Decompression stop for shallow dives?

[pipedope]

Many of the people would freak if they saw the normal dive profiles for lots of the diving I have done.

Very fast down
Very fast up

Do it again and again as needed to get the job done as quickly as possible.

There are qualifiers, these dives were generally very shallow, like 10-20'. I was doing this stuff for a living.

While fast down and up profiles are not particularly good practice for recreational diving, the very small N2 load makes DCI a very remote risk. There is some increased risk of AGE or other overexpansion injuries but as long as the divers keep their airways open the risk is still small.

Vis?
We don' got no stinkin' vis.
We don' need no stinkin' vis!

It is good to learn to deal with poor vis by using touch contact and/or buddy line but you need to make the arrangements before you submerge.

To me good vis means that I can see something.
Great vis means I can see something "before" I can touch it.

If I was at 40' for more than an hour I would make a safety stop. One minute at 40', call me "Rocketman". Not really, a good idea in general but there are times when it is better to get up and out.

Normal rec diving it is good to build the habit of making slow, controlled ascents from every dive, unless there is an emergency.

 

[DennisS]

Multiple ascents on a dive are very BAD. Cases of shallow water (ie 10m or less) decompression illness are often associated with multiple ascents.


2..

When you say decompression illness are you talking an embolism or something else. Could you please cite an article or paper I could reference. I frequently surface from around 25 feet to check my position due to currents that change with the tide. Is embolism my only worry or am I missing something. I beach dive in the 20-25 foot range for around 2 to 2 1/2 hours per dive.

 

[BlueDevil]

When you say decompression illness are you talking an embolism or something else. Could you please cite an article or paper I could reference. I frequently surface from around 25 feet to check my position due to currents that change with the tide. Is embolism my only worry or am I missing something. I beach dive in the 20-25 foot range for around 2 to 2 1/2 hours per dive.

There was an article titled "Shallow Water Bends - Fact or Fiction" published in an Australian dive magazine (Scuba Diver - Jan/Feb 1998). A survey of all Australian hospital based deco chambers was conducted to identify cases of DCS which occurred in 10m or less. They were very careful to eliminate any cases were the profile was suggestive of AGE (eg rapid ascents or short bottom times). The finding was that 10% of DCS cases for that year were for dives of 10m or less.

Nearly all of these cases had "mitigating circumstances". Most commonly these divers had made extremely long dives, multiple ascents or multiple dives. I must admit I have always found the figure of 10% surprising, and wonder if this was some strange anomaly during the year of the survey, or if some AGE patients slipped into the figures. However given that limb pain was the most frequent symptom (72% of the divers) it would seem that AGE could be ruled out in most of the cases.

Here are a couple of examples form the article:

Diver 1
5m for 30 min (4 ascents)
3m for 30 min
8m for 20 min
10m for 28 min

Diver 2
7.6m for 50 min (4 ascents)
7m for 35 min (4 ascents)
1.7m for 210 min (>10 ascents)

There were however dive profiles that were nowhere near as extreme as those listed above. So, the message is avoid multiple ascents and very long exposures, even on shallow dives

 

[Curt Bowen]

There was an article titled "Shallow Water Bends - Fact or Fiction" published in an Australian dive magazine (Scuba Diver - Jan/Feb 1998). A survey of all Australian hospital based deco chambers was conducted to identify cases of DCS which occurred in 10m or less. They were very careful to eliminate any cases were the profile was suggestive of AGE (eg rapid ascents or short bottom times). The finding was that 10% of DCS cases for that year were for dives of 10m or less.

Nearly all of these cases had "mitigating circumstances". Most commonly these divers had made extremely long dives, multiple ascents or multiple dives. I must admit I have always found the figure of 10% surprising, and wonder if this was some strange anomaly during the year of the survey, or if some AGE patients slipped into the figures. However given that limb pain was the most frequent symptom (72% of the divers) it would seem that AGE could be ruled out in most of the cases.

Here are a couple of examples form the article:

Diver 1
5m for 30 min (4 ascents)
3m for 30 min
8m for 20 min
10m for 28 min

Diver 2
7.6m for 50 min (4 ascents)
7m for 35 min (4 ascents)
1.7m for 210 min (>10 ascents)

There were however dive profiles that were nowhere near as extreme as those listed above. So, the message is avoid multiple ascents and very long exposures, even on shallow dives

Am I missing something? I dont see any extreme dive listed?

 

[String]

What computer was forcing a 3 minute mandatory stop on the dive ?

My Vyper has an *optional* 3 minute safety stop which clicks in on every dive below about 6m but as the manual clearly states, its optional and wont penalise the diver if skipped.

FWIW i do the 3 minute stop on even dives down to 30ft. Mainly for practice reasons, use the end of every dive to practice stops whether needed or not.

 

[pipedope]

I do want to clarify my position a bit.

The more nitrogen load you have the less you want to be bouncing up and down in the water.

If you are close to the NDLs then a bounce dive is a bad idea. There is a good explanation of why on the WKPP site at;
http://www.wkpp.org/articles/Decompression/why_we_do_not_bounce_dive_after_diving.htm

 

[BlueDevil]

Am I missing something? I dont see any extreme dive listed?

Yeah...I guess so. I didn't use the word 'extreme' in the sense of very deep, but rather in the dictionary sense of 'out of the ordinary' or 'at the far end of'. I referred to "dive profiles" that were extreme, and it would be hard to argue that 18 or more ascents on only 3 dives is not at the far end of ordinary (ie one ascent per dive) when it comes to ascent profiles.

 

[mtnredhed]

My Uwatec Aladins (pro ultra's) claim they may throw a shallow deco stop in if you've been really bad about ascent rates, particularly in repetitive dives. This is independent of exceeding NDL's. I've never seen it happen (luckily), but they do document it.

 

[scubajoe]

My buddy last weekend at the hole had an Oceanic computer that went to a 3 minute countdown when he ascended above 20ft. If we dropped back below 20 it reverted back into regular dive mode. We did the better part of our second dive in the 20 to 30 ft range. It was just a reccomendation on the part of his computer there was no penalty involved. Not sure what it did when we made a 5 min safety stop on the first dive. His logged time was the same as mine on both dives.

Joe

 

[RichLockyer]

Not sure what it did when we made a 5 min safety stop on the first dive. His logged time was the same as mine on both dives.

It did the same thing as any Suunto computer.
At the end of the 3 minutes, it just sat there showing "--" on the NDL/safety stop number display.

Suunto is a little quirky. If you have a rapid ascent at depth, then the safety stop becomes mandatory and it will show a ceiling as you cross 20ft, but it will quickly clear. If you violate the "mandatory" safety stop, then it will go more conservative on consecutive dives. It will also go more conservative if you get into deco, or run multiple rapid ascents... defined as violating 33fpm for even a couple of feet.

The safety stop timer that it runs as you cross 20ft on a 30ft dive is not a big deal, and certainly no reason to toss it... though it could be a reason to switch it to gauge mode and learn to plan the dive and dive the plan.