How do I calculate my consumption rate?

[Ojai Diver]

I needed to drain my pony bottle down to switch to a larger cylinder. While doing bills, etc., I breathed my 6 cf bottle empty in 17 minutes. From this, how do I calculate a consumption rate useful for diving at various depths?

Thanks.

 

[northernone]

I needed to drain my pony bottle down to switch to a larger cylinder. While doing bills, etc., I breathed my 6 cf bottle empty in 17 minutes. From this, how do I calculate a consumption rate useful for diving at various depths?

Thanks.

6 cf ÷ 17 minutes = resting surface air consumption rate

The issue with this becoming useful is while bills are stressful they are likely less of a workout than actual diving.

To convert this number to something helpful for dive planning you'd apply a theoretical multiplication factor to guess what your air consumption rate is while under stress or a workload.

To use that resulting number at various depths you'll need to multiply it by the AMBIENT pressure at DEPTH.

For example a dive at 33ft (salt water) is a dive where you'll experience 2 ATA pressure.

Take your surface air consumption rate and multiply it by 2 you'll get your air consumption rate at 33ft.

Cameron

 

[Ojai Diver]

Shucks. Thought there was more to it than that. Thanks.

 

[tbone1004]

Shucks. Thought there was more to it than that. Thanks.

make sure that you use ATA when adjusting for depth. I usually just round to the nearest ATA instead of getting pedantic with it. I.e. at 80ft, just use 4ata *99ft*, or if at 70ft, just use 3ata *66ft*, it's close enough. I would however recommend just using 1cfm and call it a day.
Look up rock bottom calculators to get an idea.

For me, I use ascent from 100ft of 4 minutes which averages at 2ata, so 2*4*1=8cf for ascent. I fix the safety stop at 1.5ata and 4 minutes, so 1.5*4*1=6cf. I.e. for any dive, I will never have less than 14cf of reserve.
After that, you need to adjust the time for "conflict resolution at depth". This is all dive dependent and will consist of how long it will take you to start your ascent. If on a 200ft long shipwreck in high ish current, you need to plan on at least 5 minutes to get back to the ascent line. If that wreck is at 100ft, you need 4*5*1=20cf on top of the 14cf you need for the ascent so anything smaller than an AL40 is not going to cut it.