Nitrox, Skin Bends and Cozumel

[ljwillia]

Not sure if this is the right place to post this question.

2 years ago while diving in Coz I developed skin bends. I was advised to dive nitrox on air tables to avoid this in the future. Last October we went to Bonaire and I used my nitrox cert for the first time. I had no issues whatsoever.

This July we're headed back to Coz. I'm a bit concerned that if I run into a down welling in Coz I could be pushed below the safe depth of a nitrox mix. Now, I've never encountered this in my 7 trips there so I'm probably overthinking this (said my husband last night).

1. Since I've had skin bends do I have to dive Nitrox from now on or this just precautionary? In Bonaire, Nitrox was the same price. It adds $200 +/- to our trip to Coz. And before I get flamed, of course I'll spend the money on my own safety. However, air would be less complicated.

2. Is there any reason to be concerned about the depth limit on a Nitrox mix?

Thanks!

 

[doctormike]

1. Since I've had skin bends do I have to dive Nitrox from now on or this just precautionary? In Bonaire, Nitrox was the same price. It adds $200 +/- to our trip to Coz. And before I get flamed, of course I'll spend the money on my own safety. However, air would be less complicated.

Thanks for posting!

There is no "right" answer to this question. Ever dive involves some risk of DCS. Things that make it more likely for any given profile include depth, time, mix and personal factors like your history of skin bends. And to further complicate things, the specific history of your skin bends itself is relevant. If it was an "undeserved" hit (I hate that phrase), then your risk is higher - you may have some sort of right to left shunt like a pulmonary AV malformation or a PFO.

Are you diving Nitrox but using an air table, or setting your computer to air? Or are you just setting your computer to the Nitrox mix you are diving and following those NDLs?

If the former, you will reduce your N2 loading, and reduce (not eliminate) your risk of DCS. If the latter, then you are getting no safety advantage from Nitrox.

2. Is there any reason to be concerned about the depth limit on a Nitrox mix?

Of course, but every mix (even air) has a depth limit. Severe downcurrents, involves risks far beyond just O2 toxicity. I don't know much about Coz, but I never heard of people avoiding nitrox for that reason.

 

[ljwillia]

Thanks for posting!


Are you diving Nitrox but using an air table, or setting your computer to air? Or are you just setting your computer to the Nitrox mix you are diving and following those NDLs?

Thanks @doctormike. My computer is set to "air". I simply make a mental note of the profile for the nitrox mix. Worked out well in Bonaire.

 

[JamesBon92007]

I've never run into a "down welling" in Cozumel--I may have gone a little deeper than planned but that was always by choice and I modified my dive accordingly. Is this a problem diving Cozumel that I've not heard of before?

I'm old so I dive very conservatively as far as NDLs are concerned and have never used Nitrox and never had any kind of the bends. I knock off a few minutes from the NDL and, since diving with Blue XT Sea, add a couple more minutes to my safety stop. So far so good!

 

[doctormike]

Thanks @doctormike. My computer is set to "air". I simply make a mental note of the profile for the nitrox mix. Worked out well in Bonaire.

Great! So just make sure that you don't exceed your MOD. The other reason not to do that (fool your computer) is that you could have an issue underestimating O2 exposure over 24 hours, but for open circuit recreational diving that's unlikely to be a problem.

 

[flyboy08]

Either have a bottom below at 50-90...or swim close to the wall and First signs of bubbles going down.....inflate and grab what’s ever available to grab that’s stationary.

I often worry about that too, but not for my sake, but for my wife’s and daughter....we’ve drilled often, but one never knows how one will react in a crisis.

May I ask what were your symptoms for skin bends?

 

[DjDiverDan]

Down currents do happen in Coz, but they are, at least in my experience, exceedingly rare. I started diving in Coz in 1989, and went there at least once a year, often 2-3 times a year, every single year until 2016 (I haven’t been for a while, and boy do I miss it!). In all those years and all those dives, I saw just one bad down current, on Santa Rosa Wall. And it didn’t affect me at all, as I stayed in tight to the wall, while the downcurrent only caught those divers who were hanging at least 8-10 feet off the wall. And all they had to do to get out was to get back in tight to the wall. Even that current was predictable, if you were paying attention. At the top of the wall there was a shallow canyon, and looking up you could see the current coming out from shore and washing a lot of sand and small debris down the canyon and over the wall, then down. And it wasn’t wide at all - I’m guessing no more than 20-30 feet, so if you kept swimming along the wall you were out of it quickly. If you are concerned about down currents in Cozumel (and they are pretty low on my own list of concerns), learn how to recognize when they are coming, how to avoid them, and how to safely exit without fully inflating your BC so that you pop to the surface like a cork when you exit the current. Don’t let that concern keep you from diving Nitrox.

 

[ReefHound]

I've encountered downward flows over the walls many times but never so much that I could not easily ascent against. The MOD for 32% at 1.4ppo is 111' and if you set your planned max to 90' that gives you some room to work it out. And your head isn't going to suddenly explode at 112'. The concern is oxygen toxicity and takes a bit of time and/or work to build up. Always best to stay conservatively within limits, of course. Most computers have alarms so set a depth alarm at 90' to remind you to start paying attention to depth. Short story - I would not be concerned about diving nitrox in Coz.

 

[ljwillia]

May I ask what were your symptoms for skin bends?

I didn't notice anything until after 4 days (8 dives). At lunch my breasts were unusually sore. I started noticing blotches on my stomach. I thought it might be a rash or a reaction to my wetsuit. The rash spread by that night. I had no other DCS symptoms which is why I almost didn't call DAN. I googled my symptoms on scubaboard and found another post that mentioned skin bends, which I had never heard of.

I talked to DAN later that night and they advise I see a Dr. Went to the dive hospital on Cozumel (can't remember the name now) and they confirmed the diagnosis. No chamber time required. Very mild. They suggested I not dive for the rest of the trip and that I dive Nitrox on air tables in the future.

BTW-The facility on Cozumel was fantastic.

 

[DandyDon]

I was advised to dive nitrox on air tables to avoid this in the future.

That was not DAN's advise, was it?

I'm going to ask a Mod to move this to the Dr.Deco forum for the best replies. Hope you don't mind.

This July we're headed back to Coz. I'm a bit concerned that if I run into a down welling in Coz I could be pushed below the safe depth of a nitrox mix.

Those are possible even tho rare in Coz waters, so the risk is possible - but getting out of a down welling is not that difficult, doesn't take long, and a brief violation is not much of a risk. Again, better answers in the other forum.