When, if ever is it safe for a diver to make multiple trips from the bottom to surface in one dive?

[Endler's]

I pop my head up to look sometimes. Had to change End Dive Delay to 10 minutes, or computer will log multiple dives.

 

[BlueTrin]

I pop my head up to look sometimes. Had to change End Dive Delay to 10 minutes, or computer will log multiple dives.

View attachment 727401

If you use subsurface to log your dives, you can combine dives after importing.

 

[Celt]

Hello all, newbie diver question here.. After witnessing divers make multiple trips from the bottom to surface in about 30ft of sea water, I have been asking myself how much risk this creates in a dive profile and how common is this profile. I assume it creates more DSC risk but wanted to see if anyone here could elaborate on it more. There must be certain divers that dive this way for recovery or for special working conditions.

At what point after ascending from depth (not counting NDL or gas left) is it unacceptable to return back to depth on the same dive? How many times can this be done in one dive?

Lets say If a situation arose where a diver was at 30ft, then had ascended to surface for some visual aid to lets say shore, then decided to descend back down to 30ft for the remainder of the dive, is this a safe action taken by the diver?



Thanks for the feedback!

Serviced 5 fore and aft moorings for 4 hours on a dive last week. Up and down cleaning rope clearing chain, replacing swivels and shackles. It is an absolute killer on your sinuses. Don't do it if you have any kind of sinus problem otherwise your good to go.

 

[CuzzA]

Not a big deal. For example, thousands of people dive Rainbow River in Florida and that is the exact profile. Bouncing up and down from surface to 30 feet throughout the dive.

Yesterday I did 7 dives in 60 ft. 20 minutes up, 20 minutes down. Slow ascents, no problem.

 

[Nitrox_DiverNY]

Yes, it is fine to do a dive like that within the no-stop time, by definition of no-stop time. If you are using a computer (correctly), it will keep you safe on dives like this. With a slow ascent rate, I'm aware of no evidence that repeatedly descending to 30 feet, ascending to the surface, and then descending again for an entire tank can cause DCS... it might bother your ears or sinuses though, especially if you're congested.

The reason it's OK is that neither compression nor decompression happen instantaneously, they gradually occur over time. So it is not just the repeated depth changes that matter, there is a time component: how long you are at depth versus how quickly you ascend. In shallow dives such as 30 feet max, the no-stop time is always going to be way longer than the amount of gas you have, regardless of the profile.

If you haven't read it yet, I recommend picking up the book Deco for Divers by Mark Powell. The second edition (2014) is available for around $30-$40 online. The first few chapters of this book go into detail on the history of deco science, and the physiology of diving.

This type of dive profile is often called a sawtooth, by the way -- if you search for that term, you'll find a fair amount of discussion on it, on ScubaBoard and elsewhere.

thanks for the detailed response, this was very helpful in answering my question! I will definitely check out Deco for divers I would like to learn more about it. I have heard the term Sawtooth but did not really know what it meant to now, ill try to check out some of those archives. Thanks again

 

[Nitrox_DiverNY]

Yes, often maybe 5 or more times on a single dive. Brett explains it well. I am lucky as I have never had any problems with my ears and equalize internally with no motions. The up & down thing can affect some people. That is why there is the discussion of instructors doing many CESA's (controlled emergency swimming ascents) with a class of students over a short period of time on a single dive.
I believe the No Stop time for 30 feet is about 2 hours 30 minutes. At about 20 feet (it's either 18 or 22 I think) you could stay down for an unlimited amount of time (with unlimited air of course...) and ascend directly.

oh wow, and yes he did. I remember doing CESA and then descending again with instructor but at that time I wasn't even thinking about it that was a safe or common thing, I was totally new. Thanks again for your input

 

[Nitrox_DiverNY]

Doing one or two or a few ascent/descents like that on a tank is not a big deal, but you want to keep a conservative ascent rate.

Do the same thing all day with many cycles, your chance of getting bent goes up. Freedivers can go up and down from 30 feet all day and few have problems.

thanks for the input, and I didn't think about freedivers

 

[tursiops]

Suunto computers will penalize you for a sawtooth profile.

 

[Nitrox_DiverNY]

When teaching Sports Diver (10m), Dive Leader (15m) or Advanced Diver (20m) rescue lessons multiple assents are common, but we stop the assent at 6m and go back down. That said there is the potential of 6 assents. DCI is a consideration, any polaris assents finishes the lesson and diving for the day.

Neither tables nor computer algorithm were developed for this type of diving.

interesting! thanks for the reply!

 

[Nitrox_DiverNY]

There are great replies here so far! Aside from the above:

Remember, the biggest relative pressure-change occurs the closer you are to the surface. Take those last 15 feet to the surface slowly, if you're doing it several times to minimize decompression stress. While not risky as ascent, I'd also slow your descent too.

Your chances of injury or feeling sick do increase if you're going between 0 and 30ft a bunch of times. While you may not have to worry about nitrogen, there are a bunch of other compression/decompression injuries that can occur.

--

All that said, there are two scenarios where I've surfaced many times on a single tank/dive:

• Is one specific location I dive, where I may surface up to 10 times on a single dive/tank, typically staying about 20ft or less, in order to check something on the surface.
• I've also surfaced a bunch of times on a single tank, while practicing skills, like DSMB deployment, or making adjustments to my BCD/harness/rigging/etc. Also staying 20ft or less.
• I have felt sick or very tired doing this type of diving, not often, but it has happened.

In these scenarios, I have always surfaced and descended at a slower rate than usual, and try to remain shallow. You may also wish to learn free-diving, if you do this type of dive often. Being able to dive without scuba-equipment is awesome, minimal setup, and a LOT more speed!

You are right there is a ton of change in the last 15ft, and going slow is probably a very smart move. When you say feeling sick, do you mean nausea? If so this is cause by the pressure change and not nitrogen? Thanks for your feedback t was very helpful!