Deep Diving 108 feet w/ a single AL 80 (Air.) No redundancy.

[chillyinCanada]

I've done a number of dives to 130' with an AL80. 8 minutes at depth and return to 20' for 20 minutes, still come out of the water with at least 500 psi.

 

[J-Vo]

3rds is sometimes way too conservative, at other times not conservative enough.

Min gas. The only sensible standard. Do the math and compare the two.

Agreed, min gas is the proper way to plan for any open water dive, deco or no deco.

 

[Bob DBF]

John Denver couldn't access his reserve either
probably thought he could, like a buddy diver

Proving that a CESA is much safer than an emergency open ocean landing.

Or perhaps, a reminder to be careful with used homemade equipment.

 

[Ayisha]

Are we answering the OP's question based on the specific site/conditions which he outlined and OTF elaborated on in regard to potential hazards or are we answering just based on a typical 108' dive?

It seems there are both varieties of answers...

 

[Storker]

Are we answering the OP's question based on the specific site/conditions which he outlined and OTF elaborated on in regard to potential hazards or are we answering just based on a typical 108' dive?

It seems there are both varieties of answers...

Well. I took the OP as a question of whether diving to 108' (33m) carrying only a single Al80 (11L 207 bar) is insane. It might be, if people dive like he describes his fellow divers at that particular dive ("Divers would come back on board with extremely low pressure readings on their gauges"), or it might not be if people follow proper min gas calculations and watch their gas.

On the other hand, coming back on the boat with little gas left in the tank might not be insane at all. Watch your SPG, follow min gas calculations and breathe down the tank in the shallows before surfacing. As a bonus, you get an extended safety stop or even a good, long deco stop. If my last 50-ish bar are spent at 5m or shallower (and the surface conditions are benign), I don't think surfacing with some 20-30 bar (300-400 psi) left in the tank is particularly reckless. Even if the tank is a puny 11L.

The only correct answer to almost any question is "it depends..."

 

[Storker]

Agreed, min gas is the proper way to plan for any open water dive, deco or no deco.

Why only open water? AFAIU, min gas should work for any kind of dive. It just depends on the margins you require.

Thirds is inflexible and doesn't take the depth profile into account. To me, min gas should be way superior to thirds as long as you have an inkling of your expected depth profile and your required reserves.

 

[Jack Hammer]

Thirds is a basic guideline as a starting point for gas needed in reserve for penetration dives and really doesn't apply to this thread. Minimum gas/Rock bottom applies to OW diving. Lotsa folks don't understand Minimum gas/Rock bottom and tragically could care less. It is a simple concept in understanding gas management.

What defines how much reserve is required is debatable and in the real world is going to vary quite a bit between different divers, different conditions, risk assessments, etc.

 

[GrumpyOldGuy]

Personally I don't go over 100' anymore, just me and knowing my comfort zone. I have done more than 100 on a single 80 and have a very low SAC, its definitely a gray area. If there are cameras, hunting or low vis involved I know I am less than perfect monitoring time / gas and would not. Planned gas reserves are wonderful, but the idiot diving the plan can always manage to screw it up.

 

[Ayisha]

Why only open water? AFAIU, min gas should work for any kind of dive. It just depends on the margins you require.

Thirds is inflexible and doesn't take the depth profile into account. To me, min gas should be way superior to thirds as long as you have an inkling of your expected depth profile and your required reserves.

Are you just using GUE Minimum Gas by itself or using it within a GUE Minimum Deco (now called Pragmatic Minimum Deco) profile?

Minimum Gas by itself is just "all usable", "half usable" or "1/3 usable". That MG calculation is intended to be put into a PMD calculation and profile.

I used to use the old rock bottom back in the day as well, and liked it.

 

[boulderjohn]

Does PADI or the other training agencies define the minimum tank size for a 100 plus foot dive? If not, then calling the practice (of using an 80) "insane" seems a little "dramatic" to me.

I wonder how many divers go to 100 feet with an AL 80 in Cozumel on an average day. 100? 200? I can't even guess.

I wonder how many dive sites around the world offer similar diving experiences every day. I can't even guess.

I wonder how many thousands of divers around the world go to 100 feet with an AL 80 every day. I can't even guess.

I wonder how many fatalities have occurred on an annual basis on such dives, for whatever reason. On this, I can provide a reasonable guess because of a past history of reading the DAN fatality reports. I would guess it is only a handful.

Is it a good idea to do so? That is a matter of opinion. Is it "insane" to do so? Well that is also a matter of opinion, but you will have a hard time convincing me that it is "insane."