The Pressure

Let's dive into an underwater world for a safe experience with WADI instructor. Initially this will be in a confined water environment allowing us to explore the differences that it makes when we are surrounded by water and how it affects us as divers.

 Water is denser than air and therefore the weight of the same unit of water is much more than the weight of the same volume of air. While you read this information now there is already pressure upon on you from the molecules of the air. Air pressure is defined as the force per unit area on any object or any person. At sea level this is 14.7 pounds per square inch or about 1kg on every square centimeter. This is defined as 1 atmosphere or 1 bar at the sea level. This pressure has been on your body since birth, the higher you rise above sea level the more it is reduced.

Underwater pressure changes very quickly as the pressure increases by the equivalent of 1 atmospheric pressure when descending every 10 meters of seawater.

            Another characteristic of water is that it is incompressible, thus, its density will not change, unlike air that accepts compression, and therefore air will affect you as a diver in the following ways:

1. Air spaces in the ears, sinuses, and face mask.

2. Breathing air that becomes denser underwater.

In order to understand these effects, it is necessary to understand the relationship between three variables - air pressure, density, and volume

• The relationship between pressure and depth is a direct relationship. The greater the depth, the greater the pressure.

As we mentioned earlier, every 10 meters depth of seawater equals 1 bar, and the greater the depth, the greater the pressure.

• The relationship between pressure and volume is an inverse relationship, the higher the pressure, the lower the volume. If you take a balloon from the surface at 1 atmosphere to 10 metres depth, the balloon will decrease to half its original volume.

• The relationship between pressure and density for gases is a direct relationship, the higher the pressure, the higher the density.

In that balloon, which was compressed in half, the air molecules inside became closer to each other and thus the air inside it became 2 times denser than it was on the surface, the following table explains this relationship more.

How do you benefit as a diver from these relationships?

About three-quarters of your body is made up of water, so pressure only really exerts effects on the air spaces.

  1. Respiration: Diving equipment provides easy breathing because it gives you the air at the same pressure as your surroundings, for example, you dive down 10 meters the pressure surrounding you is 2 bar and the air pressure you breathe will be 2 bar equal to the pressure surrounding you. You will only be required to breathe at your normal rate to breathe slowly and deeply. You also have to remember not to hold your breath completely when diving with equipment, in order to avoid developing an expansion of the lungs specifically when ascending. If you held your breath with lungs fully inflated at 10m then tried to surface, the volume of the air in your lungs would try to double in size which would cause the lungs to over expand and become damaged. This can easily be avoided by never holding your breath under while using scuba equipment. When the air becomes denser, your air consumption becomes faster, if we assume that it will take an hour to consume the air cylinder at the surface, then at a depth of 10 meters the time will be reduced by half to become half an hour, and at a depth of 20 meters the time will be reduced to a third to become twenty minutes. Thus, the diver's consumption of air will become faster as the depth increases.
  2. Pressure equalization in the ears and sinuses: The air in the space between the body tissues in the ear and the sinuses is compressed, which leads to the tightening of those tissues to compensate for the volume of compressed air, and therefore you have to learn how to equalize the pressure in those air spaces. As there is more than one way to make the equalization in general, all methods depend on the mechanism of pushing the breathing air from the mouth through the nose to the sinuses and the Eustachian tube to the ear. The equalisation can be easily be achieved by inhaling through the mouth and closing the nose with two fingers and blowing moderately in the nose while keeping the nose blocked so that the air goes to the sinuses and the inner ears thus equalising the air pressure inside it to the surrounding pressure. Blowing too hard or prolonging the equalisation period should be avoided, to avoid damage to the ear drums or sensitive sinus tissues. WADI advises you to use another method before relying on the previous method, take a breath through your mouth and using your fingers to block your nose, swallow Swallowing pulls open your Eustachian tubes while the movement of your tongue, with your nose closed, push the air into the ears and sinuses, this method is safer for you. A WADI instructor will also guide you to the most appropriate way for you to do the equalization efficiently and safely.
  3. Mask equalization: The air in the mask is compressed, causing the mask to feel jammed against the face and causing discomfort in the face area under the mask. Especially if you tighten the strap of the mask on the face too much. All you have to do is not ignore or neglect this feeling and blow from the nose into the mask, which will lead directly to adding some amount of air to equalise the pressure inside the mask with the surrounding pressure.
  4. Clearing the mask: You may like to take off the mask underwater to get a picture of you without it and at that moment the mask will be full of water, or it can be that the mask itself sometimes allows water to enter because it is not completely suitable for your face. Do not be concerned and do not finish your dive, as you can use some of the physical properties surrounding you with the application of some skills to get rid of the water inside the mask You are going to start learning how to do that at the diving skills in confined water training dive number one.
  5. Neutral buoyancy

Buoyancy is the force that pushes the bodies in the water upward, and that force in saltwater is greater than in freshwater because of the presence of dissolved salts in it.

Objects are divided in terms of buoyancy into three types:

  1. Positive buoyancy: objects that float above the surface of the water, such as a large ship. The ship displaces water that weighs much more than its actual weight and therefore the upward force is greater than the force of the weight that acts downwards and the object remains on the surface.
  2. Neutral buoyancy: the objects that stand at a certain depth and do not float above the surface of the water and do not sink to the bottom. This object displaces a weight of water equal to its own weight, and therefore the upward motive force is equal to the force of the weight acting downwards, so it becomes neutral buoyant.
  3. Negative buoyancy: the objects that sink to the bottom, such as a small coin. Which displaces a weight of water whose weight is much less than the objects weight, therefore the upward force is less than the force of the weight that is acting downwards and sinks.

By controlling the volume of air inside the lungs and the buoyancy compensator device (BCD), you will get neutral buoyancy.

Later in the diving skills of the third confined water dive, you will learn how to maintain a neutral buoyancy to swim without much effort, depending on equipment, breathing and other factors such as adjusting the appropriate weight in the buoyancy check skill which you will learn during the second confined water dive. What matters here is that we clarify to you that the volume of air inside the buoyancy compensator device will be reduced as you go down to deeper depths, and therefore you will need to add some air inside it to be able to maintain your buoyancy and swim calmly.

The process of breathing also affects your buoyancy, as inhaling increases your buoyancy and exhaling reduces your buoyancy.

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