Breathing air maximum terminal depth

[sipadiver]

Pardon me, but just out of morbid curiousity.

What is the maximum depth a diver can make while breathing air underwater before becoming crazy, unconscious and dying? What exactly happens physiologically when a diver descends too deep while breathing air?

I saw this infamous video on youtube of this diver who descended deep before he lost his mind. And all sorts of questions rose up.

 

[RainPilot]

This is a VERY involved and often controversial subject. The very short answer is:

As far as oxygen is concerned, it is generally recommended to not exceed a working partial pressure of oxygen of 1.4 bar. This will be reached at 56m depth.
The limit where it appears that it goes from "pretty safe" to "really unsafe" is at 1.6 bar which will be reached at 66m.
Exceeding these limits CAN lead to convulsions etc, bad news underwater. Google "oxygen toxicity" for more info.

The other element is nitrogen, this is a narcotic with increasing depth. Generally it is felt that the effects become noticeable deeper than 30m, deep divers will substitute helium for nitrogen in order to reduce this effect. The gas is then known as trimix (oxygen, helium, nitrogen)
Google "nitrogen narcosis" for more info.

All of these numbers are VERY flexible depending on personal tolerances and physiology.

And for the record, DO NOT attempt to breathe ANY gas underwater without the appropriate training, getting this stuff wrong WILL kill you.

 

[Vicko]

I know people who work at 100+ meters on air, hunting for red coral, they have ALL taken heavy DCS hits and most have serious health problem (brittle bones, brain damage, tinitus, partial paralization)
Most of them dive with a Suunto D4 or mosqito for their decompressions.
EDIT: Also a lot of the sponge divers I know dive 70+ every day during the summer season, a lot of DCS hits.
Obviously some people can adapt to a lot more O2 then the safery margin is.

 

[tursiops]

Some argue the PPO2 1.4-1.6 limit for air needs to be adjusted to account for the narcotic effect of the N2. The argument is that O2 convulsions are inhibited by the N2 effects. Thus, they say, you can go deeper on air (21/0/79) than you can go on heliox or trimix with the same O2 content, for example 21/50/29. I have no idea if any research has been done on this.

 

[JohnnyC]

Regardless of whether or not the recommended PO2 limit of 1.6 should be reevaluated within the scope of any set of variables, what's the point? Risk increases as depth increases, there are viable tools to mitigate that risk. To ignore those tools is silly.

 

[RyanT]

What @RainPilot said.

 

[wedivebc]

I was reading an old Aquacorps magazine the other day and was looking at the Hall Watts 40 Fathom Grotto advertisement for his deep air diver course. Level 7 was to 300ft. I may have taken that course but can't be sure

 

[Kevrumbo]

Pardon me, but just out of morbid curiousity.

What is the maximum depth a diver can make while breathing air underwater before becoming crazy, unconscious and dying? What exactly happens physiologically when a diver descends too deep while breathing air?

I saw this infamous video on youtube of this diver who descended deep before he lost his mind. And all sorts of questions rose up.

This is an interesting, informative and cautionary lecture by @Dr Simon Mitchell , about the deleterious effects of Work-of Breathing a dense gas like Air at deep depth, and even at extreme depth on Trimix -he explains the pathophysiology of the vicious cycle of CO2 retention/poisoning combined with negative static Lung loads, resulting in Dynamic Airway Compression & Collapse, spiraling into acute Hypercapnia and then unconsciousness and finally death (i.e. David Shaw Accident):

 

[Akimbo]

I was reading an old Aquacorps magazine the other day and was looking at the Hall Watts 40 Fathom Grotto advertisement for his deep air diver course. Level 7 was to 300ft. ...

Qualification dives for US Navy First Class divers in the 1970s included dry chamber and wet-pot dives to 285' on air. Keep in mind that 2.0 was the PPO2 limit then.

Just a reminder, 1.4 and 1.6 is a dumbed-down version of the current rule that includes a wide safety margin. Time is also a component when you really drill down. See:

Oxygen Toxicity Limits & Symptoms

How did old-school deep air divers avoid ox tox hits?

What is the deepest you have been on pure O2?

Edit: Typo: changed "UN" to "US"

 

[Storker]

One thing which usually isn't considered is gas density. After reading @Dr Simon Mitchell 's thread on gas density, I started doing some calculations. It turned out that maximum recommended gas densities are reached at roughly the same depths where an equivalent air depth of 30m is reached. So, it's not just the narcosis, but also the WOB and CO2 ventilation that is affected by depth.

The numbers I got from that exercise cemented my personal choice of staying shallower than ~30m/100' unless I have a bit of helium in my gas. Which I'm not certified for, but that's different topic.