why hasnt nitrox replaced compressed air completely?

[DaleC]

It's interesting to see different veins of thought in this thread. While some claim to use EAN to increase their safety (from DCS) others seem to use it to push the limits as far as they can.

Large tanks, long BT's, the most repetitive dives, foreshortened no fly times... Could the indiscriminate use of nitrox actually be encouraging a mindset that courts injury? Where does conservatism fit into all this.

 

[KeithG]

People who dive near limits regardles of gas of course wouldn't see any out of water benefits of Nitrox.

They will see less out of water time. That is often a benefit!

---------- Post added July 11th, 2014 at 02:22 AM ----------

It's interesting to see different veins of thought in this thread. While some claim to use EAN to increase their safety (from DCS) others seem to use it to push the limits as far as they can.

Large tanks, long BT's, the most repetitive dives, foreshortened no fly times... Could the indiscriminate use of nitrox actually be encouraging a mindset that courts injury? Where does conservatism fit into all this.

I disagree. I do not believe ean divers are any less conservative than air divers. Repetitive divers generally end up running into NDLs and no fly times. Regardless of their gas. The air divers just get less bottom time if the location is deep. In Bonaire I get just as much bottom time as ean divers. In Turks & Caicos my bottom time gets cut short compared to ean divers (except for the noobs that suck their tank dry).

All of the operators I currently use enforce a 24 hour no fly time based upon the assumption that you are a repetitive diver. The live aboards I use also enforce at least a 1 hour surface interval (generally longer, sometimes over 2 hours). So I believe there are operations out there that are attempting to keep us safe despite our best attempts at loading up on nitrogen.

Unfortunately the day boat operators I have used in the past routinely try to cram 2 one tank dives in each morning. This means short dives and short surface interval in order to be back to the dock for lunch. Divi in Bonaire does a 40 minute dive, 40 minute SI and 40 minute dive each morning. I no longer go out on the morning boat since 40 minute dives are just way too short...

 

[MXGratefulDiver]

Divi in Bonaire does a 40 minute dive, 40 minute SI and 40 minute dive each morning. I no longer go out on the morning boat since 40 minute dives are just way too short...

... that's actually just one dive, with a "half-time" ... I wouldn't even need to swap out my tank. Thanks for the heads-up, now I know who to avoid in Bonaire ...

... Bob (Grateful Diver)

 

[Lorenzoid]

. . .

AFAIK, DAN actually recommends 24 hours ... they specify the 12/18 hours as "minimums" ...

... Bob (Grateful Diver)

Has this information on DAN's web site been superseded? It's what I have been led to believe is DAN's present position on flying after diving:

What is Decompression: Flying after Diving ? Medical Dive Article ? DAN | Divers Alert Network

It says:

• For a single no-decompression dive, a minimum preflight surface interval of 12 hours is suggested.
• For multiple dives per day or multiple days of diving, a minimum preflight surface interval of 18 hours is suggested.
• For dives requiring decompression stops, there is little evidence on which to base a recommendation, and a preflight surface interval substantially longer than 18 hours appears prudent.

 

[redacted]

Not that I would trust it to make an early flight but most computers have "desat" time as well as a "No-fly" time. Using Nitrox makes the desat time much much shorter.

For people who live at altitude and dive at sea level(not at all uncommmon in Hawaii), there is no practical way to wait out a no-fly time to go back to altitude, so Nitrox makes a lot of sense because it minimizes nitrogen loading. Since most computers auto shut off unless they are dove to 3 m, it's not easy to do it properly*** and have the computer actually do the proper calculations.

Part of why my 'rule of thumb' is always load the minumum nitrogen on any dive if using Nitrox, which is different than a lot of people do.

(Personally, I never dive Nitrox (money), but I do use 100 o2 for deco/safety whenever possible. In many senses, the best of both worlds: no depth restrictions, and reduced Nitrogen loading.)


*** Can you set Shearwaters to not shut off and properly do these calculations for people living at altitude, and diving at sea level?

I do monitor my dsat status after my last dive as I approach flight time. Most of my computers are from the last century so info is quite limited. The 24 hour no-fly clock is a waste of battery power. I have only one (somewhat newer) computer that provides a dsat time but it is of no use in dive planning. I was hoping that more modern computers would provide a dsat time while in the dive planning mode that could be used to plan dives before flying. Right now, I do that planning based on experience. I know that when I dive fairly hard like on a Cozumel trip, I often still have some residual loading 24 hours after my last 2-tank dive. The load is less than 10% in the lead compartment which, since it is over 24 hours, must be acceptable. In Bonaire, where the profiles can be much shallower, that same computer usually drops the last remnant of N2 well before the 18 hour mark.

If computers provided dsat forecasts in the dive planning mode, that info could be used to plan the last dive so dsat is completed before scheduled flight times. User would have a basis for changing planned depths, time, or gas to control DCS risk during scheduled flights.

 

[MXGratefulDiver]

Has this information on DAN's web site been superseded? It's what I have been led to believe is DAN's present position on flying after diving:

What is Decompression: Flying after Diving ? Medical Dive Article ? DAN | Divers Alert Network

It says:

• For a single no-decompression dive, a minimum preflight surface interval of 12 hours is suggested.
• For multiple dives per day or multiple days of diving, a minimum preflight surface interval of 18 hours is suggested.
• For dives requiring decompression stops, there is little evidence on which to base a recommendation, and a preflight surface interval substantially longer than 18 hours appears prudent.

That says exactly what I said ... they specify 12 hours/18 hours as "minimums" ... if you read what you just posted you'll see that exact word is used.

The 24-hour interval is not a minimum ... it's a recommendation. It's been DAN's recommendation since before I was initially trained in 2001, and AFAIK it still is. That's why most dive operations around the world have been using it.

... Bob (Grateful Diver)

 

[dive_more]

i always dive nitrox, my dives are around 90-100 i have a 120cl tank (in Europe 15L) and on air it is quite common to touch de NDL, i even get close on nitrox,
i changed the dive shop, and in the new one they charge me the same for air as for nitrox, so i dive nitrox
It is really worth it (for me)

On Holiday the dives are shorter due air consumption of the "holiday divers"
but i also prefer nitrox here (I feel less tired making 2-3 dives a day)
some people call this "placebo" but i am happy with it

 

[Lorenzoid]

That says exactly what I said ... they specify 12 hours/18 hours as "minimums" ... if you read what you just posted you'll see that exact word is used.

The 24-hour interval is not a minimum ... it's a recommendation. It's been DAN's recommendation since before I was initially trained in 2001, and AFAIK it still is. That's why most dive operations around the world have been using it.

... Bob (Grateful Diver)

Bob, what I meant was I don't see where DAN "recommends" a 24-hour interval. The number "24" doesn't appear anywhere in what I quoted from their web site. That's why I asked if you got the "24" from some other DAN-related source than what I quoted from their web site.

 

[boulderjohn]

Bob, what I meant was I don't see where DAN "recommends" a 24-hour interval. The number "24" doesn't appear anywhere in what I quoted from their web site. That's why I asked if you got the "24" from some other DAN-related source than what I quoted from their web site.

There is no mention of a recommended 24 hour interval that I know of on the DAN site. I would love to see someone who thinks there is provide a link.

Here is my understanding of the history. I do not have a link for this understanding--I heard it in a presentation by a DAN employee.

Quite a few years ago, a couple of people got bent during a flight after they had been diving earlier in the day. I think they were pilots. Someone called DAN and asked how long someone should wait before flying. With nothing whatsoever to go on, Dr. Bennett said 24 hours. It was really just a guess, but it made them realize that study was needed. After a long study, they determined that for the kind of diving they describe, the current recommendations of 12 and 18 hour intervals would suffice. Most agencies adopted those recommendations and made them part of their OW instruction. It has been part of PADI instruction for as long as I know. Many people still remember that original 24 hour recommendation and repeat it, just as it was repeated in this thread. Those people will then tell others that DAN recommends 24 hours, which they know because they read it somewhere. The people they tell will in turn repeat it to others.

---------- Post added July 11th, 2014 at 09:40 AM ----------

Here is an addendum to what I just wrote...

I was recently on a liveaboard trip on the Great barrier Reef in Australia. On the last day of the dive, we were all assembled for the dive site briefing. By "all," I include the passengers and all the diving staff members, all of whom were PADI instructors. The crew member in charge of diving asked if anyone was going to be flying the next day, in which case they could not do any more diving because "PADI requires a 24 hour interval before flying." I didn't want to create a scene, so I went to him privately after that to ask about it. I said that PADI does not require 24 hours, and I said every member of the crew who heard him say that had to know it, because it is a question on the OW final exam, and they are required to go over any questions students miss. He admitted that he knew it was not a PADI policy--it was a company policy.

I had already noted that they had several other policies that were not normal and which made the diving more conservative than it would normally be. In each case, when they described the policies, they cited an authority like PADI or DAN as the reason for it. IMO, the reason was that they wanted to make absolutely certain that no one got bent on the trip and caused either the chaos of an evacuation or a lawsuit. Knowing people might rebel if they said it was a just company policy for their own benefit, they simply cited another authority, implying that they had no choice in the matter. That boat probably serves close to 2,000 divers a year, which means 2,000 divers a year hear the same misinformation.

 

[MXGratefulDiver]

Bob, what I meant was I don't see where DAN "recommends" a 24-hour interval. The number "24" doesn't appear anywhere in what I quoted from their web site. That's why I asked if you got the "24" from some other DAN-related source than what I quoted from their web site.

It's possible they've changed it. Some years back I took a bunch of DAN courses and was more conversant on their recommendations for quite a lot of things. I'll admit I haven't kept that knowledge current, and rarely go to the DAN website anymore.

... Bob (Grateful Diver)

---------- Post added July 11th, 2014 at 08:55 AM ----------

Here is my understanding of the history. I do not have a link for this understanding--I heard it in a presentation by a DAN employee.

Quite a few years ago, a couple of people got bent during a flight after they had been diving earlier in the day. I think they were pilots. Someone called DAN and asked how long someone should wait before flying. With nothing whatsoever to go on, Dr. Bennett said 24 hours. It was really just a guess, but it made them realize that study was needed. After a long study, they determined that for the kind of diving they describe, the current recommendations of 12 and 18 hour intervals would suffice. Most agencies adopted those recommendations and made them part of their OW instruction. It has been part of PADI instruction for as long as I know. Many people still remember that original 24 hour recommendation and repeat it, just as it was repeated in this thread. Those people will then tell others that DAN recommends 24 hours, which they know because they read it somewhere. The people they tell will in turn repeat it to others.

Not sure where that comes from John, but given the worldwide use of the 24-hour wait period I don't find the anecdote very plausible.

As I just said, back around 2005-2006 I took a bunch of DAN courses ... and at the time that was the recommendation I found in their literature. I could probably go dig that old literature out of a box somewhere (I don't teach those classes anymore, because there just wasn't much demand for most of them), but I'm willing to concede that the standard isn't any longer on their website.

Personally I've been using the 12/18 standard for several years ... but I chronically dive nitrox and that's been the nitrox standard for as long as I've been breathing the stuff. On dive trips, I go with whatever standard is imposed by the dive op. Their house, their rules ... like so many other things involving scuba.

... Bob (Grateful Diver)