1.4 ....1.6...or ?????

[sphillips3]

Are you sure about that? I have not heard of any verified cases below 1.4. If you have any references I would like to see them.

There was a death earlier this year at Ginnie Springs with a reported max P02 of about 1.3. Several tech diving instructors I know are reducing the max PO2 for the working portion of the dive to about 1.2. I'm not an expert, but I have heard that the Global Underwater Explorers (GUE) folks are specifying standard mixes to hold max PO2 to something close to 1.2.

There is a tech diving board - the Deco Stop - where you can find extensive discussions on this issue.

 

[D_B]

my instructor has said the same thing to me sphillips3, about being more conservitive in the P02 levels that he is going to follow now

 

[Blowin' Bubbles]

1.6 is the Navy's limit, and 1.4 is the sport limit. Obviously they moved it to 1.4 for recreational diving for a reason. The Navy is a branch of the US military, as you all know, and therefore, they have an acceptable number of losses. For some people, there may not be much physical difference between 1.6 and 1.4 ata but for others, 1.6 is pushing it way too far. That is why they pushed the recreational limit up to 1.4, so there would be no losses. You should never go past 1.4 unless it is really absolutely necesary (i.e. you drop your camera on a 100 foot dive using 32% and you go down to 120 feet to retrieve it, then come right back up to 100 ft).

 

[redacted]

I still use 1.6 as my limit. My computer (Oceanic Data+) is pretty rough on anything over 1.4 so I don't spend too much of any dive over that. Also, I don't do anything very stressful over 1.4. Just hover and wait for the big guys to come by so work level is comparable to a deco stop.

I'll probably stop doing that when the CPSC has my computer recalled because of the built in 1.6 limit. I don't see that happening.

 

[String]

Im happy with 1.6 for deco (no effort hang). 1.4 for working part generally but i will break it briefly depending on conditions, CNS clock etc but generally im 1.4 dive, 1.6 deco.

 

[don Francisco]

There's some room for debate here. I consider 1.6ata the absolute limit for safe diving under normal conditions and 1.4ata as my max for planning and diving. This leaves the difference as a margin of error, and I wouldn't be overly concerned dropping into that range momentarily if I had a reason, and no other contra-indications.

Like NDLs, minimum air guidelines and other considerations, we set limits and back off to increase our safety margins. Nothing wrong with diving to the limits, but if you make a steady diet of it, eventually it'll catch up with you.

 

[Blackwood]

I thought the navy required that its divers be able to tolerate extended exposures at 2.0 (ie oxygen at 30). I could easily be wrong about that, but the point is that established maximums are conservative on average. The OPs dive buddies may very well be able to dive at 1.6 (which is within NOAA guidelines).

I wouldn't push it myself, but I also won't jump on these guys for doing so.

 

[Meng_Tze]

1.4 was a pull back for recreational diving to have a certain margin of safety. I am sure there are entities (read military or professional diving teams) that dive beyond that on a regular basis. They usually have support personnel, equipment and such to deal with issues.

The fact is that oxtox can hit anyone at any time when diving. You do not have to be deep, at a higher PO2. But when you do go to a higher PO2, the risk DOES increase. As a recreational diver you need to assess if the risk is worth it and if you can recover from a situation you knowingly put yourself in by increasing this risk.

I personally dive 1.3- 1.4 on normal dives. On more challenging (longer, deeper, higher flow etc) I drop this down to 1.0- 1.1, sometimes 0.9.

There is no heroism in diving a higher PO2 (1.6) for the main part, doesn't make you a better, more macho diver. It just tells me you are pushing the limits unnecessarily and people may have to rescue you butt.

 

[Damselfish]

it's difficult when a lot of places just pump 32, but it really makes sense to just pick a different mix in this case.

 

[John_B]

I have my Nitrox certification however dive air everywhere except places like Bonaire and liveaboards (assuming the staff deem it acceptable for the sites and conditions).

The staff? I decide this stuff for myself based on the site (depth) information available. I would never someone else make this kind of call for me.

1.6 is the Navy's limit, and 1.4 is the sport limit. Obviously they moved it to 1.4 for recreational diving for a reason. The Navy is a branch of the US military, as you all know, and therefore, they have an acceptable number of losses. For some people, there may not be much physical difference between 1.6 and 1.4 ata but for others, 1.6 is pushing it way too far. That is why they pushed the recreational limit up to 1.4, so there would be no losses. You should never go past 1.4 unless it is really absolutely necesary (i.e. you drop your camera on a 100 foot dive using 32% and you go down to 120 feet to retrieve it, then come right back up to 100 ft).

Who is the "they" in "they"? More to the point, is 120' on 32% your temporary limit for a dropped camera? What about 130'? 140'? How far would you push that for a camera? A video camera? A buddy?