MiniDive, SpareAir, etc. and Decompression Sickness

[Yousif]

Hello,

There are a lot of gadgets nowadays that let you stay underwater for longer periods of time; however, I was wondering, if you freedive to a certain depth and then breath from those equipment while you're under, assuming it's filled with regular air (not oxygen or any special mix) and letting the air out before starting to ascend, would that give you the bends if you stay underwater for more than 10 minutes and go deeper than 10 meters? This sounds to me like a crossover between diving and freediving and I'm not sure how it should be dealt with.

Other than air expansion during ascend, since the air will be exhaled before starting the ascend, what dangers are associated with these little tools?

 

[MAKO Spearguns]

Very good freedivers (ones considerably better than myself) can and do get decompression sickness from deep breathhold diving with NO breathing apparatus.

So it is easy to suspect that using compressed air and doing the rapid ascents which are typical of a freediver could result in decompression sickness. Exhaling on the bottom would also seem to make it unlikely that the diver could perform a relaxed and SLOW ascent that is necessary for compressed air diving.

Of course lung over expansion from using the compressed air is also a significant danger if normal scuba ascent protocols are not followed.

In general, I think the recommendations are that scuba and freediving are distinct activities and should not be performed on the same day. In any regard, aggressive freediving immediately after scuba should be avoided.

 

[2airishuman]

There are a lot of gadgets nowadays that let you stay underwater for longer periods of time; however, I was wondering, if you freedive to a certain depth and then breath from those equipment while you're under, assuming it's filled with regular air (not oxygen or any special mix) and letting the air out before starting to ascend, would that give you the bends if you stay underwater for more than 10 minutes and go deeper than 10 meters? This sounds to me like a crossover between diving and freediving and I'm not sure how it should be dealt with.

Welcome to ScubaBoard, and thanks for your quesiton.

I agree with Mako Spearguns' reply above.

Freedivers who are pushing depths of 10 meters and beyond should have training. It's a potentially hazardous activity. Part of the training is a discussion of the additional hazards of breathing stored air during a freedive, whether from the equipment you describe or a "found" source of air in a bubble trapped under an inverted object. While I am not a freediver, it is my understanding that freedivers are taught to never use such air supplies while freediving.

Freediving and SCUBA are separate activities that should not be mixed on the same dive.

Other than air expansion during ascend, since the air will be exhaled before starting the ascend, what dangers are associated with these little tools?

First of all, at depth, it is insufficient to merely exhale before the ascent. It becomes necessary to exhale during the ascent as well because even with a "full" exhalation enough gas remains in the lungs to lead to an overexpansion injury during ascent beyond a certain depth. Exhalation during ascent is contrary to freediving practice, making it problematic. It is avoided in freediving because it can contribute to blackouts and to aspiration of water.

Any of these devices is best understood as a means of SCUBA diving. Whether and under what circumstances they can be used safety is unclear and controversial, since by themselves they do not meet accepted equipment requirements that SCUBA students are taught (because they do not meet air reserve requirements, do not have an alternative air sources, and do not incorporate a buoyancy compensator).

 

[blac86]

The best rule to follow is if you breath compressed air at depth you're now scuba diving and need to follow scuba diving procedures related to ascent and decompression.