Limited visibility diving will be encountered by every dive team at sometime. It can occur due to mud, pollution, plant life, or just be night time. In limited visibility, preplanning and training, are the keys to success. Be sure the team has planned and practiced night operations. Try all search operations in the area and determine which work best then practice at night. Train at the site. When water has bad visibility during the day it will have worst at night.
Dive site setup for night operations are about the same as day, however certain changes must be made and equipment added. Most important is entry and exit points. Be sure you have dove the site at least once during the day before conducting a night dive. The command post should use a white gas lantern to light the area, they are economical and do not require a generator or extra batteries. They have long light time when full and take up little room.
The entry and exit point should be selected for ease of movement. For divers to locate the point a two light system should be used. These two lights should be a 360 degree white or red strobe and a 90 degree continuous burning light. The strobe should be able to be seen from all locations on water and land. The continuous burning light is placed in front of the strobe a few feet away by the water's edge. With this system divers surfacing in the water will see the strobe and swim towards it. When in range to see the other light, they will line them up. By keeping the continuous burning light with the strobe the divers have a straight line to the exit point. Divers stay on line because the 90 degree light can only be seen when heading straight at it. This works extremely well in difficult entry and exit areas.
Divers should carry two lights and a buddy line. They also should carry at least two markers and chem lights. When the object of the search is found the diver attaches the chem light to the marker before sending it up. By doing this the shore team can see all marker buoys. Each diver entering the water should attach an active chem light to themselves to be seen by shore, other divers and boats in the area. This chem light can be attached to the diver by placing it at the point the yoke screw holds the first stag to the tank or by taping a small one to the snorkel. Another thing divers should do is place reflective tape on their tanks. This tape can be got at the hardware store or reflective dive flags can be used from the dive store. Each tank should have the reflector placed where it may be seen from the back and on the bottom of the tank. The purpose is so divers shining light will hit the reflector indicating another diver. The reflector on the base of the tank does the same thing except it shows when the diver is swimming away from the light source.
Assign areas to be searched and mark with surface markers that have chem lights attached and glow in the dark or red strobes. Reflective tape also should be on every marker used, above or below the surface. When dive operations are underway the team must signal to other vessels in the area there are divers are in the water. During daylight, the divers fly the Code Alpha flag offshore, or the Sport Divers Flag inland. At night however, the divers must display three lights that are, red over white over red. This light arrangement means basically the same as the dive flag.
Discuss best type of search to be used for both the surface and water visibility. These search patterns should have been practiced before hand. If the area has bad or no visibility, the surface controlled searches work best. At night the search pattern may be the same as the search used during daylight. The only modification is that the divers must carry a light to search. For night searches in good visibility, 2 feet or mare, head lights can be used. Ahead light is a light used by wreck and cave divers. These light attach to the mask or more commonly are worn as a head band. Head lights allow the divers hands to be free and are very useful to the dive team. They can be purchased at a dive shop or rigged by the divers be fore hand. Even if head lights are used, the divers must still carry at least two hand lights.
Review signals and emergency procedures for light failure, loss buddy, entanglement, disorientation, and out-of-air situations. These are the same as in daylight. Loss of buddy is always the same, the diver surfaces once the buddy is not noticed after no more than a one minute search. However, at night when loss buddy contact is fist noted the diver should turn off his light to look to see if he sees his buddy's. If another light is not noted, then the diver should turn back on his light, and rotate in a full circle, slowly looking for the reflectors on the tank. If after one revolution, the diver should surface if his buddy was not spotted. When both divers do this they shall meet on the surface. In zero visibility the diver should be in contact with the surface team via a line and all emergency line signal and procedures should apply.
National Association of Rescue Divers
P.O. Box 590474, Houston, Texas 77259-0474
Site Made & Maintained by: RescueDiver.org
Any Inquires Should Be Made To: WEBMASTER@RescueDiver.org
Copyright 2006 National Association of Rescue Divers ©