Should all divers have a redundant air source on every dive?

[Blackwood]

But in engineering you have a known strength and a known stress and you add a safety factor to those knowns

In diving you have only one known, the amount of gas you are carrying. The stress is the chance of something happening and the unknown amount of gas needed to deal with the happening. That's why what ever safety factor you add is just shot in the dark

You have a known strength, and you compute a stress based on design loads, plus some padding. But since don't know how much you are going to exceed your design limits by, that padding you are carrying is arbitrary. It has to be arbitrary. If you knew exactly what the maximum load case would be, you would not need to carry margin.

I agree it's not a 1:1 comparison, but I think it's sound enough.

I do believe you can know pretty closely how much gas you will use for a planned ascent (based on assumed consumption rates and tank specifications). You can also know pretty closely how much gas two people will use (based on the same assumptions). What you don't know is how much more gas the emergency will consume. So you WAG it.

 

[LeadTurn_SD]

I may only hurt you once, but the pain placed on your family and friends continues for a long time.

I do agree that diving with some sort of redundancy, be it a buddy or additional gear, is a divers choice and responsibility.

If you care one bit for those who care about you, you take that responsibility more seriously.

Point well taken Dave. Years before you made it

Captain and Nemrod can speak for themselves. The post I made was partly tongue-in-cheek in response to blanket "redundancy is always required" statements, and is certainly made for the conditions I dive in: warm, high viz, shallow, calm.

If I dove in California, or the PNW, or the NE, my answer would have been different

Don Francisco summed it up very well with this statement:

"An independent redundant air source is only a benefit for two types of situations. OOA due to a total failure to manage primary air supply, which is 100% avoidable. Or OOA due to a sudden catastrophic failure of the primary air supply. The likelihood of the second varies with conditions and is highly unlikely in warm tropical waters, and becomes more likely with lower water temps in the north."

A sudden catastrophic air source failure is such a remote possibility with well-maintained equipment here in the tropics that it is almost not a consideration. That leaves OOA due to "operator error" as the most likely culprit where I dive. Entanglement risk is low-to-none.

Having said all that, I do still wrestle with where "the line" is for me, and as a result generally stay at depths that I can still freedive to. Which these days means pretty darned shallow compared to 30 years ago.

Best wishes.

 

[LeadTurn_SD]

Ok, if I'm at 50ft or less aren't I able to go up in a controlled manner without a pony? This assumes the entire dive is not below 50ft.

Oh, this is sure to generate some flames, but here goes:

Yes. If you are within NDL, you can swim to the surface from any depth you can swim to the surface from.... Make sense?

CESA's have been made from depths far deeper than 50'. CESA's used to be routinely taught and practiced at about double the depth they are taught today. I was taught to perform CESA's from the 60-70' range. I've most currently practiced them from the 30-40' range.

If you were taught and practiced CESA from 30' in your open water class (I think this is the depth currently taught?), than you know that in an emergency you could surface from that depth, because you've already done it. And intuitively you should know that you are able to do it from 50', assuming 30' was not a problem for you.

There does come a point, which is different for each individual, that CESA no longer is an option (you will black out before surfacing). This is the "line" that each diver needs to evaluate for themselves. And it could be that for some divers and/or some condtions, the line exists at the surface (i.e., they would not be safe without a redundant air source).

Best wishes.

EDIT: Please don't take the above as a recommendation to include CESA in your gas management strategy Just trying to answer mpgunner's question.

 

[Nemrod]

It is kinda like this, y'all can become inmates of the nanny state, I am going to opt out and if it leaves me dead in a gruesome fashion and my friends weeping, make those roses red. I will go out fighting, my way, with my boots on. Don't cry for me.

I do carry or utilize various forms of redundancy on certain types of dives, every dive, no thanks, I will pass on that, I will take my chances.

N

 

[DaleC]

Too much???

 

[NudeDiver]

Guy looks like an action figurine

 

[DaleC]

Why mount a pony when you can ride a horse!

Seriously though, I've altered the way I use my pony.

At first I dove it all the time. Now I use it if I'm going deeper than I'm comfortable doing an ESA from or if I'm soloing somewhere I'm not familiar with.

You could drive yourself crazy trying to account for every concievable scenario so I try to go with the concept of planning a contingency for one problem.

I usually end my shallow dives with a larger reserve than I used to so that reserve accounts for solving a problem under water like entanglement.

The pony accounts for a serious equipment failure at a depth I may not be able to ESA from.

 

[mpgunner]

Oh, this is sure to generate some flames, but here goes:

Yes. If you are within NDL, you can swim to the surface from any depth you can swim to the surface from.... Make sense?

CESA's have been made from depths far deeper than 50'. CESA's used to be routinely taught and practiced at about double the depth they are taught today. I was taught to perform CESA's from the 60-70' range. I've most currently practiced them from the 30-40' range.

If you were taught and practiced CESA from 30' in your open water class (I think this is the depth currently taught?), than you know that in an emergency you could surface from that depth, because you've already done it. And intuitively you should know that you are able to do it from 50', assuming 30' was not a problem for you.

There does come a point, which is different for each individual, that CESA no longer is an option (you will black out before surfacing). This is the "line" that each diver needs to evaluate for themselves. And it could be that for some divers and/or some condtions, the line exists at the surface (i.e., they would not be safe without a redundant air source).

Best wishes.

EDIT: Please don't take the above as a recommendation to include CESA in your gas management strategy Just trying to answer mpgunner's question.

Thanks LeadTurn_SD, very helpful.

 

[Buoyant1]

Only if said buddy saves some for you.

And he's within a couple-two-three fins kicks.....

 

[MXGratefulDiver]

And he's within a couple-two-three fins kicks.....

Seriously? Didn't your OW certification include an underwater swim test? Mine did ... 50 feet for OW ... 75 feet for several higher-level certifications.

Now, I'm not saying that your buddy shouldn't be within two-three fin kicks ... but if you're proficient you should be able to travel farther than that without breathing. The key is to keep your cool and not have to struggle at it.

And besides that, if you're relying on a buddy, then diver awareness is at least as important as distance. You'd better have some way to get your buddy's attention ... because otherwise they just might be moving away from you while you're trying to catch up with them ... and that would be downright aggravating if you happened to need their air at the time ... :depressed:

... Bob (Grateful Diver)