Max. depth on Air

[Beach Bum k10]

Doppler once bubbled...
Hi Dizzy:

I don't Dive Air... I use it to inflate my drysuit and the tires on my mountain bike.

I usually mix for a nitrogen load of 3.1 ata which brings things out to a little less than a EAD/END of 100 feet air... however, I also think oxygen should be included in the calculations and so add 1.4 ata (low exposure cold water dose) to the nitrogen load... which of course gives a total of 4.5 ata. That's a lineal depth of about 120 feet.

So I dive to about 120 on nitrox and use trimix after that.

WHY? Well, I can and it's easy. I feel better post-dive. I shoot better video. If the **** hits the fan, I feel better prepared to deal with it. Thermal narcosis is a factor in most of my diving.

Thanks Hope this answers your questions

You don't Dive air? Really? Then what's in your tank??!!

 

[Doppler]

Beach Bum k10 once bubbled...


You don't Dive air? Really? Then what's in your tank??!!

Probably only dive air once or twice a year -- average more than 140 dives per year -- the rest of the time, nitrox and trimix... yea, I know you have to put air in to top the tanks off!!!

 

[diverbrian]

I rarely use straight air as a breathing gas myself. I am not yet certified below 130 so my dives are all 130 ish or above.

These are my preferred mixes for this point in my diving career. Keep in mind that they may vary due to tank top-offs (sometimes a necessary evil):

110-130 EAN28
100-115 EAN32
100 or above EAN36

If I did dive much below 130, I would take a trimix course to learn to do it without the narcosis.

 

[DA Aquamaster]

Charlie99 once bubbled...
What article was this?

I was not able to find the article I more recently read that referenced the study, but that's ok the whole thing sounded very familiar. So I dug through some books and sure enough, I found a more original source of the study.

It was a 1965 study by Tom Mount and Dr. Gilbert Milner to determine the effects of anticipated behavior modeling in diving students with respect to narcosis. Three control groups of 4 student divers each were used in the study along with a group of 10 experienced deep divers who were tested concurrently with the students.

Group 1 was taught that a diver would get narcosis at 130 ft and that there was a very high probablility that symptoms would be severe.

Group 2 was taught about the existance of narcosis with symptoms normally occurring about 100 ft, but were not given an intimidating lecture or told that it was an insurmountable barrier.

Group 3 were given a full three hour lecture on narcosis on symptoms, risk factors, dangers, and known research. They were also told that dvers with strong will power could mentally prepare themselves and greatly reduce the effects.

Various baseline tests of mental acuity and dexterity were done an all groups at 50 ft. consiting of handwriting, peg bopard testing, math and other tests like placing a ball bearing in a long necked bottle. the test protocols were then modified to prevent the students from performing the tasks from memory during the actual testing at depth.

The initial test depth was at 130 ft and the Goup 1 divers had minor to above average narcosis symptoms while Groups 2 and 3 showed no significant effects on test performance.

At 180 ft, two Group 1 divers had severe narcosis symptoms and were removed from the study. All the Group 2 divers experienced about a 50% reduction in test performance and the Group 3 divers showed minor impairment based on overall test performance.

At 200 ft., All Group 1 divers were terminated from the study due to severe symptoms and two divers from Group 2 were dropped due to narcosis and apprehension. Group 3 divers actually showed a slight overall improvement in test scores.

At 240 ft, one diver from both Groups 2 and 3 were dropped from the study due to severe narcosis. The remaining Group 2 diver and the remaining three Group 3 divers showed some impairment overall but again the test scores showed overall improvement over the previous depth level. One female Group 3 diver showed her highest scores on all the tests at the 240 ft level.

As for the experienced deep divers, 7 of the 10 showed no decrease in test performance down to 200 ft and the remaining 3 finished the test (2 with perfect scores) but required adiditonal time to complete the tasks.

At 240 ft, 5 of the 10 performed all tests with no decrease in performance. One had problems with the ball bearing task but comleted all the other tasks successfully. Two other divers showed up to a 42% deficit and had problems comleting thew tests.

The conclusions were that performance at depth and tolerance to narcosis is subject to adaptation (the more you dive to depths the more likely you are to perform better) and that modeling is a key factor as most divers will experience what they expect to experience. So if you teach divers to expect to be debilitated by narcosis, they will be.

This was paraphrased from Bret Gilliam's 1995 revised edition of " Deep Diving. An advanced Guide to Physiology, Procedures and Systems". The conclusion at the end of the chapter is that diving as deep as deep as 200' on air is possible with experience, frequent exposure to deep diving and a high degree of training. But also that divers need to be cautious and prudent, obtain experience before attempting progressively deeper dives and should seek training under an experienced deep diving instructor before diving below sport diving limits.

I'd love to find the actual journal article and look at the methodolgy used and explore the reliability and validity of the study in more detail, but the results agree what I have found at depths down to 150 ft on air.

I doubt that I would want to do something extreme like dive the Andrea Doria on air, but then I also do not agree with the overly conservative views on depth limits with air either. I also do not agree with scaring students about diving below 60, 100 or 130 ft and about the effects of narcosis as a means of promoting saftey in the industry.

 

[JDostal]

Interesting article. I know similar studies have been done w/ alcohol as well - ie, giving people things that taste like alcohol, telling them it will get them messed up, and they get drunk even though there is no alcohol in their beverage.

 

[Charlie99]

diverbrian once bubbled...
These are my preferred mixes for this point in my diving career.....

100 or above EAN36

How long are you willing to breathe EAN36 at 100'?

If you use 36% at 100', why not 32% at 130'?

 

[Charlie99]

Thanks for the info DA Aquamaster. I was hoping for a more recent study.

It seems like human susceptibility to narcosis, particularly at 80-120' has dramatically increased over the last few years

 

[scubasean]

Charlie99 once bubbled...

It seems like human susceptibility to narcosis, particularly at 80-120' has dramatically increased over the last few years

Or maybe human susceptability to lawsuits has increased....

 

[diverbrian]

Charlie99 once bubbled...
How long are you willing to breathe EAN36 at 100'?

If you use 36% at 100', why not 32% at 130'?

The 95 to 100 ft range for me is a grey area. If most of the dive (ie. the Arabia) will be at 100', I will be using EAN32. If the sand is at 100' and the longest that I may be down there would be to recover a dive light IF DROPPED (ie. most shipwreck dives in the Great Lakes listed at 100'), I have no problem with using EAN36 and staying my usual 5ft or better off the bottom. Most of the wrecks that I dive at 130' are similar to the Forest City where they could actually get down to 150' and I may get to 134-135' on a "bounce". After that, we are talking emergency situation to go to the bottom.

My point was that I seldom dive STRAIGHT AIR. The exact mix that is used varies with my situation.

 

[captain]

Until I started reading this post I didn't realize how much the dive shops have brainwashed divers to make an extra buck.

Captain