Divers should be able to cope with a sudden loss of underwater visibility. Divers faced with this predicament can feel around their regulators’ exhaust ports to determine the upward direction since bubbles always go up. Divers should also check their flashlights if they are still switched on.
There’s got to be a pretty good reason to start a dive in very low or no visibility – like someone is paying you or you’ve been off scuba too many weeks and your psyche is drying out! A more likely scenario is to start a dive in reasonable visibility and then have the situation deteriorate, so you end the dive by the Braille method. Whether you panic or cope with a sudden loss of visibility depends upon your training, experience and equipment.
Sudden loss of visibility underwater can be grouped as a blackout, greenout or whiteout. Some water starts out dark, such as the brown cast of a Midwest lake rich in tannic acid. This water is brown every day, so it is no surprise you can’t see an arm’s length. Since the conditions are stable, this is expected to be low visibility diving. This article will address what starts as an “I can see” dive and turns into a “Who turned off the lights?” dive.
Regardless of how your world goes dark, remember that bubbles always go up. By feeling around your regulator’s exhaust port, you always know one direction (although it may not be where you want to go at the moment). The second rule is that, when using a light that suddenly fails, see if it is still switched on.
Blackouts usually occur when muddy silt gets stirred up. Rivers with soft, oozy bottoms can go from low visibility to zero visibility with the flick of a fin. Luckily, the river current either carries you or the silt away from the blackout locale and visibility is restored.
If you are inside a wreck or cave and touch the lightly settled sediment in the interior, your whole world could go to instant zero visibility. In a confined environment, the walls or floor can contain silt and blackout potential. Training and equipment are required to safely exit the area. Training keeps you calm and confident in your ability to reason and use equipment to find your way out.
It can take hours for the silt to settle in a wreck or cave – time you don’t have. If you used a reel and line to mark your route when entering the confined space, the way to safety awaits. Reel and line handling skills practiced in a pool or on past dives give you the confidence to turn around without getting entangled and begin winding in the line, while moving toward better visibility.
Practice in controlled conditions builds an awareness of how wide or high you, are underwater or how to maintain neutral buoyancy by feel, as opposed to seeing yourself rise or fall in the water column. Reeling a line by feel, rather than sight, is a trick. Keeping the line from getting knotted, loose or overflowing one side of a reel are learned skills. Training classes for cave, wreck, ice and rescue diving devote time to blacked out mask exercises that teach students how to optimize other senses and manual skills to overcome a lack of visual input. Advanced training also gives you the confidence to stop, assess the situation and then devise the best course of action. When a blackout starts, one way to minimize the effects is to stop all motion immediately. Sometimes stopping movement is hard, because your adrenaline charged body is saying “run away from danger.”
Greenouts are a general term for algae or plankton blooms that turn visibility to nil. If the water is soupy on the surface, it may or may not be greened out at depth, but it will certainly be dark, owing to reduced light penetration. Freshwater lakes can have an algae that looks like smashed green peas on your mask face-plate. The particles seem to dance on the glass and you can’t see past them or getaway visually. It takes an incredible Constitution to avoid vertigo when you are socked in by an algae bloom.
Greenouts can be depth specific. The surface to 10 feet could be OK, followed by a band of green water from 10 to 30 feet, then the visibility opens up all the way to the bottom. Using a descent line or anchorline makes it easier to traverse a greenout band. While holding onto the line divers are less likely to get disoriented or suffer vertigo. Descending feet first through low visibility water also helps maintain your equilibrium.
Whiteouts usually describe loss of visibility owing to sand suspended in the water. Because sand particles are so reflective, how you use a dive light makes a difference in a whiteout. A narrow beam light seems to give more “visibility” than a wide beam. The narrow beam can be brighter and seems to pierce the sand blizzard and provide some “vision” space. A wider beam lamp illuminates a broad swath and gives the appearance of a reflective, twinkling, close-in landscape but little “vision.” If your light beam seems only to illuminate the scatter, use your hands to form a tight collar, narrowing the beam and perhaps getting a better distance view.
Another technique for underwater lights is to point the beam down oral a low angle, instead of aiming parallel to the bottom and sweeping the horizon. This downward beam can show features that get lost in the backscatter of direct lighting. As always, hold and aim a light, rather than letting it dangle from a lanyard. The randomness of a dive light bouncing around can cause nausea in some divers. Also, a light shined in your buddy’s eyes will ruin his/her low light vision, until he/she reacclimates.
Sand settles nearly as slowly as :muddy silt. If you are in an area where you caused the whiteout by thrashing around, move away. It is easier to move right, left or above the suspended sand than to try and see through the cloud. Inflate your BC slightly and rise above the mess you caused. If you can avoid kicking while close to the bottom, you can lessen the additional sand you put in suspension. Consider what you might do differently to avoid a repeat whiteout before settling in a new “clear” space.
If not you but currents, surge or waves are stirring up the bottom, consider whether it is time to terminate the dive. Sometimes we need to be reminded that the purpose of our activity is to have a safe, fun, enjoyable dive.
Zero visibility diving has potential for becoming dangerous. If your diving activities include situations where black-outs, greenouts or whiteouts could occur, plan ahead and take advanced training before you get in a jam. If you plan to do confined or restricted space diving, advanced training is particularly prudent. Learning skills in a pool with a blacked out mask is fun and safe. Practicing those skills in open water under the supervision of an instructor will increase your confidence and enhance your ability to make correct decisions when faced with sudden low visibility.
Diving in near zero visibility is an advanced skill that adds to your diving experiences and allows you to stretch your comfort zone. It is a very personal decision to make or cancel a dive in challenging conditions and your respect of another’s decision is a clear sign you are a philosophically advanced diver.