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Diving Safety, Accidents and Incidents Post here to discuss accidents, incidents, ideas, gear, or anything else to improve spearfishing safety. Memorials and condolences threads should be placed in that separate forum.

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Old 09-24-2016, 09:49 AM   #1
lictol
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Nitrox question

Is there any advantage or disadvantage to loading my bailout bottle with a high mix, say 38%???

My thought is regardless of operating depth, in the event a switch over is made, an emergency situation requires immediate ascent. Would a higher mix possibly help or add an additional margin of safety? Or, am I possibly creating additional risks?

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Old 09-25-2016, 08:43 AM   #2
jfjf
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Re: Nitrox question

Air is simple, cheap and won't get you in trouble if you are a little deeper than you should be and it makes topping off the bottle a lot easier if you just add air when it leaks down.

Often a pony bottle is not that large, so you probably want to keep it filled. Most dive shops aren't going to charge you to add 800 lbs of air when you are getting your other tanks filled.. Now if they have to drain it and do a complete partial pressure mix - just to add 400 lbs.. they might not be so generous.
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Old 03-11-2017, 08:28 AM   #3
acteg
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Re: Nitrox question

I don't think a higher mix will help much during a rapid emergency ascent. The risk of DCS due to the nitrogen in your body is already present, and the amount of additional nitrogen you are inhaling during a rapid ascent would be minimal in my opinion. I'm not a doctor or a physicist so take that with a grain of salt.

Also depending on depth, your pony mix might exceed your MOD. Do you plan on changing your pony mix to match your tank mix, or do you always dive shallower than 89'?


That being said.....

Personally, I size my bailout bottle to give me enough time to make a controlled ascent in the event of emergency. Most of my diving is in the 85' range so my pony and my main tank usually have 36% in them. If I intended to go deeper, I would have my % reduced to accommodate the dive profile.

My rationale for keeping nitrox in my pony/bailout is as follows:
1. My pony could be used as another option for an "oxygen bottle" in the event of an emergency situation. I carry an O2 bottle/kit with me anyway, so this is probably a bit overkill, but the idea is if it's good to use your remaining back gas as enriched O2 (assuming the O2 bottle is used up) for someone suffering from DCS, then having even more enriched back gas available is better.
2. I have enough gas to do a controlled ascent, and if I am getting close to deco, switching to air at depth might push me into deco, further complicating the situation.
3. Switching to a second gas mix (on my computer) is one more thing to worry about in a potentially stressful situation. Probably not that big of a deal if you are in a hurry to get to the top, but with enough gas for a controlled ascent, i'd like to track any NDL deltas that arise. Like I said, this concern is probably not realistic in an emergency situation
4. Along the same lines as 3, if I have to switch to my bailout, and if my computer happened to fail as well, I can still fall to my backup dive plan, and everything remains the same since my mix is the same.
5. The additional cost is negligible and I don't see any draw backs for my typical dive profile.

My pony is setup as a bailout bottle. I can quickly detach it from my main tank (using the quickdraw system), and hand it off to a buddy, who can then clip it on to a D-ring and ascend. I go over this with my buddy prior to the dive, so in the event that there is an emergency they can just grab it and go. It is also setup in such away that I can grab the pony regulator 2nd stage and breathe it myself without having to undo anything (besides one clip on my hip D ring).

I actually had a buddy go OOA during a dive. It was a lobster dive, and the guy wasn't paying attention to his air. The current was really ripping. I was trying to yank a lobster out of his hole, and felt my buddy hit me. The current was so strong though, he wasn't able to grab me and just floated away. I think he was actually going for my main reg or my Octo (bright yellow hung around my neck), but missed. I had no idea he was out of air (we were only 15 min into the dive), and he ended up doing an emergency ascent from 70'. When I got to the surface he was on my boat sucking down oxygen from my O2 kit. I checked on him then we immediately headed for the inlet. Fortunately, he did not have any side effects.

Last edited by acteg; 03-11-2017 at 08:39 AM.
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Old 03-11-2017, 10:13 AM   #4
SEATUX
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Re: Nitrox question

I see it differently, a bail out is most likely for an OOA situation ( or malfunction of equipment that restricts your ability to get air) . My 19cf pony is charged @45% O2..All I need to do is get up to 70 fsw to be safe drawing off it, then I have 19 cf to get to the surface, and all the while I am "cleansing" the nitrogen at some rate.
I have never had to use it, and hope not to, it is for the rare un-forseen emergency.
So Obviously I have never had to "top it off"...If that is happening, IMHO, your doing something wrong.
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Old 03-12-2017, 08:27 AM   #5
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Re: Nitrox question

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