Beyond 130 feet: always a deco dive?

[DevonDiver]

So then it becomes a mandatory optional stop? Or is it an optional mandatory stop??

It is a dive planning instruction.

In most cases, PADI don't specify a safety stop for conservatism. It is the dive community that, by consensus, chooses to safety stop on the majority of dives. For those dives, there is little reasonable risk of DCS, even without a safety stop.

In certain cases, where the dive will leave calculated nitrogen close to the calculated parameters of the RDP, PADI insist that a safety stop should be planned.

Nonetheless, in either circumstance.. in any circumstance, as a PADI recreational diver diving within the recommended limits of their training, the diver retains the ability to immediately ascend from any dive to the surface, in the event of an emergency, at a speed no greater than 18m/60ft per minute. To do so does not entail an unreasonable risk of DCS.

If a diver goes beyond the limits of the RDP, or enters decompression by whatever means they calculate their NDL, they cannot immediately ascend to the surface in the event of an emergency. They must stop at specified depths (as provided by their computer or tables procedures) for specific time periods. To do otherwise entails an unreasonable risk of DCS.

---------- Post Merged at 01:03 AM ---------- Previous Post was at 12:59 AM ----------

So...would it be correct to say that a tec diver plans a deeper dive much more carefully,...

Yes, in infinitely more detail that a recreational dive.

....prints tables specific to the dive/gas profile,

Tables may be a primary or secondary (back-up) method of conducting decompression.

...and uses the computer only as backup?

An appropriate technical diving computer may be a primary or secondary (back-up) method of conducting decompression.


Most, if not all, technical diving courses are taught on the basis of using custom tables, calculated via laptop/desktop computer, based on specific parameters unique to the dive (depth, bottom time, travel/bottom/deco gases used) and the diver (air consumption, personal preferences in padding/shaping of deco).

A technical dive may be conducted on the basis of those tables, using a bottom timer and depth gauge - or by using a technical diving computer. In either case, an appropriate back-up is utilized for redundancy (lost tables, broken gauge or failed computer). That back-up may be the same method (another set of tables/gauges or another identical computer) or it may be the alternative method (primary use of tables, back-up computer or vice versa).

 

[boulderjohn]

So...would it be correct to say that a tec diver plans a deeper dive much more carefully, prints tables specific to the dive/gas profile, and uses the computer only as backup?

Different technical divers do different things. Some never use a computer at all. Some use tables and have computers for backup. Some use computers primarily and have tables for backup. Some use a concept called Ratio Deco, and the two agencies that advocate it use it differently.

I would say that except in the theoretical case of some fools I haven't met, tech divers do plan more carefully. That is because they don't have the luxury that recreational divers do of simply going to the surface when things don't work out as expected.

 

[cbrich]

The reasons don't have to be guessed at. The research was published in peer reviewed journals. PADI conducted extensive tests on divers and used Doppler bubble imaging to check their blood after dives. Their numbers were based on the results. The mandatory safety stop rule was established because their research indicated a gray area (literally on the tables) between dives that did not require a stop and dives that did.

You have to remember that in all cases we are dealing in probabilities and not absolutes. In the NDL dives, you are extremely unlikely to get DCS if you follow those numbers. If you go off the table, the likelihood increases to the extent that it was considered unacceptable to go without a decompression stop. The mandatory safety stop region is the transition between the acceptable risk and the unacceptable risk.

Interesting, can you send me those peer review journals.

 

[boulderjohn]

Interesting, can you send me those peer review journals.

No, I don't have them. I have only read about them. If you go to the ScubaBoard forum called Ask Dr. Decompression, you can ask Dr. Decompression. He can give you all the details. He was one of the researchers on the project.

 

[Dive Bug Bit Me]

I would start with "decompression theory" by Wienke.

It is 186 pages of math. The references and Related Reading sections can keep you going for years.


Deco for divers by Mark Powell turns this into understandable English.

 

[lindenbruce]

The Cobra gave you a ceiling... did it also give you a reliable means to cope with any factor that might otherwise force you to break that ceiling?

All I can say is it gave my the ceiling symbol that Suunto has chosen to use in the Cobra along with the word ceiling. After the time ticked off I ascended to 15 feet for three more minutes per my computer. It does seem weird it would choose a 20 foot ceiling thinking back on it three and half years later. I had lots of air and was with a good group of divers along with a great DM from Aldora leading the group. Bruce

 

[PfcAJ]

So...would it be correct to say that a tec diver plans a deeper dive much more carefully, prints tables specific to the dive/gas profile, and uses the computer only as backup?

I don't use a computer. Never have. Its just not needed.

Personally, I print tables for a range of dives. For instance, I'm looking at a set of tables for a series of dives we friends and I were doing a few months ago. 180ft, bottom gas 18/45, with 35/25, 50%, and 100% for deco gases, and bottom times from 20mins up to 100mins in 10min increments. On the reverse, its the same table, but for for 190'avg depth. So for a range of about 160-210ft, I have 5 pieces of laminated paper in my wetnotes for the times around my planned bottom time (which was in the 50-70min range). I have a bunch of these for different gases, bottom times, and depths, and I just grab the range of tables for the dive I'll be doing and stick it in my wetnotes. If something is wonkey during the dive (deeper avg depth, for instance) I can just fli it over or flip to the right one. I augment that with ratio deco for short BTs and dives I'm real familiar with.