Dive safe! A short story from a chamber operator

[caydiver]

As one of Tony’s cohorts I am delighted that he posted this. I have everyday since Thursday with a lovely gentleman who is an instructor with 3,500 plus dives. He had no use of his legs or arms and much of that has come back but he is not out of the woods yet. He was down here with a group. Trying to get in as many dives as possible on his trip. (Same as the case Tony mentioned). That patient was medi vaced in police helicopter (no chamber on Sisters anymore). It costs a lot of money which some folks who save for their holiday and want to squeeze in every possible dive just don’t have. Please be smart and make sure your dive insurance is up to date!!!! We all think we dive safe, we can know if we are insurance safe. Just got the call. Going back for a ride with this delightful but unfortunate gentleman. You all should go check your dive insurance!!!!

 

[mi000ke]

As one of my esteemed professors in college once told us, "There will always be more horses asses than horses in this world."

I do mountain climbing as well as diving, and I am astounded by the lack of preparation of some folks we'll meet on a climb. And we read so often about someone getting lost on a trail or being taken down by the elements during their climb, having not prepared or geared up for it in any useful way. (We always pack out expecting to spend an unplanned night on the mountain, even for "easy" day climbs.) Rescue teams here in the Northeast are at least starting to charge negligent climbers for their rescue.

My sister was a competition skydiver, and she had many stories to tell about even experienced divers having to go to their reserve chute due to their own preparation errors. Fortunately no deaths, but you do hear about them occasionally.

It's just inconceivable to me that someone would put their well-being at risk by not understanding the physiology of scuba diving and how a computer works. Then again, I recall when I first did some discovery dives before getting certified, thinking out of complete ignorance that this was a pretty safe and risk-free sport. Of course we had a DM checking our air and computer every few minutes.

Thanks for the great description of the bari chamber process. Btw, I attended a dinner event on the island a couple of years ago, and had the pleasure of sitting with the doctor who runs the chamber on GC, and he put the fear of god in me. I've always dived conservatively, but that's when I started diving nitrox on 100% of my dives.

Dive safe, my friends!

 

[miked]

@miked did you dive again? What precautions did you take/what did you do differently?

I resumed diving into 2006. I was always a pretty cautious diver, and the doctors had a hard time explaining why I took the hit, as everything seemed in order after they downloaded my computer.
a few changes would be diving nitrox when and where available,being extra careful on NDLs and ascent rates, and making safety stops of at least five minutes.

 

[Kimela]

@Divetech Cayman - I had a couple of thoughts after reading the original post. I have been that person who lost track of my depth as I pursued a critter - sometimes even stationary critters like what 'looks like' a nudibranch - and then had to work a little harder than I'd like to get back to the appropriate depth and catch up with the group. I always do my 5 minute safety stop, no matter what. You said that when we overexert at depth we push more nitrogen into our tissues, so I'm wondering if I do some extra activity at the safety stop, will that help me to off-gas more efficiently? Generally, everyone uses their safety stop to be 'still' - like it's a contest to see who can stay at exactly 15 feet without holding onto a tag line and without finning. I don't like to sit still anyway, but if you tell me that it's even better for me to swim around and look at things above and below me I'll take it.

I'm in that 50-70 age (59 on Sunday) and, lucky me, I have hot-flashes. What you described in the chamber sounds truly awful, and add hot flashes and I just might manage to commit a crime inside a chamber. I'll be working very hard to make sure I stay away. We'll be in GC July 27th-August 3rd. We're staying on the East End and diving with Ocean Frontiers. Unless we run into you in the water, I hope we don't see one another.

 

[Divetech Cayman]

You said that when we overexert at depth we push more nitnday)

This is something I was taught by Dr Neal Pollock about 10 years ago. Upon reflection it makes perfect sense.

When you work harder, your cardiovascular system works harder as well, pumping more blood quicker to your tissues that need the increased oxygen supply. When this increase occurs at depth you are also increasing your blood carrying nitrogen that has been absorbed by your blood at that depth. Often people will ascend, and their workload at their safety stop does not match what their workload was at the bottom. So during the on-gassing phase your blood is pumping harder. In the off-gassing phase, it isn't. Leaving residual in your tissues.

So the idea is to be calm and zen when at depth. Don't work hard. On your safety stop, do some light exercise. As in, swim around a bit. Don't do a cross-fit routine.

Dr Pollock was one of the researchers who was able to knock several hours off an astronauts pre-breath session prior to EVA activity using this very same principal. Now all astronauts on the ISS pre-breath o2 while performing light cardio exercise before their spacewalks.

 

[yle]

Do you actually think divers using Nitrox on an air profile are going to track their O2 exposure?

I know people who actually dive Nitrox without setting their Nitrox enabled computer for Nitrox. Multiple day trips with 4-5 dives a day for at least 3-4 days. They admitted they don’t keep track of their O2 exposure, when I specifically asked them. That’s why I posted this question.

Were they diving long enough for it to be a factor ?

Only way to answer that question is to track it, right?

It's interesting how some "experienced" people are responding to the O2 exposure issue with "oh it's not an issue with the kind of diving being described here." And you know that... how? Again, only way to know definitively whether or not it's an issue is to actually measure it.

We do new divers a grave disservice when we give them the impression that "when you become experienced, there are some things you just 'know' and don't have to keep track of any more." Much better to ensure that new divers understand how to use their computers properly, that they can see how their computer tracks their O2 exposure, and they can then verify precisely whether or not that O2 exposure is an issue for a particular day of diving. Unfortunately there are plenty of "nitrox certified" divers who have no clue about O2 exposure... likely because they were taught by "experienced" instructors who decided that their students would never do the kind of diving that would require them to keep track of O2 exposure.

My experience has been that four dives in one day on nitrox does have the potential to approach O2 exposure limits. Your experience might be different.

 

[yle]

in order for O2 exposure to become an issue in recreational diving you would have to be doing some absolutely crazy ass diving

Marie describes people doing 4 to 5 dives in one day. Nothing "crazy" about that, happens all the time on a liveaboard (and elsewhere.) If all five dives were on 32% to a max depth of 100 ft or so, and there was an appropriate SI between dives, the divers could ostensibly reach 100% O2 exposure while staying within their NDL all day.

Granted, this is an unusual day of diving. But I wouldn't call it "crazy". All it would take is the right combination of the number of dives on the right dive sites with the right gas.

The problem is that once people believe that O2 exposure is not an issue for recreational diving, they put it out of their minds. Regardless of how "crazy" anyone thinks the idea is, it is something that dive computers measure and keeping track of it is part of knowing how your dive computer works.

 

[iamrushman]

very good information in this thread......

 

[Esprise Me]

Thanks Marie13 and yle. I was actually just thinking about this issue last night, before seeing this discussion, as I'm booked on a LOB to Turks and Caicos this coming winter. I'll be diving Nitrox; I got certified on it last winter but haven't used it since, as my local dives tend to be limited by my air consumption and cold tolerance (and more recently my buddies' air consumption, as mine has improved but now I've gotten my friends who got certified with me but hadn't dived since to come out diving with me.) On this trip, though, there are 5 dives per day available. The water should be close to 80F and I'm leaning toward bringing my 7mm just because I have it and have my weight dialed in, so the cold won't stop me. I rented a 100cf tank, so my (now pretty decent, likely to improve further by then) SAC rate won't stop me. And it's wall diving, so I can easily go right up to (and right past if I'm not careful) the MOD. I was looking over the chart for exposure over a 24-hour period, and while I don't have it in front of me, I think I remember it being 150 minutes at 1.4 partial pressure over 24 hours. With 5 dives in one day, that's only half an hour per dive at depth--easy enough to do. Please correct me if I'm misremembering the numbers or getting the math wrong, but I'm taking from this that 1) I should set my computer accurately, and 2) I should definitely not do all 5 available dives per day anywhere near the MOD.

Also, I have definitely heard people advocating for diving Nitrox on air settings for safety without any mention of keeping track of O2, including one seminar presenter at the Long Beach Scuba Show this year. I'll see if I can remember who it was, but if anyone else was there, I was the blonde in the back who asked about doing that vs. choosing a more conservative setting on your computer. His response was along the lines of "that works too, but this is easier because you don't have to futz around with the settings," which is very much NOT in keeping with what Divetech Cayman is advocating (using Nitrox setting but planning dive to stay within air table limits.) Much of his talk was also geared toward older divers and how they're more in need of this safety margin--but aren't older divers the majority of LOB customers?

 

[JohnN]

Marie describes people doing 4 to 5 dives in one day. Nothing "crazy" about that, happens all the time on a liveaboard (and elsewhere.) If all five dives were on 32% to a max depth of 100 ft or so, and there was an appropriate SI between dives, the divers could ostensibly reach 100% O2 exposure while staying within their NDL all day.

Granted, this is an unusual day of diving. But I wouldn't call it "crazy". All it would take is the right combination of the number of dives on the right dive sites with the right gas.

The problem is that once people believe that O2 exposure is not an issue for recreational diving, they put it out of their minds. Regardless of how "crazy" anyone thinks the idea is, it is something that dive computers measure and keeping track of it is part of knowing how your dive computer works.

I'd love to see those profile(s) and the O2 exposure you calculate for each one. Even with the NOAA (suspend any belief in physics model). I don't see how you'd get there