Mask leaking shallow not deep-normal?

[GreggS]

Okay, think about it this way. When you go to your LDS and try on masks, if you simply hold it to your face without the strap around your head, it will fall off. That's because the air pressure is the same inside the mask as it is outside the mask. But if you inhale thru your nose, if the mask fits and you have a seal, the mask will stay on your face even without the strap because you have lowered the air pressure inside the mask to less than that outside the mask. The higher air pressure outside the mask is pushing it against your face. This is the same thing that is happening under water except that you have replaced the higher air pressure with higher water pressure. If the air pressure inside your mask is equal to the water pressure outside your mask, it would not seal.

 

[stuartv]

Hi I went out yesterday with Sea Experience in Ft Lauderdale (they are fantastic by the way, such amazing staff). On the first dive at 70 ft my maskdid not leak at all! On the second dive though at 30 ft, my mask constantly leaked. Very annoying. Someone else on the boat experienced the same.
Q) is this normal and what can I do to avoid it in future.

Some good suggestions have already been given.

But, for the scenario you described, the first thing I would suggest for next time is to press just a little bit on the mask lens to "burp" the mask.

When you are deeper, you get more mask "squeeze" (as has been previously noted), which creates a stronger seal. At shallower depths, you don't get the same squeeze, so you don't get as strong a seal. But, if you press on the mask to burp it, you can give yourself the same effect. It's really the same as sucking in through your nose a little bit to create more suction in there. But, if you're underwater and your mask is leaking, sucking in through your nose is not the best idea.

If you press too hard and burp too much air out of your mask, it will create too much squeeze and make the mask uncomfortable. If you do that, just exhale a little bit out your nose to equalize the mask with the outside water pressure.

Tightening your mask strap is only the answer if your mask is trying to fall off. it should only be tight enough to hold it against your face even when you exhale through your nose. If you can't get a good seal that way, you need a different mask, not a tighter strap.

 

[Kmart921]

No, even if you breathe out thru your nose and vent, the water pressure pushing the mask against your face is always going to be greater than the air pressure inside your mask. And the deeper you go, the greater it will be.

The first part of your statement is accurate. But I don't think the pressure differential is necessarily greater at depth, is it? The whole point of having a nose pocket is so that you can equalize the pressure in your mask with the ambient water pressure. If you don't continually do this, you end up with mask squeeze.

Your mask can only hold so much air and will not compress much inside it. That's why it will vent when you exhale thru your nose. It temporarily exceeds the pressure exerted by the water.

The volume of air in your mask is constant, but the pressure is not; it does compress, just like the air in your lungs. That's what causes the squeeze.