What exactly is squeeze?

[elmer fudd]

I've experienced it many, many times, so I do know what it feels like and that adding a little air to your suit eliminates it, but I've been wondering what exactly causes it. It's not just pressure, because you don't get it in a wetsuit and you're still under the same pressure once you've inflated your drysuit a little.

I think I notice it much more in my Mobies trilam than I did in my Harvey's neoprene suit. I'm also wondering if it could be completely designed out of a drysuit. Say for example that my wetsuit was completely watertight. I doubt that I would experience squeeze with it. I think all of us have had that experience once where we take off a hood and our hair underneath is dry or where we wore a swimsuit or boxers under a wetsuit and they were still mostly dry after the dive. Even though your hair never got wet, your head didn't feel squeezed.

 

[boulderjohn]

A wet suit is a collection of bubbles with the inside edge pretty much right next to your skin to begin with. The suit fits your outer body very well, with little or no space between you and the smooth skin. As pressure increases, the bubbles inside the suit compress, which has no effect on you. The inside edges of 90% of the suit, which are smooth and right next to your body, have no change--there is no air to compress. It can't get any closer to your body than it was to start with. The few gaps either get pushed next to your body quickly or get water in them. The result is that you do have a suit pressed against your body evenly, but that is pretty much what you started with, so it doesn't feel any different.

Your dry suit started with a layer of compressible air between you and an outer skin. As it is squeezed by pressure, that layer of air compresses. The outer skin wrinkles and becomes crushed next to your body. It creates very uneven pressure on your body and will result in bruising if not dealt with.

 

[elmer fudd]

So it's basically a magnification of the pressure at depth caused by irregularities in the suit and undergarments?

When I've experienced it, it generally seems to affect my entire body, or areas of my body if I'm vertical, and not specific points that are being crushed, but things like that can be deceiving.

This would also seem like something that could be minimized or eliminated entirely with the right suit and undergarments.

 

[boulderjohn]

I think your experience depends upon the composition of your suit. For me, my grand experience was the time I descended rapidly, realized my argon bottle was closed, and took a little too long to open it. I wear a Fusion, which is different from most suits. I didn't feel all that bad, but I had wrinkle marks on my torso when I undressed.

The undergarments won't help you all that much. I had a base layer and medium weight undergarments in the situation above. You just need to keep adding the right amount of gas to the suit.

 

[elmer fudd]

I had a somewhat similar experience once when I descended to 30' following my buddy and realized along the way that I had failed to connect my inflator hose.

 

[Quero]

I've experienced it many, many times, so I do know what it feels like and that adding a little air to your suit eliminates it, but I've been wondering what exactly causes it. It's not just pressure, because you don't get it in a wetsuit and you're still under the same pressure once you've inflated your drysuit a little.

As you may recall, a squeeze can occur when there's a pressure differential with the external ambient pressure being greater than the internal pressure. The pressure differential causes the higher ambient pressure to compress or "squeeze" whatever is contained within the area of lower pressure. So if you've got lower pressure behind your mask, for example than outside the mask, you can get a "mask squeeze." And if the pressure inside the dry suit is lower than the pressure outside, you can get a "suit squeeze." By adding pressure (air) to the inside of the mask and to the inside of the dry suit, you "equalize" the pressure to prevent the squeeze.

The reason you don't get a squeeze when wearing a wetsuit is that the water flows through it at whatever ambient pressure you find yourself in. However, the little bubbles that make up the fabric of the wetsuit DO get compressed. After repeated compressions (many dozens), wetsuits tend to get thinner and lose their insulating capacity as the bubbles get crushed to the point that they don't return to their original size when the pressure is released.

I think I notice it much more in my Mobies trilam than I did in my Harvey's neoprene suit. I'm also wondering if it could be completely designed out of a drysuit. Say for example that my wetsuit was completely watertight. I doubt that I would experience squeeze with it. I think all of us have had that experience once where we take off a hood and our hair underneath is dry or where we wore a swimsuit or boxers under a wetsuit and they were still mostly dry after the dive. Even though your hair never got wet, your head didn't feel squeezed.

I am very skeptical that your hair doesn't get wet and your boxers don't get wet when you're wearing a wetsuit. Just because they are not dripping wet doesn't mean that the water has not flowed past to dampen them, and if the water got in, so did the pressure. A wetsuit is, by definition, "wet" and not watertight. A watertight suit is a drysuit. Any space that is sealed, such as a drysuit, to keep out water will also create a seal against changes in ambient pressure. Perhaps you have a different undergarment for each of the drysuit types you have used and one of them provides a better "cushion" against the welts that an unequalized drysuit can produce?

 

[MXGratefulDiver]

You certainly do notice squeeze in a wetsuit ... the deeper you go, the colder you get.

... Bob (Grateful Diver)

 

[DevonDiver]

As Quero and NWGratefulDiver have said: a squeeze is defined as the effect of external pressure exceeding the pressure of a sealed air-space. That pressure differential causes reduced volume in the air space, as dictated by Boyle's Law (Boyle's law - Wikipedia, the free encyclopedia).

In respect of dry-suits, the sealed suit creates a fixed-mass air space and any increase in external (water) pressure will reduce the inner volume of that air space inverse proportionally to the increasing pressure. As the air-space inside the suit reduces in volume, the suit material will wrinkle and 'pinch' the flesh of the diver inside. This can cause pain and bruising.

The material used to make the drysuit will influence the severity of the 'pinching' effect - as thinner material will wrinkle more tightly. In addition, trilam type suits tend to have greater air space (less closely fitted) than neoprene types, allowing greater volume reduction. However, any material will eventually cause squeeze if the air space is compressed enough.

The same would be true of a wet suit, or hood, if an airspace was contained inside - although the nature of the material may prevent painful squeeze at anything other than exceptional pressures, as it is not as prone to wrinkling.

The squeeze effect in drysuits is easily eliminated by adding sufficient quantities of air into the suit (via a dedicated low pressure inflator hose) to maintain a comfortable air volume on descent.

 

[TSandM]

You SHOULD feel squeeze evenly over your entire body, because the air bubble in your suit is collapsing at the same rate everywhere. You can't design squeeze out of a laminate or compressed neoprene dry suit, because the air in the suit IS the insulation. I suppose you could have a very closely fitted full neoprene dry suit, where the suit itself would be your insulation and there would be virtually no air in the suit, and you wouldn't feel much squeeze in such a suit, but you would be very cold at depth.

I'm a little concerned that the basic concept of the air in the suit compressing as you descend isn't clear to you. This is one of the many manifestations of Boyle's Law in diving. You have to add air to the suit as you descend, to maintain suit volume unchanged, because the gas in the suit is becoming more dense as you go down. The suit is basically a big balloon with you inside it; pressure changes in the water are transmitted immediately to the contents of the suit.

 

[elmer fudd]

You SHOULD feel squeeze evenly over your entire body, because the air bubble in your suit is collapsing at the same rate everywhere. You can't design squeeze out of a laminate or compressed neoprene dry suit, because the air in the suit IS the insulation. I suppose you could have a very closely fitted full neoprene dry suit, where the suit itself would be your insulation and there would be virtually no air in the suit, and you wouldn't feel much squeeze in such a suit, but you would be very cold at depth.

I'm a little concerned that the basic concept of the air in the suit compressing as you descend isn't clear to you. This is one of the many manifestations of Boyle's Law in diving. You have to add air to the suit as you descend, to maintain suit volume unchanged, because the gas in the suit is becoming more dense as you go down. The suit is basically a big balloon with you inside it; pressure changes in the water are transmitted immediately to the contents of the suit.

My understanding of pressure is that you are exposed to 1 atm for every 10m of depth and I could be wrong, but I think that the amount of air in your suit should have zero impact on that. That air volume is inversely proportional to depth is understood.

To my way of thinking, cold is a good reason to inflate a suit, but squeeze brought on by an ill fitting suit isn't. If you could design it out or at least minimize it that would be a very worthwhile goal.