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CHAPTER 9 — Air Decompression 9-1 CHAPTER 9 Air Decompression 9-1 INTRODUCTION 9-1.1 Purpose. This chapter discusses the decompression requirements for air diving operations. 9-1.2 Scope. This chapter explains the theory and provides general guidance to safely conduct air decompression dives. Air dives are completed utilizing No- Decompression, In-Water Decompression, In-Water Decompression on Air and Oxygen, and Surface Decompression tables and procedures. This chapter also explains charting air dives, exceptional exposure diving, altitude diving, and emergency procedures. 9-2 THEORY OF DECOMPRESSION As a diver descends, the partial pressure of nitrogen in his lungs rises above the partial pressure of nitrogen dissolved in his tissues. This pressure difference causes nitrogen to be transported from the lungs to the tissues via the bloodstream. Transport to a given tissue will continue as long as the partial pressure of nitrogen in the lungs is higher than the partial pressure of nitrogen in that tissue. The process will stop when the tissue has absorbed enough nitrogen to raise its partial pressure to a value equal to that in the lungs. Different tissues absorb nitrogen at different rates. A tissue with a high blood flow, like the brain, will come into equilibrium with the partial pressure of nitrogen in the lungs faster than a tissue with low blood flow, like muscle or tendon. The total amount of nitrogen absorbed by a tissue will be greater the deeper the dive and the longer the bottom time, until the tissue becomes saturated. As a diver ascends, the process is reversed. The partial pressure of nitrogen in the tissues comes to exceed that in the lungs. During ascent, nitrogen is transported back from the tissues to the lungs through circulation. The ascent rate must be carefully controlled to allow time for this process to occur and not allow the tissue nitrogen partial pressure to exceed the ambient pressure by too great an amount. The more the tissue nitrogen partial pressure exceeds the ambient pressure during ascent, the more likely nitrogen bubbles will form in tissues and blood, causing decompression sickness. To reduce the possibility of decompression sickness, special decompression schedules have been developed for air diving. These schedules take into consideration the amount of nitrogen absorbed by the body at various depths and times. Other considerations are the extent to which the tissue nitrogen partial pressure can exceed the ambient pressure without excessive bubble formation and the different nitrogen elimination rates associated with the various body tissues. Because of its operational simplicity, staged decompression is used for air decompression. Staged

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