A few tank questions

[Fey]

Hi, I tried another diving board but haven't really had any answers so I'm hoping people will know here.
I'm a total newbie to diving (though I'd really like to sometime) but I recently thought of a warning system for if you're running low on air, I don't think it would be popular with people who dive regularly for fun but it might be useful for commercial stuff like diving schools, police divers etc. places which need to cover themselves more in the case of health and safety. I don't want to go too deeply into how it works because this is really just the beginnings of the idea and I'm not even sure it's viable yet

Anyway... in diving
You know how much air you have by the pressure in your breathing tank(s) right?
Are tanks refilled? If so...
How is a tank refilled?
Do you need special qualifications to refil a tank?
Is all pressure within the tank lost to refil?
How much time is an adequate warning to have if you are running low on air and you need to get up? (at average levels under the water)
How much time left in your tank is usually left as a safety margin if all goes well?

In deep sea diving...
What happens to the pressure in the tank the deeper you go?
Do the different gases in deep sea diving tanks create different pressures to normal diving tanks, less or more or the same?
Are tanks refilled? If so...
How is a tank refilled?
Do you need special qualifications to refil a tank?
Is all pressure within the tank lost to refil?
How much time is an adequate warning to have if you are running low on air and you need to get up?
How much time left in your tank is usually left as a safety margin if all goes well?

 

[OldNSalty]

You know how much air you have by the pressure in your breathing tank(s) right?-Mostly, yes
Are tanks refilled? If so... Yes
How is a tank refilled? by pumping clean air into them using a compressor
Do you need special qualifications to refil a tank? You need training-don't know about 'qualification
Is all pressure within the tank lost to refil? If you are asking do they drain a tank before refilling-No, not normally
How much time is an adequate warning to have if you are running low on air and you need to get up? (at average levels under the water)-There is no universal answer to this. Your warning system would have to be flexible to allow me to determine when I want the alarm based ont he dive I am doing at that time.
How much time left in your tank is usually left as a safety margin if all goes well? Many people will say hit the surface with 500 psi as a rule of thumb-but again, this should be flexible.

As to 'deep sea diving' I don't know exactly what you are thinkng here but the pressure in your tank will not change simply because you go deeper. The PSI in the tank changes becasue you take air out of it constantly-at depth, you tend to drain a tank faster.

I don't know what you are thinking but for your FYI...some dive computers already have alarms that go off based on the amount or lack of air in your tank..amd other factors.

 

[robint]

FEY - you will learn all this in your certification class. It will all make sense to you then. For now I think you are getting worked up over details. The first part of your OW class will discuss how the gear works, how a tank works, how a regulator works, how a gauge works, etc. You as a scuba diver are responsible for reading your gauges and knowing how much air you have at all times, that is what the gauges are for. At no time underwater should you be "surprised" by the reading, you are responsible for managing your dive and dive time and dive depth. The certification class teaches you about the equipment, all the things you need to be aware of, and gives you some practice with an instructor doing all of the above.

If you are not yet scheduled for your OW certification class but you still want the information, buy the book and DVD and it will explain to you the answers.

 

[TMHeimer]

It's an interesting idea I have pondered. The old J Valves were the warning before the SPG. Of course, you should constantly moniter your air. Also, as stated, how much reserve you should have when beginning your ascent varies with the dive's depth. And, a big percentage of divers now use computers. But, with today's technology and safety precautions, why not have an additional "alarm" on the tank that would alert a careless diver (of course, it's his responsibility to not be careless, but....)? And one that the diver could adjust according to the depth he plans. A modern day J Valve in addition to everything else.

 

[RJP]

But, with today's technology and safety precautions, why not have an additional "alarm" on the tank that would alert a careless diver (of course, it's his responsibility to not be careless, but....)? And one that the diver could adjust according to the depth he plans.

The perfect combination of...

1.) A gear solution to a skill problem

and

2.) A solution to a problem that doesn't actually exist

All you need to solve the stated problem is an SPG and good situational awareness.

Failing that, even the most basic computers have programmable alarms to signal a specified pressure.

 

[TMHeimer]

RJP, I agree with #1, but if someone IS careless and solo at 80 feet (the "Darwin Awards") and OOA it will be serious. All told, I'd rather see him alive and without a lung overexpansion injury. As I said, such a warning device should NEVER reduce the training regarding air checks. It's perhaps akin to all the bells and whistles we have on modern cars that prevent us from not buckling up or lesser things like leaving lights on or locking ourselves out, not to mention the costly "chip" ignition keys. We shouldn't need these things (except maybe the chip key for security) and I find them annoying. But I guess some people do. Re #2: I would say there IS a problem as careless divers do in fact go OOA. As well, still not all divers own computers.

 

[iztok]

Here is what I don't understand. The questions you've asked are really some basic physics problems. Amount of gas in limited space and how this relates to pressure. Then simply that air is delivered to the diver at the pressure at depth so one can actually inhale. Rest is just math (pressure relation to remaining gas supply etc...).

So having that I might be wrong but it looks like you don't understand the basic physics behind the operations and as such it would be hard to come up with something really useful. Just my opinion.

 

[M2]

I don't have an air integrated computer but couldn't it have a beep or alarm feature that could be optionally turned on once you reach a certain tank pressure? Do these exist? Personally I feel proper air management is a key skill that should be mastered from the get go and it not necessary but could give some divers added comfort.

 

[vinegarbiscuit]

Hi, I tried another diving board but haven't really had any answers so I'm hoping people will know here.
I'm a total newbie to diving (though I'd really like to sometime) but I recently thought of a warning system for if you're running low on air, I don't think it would be popular with people who dive regularly for fun but it might be useful for commercial stuff like diving schools, police divers etc. places which need to cover themselves more in the case of health and safety. I don't want to go too deeply into how it works because this is really just the beginnings of the idea and I'm not even sure it's viable yet

Anyway... in diving
You know how much air you have by the pressure in your breathing tank(s) right?
Are tanks refilled? If so...
How is a tank refilled?
Do you need special qualifications to refil a tank?
Is all pressure within the tank lost to refil?
How much time is an adequate warning to have if you are running low on air and you need to get up? (at average levels under the water)
How much time left in your tank is usually left as a safety margin if all goes well?

In deep sea diving...
What happens to the pressure in the tank the deeper you go?
Do the different gases in deep sea diving tanks create different pressures to normal diving tanks, less or more or the same?
Are tanks refilled? If so...
How is a tank refilled?
Do you need special qualifications to refil a tank?
Is all pressure within the tank lost to refil?
How much time is an adequate warning to have if you are running low on air and you need to get up?
How much time left in your tank is usually left as a safety margin if all goes well?

Solid pre-dive planning (which should always cover gas management) and frequent gauge monitoring should negate the need for an alarm. (That said, I did see a cartoon in a cave diving manual showing a dive-shop owner with a prospective customer. The owner was proudly showing the customer his latest equipment delivery, which featured a pressure gauge that played "Nearer My God To Thee" when it hit 500 psi. Brilliant!!!)

Yes, tanks are filled via a compressor at your friendly local dive shop. Employees receive training on operating the fill station. (Some employees are also qualified to make visual inspections of tanks that are out of VIP (Visual Inspection Program&#8206, and will perform an inspection to ensure it's OK to be filled before actually filling them.) Shop employees don't open the tank's valve and drain the cylinder prior to filling them (I assume that's what you mean when you queried, "Is all pressure within the tank lost to refill?"). Dive certification agencies also offer a 'gas blender' certification that qualifies divers with more exacting requirements (trimix, heliox, et.al.) to blend their own breathing gases.

It's hard to answer your question about "How much time is an adequate warning to have if you are running low on air and you need to get up?" It depends on so many factors. For example, having 1000 psi in one's Al80 tank while tooling around a 30-foot reef should give you ample gas to begin your ascent up the anchor line, as well as enough gas to help out a buddy, if required. Conversely, having 1000 psi in your Al80 tank at 130-feet when you're nowhere near the boat isn't the most ideal situation to be in, and gives you little time to make a safe, controlled ascent, let alone help someone else out who's low on air.

As for tanks and safety margins, again...it depends on the planned depth, conditions (you may consume more gas in cold water, especially if visibility is lower and you're nervous), and so on. Cave divers are taught to abide by the rule of thirds...that is, to use a maximum of one-third of your tank's supply for the inward journey, and save the remaining two-thirds for the exit as well as a buddy's emergency requirements. It's a good, solid rule, but may be considered overkill so if your dive consists of examining reef critters in crystal-clear, current-free water right under a dive boat in 30-feet of water! Don't worry. Calculating your 'reserve' is part of pre-dive planning, which you'll learn as your dive education progresses.

 

[RJP]

I don't have an air integrated computer but couldn't it have a beep or alarm feature that could be optionally turned on once you reach a certain tank pressure? Do these exist?

Yes, they do. Nearly every AI computer has this feature.