How long does a SCUBA tank last? - Gas Calculation for Scuba Divers

#scubadiving #divegue #gueheroes
This video answers the question every diver is asked by non-divers sooner or later: How long does a scuba tank last? If the person is really interested I always start a very simplified version of GUE's gas calculation for scuba divers using the CAT formula to quickly estimate your necessary gas reserve and alongside with that, the expectable bottom time.
For scuba divers, it's vital to realistically estimate the necessary gas reserve, called the Minimum Gas, becuase this is what ultimately limits the dive time or essentially, what non-divers mean by asking, How long a scuba tank lasts.
00:00 Start
01:21 Available Gas
02:18 SCR and DCR
03:57 Minimum Gas
07:18 Practical Tips
Please note that this video is not the entire part of the gas management lesson taught during a Fundamentals Class. It's just a very simplified, quick explanation. If you like to know more about gas management, subscribe watch my other videos or even better, consider taking a fundamentals class with my or any other GUE instructor. If you need more information, just leave a comment!

[@ozjohnno]

Good education point on minumum gas requirements...... I will remember them. I am a product of the PADI system and I am surprised that something as important as min gas requirements were not covered in my OW class or for that matter my advanced OW class.....

[@DoktorBEN]

It’s (worryingly) not even covered in most instructor development courses…and the concept is so simple yet helpful

[@carlgosselin]

Love your diving series!!! Thx!

[@DoktorBEN]

Thank you very much! And thank you for watching!

[@carlgosselin]

DoktorBEN Can I suggest a video on the reasons why you would need a wetnote and what should be in it as an in-dive reference?

[@felipesantossilvafonseca8412]

Nice video and methodology!

[@DoktorBEN]

Thank you very much! Anything you’d like to see in future?

[@felipesantossilvafonseca8412]

Thank you for making the videos! They are really nice! And thanks for asking about potential topics. From the back of my head I’d say types & uses of gas, buddy & team work and maybe an overview of GUE courses, wreck, cave or deco/tech diving could be interesting themes if you haven’t discussed them yet. On the more practical side, I think the do’s and don’ts of kicks and drills are always nice. But sure there are other topics (and maybe more advanced ones) that could be nice as well.

[@rubikfan1]

Seems the deeper you go, the more rebreathers make sens.

[@DoktorBEN]

Exactly

[@complicatedmechanics9599]

Well. Now every non-diver seen this can plan better than most novice divers.

[@DoktorBEN]

Yeah probably! So I consider my job done 😄

[@caleb4952]

Hey ben. Glad i came across you Reddit post. Hopefully doing my fundies class soon. When will you be making your bp/w video about how you set your up.

[@DoktorBEN]

Thanks for watching my videos. It’s going to be one of the next videos. I’m now working on an accessories video for the Fundy and then I’m doing the bp/w Setup video. When is your class?

[@caleb4952]

Hopefully late October

[@DoktorBEN]

@@caleb4952 Yeah, I'll finish it before, so you can adjust your BP before the class. Who's your instructor?

[@caleb4952]

No rush. More than likely jason in Ft worth.

[@DoktorBEN]

@@caleb4952 Guess you'll have lots of fun :)

[@ChrisShaferKTM]

This is a great video, can you redo it for people diving with imperial units (and yes I know imperial is needlessly complex and silly)

[@DoktorBEN]

Well…i can try, since I‘m not really used to imperial units…

[@ChrisShaferKTM]

@@DoktorBEN it’s the best explanation of CAT I’ve heard yet. Sadly us Americans are stuck with some crazy combinations of cuft, bar and psi. I’d be happy to help check the math and video if you want to make sure it looks right.

[@DoktorBEN]

Sure, we can start a collaboration on that!🙂

[@LarsDennert]

So I'm ashamed to say having dived and living the USA for the last 28 years, and being German originally, i dive imperial. I'm tired of it and migrating to Metric. Your video is that perfect start to running through the basic GUE gas calculations again but I'm metric. Once it becomes second nature, the math will be simplified over imperial and also easier under water I'm sure when checking on consumption rate and such. Danke!

[@DoktorBEN]

I find metric easier. However, maybe if I get used to imperial, it might be the same.

[@Uk.mattdaniels]

Why not simply use the rule of thirds and divide by 3? 1/3 Descent and explore 1/3 Go back and Ascent 1/3 safety stops and emergencies

[@DoktorBEN]

Because in many cases, it’s too aggressive

[@DoktorBEN]

Hey guys! Do you plan your dives accordingly or what is your method to estimate the gas reserve?

[@Gengosyma]

or WHAT....

[@Gengosyma]

2:06 sound like 3000 not 2000

[@SaschaAtrops]

If my buddy has an out of gas situation and we're have no obligatory deco... why should I accent with just 3m/min? I can do so, if my buddy is calm (20l/m) and I have a lot of air left. Why not. With a recreational diver - as I am - I would go up with 9m/min and actually calculate with 10m/min. Which means from 30m to the surface I need 3 minutes at least. Calculating with 60 liters because my buddy might be stressed I cannot calculate with 2x20l. I need more, especially on depth, when the stressing situation happens. Let's asume 60l ensuing from a controlled donator (20l/min) and a stressed receiver (40l/min). In recreational diving I have to expect up to 40l for beginners stating they feel comfortable and calm. But they are usually diving shallower than 20m or diving with a 15l tank. :D So: 60l*3min * 2,5bar = 450l which is less than 40bar in a 12l tank. If I now add the safety stop I calculate 3 additional minutes at 1,5bar. 60l * 3m * 1,5bar = 270. In sum 740l: 60 bar in a 12l tank in the case that the receiver is still breathing heavily which should not be the case at 5m. That stop is useful - especially if we might be close to the no decompression limit - but it is not mandatory. If we now add an addional minute at 30m for solving problems we add another 240l: 980l: ~80bar. 80 bar for a regular ascent within 7 minutes including one minute solving a problem at 30m in a open water scenario. But the most time we stay at 1,5bar / 5m. Actually needed is 450l for traveling to the surface and 240l to solve the problem. Together 690l or

[@DoktorBEN]

Yeah... the CAT formula is an estimation. We pretend to ascend with 3m/min although the true ascent profile is faster to be more conservative. As I said, if you recognize you breathe more, you can (and should) adjust the Minimum Gas. It’s advisable to know the true SCR. In reality it’s very unlikely to instantaneously lose the entire gas supply. However, we assume this situation in the calculation.

[@SaschaAtrops]

@DoktorBEN Isn't that conservatism at the wrong place? If I know that 60bar will be enough to ascent without a safety stop and 80 bar is enough for a regular ascent, then I know that with less then 80 bar I have to improvise and with less than 60 bar I have a problem. Which means with 90 bar I will not have a problem there is no reason for stress. Calculating 90bar as the final reserve seens to conservative for me and put an additional reserve on top. Of course you should use the last liter of air for your regular dive. Your calculation puts the higher breathing rate into the lower ascending rate. I guess that leads into confusion when teaching. Additionally the result might be used as latest point of return. You don't need 100bars as reserve. 100bars is enough to ascent with your buddy. You can define this as the minimum amount of gas when leaving 30m. You can use this gas for your own ascent. I am still considering to join your fundamentals class. Might be interesting in many ways. :-D

[@diveinstructordaniel1095]

Is it true that I can’t take the Fundis course becouse I smoke ? :/ I wish I could since you teach in my area.

[@DoktorBEN]

Yeah that’s true. Als GUE course are just for non-smokers. Maybe this is an incentive to stop 😉

[@diveinstructordaniel1095]

DoktorBEN I might be stopping for that course 🤙

[@diveinstructordaniel1095]

DoktorBEN would it make sense to take that course before I do my instructor? I wanted to take that course to focus on my buoyancy and trim. Or would it be enough at the moment to get someone with a camera and a little bit of knowledge?

[@DoktorBEN]

In my opinion - and it’s my honest opinion, although teaching classes is my job - it makes perfect sense. You’ll hugely polish you trim and get some more ideas on dive planning which are especially useful as instructor. Reach out for me with [e-mail] if you like. Maybe we can work something out for you.

[@diveinstructordaniel1095]

DoktorBEN i send you an fb friendship ( Daniel Gie) I’ll finish my dm first in about 3-4 weeks and quit smoking then we figure something out. Would that be ok ?

[@Uk.mattdaniels]

Ascent rate is no more than 9m per minute

[@DoktorBEN]

Well…according to PADI it’s 18m/min max 😉

[@jonnieinbangkok]

CAT way too conservative and unrealistic in a typical recreational scenario...why not make minimum air reserve 150 bar for an even greater margin of safety 🙄

[@DoktorBEN]

In some (even recreational) scenarios, plain CAT is not conservative enough. However, if you want to get closer to the edge, you can at anytime use lower SCR or shorter time when you calculate MG by CAT. So what approach would you suggest to be less conservative (yet more realistic?)?