Should I use Nitrox on liveaboard?

[Dan]

Oxygen toxicity, actually. There are some other threads that say it takes time to build, that it doesn't happen all at once.

Oops. My bad. Yes, I meant oxygen toxicity. Thanks for the correction. The post is edited accordingly, while I still can.

 

[Ayisha]

About the only time a diver with good buoyancy control may abruptly lose their buoyancy is if they are caught in a serious downcurrent, in which case they need to get out quick no matter which gas they're using or if they're having a medical emergency. Otherwise, there shouldn't be any abrupt loss of buoyancy.

I've seen divers dropping their weights accidently...Did you mean upcurrent?

I did mean downcurrent, where converging currents sometimes near a wall can create an extremely strong downcurrent that can push divers down drastically and suddenly. I have been caught in one that held me about 15 feet down and I kicked away from the wall and got out. Friends of mine were caught in one at 90 feet which brought them to 130 feet and they followed their instructor and kicked their way out, but much deeper than he did.

Another friend of mine got dragged from 70 feet to 180 feet rapidly in the Lillie long drift (not to be confused with the typical Lillie drift) in the St Lawrence river, but you are supposed to be at 90 feet in that portion to avoid the back eddy and potential downcurrent. Once when my buddy was not descending past 60 feet even after I signaled that we need to descend, we were suddenly in a strong back eddy rather than drifting and also got pushed around and down 5 - 10 feet suddenly. We immediately went to our target depth and it was all smooth from there as usual. It's a dive that requires a certain time at 2 particular depths.

So if you are caught in a serious downcurrent on a deep wall, you could be in trouble with nitrox, but you could also potentially be in trouble with air if over 187 feet for example (21% O2 at a PPO2 of 1.4). Oxygen toxicity is a factor of time at depth, so that is one concern, but an even greater concern IMHO is having enough gas left to ascend safely. For the situations I mentioned, each of the downcurrents happened near the beginning of a dive, so each diver had enough gas to kick their way out and ascend safely and complete any deco obligations they may have incurred. If they were caught in a downcurrent further along or near the end of their dive and didn't get out fast enough, it could be a very different situation.

Having said that, if you're watching what the particles are doing ahead of you as you dive, you can see which way the current(s) is/are going in high current areas, and avoid going too close to the wall in those areas.

As someone else said, the result of losing a weight belt would be similar whether you're using air or nitrox. I haven't worn a weight belt in over a decade. I wear a backplate/wing and use trim weights on my cambands. If you use a weight belt, you could check it while you're descending or at depth; there are depth compensating ones; you could put a second stainless steel buckle on it; put the belt on under a crotch strap (YMMV); or wear a weight harness instead. Lots of ways to decrease the risk of losing your weight belt at depth.

 

[scubadada]

Back on topic. I can't imagine why anyone would not dive nitrox on a liveaboard in the Red Sea with 4-5 dives per day.

 

[tarponchik]

Back on topic. I can't imagine why anyone would not dive nitrox on a liveaboard in the Red Sea with 4-5 dives per day.

Sure, with 4-5 I'll go for it. Though my personal record is 6 dives in one day, all on air.

 

[tarponchik]

I did mean downcurrent, where converging currents sometimes near a wall can create an extremely strong downcurrent that can push divers down drastically and suddenly. I have been caught in one that held me about 15 feet down and I kicked away from the wall and got out. Friends of mine were caught in one at 90 feet which brought them to 130 feet and they followed their instructor and kicked their way out, but much deeper than he did.

Another friend of mine got dragged from 70 feet to 180 feet rapidly in the Lillie long drift (not to be confused with the typical Lillie drift) in the St Lawrence river, but you are supposed to be at 90 feet in that portion to avoid the back eddy and potential downcurrent. Once when my buddy was not descending past 60 feet even after I signaled that we need to descend, we were suddenly in a strong back eddy rather than drifting and also got pushed around and down 5 - 10 feet suddenly. We immediately went to our target depth and it was all smooth from there as usual. It's a dive that requires a certain time at 2 particular depths.

So if you are caught in a serious downcurrent on a deep wall, you could be in trouble with nitrox, but you could also potentially be in trouble with air if over 187 feet for example (21% O2 at a PPO2 of 1.4). Oxygen toxicity is a factor of time at depth, so that is one concern, but an even greater concern IMHO is having enough gas left to ascend safely. For the situations I mentioned, each of the downcurrents happened near the beginning of a dive, so each diver had enough gas to kick their way out and ascend safely and complete any deco obligations they may have incurred. If they were caught in a downcurrent further along or near the end of their dive and didn't get out fast enough, it could be a very different situation.

Having said that, if you're watching what the particles are doing ahead of you as you dive, you can see which way the current(s) is/are going in high current areas, and avoid going too close to the wall in those areas.

As someone else said, the result of losing a weight belt would be similar whether you're using air or nitrox. I haven't worn a weight belt in over a decade. I wear a backplate/wing and use trim weights on my cambands. If you use a weight belt, you could check it while you're descending or at depth; there are depth compensating ones; you could put a second stainless steel buckle on it; put the belt on under a crotch strap (YMMV); or wear a weight harness instead. Lots of ways to decrease the risk of losing your weight belt at depth.

I've seen people dropping "integrated" weights too. Re downcurrent, I've done intentional dips down as deep as 185 ft and just considered this to be deco dives. With upcurrent, however, you can not only exceed the recommended ascending speed but also blow your safety stop.

 

[Ayisha]

...Re downcurrent, I've done intentional dips down as deep as 185 ft and just considered this to be deco dives...

Of course intentional deep dives would be considered deco dives. Presumably you would have the redundant gas, experience and training to complete the dive safely, which may not be the case when unintentionally caught in a downcurrent, which could happen at any point in a dive.

...With upcurrent, however, you can not only exceed the recommended ascending speed but also blow your safety stop...

As mentioned by a couple of people, both EANx and air are affected similarly by ascent speed and omission of any stops, required or recommended. In fact, depending on how close you dive to the MOD and NDL/MD, you may incur less of a deco obligation diving with EANx.

 

[kelemvor]

Personally, I always use nitrox unless I'm filling car tires.

Do it, unless your planned dives are just too deep for nitrox (deeper than 130'/45m). Livaboards are probably the best place I can think of to use it. Possibly delayed access to a chamber, many dives a day for multiple days... There's no dive scenerio I've heard of that would take better advantage of the increased safety.

As others have said, many (but not all) LOBs require you to use it.

 

[Ayisha]

Yes, agreed. I've already signed up for EANx at $100 US on the Belize Aggressor III in April. I've been disappointed when my previous liveaboards didn't offer EANx. No chamber for miles and multiple dives over multiple days at typically perfect depths for EANx. It was an extremely easy decision for me as well.

 

[Divin'Papaw]

I ALWAYS dive nitrox. Air is a really lousy dive gas unless you're diving deep air ... which isn't a great idea anyway. I put air in my pony because, well, it's a pony. But I never, ever dive air and have no clue why people still do. Scuba is expensive and the cost difference of air vs. nitrox is inconsequential. The safety and increased NDL is far worth the cost.