77 replies to this topic

[PerroneFord]

How will you know you have enough to get you both to the surface safely?

[ScubaPunk]

Zero. None of my buddies "gas" is mine. I've never needed to use my buddy's air, but if I did, I would consider myself fortunate that he had air to spare. On the other hand, I have shared my air on a few occasions. In these situations, I also feel fortunate that I have plenty of air to share.

[PerroneFord]

Some very interesting responses to this question. Probably going about like I figured though.

[Basslet]

How will you know you have enough to get you both to the surface safely?

I don't know if you're talking to me but unlike your buddy on the Oriskany I check with my buddy to see how much air he and NDL he has, and share my info with with him/her. Generally, at 1000 psi, we begin our ascents. I know my son's SAC will not be that great when we go to Bonaire because he hasn't been diving in over a year so I know I have to keep close watch on him.

[PerroneFord]

Zero. None of my buddies "gas" is mine.

I'm not sure how to respond to this. Are you saying that you and your buddies leave no reserve in your tanks for emergencies?

[PerroneFord]

How will you know you have enough to get you both to the surface safely?

I don't know if you're talking to me but unlike your buddy on the Oriskany I check with my buddy to see how much air he and NDL he has, and share my info with with him/her. Generally, at 1000 psi, we begin our ascents. I know my son's SAC will not be that great when we go to Bonaire because he hasn't been diving in over a year so I know I have to keep close watch on him.

I guess wha I am wondering is how you know "what's enough". Is 1000 psi enough to get you both back to the surface, completing your safety stops? Perhaps it is. I'm just wondering. In this scenario you have "reserved" 500psi for your buddy or he for you.

[Basslet]

How will you know you have enough to get you both to the surface safely?

I don't know if you're talking to me but unlike your buddy on the Oriskany I check with my buddy to see how much air he and NDL he has, and share my info with with him/her. Generally, at 1000 psi, we begin our ascents. I know my son's SAC will not be that great when we go to Bonaire because he hasn't been diving in over a year so I know I have to keep close watch on him.

I guess wha I am wondering is how you know "what's enough". Is 1000 psi enough to get you both back to the surface, completing your safety stops? Perhaps it is. I'm just wondering. In this scenario you have "reserved" 500psi for your buddy or he for you.

I guess it depends on the type of dive. How deep, what kind of activitiy. I check my gauge quite often so that I'm not surprised. I was once on a deep wreck dive and was surprised to find that I had 600 psi left (I only started with 2400 on an AL 80) and don't want to repeat that. But the sand tigers distracted me.

[PerroneFord]

I guess it depends on the type of dive. How deep, what kind of activitiy. I check my gauge quite often so that I'm not surprised. I was once on a deep wreck dive and was surprised to find that I had 600 psi left (I only started with 2400 on an AL 80) and don't want to repeat that. But the sand tigers distracted me.

I suppose I am simply not coming across clearly. Let me try an example. Two months ago, I did a dive at a spring. There wer 4 divers. I was the only one in doubles. We were going to do a cavern dive, I was leading. Cavern opeining was at 50ft, max depth was about 80ft. Plan was to enter the cavern (in particular order), explore the cavern for until 30 minutes had elapsed in the dive, or any of the divers had used 1/3 of their tank, and then exit the cavern in reverse order, and rendezvous at 45ft. At that time we would check gas supply, swim in open water, and proceed to exit the spring at 1hr or when the first diver hit 800psi.

The reasoning for diving thirds was that we were alloting the diver with the heaviest consumption to be the limiting factor. By excecuting the deep portion of the dive with only 1/3 of a tank, we reasoned that would should be able to exit if necessary on 1/3, and 1/3 was reserved for a failure of another diver's gear. Thus the 2/3 held in reserve would become 1/3 for each diver to exit which should have given ample time to make a safe exit.

What I am wondering is if in your dive plan, you give a concrete figure for both time and gas that says "time to go". If so, how do you derive it? Is there a process you use to derive it, or is a "best guess".

[Dive_Girl]

I teach using the rule of thirds. Diver who uses 1/3 first controls the dive. In more extreme conditions, we can set aside a reserve (example, 500psi) and then plan the dive using the rule of thirds with the remaining amount. As has been discussed before, first 1/3 out may have been uneventful and so if we had to come back sharing the remaining 2/3, it is likely gas consumption would be increased thus the buffer.

[ScubaDadMiami]

As you can see from the poll, everyone is all over the place with this one. I find the fact that people do not have a discussion about such an event pretty shocking unless we are talking about shallow recreational dives where the diver could swim directly to the surface in an out of gas situation--which includes equipment failure and not just running out of gas--with "minimal risk."

Having so many differing concepts is all the more reason to make sure to have a plan and agreement with other divers in your team before hitting the water. If not, plan the dive for a solo situation. Then, you have decided to plan for and take on the risk associated with such an activity.

If you think that yours is yours and theirs is theirs, I would prefer that you let me know this before engaging in diving with me in the area. I will likely make sure to keep my distance.

[Diverbrian]

I also tend to go by thirds. However, if I have done my dive planning properly, I will be turning on planned bottom time before I hit thirds.

Oh, I have donated air more than once. I have not needed to be donated to. What's mine is theirs within reason. What's theirs is theirs. I don't count on anyone but me being around in the event of Mr. Murphy paying a visit.

[PerroneFord]

I find the fact that people do not have a discussion about such an event pretty shocking...

If you think that yours is yours and theirs is theirs, I would prefer that you let me know this before engaging in diving with me in the area. I will likely make sure to keep my distance.

Amen brother.

[gcbryan]

Interesting thread indeed. Some responses surprised me a bit. Other's were surprising at first but I actually know what they mean and perhaps aren't so surprising.

Keep in mind that most of those responding in a "surprising" way can do a straight ascent to the surface whenever they want to. Most people here aren't penetrating wrecks or caves. Also, keep in mind that an experienced diver who doesn't know "rock bottom" calculations probably is essentially doing them anyway.

Anyone, who realizes that they need a differring number (PSI) at each depth in order to get them and their buddy safely to the surface is actually diving rock bottom numbers as long as the numbers they use work. Through experience their numbers probably do work.

Those hoping to have enough air for a buddy or hoping to have enough for themselves for a planned dive are the onces that surprised me. I understand that some who responded that their buddy's air was not for them were just saying that they intend to be self-sufficient and don't need it (hopefully they have a plan for that as well).

Edited by gcbryan, 16 August 2006 - 11:24 PM.

[6Gill]

I find the fact that people do not have a discussion about such an event pretty shocking...

If you think that yours is yours and theirs is theirs, I would prefer that you let me know this before engaging in diving with me in the area. I will likely make sure to keep my distance.

Amen brother.

I'm in this camp.
The basic plan is to figure out the required gas and the needed reserve.The reserve is determined by a number of factors.If there is a 'ceiling'(deco,penetration ect) the required reserve is alot more critical.Another factor to consider is lost deco gas.Properly planned I have enough gas at any givin time to get myself and my team member to the surface safely,they are also in the same position.This then means if I end up on my own I have more than enough gas.The idea of my gas is my gas and your gas is your gas so your SOL guess you might die or get bent 'cause I only have enough to get me home is not a place I want to be in.Esspecially when it's avoidable and I care about the people I dive with.
Most people's gas management lesson consist of "get back to the boat with 500psi" which is pretty weak even for 'recreational' diving.

[Diverbrian]

Interesting thread indeed. Some responses surprised me a bit. Other's were surprising at first but I actually know what they mean and perhaps aren't so surprising.

Keep in mind that most of those responding in a "surprising" way can do a straight ascent to the surface whenever they want to. Most people here aren't penetrating wrecks or caves. Also, keep in mind that an experienced diver who doesn't know "rock bottom" calculations probably is essentially doing them anyway.

Anyone, who realizes that they need a differring number (PSI) at each depth in order to get them and their buddy safely to the surface is actually diving rock bottom numbers as long as the numbers they use work. Through experience their numbers probably do work.

Those hoping to have enough air for a buddy or hoping to have enough for themselves for a planned dive are the onces that surprised me. I understand that some who responded that their buddy's air was not for them were just saying that they intend to be self-sufficient and don't need it (hopefully they have a plan for that as well).

There is a clarification here. I have calculated out my gas planning for my working RMV on many dive profiles as part of the courses that I have taken. I am not hoping that I have enough gas. I am as close to certain as one can be. I also fudge that RMV up by little bit to account for stress.

I often don't know my buddy's RMV because they don't know. I know how much gas they are carrying, but many times I am diving double 130's and a deco gas next to someone diving a single AL80. Now, why would I even need to think about needing their gas? If I am diving with someone on a more "advanced profile" (think deco or shipwreck penetration here) then I do plan my gas accordingly.

But again, I need to be able to account for rescuing myself without my buddy in most cases. I plan to have enough to get my buddy back as well. But, I don't count on them having done the same. The buddy is nice to have, but I don't wish to completely bank my life on anyone's actions but my own. The same goes with equipment. If it is emergency gear, then I am of the school that both of us should have it. One piece carried by one team member does not count. Mr. Murphy is a mean SOB and he is very unpredictable.

Even on recreational dives, I will tend to turn the dive with 1/3 of the lowest diver's gas gone. Then we will go back on 1/3. Then we can burn off up to rock bottom prior to actual ascent from the ascent line if everyone is happy with that and wants to stay in the water for a while .

For those that think that they have budgeted enough for emergencies, I would direct them to some story problems that I did in my Normoxic class. They involve divers in various scenarios with a complete loss of gas at the farthest part of a penetration. Once the swim rate of the divers slowed or the diver's RMV's increased from the stress, in most cases, there wasn't enough gas to get them both out in the smaller diver's tanks. This was with pretty conservative gas management rules applied to the issue too! That is decent food for thought.