Chapter 8- Limited Visibility and Night Diving Limited Visibility and Night Diving 209 Diving Lights As you descend, light is absorbed by the water causing the diving environment to become darker. If particulate matter is not too great you may choose to use a dive light (figure 8-2). In water with a high concentration of suspended particles, your light may be reflected to the point that it becomes of little or no use. To use a dive light most effectively, you should hold it to the side and above the object you are attempting to see, as this will minimize the scatter problem caused by the intervening suspended materials. Use of diving lights requires courtesy, so never aim your light directly at another diver’s face. Light signals are covered later in this chapter. Always aim your light at any hand signals which you give, not at your buddy. Non-illuminated signals are pointless. Use of one or more back-up lights is advisable under low visibility conditions. Should your primary light fail in open water, you can continue the dive or safely terminate it using your backup light. If a light is necessary for safety and all lights fail but one, you and your buddy should surface and terminate the dive. Orientation As you enter turbid water, you lose the surface references of light as well as the pull of gravity, and thus, your spatial reference. This sensation can be pleasurable if you are in total control of the situation. You may, due to light changes, experience brief tunnel vision or vertigo. You can control both potential problems by remaining vertical and grasping an object (anchor line, rock, etc.). Should the problem(s) persist, you can surface using depth gauge, watch, and slightly positive buoyancy to make a safe controlled ascent. Buddies should stay close together, as the visual reference of the buddy can lessen the impact of potential disorientation problems. On your first dives in low visibility water, you should dive in a known area or with a buddy who has been in the area before. For example, dive beforehand in a similar site with good visibility. This will minimize the natural tendency to be anxious under new conditions and will enable you to practice and rehearse all techniques before you enter the low visibility underwater conditions. Further, your task loading will be increased, as you must FIGURE 8-2. DIVE LIGHTS ARE USEFUL ON DAY AND NIGHT DIVES. keep close track of your rate of descent, depth, and buddy location. It is always a good idea to use the anchor line or a drop line for a controlled descent and ascent (figure 8-3). Under near zero visibility conditions and in moderate current, the buddy team using a buddy line may also choose to use an underwater reel so that a continuous line may be run from the anchor or dropline point of attachment throughout the dive (figure 8-4). Control is assured, although you must be vigilant to avoid line entanglements as you increase the number of lines used. In some areas, permanent lines are available for divers to follow and should be used in open water areas when provided. Horizontal control can be maintained by use of a reel, line, and depth gauge or by use of depth gauge and compass. As in flying, you must, in low visibility, trust your compass and follow its directions. How you “feel” under these conditions is not an accurate method of determining direction. To enjoy diving in very low visibility conditions, you must be a competent underwater navigator.
20047TC
To see the actual publication please follow the link above