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VOLUME 33'-2 ata VOLUME 66'-3 ata CLOSED SYSTEM – DESCENT the excess air from the bag during its ascent. The same thing would happen to your lungs if you took a deep breath from a scuba regulator at depth, held it, and then swam toward the surface, even at a few feet below the surface. You must NEVER hold your breath when breathing compressed air under water. The greatest change in pressure is between the surface and 10 meters (33 feet) when you are diving in salt water or the surface and 10.3 meters (34 feet) when you are diving in fresh water. The pressure doubles from 1 ata to 2 ata. As you read further on in this chapter, you will learn how this change in pressure affects your body’s air spaces. How Pressure Affects Density The increasing pressure under water not only affects the volume of air, it also affects the density of the air. As the pressure increases, the air compresses to a smaller volume. As the air compresses, it becomes denser. At 10 meters (33 feet) or 2 ata, air is twice as dense as it is at the surface. At 20 meters (66 feet) or 3 ata, air is three times as dense as it is at the surface (figure 4-19). This explains why you use air faster when you dive deeper Bag ruptures! Bag begins to expand. Compressed air is added to bag at depth and bag is sealed. and why breathing resistance increases with depth – you are moving denser air through your lungs with each breath. When you add air to your lungs from scuba at 2 ata to maintain their original volume, your lungs contain twice as much air in the same physical space. When you scuba dive to 3 ata, your lungs now contain three times as much air in the same space compared to sea level. The overall effect is that the deeper you dive, the denser the air inside an air space becomes. Those air spaces include your lungs, middle ears, and sinuses. As the air you breathe becomes denser, it does not flow as easily. When you scuba dive, you breathe air that is compressed to the ambient pressure at your depth, which is much denser than the air you breathe on the surface. The deeper you dive, the more resistance there is to the flow of compressed air through your regulator hose (and through your air passages). This resistance makes it more difficult to breathe, the deeper you dive. The combined resistance of breathing compressed air and the restrictions of the equipment you wear to dive puts limitations on how hard you can exert yourself while under water. NAUI Scuba Diver 104 VOLUME x 3 0'-1 ata VOLUME x 1 33'-2 ata VOLUME x 1 66'-3 ata CLOSED SYSTEM – ASCENT FIGURE 4-18. IF YOU ADD AIR TO A CLOSED SYSTEM AT DEPTH AND THEN ASCEND WITH IT, THE FLEXIBLE CONTAINER WILL BURST TO RELEASE THE EXPANDING AIR. Diving Science VOLUME 1 0'-1 ata Since no air is addedo t system, the volume of the bag shr inks. FIGURE 4-17. AS THE VOLUME DECREASES IN A CLOSED SYSTEM, THE FLEXIBLE CONTAINER ALSO DECREASES IN SIZE.


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