I think this would make me swim faster, not slowerI generally do the ‘jaws’ music in my head when the safety stop is up from 15ft and surface on the ‘du NUH NUUURRHHH!’
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I think this would make me swim faster, not slowerI generally do the ‘jaws’ music in my head when the safety stop is up from 15ft and surface on the ‘du NUH NUUURRHHH!’
You're absolutely right that the safety stop is not needed from a DCS standpoint unless you spend significant time below 10m.So, I've seen blanket statements that you should always do a safety stop. However, this can't really be the case. If I'm diving in 10-12' of water, surely I don't descend to 15', wait 3 mins and then ascend.
I feel sure that at 60' I would do a safety stop, but what about less than 33'? And even in-between; would you do a safety stop at 40'?
I want to be safe but also not ridiculous. Thanks for your help
I hesitate to write this because so few recreational divers have the right equipment for it, but some computers can give you real insight into the need. Since I have such computers, I will describe how it has changed my personal procedures and what I have learned about safety stops from following those procedures. That learning may be instructive to people without those computers.
The idea of a slow ascent during an NDL dive is to allow tissues to off-gas enough nitrogen to make it safe to go to the surface and the greatly reduced pressure there. The last 10-20 feet of the ascent is when pressure drops dramatically, so the idea of stopping at that level for a few minutes just to be sure was developed, and that is the purpose of the safety stop. Some modern computers will give you a reading of what your surfacing pressure will be relative to that theoretical maximum safe pressure (gradient factor) if you were to surface at that moment. In theory, that will tell you how necessary it will be to do a safety stop, or how long to do it. If the reading (surfGF) is 70, then if you were to surface at that moment, the nitrogen pressure in your tissues would be about 70% of what is considered safe, so that would be considered a pretty safe pressure. If you were to arrive at safety stop depth with a surfGF of 70, you would probably not have much of a need for a safety stop.
So after doing this for a while, I see that if I do not come all that close to the NDL on a mid range dive (say 70-90 feet), I don't really need one. If I do get close to NDL on such a dive, then the typical 3-5 minute stop will get me to a nice, safe range. In general, if I get within a few minutes of NDL on ANY dive, a safety stop does a pretty good job.
Note that I am using how close you get to NDL as a metric rather than depth. That is because I dive mostly with nitrox. (The place in Florida where I get my tanks filled where I do my NDL diving gives me nitrox for a good price, so why not?) This past winter I did a number of shallower (50-60 feet) reef dives with friends, and we did those dives with EANx 36. Those dives lasted an hour (by captain's orders), and when we reached safety stop depth, my friends' computers started counting off their safety stops. The surfGF reading on my computer was usually 45-50 at that point, meaning we were only about halfway to the highest safe pressure for surfacing when we started that safety stop. I stayed with them for those stops, of course, but they were completely unnecessary except for the fact that their computers were requiring it.
I like this approach, however the better question for most recreational divers (that probably don't own Shearwaters or the equivalent) should be when not to do a safety stop. I'd say go read stories about all the people that got bent and plan to not do what they did.
Stopping below 20 feet on a NDL dive is a waste of time and effort. I could see some benefit to a controlled assent to 20 feet and a slow rise to a 10 foot ceiling with a 3 minute stop for the sake of good practice to gain control where the greatest pressure change is.