What is SSI's "Decompression Diver" course?

[steinbil]

Now can I plan a dive with a buddy on Nitrox 32% to 30 metres and factor in 10 minutes of deco time allow for my deco stop and still do that on a single AL 100 tank. Yes. Do I need to have a blackplate wing and long hose setup? No.

Would you mind showing the calculation of that plan? I'm interested to see how much buffer you would plan for a buddy in case of an OOG emergency with a deco obligation.

 

[Twiny]

Hi,
Some here have said that deco dive with a Rec profile is common/possible in Europe. And it is true : a CMAS level 3 diver (without advanced nitrox certification), in France for instance, is allowed to dive up to a depth of 60m but is only allowed to do his (unlimited) deco on air !
However, SSI with its recent "Decompression Diver Course" does not give more flexibility than the PADI/DSAT training program : the level Tec40 has always been possible with a Rec profile/equipment at the condition that the students does not exceed at any time the MOD of their deco gas of course. But it is just to allow a diver to have a first feel of Tec diving without having to master a sidemount/twinset configuration. Just an introduction, then SSI courses like courses of all others training organisations require a sidemount or twinset configuration with bottom gas redundancy and proper deco.
BTW, very recently, UTD has launched a new course to allow Rec divers (no stop dives) to use pure oxygen during their safety stop for increased safety. IMHO, that's the real beneficial innovation.

 

[Wibble]

Now can I plan a dive with a buddy on Nitrox 32% to 30 metres and factor in 10 minutes of deco time allow for my deco stop and still do that on a single AL 100 tank. Yes. Do I need to have a blackplate wing and long hose setup? No.

Quick calculation of gas required for this dive: 30m/100ft using 32% and 10 minutes of deco.

For simplicity, will use "ATA/mins" meaning the number of minutes x number of ATA. This is then simply multiplied by your SAC/RMV in litres to calculate your volume of gas required. Will also simplify numbers and depths, e.g. deco at 10m/33ft instead of 6m/20ft.

The dive consists of:

• 32% NDL is 30mins at 30m/100ft/4ATA. This is 30 x 4 = 120 ATA/mins
• 10 mins extra dive time (meaning roughly 10 mins of deco) = 10 x 4 = 40 ATA/mins
• Ascent to 10m/33ft for deco = 4 mins (at 5m/16ft per min), average is 20m/66ft/3ATA = 4mins x 3ata = 12ATA/min
• 10mins of deco at 10m/33ft/2ATA = 10 mins x 2ATA = 20ATA/min
• 2 mins ascent to surface = 2 x 2ATA = 4ATA/min

Total = 120+40+12+20+4 = 196, call it 200 ATA/mins

Now adjust this for your SAC/RMV. My working SAC is 15 litres/min. Will use this to illustrate how much I'd need, although for planning I'd always use a higher rate in case of stress, say 20 or 25 litres/min.

200ATA minutes x 15 litres/min = 3000 litres/107cf of gas consumed during dive.

Gas content of an ali80 is 11 (wet) litres x 200 bar = 2200 litres.
Oops, I seem to have drowned on the bottom.

But you said you'd use an ali100 tank. 1cf = 28 litres, so 100cf x 28(litres) = 2800 litres
Oops, you also drowned on deco.

Nobody would ever dive with the intention of returning with an empty cylinder. Also, you have no straight exit to the surface, so you must bring some redundancy. A single tank doesn't have this.

If you need 3000 litres, you MUST BRING AT LEAST 4000 litres.

You should have some backup gas in the form of a slung "pony" or stage cylinder such as an ali40 IN ADDITION to the 4000 litres.

Curious; have you done the planning arithmetic for the dive you've outlined above? If so, what volume of gas did you calculate you'd need?

To bring the thread to the title: "What is SSI's Decompression Diver course"... its working out the volumes of gas you'd need and how to have backup gas.

 

[inquis]

UTD has launched a new course to allow Rec divers (no stop dives) to use pure oxygen during their safety stop for increased safety. IMHO, that's the real beneficial innovation.

Why do you feel it's beneficial? It provides practically zero gain as a safety stop. (IIRC from a previous thread, use of O2 on a safety stop adds one minute to the NDL for a follow on 60 ft dive.)

 

[Wibble]

Why do you feel it's beneficial? It provides practically zero gain as a safety stop. (IIRC from a previous thread, use of O2 on a safety stop adds one minute to the NDL for a follow on 60 ft dive.)

UTD do seem to talk utter nonsense about NDL diving. Their podcasts were pushing that nitrox was of no use as you could just use 100% for deco.

As most people know, 100% is dangerous, hard to get full fills unless there's a booster available, isn't available on most recreational trips, and many NDL dive operators won't allow deco.

 

[Twiny]

Why do you feel it's beneficial? It provides practically zero gain as a safety stop. (IIRC from a previous thread, use of O2 on a safety stop adds one minute to the NDL for a follow on 60 ft dive.)

To drastically reduce the number of bubbles, to feel fresh after repetitive dives that might follow the NDL most of the time and to diminish the chance to finish in a hyperbaric chamber due to an "unexplained decompression accident".
That's something I would definitely do if on a liveaboard for long.
Anyway most of my dives are deco dives ...

 

[Fishdip]

I

To drastically reduce the number of bubbles, to feel fresh after repetitive dives that might follow the NDL most of the time and to diminish the chance to finish in a hyperbaric chamber due to an "unexplained decompression accident".
That's something I would definitely do if on a liveaboard for long.
Anyway most of my dives are deco dives ...

Then why not just do it on the boat?

 

[Gandalf-the-Diver]

let's not drink so much of that Kool-Aid

I find this to be an interesting thread. As someone who can't do doubles, I do chase my NDL on occasion; with a single tank on my Hydros Pro. I also sling a 30cu pony, but that is strictly my get out of tank. I have also slung a 2nd pony on occasion, when I wanted more gas to extend a dive. The 2nd pony, could easily be a deco bottle. I have been slinging a pony, since my 1st dive after my OW, almost 370 dives in just over 3 yrs, and Solo cert. I would not mind doing a little bit of deco, now and then.

 

[Wibble]

To drastically reduce the number of bubbles, to feel fresh after repetitive dives that might follow the NDL most of the time and to diminish the chance to finish in a hyperbaric chamber due to an "unexplained decompression accident".
That's something I would definitely do if on a liveaboard for long.
Anyway most of my dives are deco dives ...

That’s voodoo nonsense, as is their "O2 Cleanup Course".

O2 Clean Up
The purpose of the Oxygen Clean Up course is to provide experienced recreational divers with the ability to switch to an O2 deco bottle at 20ft/6m to assist with off gassing from a recreational dive. This class is NOT a decompression class and is not designed to give divers access to run times longer than no-decompression limits, but rather to acquire the skills, knowledge, and experience to safely switch to an oxygen bottle at the end of a recreational dive.
The goals of the Oxygen Clean Up Class are to:

• To develop the students’ practical knowledge and understanding of the use and management of a single O2 bottle.
• To develop the students’ understanding of the risks associated with diving with an O2 bottle.
• To enable the student to switch to an O2 bottle for one 10-minute oxygen cycle at 20ft/6m.

This description says that the oxygen is not for decompression nor extending a dive. Basically it’s just for stage handling practice.

How many recreational live aboard vessels have 100% available? How many would allow a recreational diver to use such a dangerous gas in the water? How many would allow people to arbitrarily extend their dive duration by 10 minutes just for in-water therapy? How many "unexplained decompression incidents" happen if people are following best practices?

How many live aboard boats would accept/recognise a UTD recreational diver who’s not qualified for decompression diving but presenting this specialty course certification?

Most live aboards would supply nitrox. If you’re worried about NDL repetitive diving, then reduce your GF-hi or take a day off mid week.

 

[Gandalf-the-Diver]

As discussed, that would work if it has the same gas as your back gas and allows you the option of switching wherever a catastrophic gas failure happens. If you are carrying a higher nitrox mix for decompression then the MOD of that may not match your back gas. This will prevent you from switching on certain profiles.

... two ponies then .... one for deco, the other a redundant air source, bailout bottle if you will.