Nitrox 1st or 2nd dive

[Jerryg]

Can somebody help me understand this:
I dove the Santa Rosa wall in Cozumel last week. I wanted to dive the first dive 90ft(Santa Rosa Wall) using nitrox(my absolute first nitrox dive) and the second dive 60ft(Tormentos) on air. My friend and I ordered the nitrox tanks. When we arrived at the dive shop they suggested that we dive the nitrox on the second dive. They indicated concern over us hitting our MOD due to possible down currents. I've dove this wall several times and have never had any trouble with buoyancy. Ultimately we dove ean32(actual was 34%) on the first dive. Everything I learned in my classes indicated that we should dive the first dive on nitrox, and the shallower dive on air. While I didn't listen to the dive shops recommendation I did consult with our local dive master who indicated that Nitrox on the wall was OK. How do you folks feel about the deep dive on air followed by the shallower second dive on nitrox. Would that just be throwing money away, or would it still be helpful. My air supply now lasts long enough for me to violate the no deco limits so I am seeking to use nitrox more, and want to understand this dive sequence better. thanks for any responses.

 

[The Chairman]

I would have done the same. Was there a reason that you did not dive the second on NitrOx?

 

[Jerryg]

When I took my class the instructors recommended from a cost standpoint to dive nitrox on the first dive then air on the second. They also indicated that if you are doing a lot of diving you may want to dive nitrox on the first two dives then air on the all other dives. The assumption is that the dives get shallower as the day goes on, and therefore nitrox is not requires. I wish I had used nitrox on both. But the simple answere is $$$$.

 

[Scubakevdm]

Nitrox isn't really for going deep. I always try to dive from lean to rich if there is no MOD conflicts. I dive from deep to shallow too.

 

[The Chairman]

NOx32 is my fav gas... I dive it almost exclusively. It will take me down to a 100 fsw and I really don't want/need to go deeper without extensive planning. I do not mind spending the extra $ especially when you factor in the price of gas in relation to the overall price of the trip. Although I have to teach that feeling good after a dive on NitrOx is apocryphal, I still experience that phenomenon. Heck, I even dive it when I am doing pool skills with my students.

 

[in_cavediver]

When I took my class the instructors recommended from a cost standpoint to dive nitrox on the first dive then air on the second. They also indicated that if you are doing a lot of diving you may want to dive nitrox on the first two dives then air on the all other dives. The assumption is that the dives get shallower as the day goes on, and therefore nitrox is not requires. I wish I had used nitrox on both. But the simple answere is $$$$.

Nitrox is the best gas for most rec dives. It reduces the overall N2 loading which is helpful for ALL dives, especially repetitive and multi-day dives. The goal is the reduction of your overall N2 load at the start of each repetive dive. So make all the deeper/longer dives which really hit you with N2 loading on nitrox. Ideally make them all on nitrox.

You could make all kinds of arguements about whether there is a difference in safety compared to air and usually you here that no, there is no difference. Well, for a single dive within the limits of either air or nitrox, there really isn't much of one. For a week long trip doing repetivie dives each day, I would argue that there is a difference in safety and Nitrox is the better gas. This is especially true when people dive their computers to the edge. (and off most tables)

About the only time I wouldn't bother thinking of nitrox is when all dives are shallower than 35 feet. It really just doesn't make much difference there and most models used for nitrox will show this.

With that, unless the extra cost of Nitrox is that much, dive Nitrox all the time. When you figure what you paid for everything else on our trip, just home much more does it really cost do dive Nitrox.

Mike

 

[Scubakevdm]

Nitrox is the best gas for most rec dives. It reduces the overall N2 loading which is helpful for ALL dives, especially repetitive and multi-day dives. The goal is the reduction of your overall N2 load at the start of each repetive dive. So make all the deeper/longer dives which really hit you with N2 loading on nitrox. Ideally make them all on nitrox.
Mike

Well, its a good idea to keep an eye on O2 loading if you do alot of Nitrox. Sometimes you have to throw an air or two into the mix if you dive too much. Like me.

 

[Don Burke]

Diving the deeper EAD first would put you in a better spot on the tables. Unless there's an issue about exceeding MOD, which dive gets the Nitrox shouldn't be a concern.

 

[landlocked]

It dosen't make a lot of sense unless you simply take what they said at face value. Maybe they were just concerned that the currents could sweep you blow the MOD. Perhaps all of the divers they see are not as skilled as you?

They indicated concern over us hitting our MOD due to possible down currents.

 

[Gary D.]

Can somebody help me understand this:
I dove the Santa Rosa wall in Cozumel last week. I wanted to dive the first dive 90ft(Santa Rosa Wall) using nitrox(my absolute first nitrox dive) and the second dive 60ft(Tormentos) on air. My friend and I ordered the nitrox tanks. When we arrived at the dive shop they suggested that we dive the nitrox on the second dive. They indicated concern over us hitting our MOD due to possible down currents. I've dove this wall several times and have never had any trouble with buoyancy. Ultimately we dove ean32(actual was 34%) on the first dive. Everything I learned in my classes indicated that we should dive the first dive on nitrox, and the shallower dive on air. While I didn't listen to the dive shops recommendation I did consult with our local dive master who indicated that Nitrox on the wall was OK. How do you folks feel about the deep dive on air followed by the shallower second dive on nitrox. Would that just be throwing money away, or would it still be helpful. My air supply now lasts long enough for me to violate the no deco limits so I am seeking to use nitrox more, and want to understand this dive sequence better. thanks for any responses.

I've got mixed feelings here but I think you need to listen to the operator.

These guys/gals are communiciating all day long and SHOULD know the conditions at any given time.

If during, lets say on XX date in the past 9 out of ten years this has happened with the current, one might want to listen to the operator. Besides they have no idea as to what kind of diver you are in any given situtation.

IF you stand a chance of getting deep, fast, Nitrox might not be the way to go. Thats why we dive strictly 21% on our working dives.

"I've dove this wall several times and have never had any trouble with buoyancy."

That statement is fine but have you seen that area when conditions were not ideal or at their worst? Current is nothing to play with and Coz is a place to play it safe. It can get as bad as Tacoma Narrows can and in an instant and catch unspecting divers off guard. At least with the Narrows we know what to expect.

Getting swept off the wall to say 2 or 300' is no big deal and surviable if you keep your head. For a situtation like that a 21% Nitrox mix would be my choice.

Operators, like everyone else aren't perfect. But they do try and make it safer for YOU even though they do some wierd things themselves.

Gary D.