Reasons NOT to use Enriched Air?

[Web Monkey]

Moderator Note:

I've deleted several posts.

The "warm and fuzzy" factor seems to be missing and things have been getting a little heated in here.

Please re-read the special forum rules.

Terry Carmen, Moderator.

---------------------------

Basic Scuba Discussions Have a Scuba related question? Get a Scuba related answer here.
Please note: this forum has special rules. This forum is intended to be a very friendly, "flame free zone" where divers of any skill level may ask questions about basic scuba topics without fear of being accosted. Please show respect and courtesy at all times. Remember that the inquirer is looking for answers that they can understand. This is a learning zone and consequently, any off-topic or overly harsh responses will be removed.

 

[Thalassamania]

Don't thank me, thank Harris ... he's one of the best, and the DSO at Univ. of Michigan to boot.

 

[dumpsterDiver]

....True of all breathing media including air.

Not really, air is safer than nitrox in this regard because it is MUCH more forgiving of exceedance of planned maximum depth (at least for recreational dive limits). A diver planning a max depth of 90 feet using 36% on a wall dive could easily get in trouble, but would have to accidentally drop to well below 200 feet (on air) before a similar level of oxygen toxicity danger is realized. To me, this is a very real benefit of air over nitrox in certain conditions...

 

[John_B]

Not really, air is safer than nitrox in this regard because it is MUCH more forgiving of exceedance of planned maximum depth (at least for recreational dive limits). A diver planning a max depth of 90 feet using 36% on a wall dive could easily get in trouble, but would have to accidentally drop to well below 200 feet (on air) before a similar level of oxygen toxicity danger is realized. To me, this is a very real benefit of air over nitrox in certain conditions...

If you can't control your depth, then you can't control your depth. That's the same problem at 90' as it is at 200'. I would agree that person probably shouldn't dive nitrox.

 

[dumpsterDiver]

Far enough fetched to garner a Darwin Award for those that can manage it.

Maybe it is far fetched, but some tourists rent nitrox tanks that they DO NOT personally check the mix. Also, some people have died because they assumed a "fresh tank" was full. It is also not inconceivable for a partial pressure filled tank to NOT get the air added to it, simply because somebody forgot to open a valve. I mix my own at the dive shop and I myself have accidentally failed to add air and did not realize the mistake until I checked the mix.... In any regard, I stand by my comment that it is extra important that nitrox divers make sure their tank is full. This is a slight danger generated soley from the use of nitrox... THAt was related closely to the OP's question (I thought)

 

[dumpsterDiver]

If you can't control your depth, then you can't control your depth.

That is a ridiculous comment. Many experienced and qualified divers have lost control of depth due to gear failure, down currents, the need to rescue someone who fell off the edge of a wall...etc. etc.. The relatively smaller margin of error with respect to Oxygen toxicity of nitrox is a concern.

I personally do not like to dive nitrox in a location where I can exceed the MOD. I do sometimes, but it makes for a more complicated dive.

 

[John_B]

That is a ridiculous comment.

No its not. If you can't control your depth, you probably shouldn't dive over 4000' deep walls.

Since this is the new Basic Scuba Discussion forum, that's probably good advice anyway. Even at 200', the new diver is probably going run out of air in an AL80, long before they do the chicken dance.

Better to practice buoyancy control over a 40' sandy bottom until its under control before venturing out to the depths of a wall like that.

 

[dumpsterDiver]

No its not. If you can't control your depth, you probably shouldn't dive over 4000' deep walls.

Since this is the new Basic Scuba Discussion forum, that's probably good advice anyway. Even at 200', the new diver is probably going run out of air in an AL80, long before they do the chicken dance.

.

So if I see someone fall off a wall while working as a divemaster (breathing 36%) I can just shoot down and grab them at 200 ft and as long as I don't run out of gas I will be fine?

So how long will a diver last at 200 ft on 36% while working hard? Do you have any data on the onset of a seizure or are you making it up?

 

[Thalassamania]

2.54 ATA is a bit severe (200 on 36%) but it's still almost half an ATA under the oxygen tolerance tests we used to take (60 on 100%). I'd last more than long enough to grab someone and bring them up.

 

[John_B]

So if I see someone fall off a wall while working as a divemaster (breathing 36%) I can just shoot down and grab them at 200 ft and as long as I don't run out of gas I will be fine?

So how long will a diver last at 200 ft on 36% while working hard? Do you have any data on the onset of a seizure or are you making it up?

You are making up scenarios for DMs. Remember, this is the "Basic Scuba" forum. Your DM scenario belongs over in the "Instructor" forum.

A new-ish diver who doesn't have a hard floor and can't manage their buoyancy not only shouldn't dive nitrox where they might accidentally find themselves at 200', they probably shouldn't dive air where they might accidentally find themselves at 200'. What should we estimate a new-ish diver's SAC rate should be (for that circumstance)? 2.0?