When does "Gas Management" get taught?

[darkpup]

Take an example: perfect horizontal trim for reef diving is one of the things that doesnt make sense to me. For tropical diving, one has to look all around - in front, below and above. Being horizontal gives me a crick in my neck - I find it easier to be slightly inclined. Is that the most efficient way to dive? Probably not. But it is the most comfortable - and I've started seeing a lot more mantas since I modified my trim to be angled.

I hear you there, although I stick to the horizontal trim most of the time on reefs. It also doesn't work in big surge while maskless following a line, inside a wreck while attempting to navigate a stairwell, or when your instructor says you're OOA and you choose to use your drysuit for buoyancy rather than exhaling into your wing. I really need to get that video of our Wreck class up so others can see me looking like a flag on a flag pole in high winds while holding on to the line in a no vis simulation and attempting to stay in perfect trim. I received a good tongue lashing from the instructors for that one. Lesson learned.

~ Jason

 

[rjack321]

Has air been outlawed? Are the scuba police going to come after me for yet another infraction. Will I be excused since nobody told me that suddenly air at 80' is a no-no. Funny that it worked fine for me on hundreds of dives.:06:

I never said "air is for tires" or anything of the sort. I still dive air, mostly 40' or less.

However, there is something to be said that the tunnel vision of narcosis contributes to CFs (at depth) like this:
http://www.scubaboard.com/showthread.php?t=74063&highlight=memorial

Note that there was absolutely no gas management going on in this incident, 2x over.

 

[Charlie99]

Now that I’m thinking of working toward instructorship, how’s this sound for a plan:

In OW, introduce ‘rock bottom’ type calculations by working an example using an al80, from 100’ with an elevated SAC. I haven’t worked through the calculations, but let’s assume for the moment that it comes out to 800 psi.

This could be read (or misread) to mean that you have enough experience that you are starting to work on getting instructor cert, AND YOU HAVEN'T YET FIGURED OUT A ROCK BOTTOM FOR A 100' DIVE! How in the world have you survived so far?

There is an appropriate level of instruction for new divers. "Be back on boat at 500psi" is too little. Going through SAC calculations and detailed rock bottom calculations aren't really necessary for beginning divers. Indeed, it appears that many divers have no problem safely diving without having any idea as to what SAC is, much less knowing their own SAC for different conditions.

What worked for me as a new diver were some simple rules of thumb. Nothing more complicated than "always start your ascent with no less than 100psi per 10' of depth, and never less than 500psi. At the beginning, when your air consumption is high, ascend with a bit more air than that".

Others have posted similar sort of guidelines like 700psi for 60' and shallower, 1000psi for 80' and shallower, 1200 psi for 80-100'. This sort of 2 or 3 pressure vs. depth rule also has the advantage of being simple and easy to teach, while still accomplishing the goal of safe diving.

Obviously, this would also include a caution about needed more psi if one is diving a small tank, but small tanks aren't typically used on deeper dives.

 

[lamont]

Not having seen Rec Triox and Tech 1, I cannot comment on that. I agree with you that a lot of times, divers do make mistakes in when to leave depth. It aint just beginners, either.

However, I think this usually arises when there are other factors at play, and people get so caught up in solving them that they forget to watch their air/depth/time.

Yes it does. The important lesson is to not get caught up in solving a problem and to make the choice to get out of dodge.

I'd reckon that in a simple case of someone running low on air, going up to the surface is something that comes pretty naturally.

Even if bad decision making does come into play in this case, the correct solution is teaching better decision making. If someone is going to forget to go up at 50 bar, they can equally forget to go up at 70 bar.

That is not the issue. The issue is when something goes wrong at the worst possible moment (50 bar or 70 bar), do you have the gas left to solve the problem, collect your wits and get out of dodge. The point is that before the emergency you are watching your gas and you never let it go below 70 bar at depth and therefore you have more margin of safety than the diver who lets their gas get down to 50 bar at depth, at the moment that the emergency occurs.

If you have people who simply forget to come up at 50 or 70 bar without having an emergency occur, then you have a whole different issue in executing a safe dive.

Based on what I have seen (atleast 200+ different people hitting 50 bar at 30m and easily making it up to the surface after doing a slow ascent and a safety stop), I'l have to disagree. I suspect, however, that neither of us is going to convince the other, so let's leave it at that. Each of our opinions are shaped by the divers we see and situations we encounter.

Safe diving to you,
Vandit

I'm driven by the probabilities of large numbers. Your sample size, and any one single divers sample size, no matter how experienced or prolific of an instructor, is simply miniscule compared with the entire sample of all divers across the world. Something that you would not expect to see once in your life could be expected to happen once every year in a sample size 100 times as large as what you have contact with.

 

[darkpup]

I read these twelve pages of responses, and I still need an answer to my question...

What is gas management?

Oh, it's definitely a loaded question. A general definition for recreational diving would be that gas management includes: consumption rate at depth, reserve gas for an emergency, and a plan of 1/2s, 1/3s, or all useable based on dive conditions.

These are just tools to help the diver plan and execute a safe dive. Is knowing your consumption rate at 40' really that important? Not really. Is knowing your consumption rate at say 130' important? Yes. Are both dives considered recreational? Yes.

I think it is a loaded question. I think the answer will vary depending on the type of diving that you are doing.

On an out-and-back dive, is checking your gauges frequently, turn at a half of tank, ascend some, do a safety stop and get back on the boat with 500 psi enough? I think it is, and this was taught in my PADI OW class. Do you really need to know much more?

Above 60', this plan is very similar to the way I plan my dives. The end result is that we'd both end up on the boat with about 500 psi in our tanks regardless of how we planned our dives. The difference is that I used a quick calculation to determine my gas plan, and you used a rule of thumb. No big deal.

I would however ask at what pressure would you begin your ascent?

With the way I plan my dives, I would use a Rock Bottom calculation of 800 psi (single al80 tank) on a 60' dive, which means I would need to be heading to the surface by 800 psi. This would give me 20 cft of gas in reserves, which gives two divers roughly 5 minutes to reach the surface in an OOA situation from a max depth of 60'.

It took me about 30 seconds to run these numbers.

On a drift dive, is checking your gauges frequently, start deep, work your way shallower, ascend to your safety stop at 700 PSI and get back on the boat with 500 psi enough? I think it is. Do you really need to know much more?

Once again, your calculations are very similar to the way I do mine. For instance, if you hit 100' for 5 minutes, slowly ascended to 50' over the course of another 20 minutes, and started your ascent when you hit 700 psi, that's almost exactly the amount of gas at 50' I would reserve for this sort of dive.

Mind you, I would have had a Rock Bottom calculation of ~ 1600 psi while at 100', but would have adjusted down my Rock Bottom as I ascended. In my previous example, 800 psi is enough gas for 2 people to safely reach the surface from 60' according to my calculations. At 50' to 40' it would be less than this.

So I ask you, does knowing that 20 cft of gas / 800 psi in an al80 tank is enough gas for 2 people to reach the surface safely in an OOA emergency helpful?

I find that it calms things at a time when stress is high, because your buddy knows you have enough gas to reach the surface. The end result however is that you're method for planning the dive came to the same conclusion as mine, so it becomes a matter of preference IMO.

For recreational diving, do you really need in depth gas management? I agree that for other diving activities more in-depth gas management is needed, but for cruising around a reef on vacation I could care less about my SAC rate.

IMO, that's a judgement call each of us has to make ourselves, and I would agree with you, I very rarely track my SAC rate on vacation reef dives.

At the same time, was the 30 seconds I spent calculating Rock Bottom for a 60' dive considered "in depth gas management"?

On a square profile to 100', what pressure would you start to make your way back to the surface?

Not sure if this helps answer your question about what gas management is, but if nothing else, I hope it generates some questions regarding whether a diver has enough gas following the 300 to 600 psi rule of thumb to get 2 divers safely to the surface in the event one of them goes OOA at depth.

~ Jason

 

[darkpup]

I never said "air is for tires" or anything of the sort. I still dive air, mostly 40' or less.

Richard, sorry for throwing you under the bus on that one.

~ Jason

 

[lamont]

What has happened here? 1 person has 50 bar and the other has 0? How did that happen? In most diving instances, when the first person in the buddy team hits 50 bar, the other will have 50 or more. They thumb the dive and head up. Plenty of air - no problems. You and I both agree on that.

If you are in a situation where 1 buddy has 50 bar at 30m, and at that *precise* point, the other buddy has a catastrophic gas failure, then I'll humbly posit that skipping a safety stop in this situation wont be the end of the world. 50 bar should get both of them to the surface.

If you are in a situation where 1 buddy has 50 bar and the other buddy has 0 b/c he forgot to watch his air, hen I'll humbly posit once again that it isnt better gas planning that is needed, but a swift kick upside the buddy's rear end, to remind him to watch his SPG.

Would knowledge of better gas planning be worth it? Absolutely. That doesnt change the fact that the humble ole recreational rule works spankingly well for the most part, and has withstood the test of time. It is possible to make an argument for better gas planning, without completely disparaging the existing method and calling it "completely worthless".

Cheers,
Vandit

The problem is when you're at 100 fsw/30msw+ and one buddy hits 50bar/700psi and at that moment the other guys regulator starts to free-flow and drain his tank. Heartbeats race, SAC rates increase and perceptions narrow. Both divers task-focus on dealing with the free-flowing regulator at depth. Eventually the other guys tank is drained and they're trying to sort out the OOA. Hoses get caught and minor CFs ensue because they're rushed, maybe they have buoyancy issues and drop down to 120 fsw. Now they're down to 25 bar or so in a single tank. The team starts out swimming towards the bow of the ship at depth because they're task-focused on finding the upline and not on simply getting off the bottom (this is a super-common mistake) and they run out of gas completely at 80 fsw and both of them CESA and hope they don't embolize or get bent. This is really entirely plausible and based on poor decision making that everyone in my RecTriox class (self included) made, and which I consistantly see in every write-up of a RecTriox or Tech 1 class on the internet. The factor that makes it somewhat unlikely is getting a free-flow at precisely the unupportune moment in the right diver when the other guy is down to 50 bar -- but as an agency or as an instructor for an agency you have to assume that across all the divers certified by the agency that this chance occurance is actually not that unlikely to occur.

And also, you keep on trying to claim that we're trying to make it too difficult and really I'm fine with "don't go below 50 bar and don't go below 20msw/60fsw" as a rule for BOW divers. But for AOW divers diving to 100 fsw, they need to be aware of the basic physics that they'll be consuming gas at a faster rate the deeper they go, and that the "50 bar" rule needs to be modified the deeper they go. If they can't handle gas management at even that most rudimentary of levels then they simply have no business going deeper than 60 fsw.

 

[MXGratefulDiver]

While I am all in favor of tech training (the diving discipline and greater knowledge you learn from it really takes one's diving skills to a whole new level), it gets my hackles up when I see people who have been exposed to a little tech stuff turn around and starting to denigrate everything recreational.

Actually, I don't see gas management as a "tech" vs "rec" issue at all ... all divers have to breathe, and since the only gas they'll be breathing is what they take with them (excepting air shares), it only makes sense to understand a bit about consumption.

I liken it to knowing the MPG and gas tank size of the car you're driving. When you're just tooling around town, who cares. You see the gauge getting a little low, you pull into a gas station. But if you're planning a trip, it helps to know how many miles you're gonna get on that tank of gas ... especially if you're likely to run into one of those signs that says something like "next gas 89 miles" ...

Take an example: perfect horizontal trim for reef diving is one of the things that doesnt make sense to me. For tropical diving, one has to look all around - in front, below and above. Being horizontal gives me a crick in my neck - I find it easier to be slightly inclined. Is that the most efficient way to dive? Probably not. But it is the most comfortable - and I've started seeing a lot more mantas since I modified my trim to be angled.

I quite agree ... actually, I spend a considerable amount of my reef diving time inverted (head down, fins up) ... it's just easier taking pictures that way ...

... Bob (Grateful Diver)

 

[caseybird]

The problem is when you're at 100 fsw/30msw+ and one buddy hits 50bar/700psi and at that moment the other guys regulator starts to free-flow and drain his tank. Heartbeats race, SAC rates increase and perceptions narrow. Both divers task-focus on dealing with the free-flowing regulator at depth. Eventually the other guys tank is drained and they're trying to sort out the OOA. Hoses get caught and minor CFs ensue because they're rushed, maybe they have buoyancy issues and drop down to 120 fsw. Now they're down to 25 bar or so in a single tank. The team starts out swimming towards the bow of the ship at depth because they're task-focused on finding the upline and not on simply getting off the bottom (this is a super-common mistake) and they run out of gas completely at 80 fsw and both of them CESA and hope they don't embolize or get bent. .

Interesting scenario Lamont, and I would like to determine how to deal with it. Some assumptions: Single 80 cf tank for each diver, no redundant air source, NDL dive.

Primary mistake: not being at the upline when pressure reaches 700 psi.
If they were at the upline, they would probably begin an immediate ascent, without the drop down to 120'.
Reasons for not being at the upline:
poor or no pre-dive gas planning.
not checking the SPG.
getting lost on the wreck, especially in low viz.
being distracted by artifacts, bugs, photography.

All these are relatively easy problems to avoid.

plan the dive, check guages, keep the upline in sight, keep your head in the game, concentrating on the DIVE, don't over-taskload.

OK, now the divers have blown it, they are 100' from the line, 700 psi and a free flow blows off, what should they have done?
Share air off the remaining tank, begin immediate ascent, hold safety stop as long as possible, surface, signal boat, get picked up and monitor for signs of DCS. Not a great plan, but easily surviveable.

Why didn't they do that?
1) Distraction by free flow.
2) Fear of being blown off the wreck.
3) Inability to hold safety stop without an upline to hold on to.
4) Fear of losing the boat.
5) New divers who cannot make the right decisions without a dive leader.
6) Fear of losing the dive group.

Solutions:
1) situational awareness and prioritizing. With that little margin of gas, trying to control the free-flow is a serious waste of time. If the only gas supply is at the surface, getting to it is the only goal.
2,3,4) Being blown of the wreck can lead to the next 3 problems, going adrift, making a poorly or uncontrolled ascent and losing the boat are pretty unpleasent prospects.
Going OOA is a lot more unpleasent. The diver could deploy a SMB to signal the boat and help control their ascent, as long as the time it takes to deploy doesn't seriouly deplete the air supply. Negatives, trying to deploy a bag while air sharing could be pretty difficult, (see CF) wasting time and air. It would be better to begin the ascent, then deploying at safety stop depth when the gas supply will last a lot longer.
The best solution would be using a Jersey-style upline, where the line is tied off to the wreck. This will anchor the buddy team and make the ascent a lot easier. Of course, if the team had a jersey upline they probably wouldn't get into this kind of trouble to begin with.
Carrying effective signaling devices will make the team more confident about attempting a free ascent. Air horns, signal mirrors or other devices are mandatory in open seas.
5 & 6) These divers have already lost the group, and don't have time to find them. I think this is a very common problem, especially with inexperienced divers. Not being able to manage without a dive leader, same problem, inexperience leading to poor decision making skills.
Main points:
Pay attention to the dive.
watch your SPG.
Carry signaling equipment.
Train for adverse dive conditions.
Don't dive over your skill level.
Mentally rehearse emergencies.
And, What the heck, Carry REDUNDANT gas supply!

Comments?

 

[limeyx]

Jason,
...
Take an example: perfect horizontal trim for reef diving is one of the things that doesnt make sense to me. For tropical diving, one has to look all around - in front, below and above. Being horizontal gives me a crick in my neck - I find it easier to be slightly inclined. Is that the most efficient way to dive? Probably not. But it is the most comfortable - and I've started seeing a lot more mantas since I modified my trim to be angled.

...
Safe diving,
Vandit

I would say (shock horror) that it's not necessarily that 100% level trim is so vitally important, but to borrow someone else's words, (and kind of echoing what Jason says) It's more about being able to control your position in the water. Which may be horizontal, or may be some other orientation (preferrably not touching the bottom/destroyin the coral).

And not to diverge too much, but I have *plenty* of video on the cutting room floor of people slamming into the reef when I was in hawaii last year, including one who (i will never know how) slammed backward into the back wall of Molokini so hard I thought she had whiplash, and a person who spent the whole of a 40 minute beach dive literally crawling along the bottom as "She was scared to put any air in her BC" -- and this was a person who had just taken a refresher course two days before! (Note: The DM forced her to take her gloves off for dive 2 and she did a *much* better job of keeping off the coral