SAC rate during an emergency

[Steve50]

So far, since I've been diving with a computer that could provide good info on air consumption rates, I've not had the occasion (no heavy duty emergencies) to observe the effect on my breathing rate.

Have any of you observed the effect an emergency had on your air consumption?

 

[ianr33]

No direct observation in an emergency but a few observations.

My normal SAC runs around 0.6 (doubles/sidemount,drysuit) Working hard (high flow/strong current) it can easily get up to 1.0. Wouldn't be surprised if it could reach 2.0 in a genuine emergency with exertion and adrenaline.

Most figure on 1.0 as an emergency SAC. Bottom line is don't skimp on gas reserves.

 

[sea2summit]

I've heard it compared to a sexually aroused hippopotamus.

Seriously though I think it depends on the emergency, I have a buddy that took a CO2 hit on a rebreather and went through his and two buddies bailout gas to exit a cave and they wen't diving alpine.

 

[MXGratefulDiver]

So far, since I've been diving with a computer that could provide good info on air consumption rates, I've not had the occasion (no heavy duty emergencies) to observe the effect on my breathing rate.

Have any of you observed the effect an emergency had on your air consumption?

It really depends on the diver and the nature of the emergency. A diver who has reasonably good skills and remains calm while taking care of business won't show much, if any, increase. Conversely, a diver who is insecure with his skills or who is struggling or rushing to deal with the emergency can show as much as a four-fold increase. A diver's physical condition will also have a significant impact on how much their air consumption rate goes up under stressful circumstances.

My experience is in measuring my AOW students air consumption rates under both very calm and very stressed conditions, and comparing the differences. It varies wildly from diver to diver.

... Bob (Grateful Diver)

 

[bleeb]

I was going to defer to the replies already posted, when I realized that there might actually be a useful number for a rough upper bound as to how much gas a person can actually go through. Apparently, world-class middle to long distance runners, cyclists and cross-country skiers have the largest (human) lungs around and the strength and endurance to push air in and out of them at maximum rate for sustained periods. IIRC, typical measurements for world champions in these sports have been found to be somewhere in the 3.5-4 cfm range. High performance recreational (non-elite) athletes in the same disciplines manage around 70-80% of that, while the average untrained person has difficulty sustaining more than half to two-thirds of that for more than a minute or so.

So while it's still a generalization, 2-3 cfm might not be a bad 'worst case' value to work with. Unless you're Lance Armstrong or Haile Gebrselassie. http://en.wikipedia.org/wiki/Haile_Gebrselassie

 

[dumpsterDiver]

I was going to defer to the replies already posted, when I realized that there might actually be a useful number for a rough upper bound as to how much gas a person can actually go through. Apparently, world-class middle to long distance runners, cyclists and cross-country skiers have the largest (human) lungs around and the strength and endurance to push air in and out of them at maximum rate for sustained periods. IIRC, typical measurements for world champions in these sports have been found to be somewhere in the 3.5-4 cfm range. High performance recreational (non-elite) athletes in the same disciplines manage around 70-80% of that, while the average untrained person has difficulty sustaining more than half to two-thirds of that for more than a minute or so.

So while it's still a generalization, 2-3 cfm might not be a bad 'worst case' value to work with. Unless you're Lance Armstrong or Haile Gebrselassie. http://en.wikipedia.org/wiki/Haile_Gebrselassie

I've seen this effect myself. A large very well trained athelete can use a HUGE amount of air. It seems that everyone thinks that if you are "in shape" you will use less air. This may be true for a relatively low work load, but if you are really out of shape there is no way you can consume as much as an athlete who is working at their aerobic capacity.

 

[TSandM]

Having never really been in an emergency, I don't know how much gas I would use. But I do know that under mild to moderate stress (running line at night in current) I've more than doubled my gas consumption.

 

[Akimbo]

So far, since I've been diving with a computer that could provide good info on air consumption rates, I've not had the occasion (no heavy duty emergencies) to observe the effect on my breathing rate.

Have any of you observed the effect an emergency had on your air consumption?

People react to heavy duty emergencies in different ways. On the surface or underwater, you can voluntarily push yourself to high work loads and the respiratory rates that go with it and get pretty close.

As a Scuba instructor, you might want to experience it — in a controlled environment of course. Just put on the largest set of fins you can find and swim against the side of a pool as hard and for as long as you can. Have somebody standing by and maybe with Oxygen available. Knowing the sensations and symptoms of overexertion underwater will make you better able to anticipate the onset and recognize it in others.

You might get a buddy to do the same exercise, breathing off your octo at the same time. It will also be a confidence building test of your regulators. On the other hand, if the regulators fail, that information would be worth even more.

 

[Sas]

Mine has more than tripled (from a resting rate of 0.3cf to 1.13cf) when I have swum as hard as I could and really exerted myself.

Generally when I have been under stressful situations that don't involve being puffed out (such as having things done to me by instructors, or being very cold) it increases to about 0.5-0.6 though.

One buddy who ran out of air swimming insanely hard against a current and ended up in a lot of distress, I worked out his air consumption to be about 1.8...

 

[_Remko_]

So far, since I've been diving with a computer that could provide good info on air consumption rates, I've not had the occasion (no heavy duty emergencies) to observe the effect on my breathing rate.

Have any of you observed the effect an emergency had on your air consumption?

I once had a panic situation when all seemed to go wrong and it struck me like lightning. My average consumption after the dive was around 40 liters/minute while it normally is around 17. Since then I plan dives using a conservative breathing rate and would never use a computer to tell me how much breathing time I have left. When a buddy runs out of air and panics, causing you some stress while the both of you have to surface on one tank safely those numbers really don't mean much.