Chapter 10- Diving Techniques and Deeper Diving Diving Techniques and Deeper Diving 237 bottom topography, depth, steepness of walls, and presence of caverns. Underwater visibility should be such that divers can easily move freely around the bottom (or shipwreck) and easily locate the ascent line at the end of the dive. The water temperature must be anticipated so the correct type of exposure suit can be worn. Sea and weather conditions are not always ideal, and divers may encounter high waves and limited visibility. Anchoring a vessel, diver deployment, descent, underwater navigation, ascent, decompression, and diver retrieval must be adjusted accordingly. In some situations it may be wise to cancel the dive and return under more favorable conditions. Equipment Selection The water temperature may be colder at deep depths and a neoprene wet suit will compress, which reduces its thermal protection and buoyancy. Compensation for significant buoyancy changes will be necessary. It is mandatory that each diver be equipped with a dive timer and depth gauge, or a dive computer. Since emergency ascents are more complicated and risky from deeper depths, the availability of an alternate air source is even more important than for shallower dives. Remember, you don’t need gas just for yourself, but enough gas to to bring your buddy home, too, if either of you have an emergency. Many deep divers prefer to use an independent scuba or a dual valve/ regulator scuba for complete self-sufficiency. The small, portable combined cylinder and regulator units may not provide sufficient air for ascent from deeper depths. For dives in the range of 18 to 40 msw (60 to 130 fsw), primary equipment should be upgraded to include the following: • Scuba cylinder with minimum capacity of 2200 L (80 cf). • Primary cylinder equipped with a “Y” or “H” valve. A secondary scuba cylinder or pony bottle may be used in lieu of the special valve configuration. A separate pony bottle, which is a small (approx. 400 L 14 ft3 ) cylinder with its own regulator, can be mounted to the primary cylinder as a totally redundant alternate air source. • Two regulators for primary gas source. One may be used on secondary scuba. One regulator is to be fitted with a 100 cm (40 in) hose and the other with a hose that is at least 150 cm (60 in) long. Scuba Cylinder Cylinders for scuba diving are available in volumes ranging from approximately 1700 to 5400 L (60 to 190 cubic feet cf). Smaller auxiliary or “pony” cylinders range from 300 to 1200 L (11 to 40 cf). The standard aluminum cylinders commonly used by recreational divers are less popular among deep and technical divers because of their volume, buoyancy, and size characteristics. In selecting a scuba cylinder a diver must consider: • Maximum intended diving depth and duration (gas volume required). • Environmental protection garments (buoyancy characteristics). • Ballast requirements. • Diver’s stature (long cylinders are awkward on short divers). • The maximum weight of cylinder or cylinder assembly that the diver can handle. A diver who intends initially to dive in the range of 18 to 40 m (60 to 130 ft) and later advances to trimix and technical diving will be better served by a 2700 to 3500 L (95 to 120 cf) cylinder. Within the limits of safety, a cost-conscious diver will select a cylinder to satisfy both present and future diving needs. Cylinder Configurations and Valves A diver using a single scuba cylinder in shallow water will find the standard “K” valve adequate. Valves with integrated low-pressure warning mechanisms (“J” valve) have declined in popularity. A prudent diver will seriously consider selecting a “K” valve from one of the modular valve systems. These modular valve systems enable the diver to change valve configurations if necessary. A modular valve system may be expanded as follows: • Basic “K” valve: single cylinder use in less than 18 msw (60 fsw). • Basic K-valve with H-valve adapter: converts the
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