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CHAPTER 16 — Closed-Circuit Oxygen CC-UBA Diving 16-3 9. Once the convulsion has subsided, open the victim’s airway by tilting his head back slightly. 10. Ensure the victim is breathing. Mouth-to-mouth breathing may be initiated if necessary. 11. If an upward excursion occurred during the actual convulsion, transport to the nearest appropriate chamber and have the victim evaluated by an individual trained to recognize and treat diving-related illness. 16 - 2.1.4 Off-Effect. The off-effect, a hazard associated with CNS oxygen toxicity, may occur several minutes after the diver comes off gas or experiences a reduction of oxygen partial pressure. The off-effect is manifested by the onset or worsening of CNS oxygen toxicity symptoms. Whether this paradoxical effect is truly caused by the reduc tion in partial pressure or whether the association is coincidental is unknown. 16-2.2 Pulmonary Oxygen Toxicity. Pulmonary oxygen toxicity can result from prolonged exposure to elevated partial pressures of oxygen. This form of oxygen toxicity produces lung irritation with symptoms of chest pain, cough, and pain on inspiration that develop slowly and become increasingly worse as long as the elevated level of oxygen is breathed. Although hyperbaric oxygen may cause serious lung damage, if the oxygen expo sure is discontinued before the symptoms become too severe, the symptoms will slowly abate. This form of oxygen toxicity is generally seen during oxygen recom pression treatment and saturation diving, and on long, shallow, in-water oxygen exposures. 16-2.3 Oxygen Deficiency (Hypoxia). Hypoxia is an abnormal deficiency of oxygen in the arterial blood in which the partial pressure of oxygen is too low to meet the metabolic needs of the body. Chapter 3 contains an in-depth description of this disorder. Although all cells in the body need oxygen, the initial symptoms of hypoxia are a manifestation of central nervous system dysfunction. 16 - 2.3.1 Causes of Hypoxia. The primary cause of hypoxia in the CC-UBA is inadequate/ incorrect purge of the CC-UBA. The risk of hypoxia is greatest when the diver is breathing the CC-UBA on the surface. Oxygen is only added on a demand basis as the breathing bag is emptied on inhalation. On the surface as the diver consumes oxygen, the oxygen fraction in the breathing loop will begin to decrease, as will the gas volume in the breathing bag. If there is sufficient nitrogen in the breathing loop to prevent the breathing bag from being emptied no oxygen will be added and the oxygen fraction may drop to ten percent or lower. Since there is sufficient gas volume in the breathing bag for normal inhalation, hypoxia can occur without warning. Hypoxia on descent or while diving is less likely, because as the diver descends pure oxygen is added to the breathing loop to maintain volume which increases both the oxygen fraction in the breathing loop and the oxygen partial pressure. 16 - 2.3.2 UBA Purge Procedures. The detailed purge procedures in the UBA Operation and Maintenance Manual are designed to remove as much of the inert gas (nitrogen) from a diver’s lungs as possible prior to the start of a dive and have been thoroughly

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