Vote: What is a reasonable SAC "emergency" factor for planning?

[BobbyWombat]

One of the items that comes up continually in the SpareAir vs. Pony Bottle (vs. have a better buddy) debate is that your SAC rate will go up when you are faced with an emergency.

For gas management purposes, it seems that knowing your SAC rate in an emergency (I'll hazard calling it your "ESAC") would be important. i.e. if I wanted to make sure I had an adequately sized pony bottle, I had better have a realistic estimate of my air burn rate when the adrenaline is pumping from and encounter with a free flowing regulator at 100'.

What say you, oh Great ScubaBoard? What factor should you multiply against your SAC to get your estimated ESAC?

Please! Cast your vote or post your rock-solid reference and we'll see if we can come to a consensus on this. Thanks!

-bw

 

[Dash]

My guess is that many will answer that it is too individual to have a set value or limiter, based on knowledge, experience, etc.

Its a good question though and one Ive asked myself. I have calculated SAC for my dives and most calm ones have been around .50 - .55. One nervous one I did with extra work got me to .65-.70.

I might double that for a true, panic-encroaching, emergency. But I really dont know, it could be more..

 

[nereas]

Beginners (<100 dives) may be subject to hyperventillation, sure.

But the more you dive, the more relaxed it all becomes.

 

[BobbyWombat]

Sure, there are lots of shades of grey here, and I recognize that.

What I'm trying to arrive at is a reasonable "rule of thumb" if you will, just for basic planning purposes. It will certainly vary from diver to diver and an individual would need to take into account level of personal experience and confidence, etc.

There are studies I found online that say, while variable from person to person with some outliers, your respiratory rate increases by a factor of 1.3 to 1.5 when excercising. By extension I think the collective experience on this board could come up with something similar.

Not an absolute answer, but maybe a useful tool.

 

[BobbyWombat]

From:
http://www.randomhouse.com/features/wisdomofcrowds/index.html

The Wisdom of Crowds.
In this endlessly fascinating book, New Yorker columnist James Surowiecki explores a deceptively simple idea that has profound implications: large groups of people are smarter than an elite few, no matter how brilliant—better at solving problems, fostering innovation, coming to wise decisions, even predicting the future.

=========

So Vote! I'm interested in what turns out.

 

[neil]

For poop-hitting-fan situations, I think 1.0 works pretty well and I've verified that with SAC calculations for myself. I'm 6'1, 200 lbs. and a reasonably relaxed rate is .5-.6 and during exertion I've measured about 1cfm.

 

[TSandM]

Well, my resting SAC rate is about .4, and I know from experience that simply running a reel can raise it to about .7. So I would assume that doubling the rate for a real, eye-popping emergency would not be overestimating at all.

 

[fweber]

My primary teammate and I have been documenting our air consumption for most of our dives and our numbers are pretty solid although they vary because of conditions and work involved.

Dead rest(hand on bottom or deco stage, absolutely no movement nor effort)=.25-.35

Moderate rest(hovering, casually drifitng along reef without finning)= .35-.5

Normal bottom rate(mixture of frog kicking, sculling, photographing, etc)=.5-.75 him .65-.85 me

Working bottom rate(hammer, pull measuring tape, etc)=.65-.95

Measure heavy swimming rate(essentially combat swim, just shy of shark is chasing me)= 1.5+

Easily double your normal working SAC rate. IANTD states that up to X4 can be expected during true duress.

 

[rockjock3]

I do a similar thing for deep dive planning. When I plan a deep dive we have to figure rock bottom gas requirements. When doing that we use a SAC of 1.0 for calculating contingency gas requirements. We both have SAC rates around .4-.5 so for us is happens to be about double, but many of the people that I know use 1.0 as well regardless of their SAC rate.

 

[BobbyWombat]

Great input fweber!

IANTD states that up to X4 can be expected during true duress.

So the manual says up to 4x your normal rate, but so far the "wisdom of the crowd" says to use 2x. Interesting.....