Without doubt the greatest risk facing spearfisherman is shallow water blackout. Spearfishing Magazine has reported that 8,000 drownings occur each year in the United States, and 81% of these deaths occurred in males between the ages of 14 and 32.

Shallow water blackout is a physiological phenomenon that occurs when an ascending diver’s lungs expand, creating a vacuum that sucks the remaining oxygen out of his blood stream causing the diver to black-out. This usually means the diver will start to sink, and if not assisted, will likely drown. We urge you to read Terry Maas’s section on Shallow Water Blackout. Terry has kindly made this section of his book freely available to the general public.

At Scubas World, safety is important. We recommend that you:

• Know your limits and don’t push them. Enjoyable diving is safe diving.
• Always dive with a dive partner and practice safe “one-up, one-down” diving protocol.
• Always ensure that you are properly weighted and are positively buoyant at depths shallower than 15 ft. In this way, if you black out, you increase the chances of bobbing to the surface and being revived as the fresh air reaches your face.
• If you are concerned that you have exceeded your bottom-time, release your belt buckle, holding the free end in your hand as you ascend. If you black out there is a reasonable chance you will release it and this will help you bob to the surface.
• There are very few warning signs of SWB, which is what makes them dangerous. However, indicators that can occur are headaches from high CO2 levels, uncontrollable swallowing, or tunnel vision. If you have experienced any of these symptoms while diving, you were seconds away from a problem.
• Don’t train alone or do static breathholds in swimming pools. A surprisingly high percentage of freediving fatalities take place in swimming pools. Technically this is not a SWB, but the result is equally dangerous, perhaps more so.
• When deep diving, we recommend that you remove your snorkel prior to breathing up on the surface. On returning to the surface blast clearing of the snorkel can lead to a SWB if a diver has been very close to his maximum. Moreover, retention of the snorkel at depth complicates equalisation and when diaphragm contractions begin can lead to the unwanted inhalation of water.
• Avoid exhaling under water or forcefully exhaling on surfacing. Exhalation on descent has been known to cause problems with equalisation. On ascent it can cause dramatic loss of buoyancy so more effort will be required on the ascent which can contribute to SWB. One must remember, that with any dramatic fall in the pressure in the lungs the remaining reserve of oxygen in the blood will go to the lungs and not the brain, which could be another contributing SWB factor.
• Don’t Hyperventilate. Hyperventilation is breathing at a rate of more than 15 deep breaths per minute. Hyperventialiation predisposes a diver to begin the descent in tension and with a higher pulse rate and decreased levels of CO2. This improper balance of O2 and CO2 can prolong the “easy phase” on the decent at the expense of the “struggle phase” on ascent and could lead to a SWB. In order to properly ventilate, and achieve sensible O2 saturation levels and a slow pulse rate, we recommend a few slow, deep, strong ventilations combined with relaxation and concentration.
• Avoid rapidly turning around at your target depth. A dramatic turn around at the end of a long descent can lead to “deep water blackout.” A significant amount of blood has moved into the head on the decent with the result that a rapid turn around can result in vertigo. This is particularly true of very deep dives where blood shift into the lungs is already a significant factor.
• Avoiding looking directly up at the surface on ascent. As you get tired, tension does build up in your neck. Neck extension can affect necessary blood flow to the brain and increase pressure in the area of the baro-receptors in the neck sending the wrong message to the central nervous system which may increase the pulse rate, so try and consciously relax the muscles in your shoulders and neck.
• Try avoiding increasing your pace on the last part of the ascent. This is where you are most vulnerable, where lactic acid-build up might be present, and where economy of movement is essential to conserve O2 and keep the pulse rate stable. Try remained focused on calm, steady economy of motion.
• Blowing on an unconscious divers eyes may stimulate the body’s impulse to breath.
• Keep up to date with medical aid training, refresh your understanding from time to time, know how to administer CPR, mouth to mouth, and mouth to snorkel resuscitation.
• If you are diving with a diver that has suffered a shallow water blackout always ensure that diver visits a hospital as soon as he gets on-shore. Often a near drowning victim may have let salt water into their lungs, and the symptoms only appear hours after the event. The effects of salt water on the lungs are serious.