Stop at 15'-Why that depth?

[shark_tamer]

For the first 2 or 3 dives I have done right after buying my PDC, I was always the first of the group to "end" my safety stop and was wondering why the rest of the group always stayed a good 30 seconds longer.

During the 4th dive, as I was controling my ascend by looking at the speed ascend indicator on my PDC, I noticed that the safety stop chronometer started at about 2 or 3 meters before the 5 meters safety stop, thus I was entering my safety stop at about 7/8 meters and stoping at 5 meters for a shorter period of time.

I since do a 3 minutes and 30 seconds safety stop.

Might not be directly related to the thread, but just wanted to share this !!!

 

[knotical]

What do they use in the metric world? MSW & MFW?

Yep, but often (usually?) lower case:
msw = meters of seawater
mfw = meters of fresh water

 

[Charlie99]

I usually hang out vertically on my safety stop at 20 to 15 feet but I just kind of do a horizontal hang/swim on the other levels. Do you actually have to STOP and not be moving, I mean would it work better to off gas?

Swimming along at 15' or 20' offgasses works just as well , and in fact some believe that the mild exercise of swimming gently assists in having good blood circulation to aid in offgassing.

As Dr Bill commented above, the easiest, most enjoyable way of doing a series of stops is to do a multilevel dive.


I'm pretty sure the term "stop" goes way back to hardhat divers standing on a platform being winched back up towards the surface. A "stop" was accomplished by stopping the winch for the required period of time.

 

[Tigerman]

Yep, but often (usually?) lower case:
msw = meters of seawater
mfw = meters of fresh water

Also, what i was taught, the safety stop should be at 3-5 meters 10-15 feet, not 15 feet.

ALSO during the AOW deep dive specialty with PADI, youre instructed to ALWAYS do the safety stop. It is NOT optional, its mandatory.
Personally, I do the safety stop on all dives, regardless of how deep I go or for how long. Better safe than sorry.

 

[Walter]

I was pondering exactly that. For example, if the sea swells are 10 feet, where would you pick your stop depth? If you managed to time it for 15FSW at the peak of a swell, you’d be at 5FSW at the trough of the swell.

If you have your buoyancy down, you'll rise and fall with the swell, maintaining the same depth. If there's enough current to require holding the anchor line, use a jon line.

ALSO during the AOW deep dive specialty with PADI, youre instructed to ALWAYS do the safety stop. It is NOT optional, its mandatory.

That makes it a decompression stop, not a safety stop. Safety stops are optional, by definition.

Personally, I do the safety stop on all dives, regardless of how deep I go or for how long. Better safe than sorry.

Yesterday, I dived for 1 hour 4 minutes with a max depth of 18 feet. Where would you have made your safety stop?

 

[scubafool]

Yesterday, I dived for 1 hour 4 minutes with a max depth of 18 feet. Where would you have made your safety stop?

Find any nice teeth?

 

[james croft]

I started diving in the 60's without spg's and bc's. Used Navy tables with no safety stop. They worked fine with nobody I was diving with ever getting dcs. I dove about 20 years and never saw anybody making a safety stop. I might add that during that time I had not taken any advanced training. I did a dive charter in 1987 and was astonished to see a mob of people hanging at 15 feet doing a safety stop as I came up the anchor line. Looking back on this seems funny to me now but I had no idea why those folks were hanging there. It was about that time I decided I needed more training and began my c-card collection. But the point is that a safety stop is not mandatory, just very smart. I have seen divers in difficulty trying to make a safety stop when the best course of action would be to get to the surface and achieve bouyancy. That is something divers need to keep in the back of their mind if they get in trouble.

 

[pescador775]

thanks guys, from what I have read so far, the way we approached it in the past, taking an 80 down to 700 psi, which is usually about 40 minutes because we hunt and exert ourselves, is within the NDL's with a margin. Then taking 120 seconds to surface, even without a stop is probably enough time to off gas, since we really aren't diving perfectly square profiles, the sand is at 60', but we are constantly up an over the structure which usually has relief of at least 20'.

The guy that got me to start diving that way is no newbie, he is well over 1000 dives. But like I said in my original post, I am working on refining my planning techniques, not necessarily for those types of inshore dives (not that it wouldn't be a good idea there too), but because of my desire to move further offshore to the deeper ledges and wrecks.

Reasonable approach. Generally, IMO, safety stops are a crock. However, like any rule there are exceptions. If the diver is experiencing chill with shaking, is tired, or if the diver is out of shape, overweight or over age 50. Then, if the dive profile is near the no deco limit, I say take a stop, 5 minutes at 15 feet. I didn't and I got bent. I was a couple minutes over the limit and blew it off. Complications of the dive were chills, dehydration from several hour of freediving prior to the SCUBA dive. Trust me, drinking plenty of gator stuff or whatever is far more important than a non required stop.

 

[Walter]

Find any nice teeth?

A 2½ inch Meg in very nice shape, two small barnacle marks and a crack, but otherwise very nice. 65 total. The best viz I saw was about 6 inches.

 

[ECR]

To put it even simpler, a diver that performs a 3 minute safety stop after a dive will have less nitrogen in their body immediately upon surfacing as compared to a diver that did not perform a safety stop, but has been on the surface "off-gassing" for 3 minutes.

I, too, am not trying to be difficult, but in the interest of accurate archives, this is not quite right.

The rate of offgassing is related to the difference between the dissolved nitrogen pressure and the ambient pressure, but so is the likelihood of DCS. Since that difference is greater on the surface than at your safety stop depth, you will offgas faster on the surface. The diver who skips the safety stop will have less dissolved nitrogen after 3 min on the surface than the diver who does a 3-min safety stop. But he will also have a greater risk of DCS.

The point is not to offgas quickly, it is to offgas safely (i.e., no bubbles, or at least all silent -- asymptomatic -- bubbles). The safety stop(s) at whatever depth or depths is a compromise between surfacing immediately which will give you the greatest offgassing rate and surfacing slowly which gives you the lowest risk of DCS.

--ECR