Almost went into deco off Islamorada

[Deac in the Wake]

I was recently diving a "new" spot off Islamorada in the Keys. There's a ledge off shore with a high population of lionfish and our group went out there to do some "clean-up work." You have to anchor a little ways off the ledge and you're in the 80-90 ft range once you swim down and out to the corral heads they like to stalk. I am pretty good about watching my consumption and NDL times but I was full-on in the throes of lionfish fever. I've never pushed my NDL below 5 minutes and always have an exit plan on completing deep diver back up through a shallower profile, through my stops etc. But this time, I was caught up in bagging bad guys and went quite some time without looking at my NDL. Fortunately, one of my dive buddies came up and frantically pointed to my computer. He was on basically the same profile and caught the fact that we were down to 1 minute to deco and all that implies. We started a quick but within-the-limits ascent up the slope but my computer stayed on 1 minute for what seemed like 20 minutes. Gradually it grew: 7, 9, 11, 16 minutes until clear.

Morale of the story: Don't let what hunters call "buck fever" distract you from your no deco limits. Or other silly, unimportant things like air and depth. Owed him a couple of beers for that one.

 

[wilderydude83]

word.

 

[ErikH]

Read Bob's article about it... NWGratefulDiver.com

Also, a dive computer with an alarm function would be a good investment i guess..

 

[redacted]

down to 1 minute to deco and all that implies. We started a quick but within-the-limits ascent up the slope but my computer stayed on 1 minute for what seemed like 20 minutes. .

What do you think that implies??? BTW, your computer should have rather quickly given you more NDL time as you quickly ascended. What computer are you using?

You might want to take a look at this and you will be able to see what was going on and what would have happened had you incurred a deco obligation: http://www.scubaboard.com/forums/basic-scuba-discussions/396439-new-way-look-dive-planning.html

 

[TSandM]

It's a very good lesson . . . awareness of the basic things like depth, time, gas and buddy should never take second seat to fascination with hunting, cameras, or anything else.

But I just want to address the use of the word "frantic" in the original post. There is nothing to be frantic about about approaching no deco limits, or even exceeding them slightly. It's to be avoided, of course, but it is not an emergency or the end of the world. After all, technical divers go into deco all the time and survive it! What exceeding your no-deco limits means is that you must do deco -- that means you'd better have the gas to do it, and the knowledge to know where and how long to do it. Because recreational divers aren't taught how, and because they are diving simple equipment and frequenty with minimal redundancy, it's not a good idea to put yourself in a position where you are trapped under the water. But if you do, you simply must do the decompression called for. Most computers have a violation protocol which will call for fairly long shallow stops, and you ought to know what YOUR computer will say if you go into deco, and what it will ask you to do.

Where you get into a world of hurt is when you incur deco without having the gas to do it. Even then, "frantic" is not a good approach.

I think any active recreational diver really ought to read Mark Powell's book, Deco for Divers. Having a better understanding of what the theory is regarding nitrogen dynamics in divers can help you make better decisions and feel more confident if you end up in an unfamiliar situation.

 

[DevonDiver]

BTW, your computer should have rather quickly given you more NDL time as you quickly ascended. What computer are you using?

That's a complete fallacy, and shows some inexperience.

It depends entirely on your tissue saturation - in particular, which tissue compartments are controlling the NDL at that time. The will depend on the dive profile, your prior dive history and the algorithm used by your computer (although most computers will react the same within a given variation).

If you're gonna dive aggressively and push the boundaries of your computer, then it makes sense to understand what is happening in your body from the dive profile and residual nitrogen, particularly in the slow tissue compartments.

As TS&M said.. if you're gonna 'fly' your computer to the limits, then reading 'Deco for Divers' is the least you should do.

I've done dive series that have left me starting dives with <20min NDL at 16m. Gone (knowingly) into deco on one of those 'heavy' dives and the deco was still rising on my ascent. From the bottom (16m) to the deco stop at 6m, deco rose from <2min to over 18mins. If I'd assumed anything about the computer, I might have made the mistake of assuming that the deco would clear - which could have left me with insufficient gas to complete the stop. Knowing my dive series, I know it would hammer me with a hang... and had gas enough for the situation.

To the OP: This is a task loading issue. If your situational awareness (inc, depth, time, gas and NDL states) gets neglected because of an activity you are performing (hunting, photography, navigating...whatever), then your core dive skills obviously aren't ingrained yet. Take it easy until they are. Experience is everything.... situational awareness is what keeps you safe underwater.

 

[Wookie]

That's a complete fallacy, and shows some inexperience.

It depends entirely on your tissue saturation - in particular, which tissue compartments are controlling the NDL at that time. The will depend on the dive profile, your prior dive history and the algorithm used by your computer (although most computers will react the same within a given variation).

If you're gonna dive aggressively and push the boundaries of your computer, then it makes sense to understand what is happening in your body from the dive profile and residual nitrogen, particularly in the slow tissue compartments.

As TS&M said.. if you're gonna 'fly' your computer to the limits, then reading 'Deco for Divers' is the least you should do.

To the OP: This is a task loading issue. If your situational awareness (inc, depth, time, gas and NDL states) gets neglected because of an activity you are performing (hunting, photography, navigating...whatever), then your core dive skills obviously aren't ingrained yet. Take it easy until they are. Experience is everything.... situational awareness is what keeps you safe underwater.

To call AWAP inexperienced would be a stretch, I think. And to discount what he said is also a grave mistake. In my vast experience (I have over 6,000 computer dives on Pelagics, Uwatecs, Suuntos, and now a Shearwater), it is overwhelmingly my experience that as you ascent from a RECREATIONAL dive, without ever going into deco, you will indeed be further away from the NDL as depth decreases. In fact, as your depth approaches 30 feet, your NDL will be 99 minutes, because that's as far as the computer will go.

Computers don't measure tissue compartments, they measure depth, time, and gas pressure if you buy that kind. They then take that data and compare it to an algorithm developed to simulate tissue loading. Computers don't get bent, nor do they measure what is happening in the body. Those that choose to rely on computers for their dive sfety (not an unheard of concept) rather than learn decompression theory should take exactly the stance that the OP had.

 

[Deac in the Wake]

TS&M: the "frantic" was more tongue-in-cheek as was the reference to "all that implies." My meaning was more legitimate concern about being locked out from diving for the next day (DM's rules when you go into deco) and a less important concern about getting ribbed topside for effing up. I was not "frantic" about going into deco like it's life or death. It was just humorous to think about the crap we'd heard for getting caught up in the heat of the moment. We were not panicked or anything of the sort and we had plenty of gas. But the underlying message was more to the point of avoiding pushing the limits on your dive plan due to being distracted which, IMO, is probably the top or one of the top reasons divers get injured. Not paying attention.

And FWIW, I'm diving a Cobra 3 so I know we were well within safety margins. I think the only thing more conservative than Suunto's algorithms is just not to dive. And to Erik's point- my NDL alarm was going off. Again, being caught up in the moment, I thought, like an idiot, it was someone else's. Duh.

 

[redacted]

That's a complete fallacy, and shows some inexperience.

It depends entirely on your tissue saturation - in particular, which tissue compartments are controlling the NDL at that time. The will depend on the dive profile, your prior dive history and the algorithm used by your computer (although most computers will react the same within a given variation).

If you're gonna dive aggressively and push the boundaries of your computer, then it makes sense to understand what is happening in your body from the dive profile and residual nitrogen, particularly in the slow tissue compartments.

As TS&M said.. if you're gonna 'fly' your computer to the limits, then reading 'Deco for Divers' is the least you should do.

To the OP: This is a task loading issue. If your situational awareness (inc, depth, time, gas and NDL states) gets neglected because of an activity you are performing (hunting, photography, navigating...whatever), then your core dive skills obviously aren't ingrained yet. Take it easy until they are. Experience is everything.... situational awareness is what keeps you safe underwater.

Sure, if you do enough repetitive deep recreational dives I'm sure you can get to the point where the faster tissues are not the regulating tissues. But that does not happen in 2 or 3 dives. In fact, it does not happen in a day or 2 of diving with 5 dives a day to the 80 to 100 ft range with 2.5 hour surface intervals.

Perhaps you can tell us what it would take to get tissues that do not completely off-gas in a 2.5 hour surface interval to get sufficiently loaded with N2 to become the controlling tissues for a recreational diver. I have been looking for that answer but have not found it yet.

Or for that matter, maybe you, with all your experience, can give us a one day set of dives that creates the situation where tissues in the slower half will be regulating a recreational dive.

 

[DevonDiver]

I can get in this scenario pretty easy, over an aggressive 3 recreational dive series (as I described above). I'm forever warning divers about the dangers of assuming that deco will clear, or NDL will increase just because you ascend and/or multi-level. Yes, on most rec profiles you can multi-level and 'fly the curve' of your NDL up the ascent. However, if you're doing repetitive deep dives, especially square profile (wreck dives & hunting) then you can get into a real sphincter-clencher quite easily and without 'warning'.

I'll dig through my computer and try to find the sequence I'm referring to.