Dedicated Nitrox equipment

[del_mo]

While studying for SSI Nitrox, the manual mentions time and time again about having a seperate air system for Nitrox. I was wondering how many divers actually have purchased a new air delivery system just for Nitrox. I know if I just happened to have a spare system (which I don't) that could easily become dedicated.

Also, it was mentioned that "many" divers use Nitrox on either their first or second dive of the day. Is this to save a couple of bucks?

 

[The Kraken]

Del,
The reason you see references to separate systems is that the higher content of oxygen in the breathing gas has a rapid detrimental effect upon standard o-rings, gaskets, etc. These are replaced with a different material to reduce the degradation caused by higher than normal percentages of oxygen.

Another issue is that some petrochemical properties of standard fittings can cause severe safety issues with higher than normal oxygen percentages.

Many divers circumvent this problem by having their equipment "O2 cleaned" and then get regular air fills with "oxygen compatible" air. This is the same "regular air" the LDS's use when doing a nitrox fill. The compressor/filtration system is specifically configured to deliver "oxygen compatible" air.

One reason some nitrox divers will do an air dive and then a nitrox dive is to be able to do 2 dives to the same depth, but effectively do a "shallower" dive the second dive due to the reduced percentage of nitrogen in the nitrox mix.

If you will remember from your class, a nitrox dive to a given depth is planned as a shallower than 21% air dive.

the K

 

[Canadian_Diver]

While studying for SSI Nitrox, the manual mentions time and time again about having a seperate air system for Nitrox. I was wondering how many divers actually have purchased a new air delivery system just for Nitrox. I know if I just happened to have a spare system (which I don't) that could easily become dedicated.

Also, it was mentioned that "many" divers use Nitrox on either their first or second dive of the day. Is this to save a couple of bucks?

A seperate set of regulators that are kept O2 clean, are only neccessary for mixtures of EAN41 or higher. This is mainly to prevent combustion from a build up of hydrocarbons. Hydrocarbons make great fuel for fires.

Anything EAN40 or lower, only requires a viton o-ring upgrade to your regulators. The increased FO2 causes oxidizing / breakdown of butyl o-rings to occur, eventually resulting in failure.

As for your second question. Most computers will actually lock you into Nitrox mode once used. Most first dives of a day are done on AIR due to profiling, you always do your deepest dives first. With the increased FO2 in your breathing gas, your chances of CNS toxicity increase with depth. Most people I know, used Nitrox on their latter dives to help gas off excess nitrogen in their system.

Cheers!

 

[freshwaterdiver]

when I got my Nitrox cert. I got my tank cleaned and Nitrox approved. I also had my reg serviced. I use my tank for both Nitrox and regular air. I have been told that is OK as long as you keep a close eye on the values and keep it clean and out of the heat.
I dive Nitrox as much as I can but still do my deep dives on Nitrox and switch to air at the end of the day.

 

[Canadian_Diver]

I use my tank for both Nitrox and regular air. I have been told that is OK as long as you keep a close eye on the values and keep it clean and out of the heat.

It depends mostly on factors such as the type of compressor being used to pump the air and the blending method used.

Why would you dive your first / early dives on nitrox, then switch to air in the afternoon? You might as well dive Nitrox all day.

 

[DA Aquamaster]

Manufacturers made big money off nitrox initially by selling deidcated equipment and training agencies pushed the industry standard/party line. The extra $ was the reason the dive industry finally legitimized nitrox.

Most currently produced regs are approved for 40% Nitrox right out of the box and most use EPDM o-rings and an O2 compatible lubricant. The more important consideration is what you put through them. EAN compatible air has a lower acceptable limit for oil particles and hydrocarbons than does standard grade E air. That said however, most shops pumping nitrox and air do it off the same compressor and that compressor will consequently pump air to the required standard. If that is the case, using one reg for both is fine. So check the air quality certificate at your local dive shop.

Some dive computers will lock you into nitrox mode for the whole day, but many of those will also allow you to set the nitrox percent at 21%, so it is not a serious limitation.

Nitrox allows a fairly substantial increase in NDL's at depth compared to air so it makes sense to use nitrox on the earlier and deeper dives. Dives shallower than about 50-60 ft however are often limited by tank capacity rather than NDL, so in those instances nitrox does not make as much sense as it will not extend bottom time. Plus, using nitrox on the earlier deeper dives, leaves you in a lower pressure group with more potential bottom time for the later dives.

 

[Canadian_Diver]

Some dive computers will lock you into nitrox mode for the whole day, but many of those will also allow you to set the nitrox percent at 21%, so it is not a serious limitation.

Nitrox allows a fairly substantial increase in NDL's at depth compared to air so it makes sense to use nitrox on the earlier and deeper dives. Dives shallower than about 50-60 ft however are often limited by tank capacity rather than NDL, so in those instances nitrox does not make as much sense as it will not extend bottom time. Plus, using nitrox on the earlier deeper dives, leaves you in a lower pressure group with more potential bottom time for the later dives.

RE: Dive Computers ---- Agreed.

RE: Nitrox / Depths

I agree with what you're saying to a certain extent. However, if you're running a higher blend of EAN (say EAN36 or higher), your MOD quickly becomes restricted and an increased chance of CNS oxygen toxicity can occur.

Diving on EAN36 @ 94ft gives you a PO2 of 1.39 ATA -- almost over the threshold of what the human body can stand, unless you're pushing the limits and using 1.5 ATA/Bar of PO2 instead of 1.4 ATA/bar.

I use Nitrox for larger margin of safety, not to increase my bottom time.

Cheers!

 

[WileEDiver]

A seperate set of regulators that are kept O2 clean, are only neccessary for mixtures of EAN41 or higher. This is mainly to prevent combustion from a build up of hydrocarbons. Hydrocarbons make great fuel for fires.

I have an Atomics T2 regulator (the T is for Titanium--lightweight, and nice for travel), and Atomics is quite clear that (due to the Hydrocarbons Canadian_Diver refers), you must decide to always use either air or nitrox, and have the reg serviced if you use standard air and want to go back to nitrox. Obviously you can use 21% nitrox if you wanted "air"--most places I've been to that provide nitrox, have hyperclean, hyperdry air at standard air-fill prices.

 

[Canadian_Diver]

I have an Atomics T2 regulator (the T is for Titanium--lightweight, and nice for travel), and Atomics is quite clear that (due to the Hydrocarbons Canadian_Diver refers), you must decide to always use either air or nitrox, and have the reg serviced if you use standard air and want to go back to nitrox. Obviously you can use 21% nitrox if you wanted "air"--most places I've been to that provide nitrox, have hyperclean, hyperdry air at standard air-fill prices.

WileEDiver --- I just about bought the Genesis OZ2 which is titanium. I opted for the model down, GS2000, which is identical minus the titanium. Interesting that Atomics would state that. I suppose they are just covering their posteriors from any liability by issuing that statement in their manuals or trying to make an extra buck.

Both NOAA and the US Navy use the 40% Rule. This rule states that no special preparation, modification, or maintenance procedures to equipment are required for use with FO2 gas mixtures of 40% or less. The only equipment this does not apply to, are cylinders and their valves. This information can be verified in the SSI EAN specialty manual.

In Atomic's defense however, the 40% Rule isn't followed by everyone. Some local laws and regulations require that oxygen clean / oxygen rated equipment be used with any gas mixture with FO2 greater than that of regular breather air.

Don't forget, some manufacturers will simply state it in their manual just to sell you a second set of regulators as well, afterall, they are in the business to make money.

 

[MonkSeal]

I dive Nitrox as much as I can but still do my deep dives on Nitrox and switch to air at the end of the day.

Very interesting ...
Deep dives on Nitrox ... What is deep? Nitrox is shallow mix.
Air at the end of the day ... Why?