Light back gas deco

[Blackcrusader]

Good to know.
On the west side of the pond you talked about, they say it's taboo which I think is not right. All dives are decompression dives physiologically as you know. The only difference is if there is a physiologic barrier (mandatory stop) to the surface.

One of the problems is recreational instructors for agencies like PADI or SSI teaching people never to do into deco instead of explaining to do deco dives you need the proper training. Yes many diver centers are PADI 5 star but why tell people deco is dangerous death to all non trained deco divers. I did BSAC Sports Diving which are all deco planned dives on air.

There is nothing fancy about deco when people are trained and plan for deco dives. When I dive at a place that says we do not accept divers doing deco dives on our NDL dives that's fine as they do not provide a DM for deco dives. If I am a private dive with others then we can do as we please.

 

[barth]

One of the problems is recreational instructors for agencies like PADI or SSI teaching people never to do into deco instead of explaining to do deco dives you need the proper training. Yes many diver centers are PADI 5 star but why tell people deco is dangerous death to all non trained deco divers. I did BSAC Sports Diving which are all deco planned dives on air.

There is nothing fancy about deco when people are trained and plan for deco dives. When I dive at a place that says we do not accept divers doing deco dives on our NDL dives that's fine as they do not provide a DM for deco dives. If I am a private dive with others then we can do as we please.

Doing a dive as deco dive with air doesn’t make sense when you could probably do the same dive with nitrox without deco.

CMAS divers are doing deco training in a local lake with max depth 80 feet with air as backgas in a single tank and even ean50 as deco gas. They switch to ean50 at 20 feet because they think that depth is safe enough for them.

I do the same dive with doubles and ean32 without deco.

Doing deco dives with air as backgas and deco gas doesn’t make sense for me. You can probably do that dive without deco when using the right gas.

 

[KenGordon]

Doing a dive as deco dive with air doesn’t make sense when you could probably do the same dive with nitrox without deco.

CMAS divers are doing deco training in a local lake with max depth 80 feet with air as backgas in a single tank and even ean50 as deco gas. They switch to ean50 at 20 feet because they think that depth is safe enough for them.

I do the same dive with doubles and ean32 without deco.

Doing deco dives with air as backgas and deco gas doesn’t make sense for me. You can probably do that dive without deco when using the right gas.

Since Blackcrusader was trained Nitrox has become part of the Sports Diver syllabus and an obvious choice if available. A twinset of 32% is an excellent choice for a great deal of diving, however the same issues still arise, just with longer dives.

 

[Blackcrusader]

Since Blackcrusader was trained Nitrox has become part of the Sports Diver syllabus and an obvious choice if available. A twinset of 32% is an excellent choice for a great deal of diving, however the same issues still arise, just with longer dives.

Yeah we didn't have nitrox when I did my BSAC courses in 1986 1987. Have done nitrox since then may add the TDI Advanced Nitrox later when I can do another long dive vacation. Deco is deco nitrox or air it's gas planning. I could plan a 30m dive on 32% Nitrox with a planned bottom time of 40 minutes and use a single tank with my regular dive buddy on same size tank I would use an AL 100. By the time we got to DECO if conditions changed we could abandon the deco part of the dive. As deco for this dive is done at the safety stop depth then not having enough air even if an incident after entering deco time for two would still be sufficient. Let's allow 3 minutes to get from 30m to 5m and max 15 mins deco time if 40 mins at 30m depth. We could bring a small pony as well.

I am wondering how much deco time and at what depth is counted for "light back gas deco? Lets say you plan a 20m dive for 70 minutes on Nitrox 32%. The issue is I know many divers would not make the 70 minutes to exceed NDL as they would be either too low on air or out of air already on a single tank.

 

[KenGordon]

I am wondering how much deco time and at what depth is counted for "light back gas deco? Lets say you plan a 20m dive for 70 minutes on Nitrox 32%. The issue is I know many divers would not make the 70 minutes to exceed NDL as they would be either too low on air or out of air already on a single tank.

Indeed, gas becomes the limiting factor and a single isn’t enough. But the aim is to do the dive, not to do deco, deco is the answer if a richer mix is not practical due to availability or depth. Also, with more than one dive a day you have to consider surface intervals etc so deco might be the necessary, especially with reverse profiles.

 

[Diving Dubai]

I did BSAC Sports Diving which are all deco planned dives on air.

A couple of points to be made here for clarity.

Under BSAC (and I belive CMAS) only backgas Deco is taught in the core curriculum 1 Star Ocean Diver, 2 Star Sports Diver, 3 Star Dive Leader?) Accelerated Deco using Higher % of O2 is a separate course.

It's important to distinguish between the two, given backgas is just for short periods and not for extended Deco diving

One of the problems is recreational instructors for agencies like PADI or SSI teaching people never to do into deco instead of explaining to do deco dives you need the proper training. Yes many diver centers are PADI 5 star but why tell people deco is dangerous death to all non trained deco divers.

Firstly you must understand the different training philosophies, under BSAC and CMAS you're more likely to be in a club where you have a lot more time dedicated to training and the cost of instruction is more easily amortized

With the commercial organisations they've aimed their "bite size" courses at the vast majority of divers who's access to diving is generally only on vacation and therefore is time limited, if for instance club divers had to pay the commercial rate for instruction the courses would either become very expensive or the amount of practice before cert would be reduced.


The issue we have in the commercial (PADI, SSI etc) world is highlighted here

On the west side of the pond you talked about, they say it's taboo which I think is not right

Currently Deco is surrounded by many myths and legends, perpetuated by those with no knowledge. (just look as some posts on SB)

Unfortunately you can become an instructor without ever having any deco experience. In "my world" Intro to Tech (what ever flavour that agency calls it) would be a requirement prior to entering a Pro level

I would dispense with Deep Diver (PADI) and put a hard Rec limit of 30m which is sufficient for most then for 40m I'd introduce basic Tech with appropriate gas planning and techniques etc etc

My wife has absolutely zero interest in Tech (she has ADD and gets bored easily - a Deco hang his her idea of hell). I made her take Tech 40. She still doesn't carry out any deco backgas or otherwise, but was amazed at how much more she learnt which gave her more tools for her Rec diving. She no longer sees Deco as a hard line to be avoided but something she could choose to do if the situation required it.

I believe the intro to tech course should be in the core curriculum of every agency, being a gateway course prior to Pro level teaching backgas deco and formally introducing redundancy before you get to the next step of introducing higher % gas for accelerated Deco

 

[Angelo Farina]

Doing a dive as deco dive with air doesn’t make sense when you could probably do the same dive with nitrox without deco.

Sure, if the depth allows for Nitrox. Here in the Mediterranean sea the nice dives are at depths ranging 40 to 60 meters, and so there is little space for Nitrox as the main gas.
Of course you can carry a deco tank filled with 50% Nitrox, to be used for shortening the deco time. But these deep and short dives usually require a short deco time already, also if breathing air, so carrying an additional tank for shortening the deco time of just 4-5 minutes makes no sense.
Furthermore, a dive when you change gas mixture for deco is already beyond recreational limits, requires a "tech" computer, and additional training which is not usually provided in basic recreational courses here.
So, for the typical rec dive we are certified for (50 meters in air with deco), I see very little possibility of using Nitrox.

Furthermore, for these deep and short dives, usually the amount of gas is not the limiting factor, and the standard tank used here (15 liters, 232 bars) suffices for both the dive and the deco.
Such tank contains 3480liters of air (123 CuFt). Let's consider a prudential SAC of 20 liters/min.
Consider a typical dive profile of 20 min at 48m, which requires 5.8x20x20=2320 liters.
In reality something less, as the dive time includes the time for coming up from 48m to 6m (something as 4 minutes, as the standard ascent speed is 10m/min), during these 4 minutes the average depth is shallower than 48m. But we keep 2320 liters for the dive, and you need to add something as 380 liters for the deco (3 min at 6m plus 11 min at 3m, according to old US Navy tables). So in total you require 2700 liters, which is around 78% of your tank capacity, you still have 22% as reserve. Not much (the recommended minimum is 25%), but plenty feasible.
In reality the SAC is usually smaller than 20 liters/minute (13, in my case), so you can see how these deep dives with deco in air are perfectly feasible with a single tank of standard size.
A twin tank is better, of course, but not strictly mandatory.

 

[Celt]

Yes you can shorten or eliminate deco stops using oxygen but air is available 100% of the time, you can pump it and it’s free. It’s simple and it works.

 

[Angelo Farina]

Yes you can shorten or eliminate deco stops using oxygen but air is available 100% of the time, you can pump it and it’s free. It’s simple and it works.

You cannot eliminate a deco obligation using oxygen, as if there is no deco stop, you breath oxygen for zero time!
You can somewhat shorten deco stops using oxygen, if you thrust those theories which are behind accelerated deco.
I have always been quite dubious of these theories, so if I have oxygen or high Nitrox available, I am very happy breathing it during the deco stops, but I simply consider it as an added safety, and I DO NOT shorten my deco times.

 

[Celt]

You cannot eliminate a deco obligation using oxygen, as if there is no deco stop,

What I mean is by using nitrox you may eliminate a stop if you had used air for the same bottom time.