padding your shallow O2 deco stop times after Day 4 or 5 of consecutive dive days (i.e. Petrel computer's real time GF adjustments & tissue loading graph features etc, and CNS Ox-tox tracking very important in this instance as well!) in order to keep slow tissue tensions reasonably below surfacing M-value levels on ascent.

Just a general Rule-of-Thumb recommendation for those Ratio Deco divers out there doing these types of daily deco dives over several consecutive diving days --even if using Standard Gases for bottom mix-- by Day 4 start adding more O2:break intervals at 20'/6m with a very slow ascent (0.5 m/min or a foot per minute) to the surface, monitoring for signs & symptoms of slow tissue type I DCS ("niggles" to obvious acute joint & limb pain and have an IWR contingency profile ready in your Wetnotes, just in case). And you should be doing no more than two deep deco dives a day with at least a minimum SIT 3hrs between them.

Better yet, take a day off after three or four consecutive dive days to off-gas those slow tissues. . .

I had no symptoms with the marks on my shoulder at all, which is one of the reasons I discounted them. But they were gone the next morning, which means they weren't bruises. I've never had anything like that again, so I remain quite unsure what happened. My solution is simply to be more cautious with that kind of profile -- can't hurt, right?

Forgot to say, became nitrox certified and now only dive air on dives below 100-110'.

Age, weight, general health, tobacco habits, alcohol use habits- all are DCI risk factors. As a 60 year old, active male at 5'10 and 205, , I make a habit of conservative profiles because I am not a 30 year old hard body distance runner. Always, pay attention to ascent rate ( mid-dive as well as at the end) and alwqays do a safety stop, sometimes a second one at 40 feet depending on profile. Thankfully, I have never been a DCI victim, and have never gone into an unplanned deco mode. ( And I monitor my gauges so I have never run out of air) So for me, conservative planning works. By the way, I have many dives over an hour long, many dives over 120 feet, and my record for dives in one day is 6 dives, just under 5 hours under water. Being conservative doesn't have to be limiting. Proper dive planning, and following your plan, is the best guard against DCI> But nothing is certain, so I plan conservatively.
DivemasterDennis

pocky21:

So how do you personally identify, assess, quantify, and implement these individual risk factors into your diving routines?

Click to expand...

Here's my method for not getting bent (or drowned or seasick). I make sure that:

• My ascent rate matches the plan (or computer).
• I feel good (inside)
• I feel good about the dive
• I'm happy with my buddy
• My DAN insurance is paid up
• Emergency services are available within a reasonable length of time.

I avoid over-analyzing things. If I happen to get bent within the no-deco limits or while following a valid, printed deco dive plan, it won't be severe, and I'll get to see what the inside of a chamber looks like. The chances of doing things right and taking a huge hit are from my perspective, nearly non-existent and don't rate a lot of concern.

The OP in the thread this was spun off from could just as easily have had a pinched nerve or some sort of other neuro event, as a DCS hit. Nobody really knows what happened and in any case, it resolved on O2 (might have resolved without O2 also).

flots.