LEARNING GOALS In this chapter you will: • Learn about ingassing and offgassing nitrogen and how it affects the amount of time you can spend underwater. • Understand the concept of residual nitrogen. • Learn about dive table terms and rules. • Learn how to use the NAUI Dive Tables to plan your dives and find your Letter Group designation after each dive. • Be introduced to the NAUI Dive Planning Worksheet and how to use it to keep track of the information from your dives and the NAUI Dive Tables. • Learn about precautionary and mandatory decompression stops and how important they are in minimizing the risk of decompression sickness. • Be introduced to the NAUI Dive Time Calculator and how to use it. • Be introduced to dive computers and their benefits. Your depth, and the number and depth of dives you have made in a series are two major factors that determine the length of time you can stay under water. This chapter explains the use of the NAUI Dive Tables, the NAUI Dive Time Calculator, and dive computers. You plan your dives with the correct time and depth limits by using either version of the NAUI Dive Tables or a dive computer. NITROGEN AND DIVING The gases in the air you breathe dissolve into your body’s tissues according to the partial pressure of each gas in the air. Air is 78% nitrogen, 20.9% oxygen, and 1.1% other gases. Your body uses part of the oxygen you inhale with each breath. Your tissues use the oxygen for the chemical processes that keep you alive, converting it to carbon dioxide and other waste products. However, the nitrogen that dissolves in your tissues during your dive is the gas you must be concerned about when you plan your dives. Ingassing Nitrogen When you breathe in and out, the air you breathe is 78% nitrogen. Nitrogen is a metabolically inert gas, which means that your body does not use it. However, nitrogen does absorb into your bloodstream and tissues as oxygen does. The pressure of nitrogen is balanced between the air and your body. This state is called equilibrium. Under increased pressure, the partial pressure of nitrogen you inhale with each breath is increased. Therefore, the pressure of nitrogen in the air you are breathing is greater than the pressure of nitrogen in your body. Your body ingasses nitrogen until the pressure of nitrogen in your body equals the pressure of nitrogen in the air you breathe. If the new pressure is constant, ingassing occurs rapidly at first and then slows until your body reaches equilibrium many hours later. You do not experience any negative effects when ingassing occurs at moderate depths. The different tissues of your body (fat, muscle, bone, and so on) absorb nitrogen at different rates when you are under water. Your muscle absorbs nitrogen quickly, but fat absorbs nitrogen slowly. There are different ingassing rates for each type of tissue. Calculating the cumulative effects of the ingassing rates for each type of tissue requires complex mathematics. Dive tables, dive computers, and dive time calculators consider all these varying rates and eliminate the need for you to make complex calculations. Offgassing Nitrogen After you spend time under water, the increased partial pressure of nitrogen has caused your body to absorb a quantity of nitrogen from the air you breathe on scuba. This quantity has been added to the quantity found in your body at sea level. When you ascend, and the ambient pressure decreases, the partial pressure of nitrogen decreases. The pressure of nitrogen in your body is now greater than the partial pressure of nitrogen in the air you are breathing. Your body will offgas nitrogen until the nitrogen is balanced between your body and the air. NAUI Scuba Diver 124 Decompression, Dive Tables, and Dive Computers
19116TC
To see the actual publication please follow the link above