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Today we are gonna talk a little bit about equalization at depth. Introduced a bit more than a decade ago, the mouthfill equalization technique quickly became the preferred one for depth. It even came to the point of mouthfill being referred to by most instructors as the only safe way of equalizing at depth, discarding any other ways. But are the other ways really so unsafe and useless? Let's have a little look into it.
Before seeing the different ways of equalizing at depth, let's have a little reminder of why we need special ways of equalizing at depth, and we cannot just keep going like we are doing on the first residual volume. The residual volume is the air we have left in the lungs after a full exhale on dry, that the air left in our lungs so that they don't collapse. This residual volume for people who are not trained is around 25% of our total lung capacity. As we go down during a dive, our lungs are going to compress because of the increase of pressure, for those who don't understand what I'm talking about, have a look at Boyle's law, but at one point our lungs are gonna reach the size of this residual volume, since around 25% of our total lung capacity, we need to have the lungs compressed four times, so around four bars of pressure, around 30 meters. That means, as you get close to these 30 meters, it's going to be harder and harder for the air to traverse naturally from the lens to the airway so that you can use it to equalize. That's why we need to find some ways to equalize when we go at depth that take us deeper than our residual volume.
So the principle of the mouthfill is really simple. Way before we reach this residual volume we are going to come and store air in the mouth, we are going to fill the mouth with air, that's the name mouthfill, and then we will use this air in the mouth to equalize our ears while keeping our glottis closed, and this way the air is not brought back into the lungs by the compression of the lungs.
But there are definitely other ways to go deep than with the mouthfill. That means if you reduce your residual volume, then you can equalize naturally deeper and without using the mouthfill. I personally have my residual volume, which is around 11% of my total lung capacity. So if you do a bit of calculation, that means up to 80 plus (meters), I can still do a very regular Frenzel without having to use the mouthfill. So that can be the first way to go deeper without using the mouthfill and I believe it's a safe way, just it takes time. Because it's about the adaptation of your body, so you need a lot of deep diving, using only Frenzel and maybe dives on functional residual capacity, which means around half of your lungs, or after a full exhale. Don’t practice this by yourself if you haven't been told by an instructor how to do it safely and properly.
Another equalization technique consists to bring air up artificially, since it's not coming up naturally, from the lungs to the airways. This is usually referred to as reverse packing. Reverse packing to me is like really the mechanical way. Now there are several ways of doing it and if you want to do it safely at depth, you need to learn to do a very very small, even tiny, reverse pack which is just bringing enough hair to do one equalization. If you do like the usual reverse pack, like quite big and putting a lot of tension on your trachea and on your lungs, then you are at risk of squeezing. But a tiny and efficient reverse pack while staying relaxed will allow you to do an equalization just after, so you can do this quite deep. Some people use only this to go past 100 meters. Now of course you have less margin for mistake. A mistake for mouthfill would be for example to have all the air being sucked back into your lungs, mistakes for reverse packing, or what we call sometimes deep Frenzel, would be to push a little bit more and then hurt yourself.
And finally, you don't have to do only one way or the others. I personally use a mix of reverse packing and mouthfill. I take my mouthfill around 20-25 (meters), a relatively small mouthfill, but then I keep equalizing with a regular mix of Frenzel and hands-free, and on every single equalization I bring a tiny bit of air into my mouthfill, because okay, I'm not using it to equalize, but it's still shrinking from the pressure. Actually, that is the only thing that makes it smaller, the air doesn't go anywhere, you put a bit of pressure in your ears to equalize, but it's still the same amount of air if it's not leaking through the glottis. So I take this small mouthfill and then keep refilling it on each equalization, and if I'm really relaxed I can do this naturally up to 60-70, sometimes even 80 meters, and then at 80 meters I have a small mouthfill but almost full.
So, this way, it's quite easy for me technically to use this air to equalize past 100 meters. If you want to experience this deep Frenzel or tiny reverse pack, I would suggest working first on dry, to detect the right technique and then being able to make it precisely and quite small, and then in the water, you can do some dives in FRC, in residual volume or in full lungs, with using just Frenzel, never push it, of course, let it come naturally, but you'll see that just by repeating your body will adapt and then you will be able to do it naturally deeper and deeper, and you reduce your residual volume, you'll fine-tune a bit your deep Frenzel and reverse
pack abilities, and that will probably take you as deeply as the mouthfill over time and don't hesitate to mix both. You don't have to do 100% mouthfill, even though, I agree, it's a bit safer than the reverse packing. I hope this video was interesting for you, let us know in the comments if you have any experience with these different dives.