safety stop question

[TSandM]

One of the problems with evaluating studies like the one cited above, is that bubbles are used as a proxy for DCS. It is not at all clear that this is valid. There are people with high bubble scores and no symptoms, although I don't believe there are any people with NO bubbles on Doppler who do have symptoms.

To the OP -- If your original instructor is also a tech instructor, I'm sure he not only believes that a slow ascent like that is advantageous, he is also looking ahead to days when the ability to hold a stop comfortably and accurately may serve you well.

 

[herbdb]

My instructor taught a 2 min stop at 1/2 the depth of the dive followed by a 3 min stop at 15 feet. There seems to be a wide variety of opinions on the subject.

The article cited above was from 2004. Here is a link to the latest DAN article on the subject. Good discussion, but no conclusion. For now, I plan to follow what I was taught.

Alert Diver | Deep Stops

 

[Garrobo]

Since most recreational dives off a boat with a dive shop last from 25-30 minutes with a 'deep' dive, like around a hundred feet and a 'shallow dive' which could be a 30 feet reef, I go by this procedure: For instance if I am diving a ship like the Speigle Grove which is about 125' to the sand I stop at 50' for a couple minutes then 30' for a couple minutes and lastly about five minutes at 15-20' depending on the wave action. On the shallow dive, which cold last for up to an hour, I do a three minute shallow stop. Using this procedure I have never had any problems and it takes only a few minutes of your life. Believe me, it's worth it if you ever knew anyone who had to go to the chamber.

 

[DivemasterDennis]

Lots of input all focusing on a few truths. First, safety stops are a good idea, and should be at 15 to 20 feet in depth for three minutes. Second, it's of additional value, but not critical, to do a preliminary stop on deep dives at 1/2 you maximum depth, more or less, though most people don't do this. What hasn't been said is that a slow and safe rate of ascent is also critical. A maximum of 30 feet per minute is ideal. Some older computers don't signal warning unless you exceed a more rapid rate, so be aware. Finally, remember this is a discussion about recreational diving. Safety stops are precautionary. They are not decompression stops. That's another thread. Perhaps one of our regular posters will start a thread on "emergency" deco stops- you know, what to do if you exceed NDL's, or your computer puts you in deco.
DivemasterDennis

 

[RonFrank]

One thing for certain, if you get bent you did something wrong! That happens to rec divers now and again so IMO take things slowly!

I ascend slowly, like maybe 10' a minute. Slower if I can do so on a reef where one can check out life on the way. It is no big deal if it takes 10 minutes to ascend from 100'. I generally do a 5 minute stop around 15'. The idea is slow controlled ascents, very slow. If one is running low on air speed it up as necessary but I always keep it at 30fpm or slower. You can also do a regular ascent until you are at 40', and then slow things down. Your gas consumption decreases as you ascend. Going slow is safe.

Since Deco stops would be done if you dive deep, it makes sense that very slow ascents and maybe a deep stop is not a bad idea. I have gone into deco a few times. No problem, I just spend time going slowly and the deco obligation is done. I have gone into deco on Punta Sur and Jupiter but slow ascents eliminate the obligation. The deeper I go the slower I ascend. That has always worked for me. Make sure you dive your plan. If that calls for a few minutes of deco make sure you have adequate gas.

 

[mathauck0814]

All "safety" stops are by definition optional. However you choose to execute them is a personal choice, just understand that it's not "required" in the same way that a decompression stop is. Depending on the gas and the profile a "deep stop" may actually cause you to further onboard gas (you can use a desktop software like v-planner to see where in a given profile you actually start to off-gas your first compartment). There's nothing wrong with shallow stops or staged stops. In fact, I tend to stop at 30, 20, and 10 on recreational dives just because it's kind of fun to hang in the water column and see what comes by. There's not a "best" way to do safety stops on a recreational dive, in fact you don't *HAVE* to do them at all - if you trust the model, that is.

 

[Jim Lapenta]

As one who has students follow deep stops in my AOW course it serves more than one purpose. First is nice slow offgassing. Second is it insures the team stays together. Next, it is great practice for buoyancy control and staying in trim. Another added benefit is increased awareness of the surroundings and for the dive plan. And finally it allows us to work on skills at each stop if I want them to.

I also know that I feel much better and am not as worn out at the end of the dive. It is also a pretty dramatic demonstration of the effect that depth has on air consumption on one dive since we observe pressures at each depth and will actually spend up to 15 minutes at the last depth to effectively turn the deep dive into a multi level. Which is why my deep dives to 95 ft in the course have total run times of 50-54 minutes and we do not go into deco. They can easily compare the drop in pressure over 15 minutes at 90 ft to the drop over 15 minutes at 20 feet. Then see how that compares to their SAC that they have already calculated on the previous dives.

 

[boulderjohn]

A maximum of 30 feet per minute is ideal.

DAN's study that compared ascent rates compared 10 FPM, 30 FPM, and 60 FPM. Of the 3, it found that 30 FPM was the best--better than 10 FPM. It is not true that slower is necessarily better. Remember that while you are ascending, some tissues are offgassing and some tissues are ongassing. As offgassing tissues approach equilibrium, the rate at which they offgas slows down, so you are not getting as much benefit as you would at a shallower depth. While you are having your offgassing slow down on that super slow ascent, the ongassing in other tissues continues. There is therefore a happy medium between too slow and too fast.

That same study found that stops were more important than the ascent rate. A moderate or even somewhat fast (60 FPM) ascent rate leading to a stop is better than a slow ascent rate that takes the same amount of time to get to the same point. It is for that reason that I am not sold on the series of one minute stops (which includes the travel time) every 10 feet for dives within no decompression limits. I do not say that with extreme conviction though--there is still too much we don't know.

 

[doctormike]

Ok, Although TSandM may be correct, It seemed a bit more like showing off how much knowledge they had as oppose to answering the dang question. In my opinion, all those stops are beneficial but not really necessary or practical for recreational diving. I would recommend doing the half way stop, and then your safety stop.

1) Yes, TSandM is correct.

2) The answer to the "dang question" is not a yes or no. As with most cases of complicated, incompletely understood biological systems under conditions for which they have not evolved (i.e. SCUBA divers), a good answer is a brief discussion of the relevant physiology and a way of translating those principles into reasonable guidelines for the real world. That is what TSandM did. I'm not sure what your recommendation is based on, but you did just say that it was your "opinion".

3) TSandM is not showing off her knowledge, she is voluntarily sharing her expertise and experience with the board. I'm grateful for that.


Sorry,

Mike

 

[fdog]

Ok, so this popped in my head the other day. Back when i took my AOW our instructor had us do safety stops where what ever depth you were at divide by half and then do 1 minute stops from there and every 10 feet up. So if we dove down to 80feet our first stop would be at 40ft for a minute, then 30ft for a minute, 20ft for a minute and lastly 10ft for a minute and then surface.

Arrgh. To cut through all the dancing around, what the OP is describing is "Min Deco". Because of it's association with early GUE, AG, and now UTD, it often gets lumped in with common hostility toward DIR and "those people". There are many subtle variations of Min Deco, as can be found with a simple Google search.

Is there a benefit to doing it this way over ascending from 80ft, or whatever depth you were at, to 15ft for 3-5 minutes? I didnt think to ask why back when i took the course.

As you've no doubt seen, this is a contentious subject, with opinions on both sides quoting the science behind Min Deco, or the lack of it.

I would submit the ultimate arbiter here is your body, and how you feel after a dive. Try it yourself and make up your own mind. Personally, I use Min Deco because I feel better, especially when on week-long recreational live-aboard trips.


All the best, James