Technically, the calculations provided aren't SAC (Surface Air Consumption) calculations, but RMV (Respiratory Minute Volume) calculations. SAC (psi/min) = psi used / (depth / 33 + 1) / time in minutes RMV (cf/min) = SAC * cylinder capacity / rated pressure SAC (bar/min) = bar used / (depth / 10 + 1) / time in minutes RMV (l/min) = SAC * cylinder volume The distinction between the two is important to understand, because air integrated (AI) computers can give you your SAC rate for the entirety of your dive. Since the dive computer doesn't know what cylinder(s) you dive with, it can only provide you with a pressure/minute number. To get to volume/min you need to convert SAC to RMV. If you're diving with a twin set of 2 Al80 cylinders, your SAC rate will be half of what it would be if you were diving on a single Al80 backmount. Since you're diving with twice the volume (and as such twice the amount of gas), the pressure will fall at half the speed, so you'll use half the pressure per minute. With RMV this value is corrected for your total cylinder volume. Your RMV will be a comparable number no matter how much gas you dive with. ------ If you need to convert RMV back to SAC for different volume cylinders, you can calculate this as follows: SAC (psi/min) = RMV (cf/min) / cylinder capacity (cf) * rated pressure (psi) SAC (bar/min) = RMV (l/min) / cylinder volume (l) Or you can convert SAC rates between different volume cylinders as follows: SAC_new (psi/min) = SAC_old (psi/min) * capacity_old / rated_pressure_old * rated_pressure_new / capacity_new - If the rated pressure is the same between the two setups, you can cross those out of the equation (like SAC_new (psi/min) = SAC_old * capacity_old / capacity_new). SAC_new (bar/min) = SAC_old (bar/min) * volume_old / volume_new

I only ever dive alone when I go to a very familiar dive site and I don’t go deeper than 22 feet. I kind of chicken out when I go somewhere new or go deeper than 30 feet which is when I insist on diving with a buddy.

@everythingscuba

2 жыл бұрын

Every diver must have their own comfort level and know the limits of what they are comfortable with! Thanks so much for sharing your comments with us Scuba Bro!

Good info and subbed. One comment though... If SAC is in volumetric units as you've shown (cu.ft/min or liters/min), that's not tank specific and doesn't need to be recalculated. It is, of course, useful to know how that rate maps to a pressure rate (PSI or bar per minute) during the dive (e.g., what's the latest I can start my ascent?), and that pressure rate will be specific to the chosen tank as well as depth.

@everythingscuba

3 жыл бұрын

Paul. Thanks for your comments. Thanks for pointing out my error. If SAC rates are given in terms of tank pressure, not volume of air, SAC rates are tank specific: 500 psi air in a standard 80-cubic- foot tank corresponds to 13 cubic feet of air. 500 psi of air in a low-pressure 130-cubic-foot tank corresponds to 27 cubic feet of air. So SAC is not transferable between different tank sizes when calculating I. Terms of pressure per minute. But they when calculating in volume. So I appreciate you pointing that out! As far as converting into PSI or BAR per minute I’d be curious if you find a mathematical formula to allow that calculation conversion from volume to pressure per minute I’d love to know. Thanks again for watching!

@pbillings808

3 жыл бұрын

​@@everythingscuba Some formulas that will be good enough for most purposes: SAC [psi/min] = SAC [cuft/min] * Tank Rated Pressure [PSI] / Tank Rated Vol [cuft] SAC [bar/min] = SAC [liter/min] / Tank Volume [liters] For example, a 0.5 cuft/min SAC using an AL80 (which is surprisingly rated 77.4 cuft at 3000 PSI) would be about 20 PSI/min at the surface. Don't forget to then scale for the rate at depth (80 PSI/min at 100 ft).

@everythingscuba

3 жыл бұрын

Thanks Paul! Much appreciated!

@ttb1513

5 ай бұрын

Thanks for this thread. I was wondering what was meant by the comment in the video.

I have no issues diving alone

Bro whats the deepest quarry in iowa? I grew up in se iowa

"Self Reliant Divers should: Maintain their equipment, be aware of the weather & sea conditions & anticipate problems & how to deal with them." Sir that is the minimum to be a safe scuba diver in the first place.

SAC rate..... if you dive at let’s say 30 meters, you already have a rough idea how long you can stay at that depth on YOUR tanks. If you are qualified for 30 meters, you choose to go deeper, your over your limit and that shouldn’t be done solo. I find experience in solo diving better than any theory you can do on land. Better off to be using your time servicing or checking your gear.

@bloodymarvelous4790

10 ай бұрын

I strongly disagree with your presumption that increasing your knowledge and understanding of SCUBA, and being able to plan your dive, has no benefit to your skills as a diver. Nor do I agree that servicing and checking and planning a dive is an either/or scenario. You should do both. Just going diving solo without proper training, planning and preparation, and accumulating experience that way, is a recipe for disaster, and the stupidest SCUBA advice I've seen anywhere ever.