What's in your pony?

[Skull]

People think pony bottles are important because "anything can happen" and they want to be "prepared" for an emergency.

Ok, I disagree but let's say that makes sense.

If we are concerned that "anything can happen" why put a mix in the bottle that excludes any emergency that could happen below the MOD for the chosen content?

You cannot have both "total redundancy in case of (nearly) any emergency" with a self imposed limit to the depth you assume you will not exceed.

Again people are confusing decompression tanks with "redundant tanks".

(and yes that includes diving with a pony containing EAN within NDL’s. If you think enriched air is "helping" then you are using it to decompress)

Takes us back to diving doubles if redundancy is the concern. Choose a mix for the floor of your dive and run with it. KISS is always a great guideline while dive planning.
Stay within your NDL's if diving rec .. or at least plan for a short deco obligation. Finally if you are taking a pony for emergency ... put the most O2 % wise you can get in it cause you are gonna need it for recovery... I like 32 % ..but that is cause most of my dives are 110' and less ...then again I don't use a pony. I like doubles or single 120's

 

[DCBC]

As someone fairly new to Nitrox diving, and with no technical experience, I'm trying to understand this a little better. One of the big teaching points in Nitrox class is that you have to watch your MOD to avoid OxTox. But what I'm reading here is that even if I'm diving air, it is not a bad idea to put Nitrox in the pony, assuming you will be using it as an emergency air source.

Diving within the envelope that the OP stated, there is no benefit to having Nitrox in the Pony Bottle. As noted, it has some benefit as a decompression gas, but this is not the intended use for a Pony Bottle. It will however facilitate an emergency ascent in a no decompression situation. Air is preferable.

 

[Herk_Man]

As someone fairly new to Nitrox diving, and with no technical experience, I'm trying to understand this a little better. One of the big teaching points in Nitrox class is that you have to watch your MOD to avoid OxTox. But what I'm reading here is that even if I'm diving air, it is not a bad idea to put Nitrox in the pony, assuming you will be using it as an emergency air source.

If I stay within the recreational limits (130fsw if I have deep training), is there any chance of running into trouble if I put EAN36 in my pony and I have to use it starting at 130 but I do a controlled ascent? (And when I say "any chance" I mean normal circumstances. I understand that in diving sometimes weird things happen.)

Thanks for the info.

First of all @ 130 fsw your recreational bottom time is about 5 minutes in reality on 21%(compressed air). Let's say you have a problem with your reg or something along those lines ... you stop and assess the situation. You begin your ascent ...fact is you will be narced in most cases. You will ascend and grab your pony reg. By the time you hit say 90 ft you most likely will not in gas enough O2 at 36 % to send you into OxTox. The ascent pressure delta on your body from 130 to 90fsw is negligible so it can be done rather quickly in a emergency .. so the gamble is how fast do you want to get to a safe depth to gather your wits and begin a safe controlled ascent to the surface. As you ascend you will be in-gassing more O2 above 90 fsw which helps. When you reach the surface you got 36% to breath off of which again gives you more O2 then if you where breathing 21%. Recovery from the dive will be quicker ..well depending on how you handled your ascent rate from 90fsw to the surface.

Finally if you are screwing around at 130 fsw and decide to use your pony as added bottom time .. you most likely will end up killing yourself ...but that is just piss poor dive planning-eh? For all of the obvious reasons regardless of what mix you got in your pony.

Appreciate the response. I went and looked at the tables (PADI) and it shows 10 minutes is the NDL for air at 130fsw. EAN36 is not available (I think I was looking at NAUI dive tables for Nitrox because I couldn't find an image online of PADI Nitrox tables) and EAN32 has a NDL of 20 minutes at 130fsw.

So you are right. Your time at 130 is very limited on air. But since EAN32 allows 20 minutes and should not put you at risk of OxTox, then an EAN32 pony should be perfectly safe.

And all of this of course assumes that for some reason your buddy can't be used to get you out of the situation. Sometimes, for the sake of discussion, you have to get past the fact that in most situations, you wouldn't default to the option in question. But there are certainly cases where a person might need a pony, despite the existence of a buddy. So the discussion is relevant.

Appreciate all the replies.

 

[Herk_Man]

Diving within the envelope that the OP stated, there is no benefit to having Nitrox in the Pony Bottle. As noted, it has some benefit as a decompression gas, but this is not the intended use for a Pony Bottle. It will however facilitate an emergency ascent in a no decompression situation. Air is preferable.

Can you expand on that? Again, my diving so far has been limited to buddy diving in recreational limits. So I'm not 100% certain what you mean when you say there is not benefit to having Nitrox in the pony.

If my emergency, again assuming that for whatever reason my buddy is not able to assist (maybe attempting to rescue my buddy got me into the situation, I don't know), requires me to go to the pony for the ascent, I can't see where air is the better option. Are you saying that I should be planning on the situation possibly putting me at a depth where OxTox becomes a factor if I have Nitrox?

Thanks for the response.

 

[Dr Wu]

Finally if you are taking a pony for emergency ... put the most O2 % wise you can get in it cause you are gonna need it for recovery...

The "most" you can get is 100%. That makes it a decompression cylinder and not a bailout bottle.

If you are talking about "recovery" from a DCS situation you need a decompression cylinder and not a bailout bottle.

I don't see why this is so hard to understand.

So you are right. Your time at 130 is very limited on air. But since EAN32 allows 20 minutes and should not put you at risk of OxTox, then an EAN32 pony should be perfectly safe.

It "should be". (unless of course your emergency occurs deeper than that).

If you are so concerned with these "potential emergencies" why are you willing to fill your "totally redundant" cylinder with something that can kill you if you breathe from it at the wrong depth?

 

[Herk_Man]

The "most" you can get is 100%. That makes it a decompression cylinder and not a bailout bottle.

If you are talking about "recovery" from a DCS situation you need a decompression cylinder and not a bailout bottle.

I don't see why this is so hard to understand.





It "should be". (unless of course your emergency occurs deeper than that).

If you are so concerned with these "potential emergencies" why are you willing to fill your "totally redundant" cylinder with something that can kill you if you breathe from it at the wrong depth?

I think I'm going at it from this angle because typically, when I look at the depth of my dive, I'm basing it on how deep the bottom is in the location I'm diving. So the threat of going deeper is not really an issue. I could certainly see your point and would probably change my thinking if I were in a situation where the bottom were deeper than my planned dive depth. e.g. I was diving a wreck but was not planning on descending below a certain part of the wreck. If my buddy got distracted and went deeper than planned (bad buddy!) and then got entangled, then your angle on this would certainly be in play.

 

[DCBC]

Can you expand on that? Again, my diving so far has been limited to buddy diving in recreational limits. So I'm not 100% certain what you mean when you say there is not benefit to having Nitrox in the pony.

The contents of breathable gas within a Pony is not considered in your gas management plan and is only considered for use in an emergency ascent. On ascent, you are out-gassing. An ascent rate of 30 fpm would take approximately 4 minutes. Without getting into different decompression models, this time is not "bottom-time" for decompression purposes. As the OP has stated that he is diving without any formal decompression requirements, the diver may surface (although it's good policy to observe a safety stop if the gas is available).

The inclusion of an increase of O2 in the breathing mixture will aid in the off-gassing process, but as the OP has not specified that he is using Nitrox as a primary gas, it accomplishes nothing to introduce this gas mixture for an emergency ascent. If Nitrox was the primary mixture, air still may be preferable depending upon the mixture used. Breathing air above 150' poses no practical narcosis considerations for an emergency ascent and OxTox isn't a factor with air in this depth range.

If my emergency, again assuming that for whatever reason my buddy is not able to assist (maybe attempting to rescue my buddy got me into the situation, I don't know), requires me to go to the pony for the ascent, I can't see where air is the better option. Are you saying that I should be planning on the situation possibly putting me at a depth where OxTox becomes a factor if I have Nitrox?

Yes, this is one consideration, the diver may have gone too deep, consumed too much gas (which often happens in OOG situations) and found himself requiring an emergency ascent from a deeper depth. Nitrox may well be an OxTox hazard, where air would be the preferable mixture.

 

[Herk_Man]

Yes, this is one consideration, the diver may have gone too deep, consumed too much gas (which often happens in OOG situations) and found himself requiring an emergency ascent from a deeper depth. Nitrox may well be an OxTox hazard, where air would be the preferable mixture.

Well, since I do the majority of my dives on Nitrox, even in situations where the bottom is lower than my planned maximum depth, I will probably opt for Nitrox in the pony too. But air is not out of the question either. I guess it is probably just one of those things you have to factor into your risk assessment when you plan the dive.

Thanks for the discussion.

 

[parkerco]

Appreciate the response. I went and looked at the tables (PADI) and it shows 10 minutes is the NDL for air at 130fsw. EAN36 is not available (I think I was looking at NAUI dive tables for Nitrox because I couldn't find an image online of PADI Nitrox tables) and EAN32 has a NDL of 20 minutes at 130fsw.

So you are right. Your time at 130 is very limited on air. But since EAN32 allows 20 minutes and should not put you at risk of OxTox, then an EAN32 pony should be perfectly safe.

Errr ... perhaps I'm remembering this wrong from my Nitrox class, but given the NOAA dive table for EAN32 (all I could find online and my PADI tables are at home), the NDL of 20 minutes at 130 fsw is at a PPO2 of 1.6. If you were diving recreational (read: conservative) limits you wouldn't exceed 100 fsw while using 32. Granted you'd be ascending almost immediately if you were relying on the pony (and therefore going quickly to lower PPO2's), but given that the pony is for emergencies, and were you in one the physical/mental stress could increase your risk of a CNS oxtox incident, why would you risk it (using 32 that is)?

If I'm remembering the calculation right (PPO2 = ATA x FO2 %), if you were going to bother using something other than air and wanted to be conservative about it you'd probably go with a lower O2 % than 32. For example, at 130 fsw (4.94 ATA) EAN28 would be 1.38 PPO2.

If my math or reasoning is off on this please lemme know!

 

[Herk_Man]

Errr ... perhaps I'm remembering this wrong from my Nitrox class, but given the NOAA dive table for EAN32 (all I could find online and my PADI tables are at home), the NDL of 20 minutes at 130 fsw is at a PPO2 of 1.6. If you were diving recreational (read: conservative) limits you wouldn't exceed 100 fsw while using 32. Granted you'd be ascending almost immediately if you were relying on the pony (and therefore going quickly to lower PPO2's), but given that the pony is for emergencies, and were you in one the physical/mental stress could increase your risk of a CNS oxtox incident, why would you risk it (using 32 that is)?

If I'm remembering the calculation right (PPO2 = ATA x FO2 %), if you were going to bother using something other than air and wanted to be conservative about it you'd probably go with a lower O2 % than 32. For example, at 130 fsw (4.94 ATA) EAN28 would be 1.38 PPO2.

If my math or reasoning is off on this please lemme know!

Nope, I think you're right. And I plan my dives for a 1.4 max so your numbers are probably more correct. But 90' is a deep dive for me anyway so most of this is not going to apply to me anyway. Heck, I don't even have a pony. I was just interested in the conversation. But I might get a pony before too long. I like the idea of having redundant sources of air.