Decompression Course

[DuboisP]

I guess things are different with other agencies, and other country's dive cultures. This post has a number of statements that are not in keeping with technical diving training as I understand it. Don't want to get into a flame war, but as others have pointed out, I don't think that the difference between recreational and technical diving is simply a quantitative difference but a qualitative difference with a different mindset.

Assuming that the "supervisor" (does this mean instructor or more advanced buddy?) will be monitoring the other diver's gas - as opposed to planning that all ahead of time and for each diver being responsible for monitoring their own gas supply - is dangerous even for a no-stop dive, let alone a dive that requires staged decompression.

With "just a few" [minutes] of decompression, what happens when the newer diver has a problem at depth and the instructor is not available? Since there is no option to ascend immediately, are they practiced at holding stops, and have those required stops somewhere written down?

If you are at the same level but one of you has a catastrophic gas loss due to an equipment failure, what's the plan then? With buddy? Without?

In my culture, "supervisor" can be an instructor, but i'm not. It's a sort of divemaster, a "super" divemaster.
A divemaster can lead up to 8 or more OWD/AOWD.
I'm limited to 4, but it's generally one or 2.
When i say "monitoring", i'm must be sure than supervised divers monitor their gas level and share the information. If they don't, i ask them, and i give mine.
As a supervisor, or in autonomy, we must be closed the buddy or the supervised diver. So, instructor "not available" is not an option (but Murphy's law ).
We don't deco with newer divers.
A true newer diver is not trained to deco, the depth is limited to 20 m. Generally, at beginning, the tank is empty before entering in deco.
A "Level 2" diver, supervised to 40 m, is not a newer diver, and can have at least 20 or 30 dives.

Catastrophic gas loss without buddy ? in that case, i dive with an isolated double, and a couple of pony (Eanx 40% or 50%, oxy). up to the Eanx MOD.
Catastrophic gas loss with a buddy ? manage.
But why a gas loss ? my hardware is good and redundant, i dive always with 2 regulators (mandatory, as a supervisor, but i did it before being one), so, in case of hose failure or freeze, i can close one. HP hose failure ? it takes some time to empty the tank. Wing failure ? up with the dry suit or the SMB.
OK, i have some technical knowledge.

 

[doctormike]

In my culture, "supervisor" can be an instructor, but i'm not. It's a sort of divemaster, a "super" divemaster.

Thanks for the reply... I think that some of the subtleties of this can be lost in translation, but I'm always interested in learning about different approaches to diving...

A divemaster can lead up to 8 or more OWD/AOWD.
I'm limited to 4, but it's generally one or 2.

So, are you a dive professional? Do you carry insurance? Do you get paid to do this, or is it just an informal buddy relationship?

As a supervisor, or in autonomy, we must be closed the buddy or the supervised diver. So, instructor "not available" is not an option (but Murphy's law ).

Don't know about that. Unless you are running an open water class, I would expect every diver to have a plan for what to do in case of separation. Maybe you have better vis there!

We don't deco with newer divers.
A true newer diver is not trained to deco, the depth is limited to 20 m. Generally, at beginning, the tank is empty before entering in deco.
A "Level 2" diver, supervised to 40 m, is not a newer diver, and can have at least 20 or 30 dives.

So you would do a deco dive to 40 m with a diver who had 20 dives? Since you aren't an instructor, and this wouldn't be in the context of a training dive, would you really take such a diver into deco simply because you are a DM equivalent?

In my experience, most tech instructors want you to have a very solid foundation before you get even close to real deco in open water. In addition to working on necessary skills, our course includes a long profile with simulated deco, so that you have the opportunity to follow runtime before you are subject to the danger of DCS from a failure to follow that plan.

Catastrophic gas loss without buddy ? in that case, i dive with an isolated double, and a couple of pony (Eanx 40% or 50%, oxy). up to the Eanx MOD.
Catastrophic gas loss with a buddy ? manage.
But why a gas loss ? my hardware is good and redundant, i dive always with 2 regulators (mandatory, as a supervisor, but i did it before being one), so, in case of hose failure or freeze, i can close one. HP hose failure ? it takes some time to empty the tank. Wing failure ? up with the dry suit or the SMB.
OK, i have some technical knowledge.

I guess I was more concerned about the gas loss in cases of a profile involving decompression stops, and having enough gas to finish the schedule.

 

[KenGordon]

On SB the culture seems to be that any deco dive is a technical dive. There are people and agencies that don't draw the line there in particular. In UK diving at places like Scapa or the English Channel there are recreational divers doing deco dives every weekend. Typically they will not be doing more that 10 minutes deco on a single, the more sensible will have an alternative supply but a pony doesn't shout 'technical' like a twinset. Part of the equation is to have a buddy within a reasonable distance. Here we are fortunate to have such poor viz that you can feel your buddy at all times.

You can find details on everyone who has died doing this in the BSAC incident reports.

Deco and planning is taught from the very first open water lesson, even if only to explain why it will not be a problem and how we know there is enough gas.

 

[doctormike]

On SB the culture seems to be that any deco dive is a technical dive. There are people and agencies that don't draw the line there in particular.

So what is your definition of a technical dive?

 

[DuboisP]

So what is your definition of a technical dive?

technical dive begins with advanced nitrox, when bringing a rich nitrox pony and switching to.
decompression is not technical, our drivers are trained to.
basic nitrox is not technical, our divers know decompression, know how to compute MOD and MIX.

 

[doctormike]

technical dive begins with advanced nitrox, when bringing a rich nitrox pony and switching to.
decompression is not technical, our drivers are trained to.
basic nitrox is not technical, our divers know decompression, know how to compute MOD and MIX.

So you define a technical dive as a dive involving accelerated deco with a deco bottle, but decompression on air doesn't count as technical?

 

[alewar]

The thing is that in CMAS divers are taught from day one to use a decompression table and do some gas planning instead of telling them to stay within NDL.

 

[DuboisP]

Thanks for the reply... I think that some of the subtleties of this can be lost in translation, but I'm always interested in learning about different approaches to diving...

So, are you a dive professional? Do you carry insurance? Do you get paid to do this, or is it just an informal buddy relationship?

Don't know about that. Unless you are running an open water class, I would expect every diver to have a plan for what to do in case of separation. Maybe you have better vis there!

So you would do a deco dive to 40 m with a diver who had 20 dives? Since you aren't an instructor, and this wouldn't be in the context of a training dive, would you really take such a diver into deco simply because you are a DM equivalent?

In my experience, most tech instructors want you to have a very solid foundation before you get even close to real deco in open water. In addition to working on necessary skills, our course includes a long profile with simulated deco, so that you have the opportunity to follow runtime before you are subject to the danger of DCS from a failure to follow that plan.

I guess I was more concerned about the gas loss in cases of a profile involving decompression stops, and having enough gas to finish the schedule.

French Underwater Federation associations are non-profit, and we're unpaid volunteers.
I give back what i received from other instructors/supervisors .

Divers are trained and informed to surface if they lost their buddies, respecting speed limit and doing their existing stops, if any.
We don't do decompression with Level 1.
I can supervise divers at 40m, but they're not beginners, they're Level 2 and know deco.
else they dive at 20 m in autonomy, with or without deco stops, else they dive at 40m supervised.
They can have 20 dives when beginning their Level 2 training, and often more than 40-50 when finishing.

Strictly speaking, I began my Level 2 with no dive, having my Level 1 (pool certification) since the University. So i did my first dives in pool (15m deep) to refresh, then fresh and salt water, and had 48 dives when Level 2 certified.

 

[doctormike]

The thing is that in CMAS divers are taught from day one to use a decompression table and do some gas planning instead of telling them to stay within NDL.

Hmmm... I see. Well, that might work, but I guess it would depend on how secure the CMAS new divers were in the water.

One of the reasons that I think that we don't put relatively new divers in overhead situations here is that for many reasons, new divers may panic, have equipment problems, have limited situational awareness leading to gas reserve issues, etc... So by never putting them in an overhead environment (physical or virtual), as long as they make a reasonably slow ascent they are unlikely to get into trouble with DCS.

I guess if the CMAS equivalent of open water diver involves much more training and weeds out people who aren't very comfortable in the water, that makes sense. Personally, that would worry me.

 

[DuboisP]

So you define a technical dive as a dive involving accelerated deco with a deco bottle, but decompression on air doesn't count as technical?

no, it doesn't count as technical.
it's a normal dive.
there is no magic to read a table or a computer to know how much remaining time before mandatory stops.

---------- Post added August 7th, 2014 at 09:54 PM ----------

Hmmm... I see. Well, that might work, but I guess it would depend on how secure the CMAS new divers were in the water.

One of the reasons that I think that we don't put relatively new divers in overhead situations here is that for many reasons, new divers may panic, have equipment problems, have limited situational awareness leading to gas reserve issues, etc... So by never putting them in an overhead environment (physical or virtual), as long as they make a reasonably slow ascent they are unlikely to get into trouble with DCS.

I guess if the CMAS equivalent of open water diver involves much more training and weeds out people who aren't very comfortable in the water, that makes sense. Personally, that would worry me.

of course, i agree.
be sure we don't put divers in situation they cannot manage