No Technical Training for Me.

[Soggy]

OK guys, educate me. I know 50% and O2 are common for deco, but my future tech instructor (likely this summer for advanced Nitrox and Deco Procedures), has told me there are time where he feels 80% is the way to go for the final 2 stops instead of O2. I believe he said it was times he felt the lower O2 clock loading was more valuable to him than the reduced deco time. Why is his choice of 80% indicating that he doesn't know what he was doing?

There are a number of reasons why 80% is a lousy choice. The biggest being that 80% is used "like" O2, except that it has N2 in it. N2 is what you are trying to get rid of. Additionally, it is used starting at 30 ft, which isn't even a PO2 of 1.6, so you aren't getting full benefit from the O2 window. At the 20ft and 10 ft stops on 80%, which is the most critical phase of the dive, the PO2 is roughly useless for decompression (1.2 and 1.0). On O2, the O2 window is always wide open regardless of depth since there is no inert gas.

Ask yourself...why do we breathe 100% O2 to treat a DCS hit?

There is no argument for using 80% that has any merit. It is an antique concept.

If he's afraid of the O2 clock, he should do backgas breaks every 12 minutes. Given the thousands of percents that WKPP divers have gone over the O2 clock, his argument has little merit.

50% is used as an intermediate deco gas as a way of getting on deco gas earlier in the ascent. Knowledgeable people tend to use 50% and extend the 70ft and 60ft stops where the O2 window is highest. This helps to get rid of helium earlier in the decompression, and starts the process earlier so that (among many other reasons), if you need to blow off or shorten your shallow stops, you are more likely to take a pain hit rather than a neuro hit. It is also used as a gas management tool...it lowers your rock bottom. In many cases, using 50% as a single deco gas is a better choice than 100%. It's always a better choice than 80% or 36%.

That being said, lots of people use 36% and 80% in the North East. We see it all the time. I don't get it.

 

[Jimmer]

Next stop; training dive for the two tech students and their instructor. Dive plan is 30 minutes at 160 feet on (air or 25% nitrox) and then deco with 80% for a total deco of around 34 minutes. One of the students is wearing double LP 95’s, steel backplate, and a 45? Cu-ft steel stage bottle. The diver is a 180 lb man of average build. He is wearing a 3 mm jumpsuit with no hood. Clearly his rig is extremely negative and I remind him to put a bunch of air in the BC before he gets in the water. He has apparently only used the double steels once in a pool on the previous day. This is some type of “extended range” course.

Wet-Willie, that's there my reference came from.

Jimmer

 

[Soggy]

Oh yeah, the other foolish part of this was that the instructor was willing to teach a class at 160' on air. Another antique of a dying age. Please don't walk, run from this instructor and find one who has a clue. The steel deco bottle is another bad sign. Oh yeah, the steel doubles with a wetsuit is foolish, also.

So far, I can't see anything good about this "class" (debacle). It's your life. Go get some instruction that will allow you to live it longer.

 

[Jimmer]

Soggy, thanks for the post. Your points definetly make a great deal of sense to me. I was told by this instructor that 50%, O2 was his "standard" deco mixes, but that he occasionally felt that 80% had merit. I will definetly bring that up with him and hear all sides of the argument and his reasoning for it. Thanks again for the input!

 

[Willie]

Dive plan is 30 minutes at 160 feet on (air or 25% nitrox) and then deco with 80% for a total deco of around 34 minutes. One of the students is wearing double LP 95’s, steel backplate, and a 45? Cu-ft steel stage bottle.

Right you are. Sounds like it would be an interesting profile to see.

Soggy, thanks for the thorough response on 80%.

Willie

 

[1_T_Submariner]

Wow...Good post and follow up posts.

 

[Rick Inman]

I have been told that some people prefer 80% at 20' to compensate for poor buoyancy skills.

Go figure...

 

[kidspot]

but if you have poor bouyancy skills ... what are doing on a deco dive to begin with??? (I know ... that was your point to begin with wasn't it? )

 

[grazie42]

There are so many things wrong there that you have to wonder who made him an instructor...Of course, it´s no reason not to get into technical diving in the same way as most ow-courses aren´t a reason to stop diving alltogether...

Originally Posted by Soggy
There is no argument for using 80% that has any merit. It is an antique concept.

Thank you for clearing that up!

80% is clearly on of those gasses that give divers bad bouyancy control...
The rest of your "reasons" are only valid if you accept the premises that they are built on which is fine if your way of diving sets those premises in stone, the rest of the world is a bit more flexible...

Anyway, it´s just a gas choice, get over yourselves...

 

[MikeFerrara]

In any case...the training the diver was getting doesn't appear to be very good but his performance would sure indicate the need for LOTS of training. I think it's a good example of what would happen to a lot of divers if they tried a free ascent and had to do a few other things like shooting a bag and gas switches or whatever. The correct solution to bad training would seem to be good training...not no training.

I'll say this. After some experience teaching entry level technical courses and assisting with a few technical classes, I didn't have any trouble deciding NOT to become a technical instructor. From what I saw of it, recreational training just doesn't do a good job of preparing divers to even start technical training. You almost have to start a lot of them over from OW skills, because they either learned everything wrong or not at all.