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Are the mini scuba sets (e.g like the ones by Smaco, with tanks of a few liters that are filled using a hand pump) safe for open water diving up to a depth of around 10m?

I have no experience in diving but my Dad was both a navy and commercial diver. He misses it and it's his birthday soon so I thought about getting him one of the kits to take with him on holiday.

He's too old to be carting around a full set of equipment so thought this would be a good alternative, but have seen mixed reviews online.

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    Hi Aaron, I made a small amendment to my answer — those Smaco bottles can hold 200 bars, not 5 bars of gas (the description which was translated from Chinese was confusing)! However, that doesn't change the gist of the answer... 1L@200 bars would give less than five minutes of breathing underwater :) – Alexander Jan 26 at 11:04
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    Buy him a "Discover Scuba Diving" trip. Essentially some time underwater with a dive instructor, so nice and easy. It's especially nice if the water's warm and clear. – GlennG Apr 10 at 16:51
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TL;DR, short answer: NO, THEY ARE TOTALLY NOT SAFE TO DIVE WITH! YOU WILL DIE.

Longer answer

If you check out the description of such gimmicky gadgets, you will notice that they're billed as "pony bottles / last resort air source", to be used by trained, fully equipped divers as a backup only (side note: those "pony bottles" are generally frowned upon and their use is discouraged by instructors / experienced divers, as they actually add more risks and danger... but that's out of the scope of this question).

Why those bottles cannot be used as a standalone diving air source? Because they miss one critical component - a buoyancy compensation device (a wing/jacket worn by divers). Without it a diver would not be able to control depth and either fall down quickly, run out of gas and die, or would descend normally, then ascend too quickly, suffer lung barotrauma from the expanding gas and die. Contrary to the common belief, dives to shallow depths up to 10m/33' are the most dangerous from the barotrauma point of view — during an ascent from 10m to the surface the gas inside your lungs/inner ear would expand its volume TWICE. Guess what happens next! Yes, you'll die :)

Then, there is a specific concern related to those pony bottles. They're very small in volume, meaning low amount of breathable gas. Here's a quick calculation: my SAC (breathing rate on the surface) is around 20L/min. Those Smaco 1 litre bottle can be pumped up to 200 bars, which would give us 200 litres of air. That's theoretically good enough for ten minutes of breathing (that's on the surface! if you'd dive to 10m, you'd halve the time due to higher ambient pressure). However, you'd not just sit underwater, you'd swim and would want to look around, which, with added excitement, significantly increases gas consumption. When I measured my consumption during strenuous swimming, it went over 80L/min, meaning a little over one minute of breathing at 10 metres.

Now, to address your specific situation (an ex-navy diver dad): wearing a jacket with a proper bottle is not actually very strenuous, I've seen people in advanced age go diving... and there're smaller bottles if you're concerned about bulk/weight (I think 5L or so is the smallest tank used for breathing gas).

Then, there's another style of diving called "sidemount", where you wear only a lightweight wing/harness, go into the water then clip the tanks with gas to yourself (you basically don't feel the weight of the tanks when underwater). When you go out, you unclip the tanks and some strong young lad takes them from you :)

This is what I would actually recommend, if your dad really wants to go back into diving but is concerned about weight/his knees/back. Note that YOU CANNOT teach yourself how to dive from Internet forums, one needs to learn from a certified instructor (otherwise, you will die).

Coming back to the pony bottles. The only way they could be used safely for diving is when "diving" in a backyard pool of less than 2m/6' depth, where you could simply stand up in case of any problems / running out of gas. If the pool is deeper - you will die!

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  • Thanks for the in depth answer Alexander! I had also read that air quality could be an issue due to using a hand pump and not a compressor? – Aaron Jan 26 at 17:28
  • You’re welcome Aaron! Yes, absolutely, because diving compressors have (rather expensive) air filters which should be replaced regularly. Moreover, if using a hand pump, you’d spent 30 minutes doing very hard work… to have a five minute dive :) – Alexander Jan 26 at 21:42
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    Fair enough. I suppose you came out with exactly the same points as the reviewers, since you started from the same experience. My bad. They all say the same thing, so I defer to your judgment. Mmmm, I wonder if my really unpleasant Tahiti dive involved a BCD or not. They were pretty much missing everything else on that one, except the tank. It probably did. So... you're addressing not so much the bends as someone holding their breath in while ascending and blowing lungs up? Makes sense with the intended customers, people who don't dive. OP's dad did dive so at least that's covered. – Italian Philosophers 4 Monica Jan 28 at 17:56
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    @DanubianSailor and if you don't die outright, then maybe it's even worse. Because you'll go out all smiley and happy and think that this gadget (or plastic bulletproof vest) really worked, or, worse, that you're so awesome that you can do anything! In technical diving we call this attitude "normalisation of deviancy". You cut corners once and nothing happens. You do it two, 3, 4 times and you obtain a belief that you're really good and what you're doing is correct. Think Nassim Taleb's "Fooled by randomness". Then you go for the fifth time... "he was such a good diver!" your friends will say. – Alexander Feb 3 at 19:33
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    @DanubianSailor it's a huge difference between managed, calculated, mitigated risk-taking and recklessness admixed with complacency and Dunning-Kruger's arrogance of the ignorant. Choosing to ride a powerful motorbike is a risk [acceptable or not]. Riding that bike without a helmet, driver's licence and any training is plain stupid. Diving with that gadget is exactly like this — no training, no safety protocols, no backups, no experience, lack of understanding of implicit hazards but relying on poor quality life-support equipment instead... – Alexander Feb 8 at 10:23
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Why not get him some gift cards at a reputable * local dive shop, to be used on group outings? Equipment issues are gone, he can be helped into the gear once in the water and he has certified diving instructors around to help.

I suspect that if you gifted this to your father, he would be put in a rather bad spot. The reviews cited go on quite a bit about the physics of diving and basically shoot this turkey straight out the air. For two reasons.

First, because the whole thing aims to short-circuit the training you need to undergo to get scuba-certified. That training is about keeping you alive and they go into details about not surfacing while holding your breaths, air consumption, how long you can stay down with given tank capacities, etc...

Second, the gear itself looks very unsafe, especially to an experienced diver. It basically seems designed to let you go down just deep enough to put you in grave danger once the very limited air supply runs out. If you were free-diving you wouldn't go that deep and the air in your lungs could only re-expand to sea-level volume (note that free-diving can be a bit scary once you go down past 5-7m/15-20ft - you lose buoyancy from your lungs compressing so going back up can be harder than expected).

That's what your dad will be looking at: I just got this really, really, dangerous gift. What should I do with it?

So reason #1 does not really apply to him, but reason #2 applies doubly so.

And in any case, no one should be diving alone.

* I gave up scuba diving after being taken down under really unsafe conditions, past my cert limits, with insufficient equipment, on a commercially-run group dive. So it pays to make sure you are dealing with responsible people.

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  • +1 for "gift card for a dive shop"! – Alexander Jan 28 at 9:50
  • I think his dad as an experienced diver would have no doubts that that gadget is a toy, and can be using only as a toy. – Danubian Sailor Jan 28 at 20:16
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The "hand pump" scuba cylinders sold on e-bay, etc. are down right dangerous. There's loads of reasons, not least they're very small so you can't dive for long. The biggest concern is that they would take ages to fully fill -- 200 bar is 200kg per cm2 (or 3000psi) which is an enormous pressure to hand pump! An exhausting 30 mins to pump up for 5 mins underwater!

Ignoring buoyancy issues underwater, the biggest safety issue is an inexperienced diver not monitoring how much air is in the cylinder, emptying it, unable to breathe then panicking and drowning.

Other concerns are that these cylinders and the regulators are just cheap and nasty. Diving cylinders need to be periodically tested (every year or three depending on country). Breathing regulators need servicing and keeping clean and dry. These are just horrible and an accident waiting to happen.

As an experienced diver, I wouldn't even think about diving with one, even if it were to free off an anchor or clear a propeller on a boat -- I'd sooner freedive and be safe.

If I were buying an "emergency dive kit" for a boat, I'd probably buy a 3 litre steel cylinder and a simple regulator kit (such as for a decompression stage: 1st stage, 1m/40" hose, second stage and a gauge on a 15cm/6" hose. Some form of harness would help, depending how warm the water is (if cold, then would need weight; if warm then maybe attach it to a weightbelt. All of this should be kept stored in a drybag. Also get it tested every year.

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