Chapter 5- Decompression and Recompression Decompression and Recompression 171 What should you do to avoid the potential problems associated with diving at higher altitudes? Obviously, you should decrease the amount of weight which you use to establish neutral buoyancy in the water. Additionally, to avoid the problems associated with potential decompression sickness at altitude, you should, if possible, adjust your depth gauge to compensate for increased altitude. Some dive computers automatically compensate for altitude diving, although they may not necessarily take into account diving on the first day of arrival at altitude when you may already be offgassing. Check the manual for your computer to see how it treats this situation before using it. Since you are effectively heavier (when equipped with typical ocean equipment) at altitude and in fresh water than when diving in the ocean, weight must be removed if true neutral buoyancy is to be achieved. You’ll need to determine your normal total ocean weight of your body plus all equipment to calculate how much weight to remove. If you dive without a wet suit or weight belt in the ocean, you’ll need to add air to your buoyancy compensator for altitude diving. Salt Water vs. Fresh Water Displacement How to Adjust Weighting from Ocean to Fresh Water Saltwater has a density of 1.026 kg/L (64 lbs/ft3). If you weigh 63.6 kg (140 lbs.) and have 27.3 kg (60 lbs.) of equipment on when prepared to dive at sea level in salt water, you will displace this amount of salt water: 90.9 kg = 88.6 L of salt water displaced Fresh water weighs 1kg/L (62.4 lbs/ft3). Given the same diver and equipment, the weight of fresh water displaced will be: 88.6 L X 1 kg/L = 88.6 kg 3.125 ft3 X 62.4 lbs/ft3 = 195 lbs. So, the difference in weight is 2.3 kg (5 lbs.), and the diver will need to remove 2.3 kg (5 lbs.) from your weight belt to approximate neutral buoyancy in fresh water. Procedures for Altitude Diving The procedures for altitude diving obviously vary from those used for diving in sea water and at elevations below 300 m (1000 ft)(table 5-4). The differences in diving practice, however, are not as difficult to master as you might imagine, and with proper training and equipment, any qualified open water scuba diver can enjoy scuba diving at altitude. A summary of necessary procedures for use by ocean divers when diving at altitude is included in table 5-4. Having made the changes in preparation for your altitude diving experience, it is important that next you clearly understand how to make adjustments for the effects of reduced atmospheric pressure at altitude. Table 5-5a shows information regarding changes in atmospheric pressure at altitudes from sea level to 4,500 m (15,000 ft), tabulated in increments of 300 m (1000 ft) and table 5-5b shows the changes in Imperial Measurements. You should be aware that the closed cell neoprene of your wet suit will expand as the suit is taken to higher altitude, making it more buoyant. This buoyancy increase is small but may be noticeable at higher altitudes. It should be clear at this point that all altitude dives must be formally calculated, especially at higher altitudes. In no altitude diving circumstance should you “guess,” even though the dive is planned to be relatively short and shallow. An additional reason for you to be especially careful in dive planning and execution at higher altitude is that most dive sites are located a great distance from hyperbaric facilities. If an accident did occur, you might not be able to get to a recompression chamber in a reasonable amount of time. Among the precautions you should take when you decide to dive at altitude are: 1. If you’ve recently made an ocean dive, you should wait at sea level for at least 12 hours before ascending to altitude. As in “flying after diving” procedures you must avoid the potential problem of bends due to the lower atmospheric pressure at altitude or the lower cabin pressure in the airplane which transports you to the altitude diving site. 2. You should consider yourself to be in a repetitive
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