How Much Air Do You Have??? Let's Do The Math

[@stevenlovell3466]

Bryan, full marks to you for knowing the metric system. Us Brits gave you Imperial measurements, then went to Metric. Americans and sometimes Canadians are the only ones in the world who use Imperial (including areas they frequent, like the Carribean). Believe me, Metric is easier. However, the measure of a knowledgeable and professional Instructor, is someone who can speak both systems..

[@LakeHickoryScuba]

Thanks Steven Lovell.

[@ChadBIsRacing]

This is a great video, I've watched it at least 5 times..

[@LakeHickoryScuba]

Glad you liked the video @ChadBlsRacing.

[@ivoryjohnson4662]

Very informative

[@LakeHickoryScuba]

Thank You.

[@abtuben]

Thanks for covering the metric as well!

[@LakeHickoryScuba]

You're welcome.

[@zebrastrong9291]

Could you do one that includes a steel 80? I’m vertically challenged so I need the shorter cylinder. Plus it holds actual more air than the aluminum 80 from what I understand. The steel weight will also help with my extreme body buoyancy. Plus the smaller buoyancy change from full to empty

[@LakeHickoryScuba]

We sure can.

[@johnwilliams2014]

@@LakeHickoryScuba Up in the north east the Faber HP 80s & 100s rule the day

[@clarkeysam]

I appreciate you taking the time to include metric units, because, frankly, when imperial units are used it might as well be a different language, I need to translate (convert) them into what I can understand. The smallest of minor points, Al80s are not very common in the UK (and I presume many cold water diving locations). 12 ltr steel tanks are the most common and then 15 ltr steel tanks. I'd estimate that there's more rebreather divers in the UK than OC divers using AL80s!

[@LakeHickoryScuba]

You’re welcome. I’ve had others in the past ask us to include metric into our videos, so that is what we are trying to do.

[@MethosFilms]

i have a pony plus a emergency spare air for extreme emergencies. lets say 2 people run out of air. i work on the rule of double redundancy. my instructor said i do not need to do this but i feel like i wanted to and he said it was my call. it sorta bulky but that is okay with me. i bought a mares dragon bcd. i have the spare air attached to it on the right side on a d ring. the pony is attached to my primary tank. i just like being safe and it gives me more confidence. ill be learning twins next year. :) best wishes

[@LakeHickoryScuba]

In my opinion, there is absolutely no problem diving with your setup. I encourage all to dive in a manner that makes them feel comfortable.

[@sparkyobrian6417]

thats triple or quadruple redundancy, but if you like it, I quite agree , go for it, just remember with an increase complexity comes an increase in failure modes and confusion possibilities.

[@sparkyobrian6417]

@@LakeHickoryScuba Im glad this came up, the trend lately i see and experience is the " Im safer than you" culture, many new divers I have come in contact with panic if someone is on a 40' rec dive without a back up computer, side mount twins with quad regs and a pony. That seems exaggerated but its showing up more and more, I was lectured by a new 62 dive tech/deep/sidemount student for diving doubles without an iso manifold and backup pony. It was a cleanup dive in about 15' seawater. theres great value in safety and training but it needs to be tempered in many cases, everyone wants to dive the Andrea Doria with 40 dives under their belt it seems. In 40 years ive never had one ooa, and have only seen two- neither were equipment failures, just inattention,(relying on the computer in one case. ) if you expect a double ooa, I dont want to dive with you or your group.

[@brianc5212]

Are the metric numbers listed in the Cylinder column the unpressurized volume sizes - also known as water volume?

[@LakeHickoryScuba]

Yes, that is correct

[@ronaldlee668]

When you do the equation for the AL80, and finish the initial calculation you state that you end with "45.39 cf still in the cylinder" (8min into the video), but I believe that answer still needs to be divided yet one more time by 3 (or divide everything by 3 at the begining) , to give you an actual ending of 15.13 as there is no way you can start with 26.66cf and end with 45.39. OR, divide everything by 3 at the start and then do the calculations, which would look like this: AL80 (cf) 80/3 = 26.66 starting pressure 3000/3 = 1000 ending pressure 1700/3= 566.66 AL80: 26.66 / 1000 = .02666 .02666 * 566.66 = 15.10cf So the correct amount of remaining air for that cylinder with 1700 psi, has a total of 15.10 cf

[@LakeHickoryScuba]

Hello Ronald, in this video we break down how much psi is in a cubic foot of air. This video is not meant to be apart of the the rule of thirds. We have a separate video on that. You seem to have confused the .026 with 26.6 cf. Great question though.

[@shannonbriscoe8425]

Ronald Lee, Bryan's calculations in the video are correct. You've made an error in believing that the starting volume is 26.66 cf when that is in fact the volume of air in the cylinder when you are at 1/3 of working pressure (1000 psig). The full volume of the cylinder is actually 80 cf, not 26.66 cf. Given that the 1700 psi that Bryan used as an example is greater than half of the starting pressure of 3000 psi, you would expect the amount of air left in the cylinder at 1700 psi to be greater than half the original 80 cf. With that in mind, 45.39 cf remaining at 1700 psi makes perfect sense.

[@sparkyobrian6417]

another excellent video AAAA+++

[@LakeHickoryScuba]

Thank You sparky obrian

[@markfrantz4612]

Oh my god. That is my mom's calculator. She is an accountant. I learned math with that calculator XD

[@LakeHickoryScuba]

Hello Mark Frantz, we use several of the calculators around the shop. They seem to be very popular.

[@joelafrite7850]

Theoretically yes, but in reality no one cares about the working pressure as a measure of content at the start of the dive. I have seen "full" AL80 and AL100 anywhere between 148 and 232 bar, depending on how rushed the people at the fill station were, or whether or not they want my recurring business My RMV varies between 15 and 25 l/min depending on the work load. If I have to follow a person or a group, I have little control over the depth. And then there are dive instructors that send students on an AL80 down to 40m until non-deco time is up - rule of 5th or 6th? Theoretically you are right, but that's not how the diving industry works 🤔

[@LakeHickoryScuba]

Sorry to here about you misfortune. The purpose of the video was to show divers how you calculate what is left inside a cylinder at the end of the dive. Happy Diving.

[@joelafrite7850]

@@LakeHickoryScuba misfortune? I listed variables that affect what's left, and what can be done with the remaining air in the tank. I just think that a beginner (or the occasional vacation diver) shouldn't even think about what can be done with the remaining air. That's all. Peace out.

[@LakeHickoryScuba]

Your Quote """" If I have to follow a person or a group, I have little control over the depth. """" End Quote I guess being controlled by others is a misfortune to me. In regards to your RMV rate, a divers RMV rate never changes regardless of work load. The RMV rate (Respiratory Minute Volume) is only controlled by the volume of their lungs. Thus this volume never changes, the RMV never changes. Your SAC rate (Surface Air Consumption) does change, based off the size of cylinder you use, and the work load. The calculation for remaining cubic feet of air in a cylinder has nothing to do with how much a cylinder has to begin with, but is based off what the working pressure is, which is a known variable, and unchanging variable because that is what determines the volume of the cylinder, and the ending pressure. Here is an example. An 80 cf cylinder filled to 3000 psi, is 80 cf. An 80 cf cylinder filled to 3500, would be the equivalent to a 93 cf cylinder, but once it reaches 3000 psi, it is still an 80 cf cylinder (we didn't physically change the size of the cylinder). All other variables being the same as listed in the video, at the end of the dive, regardless of the beginning pressure, you would have an 80 cf cylinder with 1000 psi. So the ending cubic feet of air would still be the same, only changing if the ending pressure is more or less. You have to remember, we are not trying to figure up how much air you used, but how much cubic feet of air you have remaining. Lastly, I encourage all divers to be aware of how much air they have. You never know when an emergency may happen, and they have to step up to handle the problem. Safe Diving

[@joelafrite7850]

@@LakeHickoryScuba I wouldn't call diving in a group and staying with the group (and thus not being able to determine the depth) being controlled by others, to the level of misfortune, can you please point me to a source that defines the RMV, and supports your statement, that the RMV is constant and not depending on the work load (on land or under water)?

[@LakeHickoryScuba]

You can contact the Divers Alert Network and they have a great article on Respiratory Minute Volume otherwise know as Tidal Volume in the medical field (unfortunately I do not have it in front of me to tag in this response). In short, our lungs are made of flexible material, but the maximum amount of cubic feet does not change. Send me your email, and I will see if I can find the article mentioned. I will be happy to email the findings. Anytime you are diving with a charter service, pre-determined depths will be put into place. A proper dive plan with your buddy can mean all the difference in the world in regards to controlling your dives. If your goal is to reach a depth not allowed by either the dive site itself, or the charter not letting you go any further, then you can simply provide your own charter and it solves the problem.