Watch Out for Deep Water Blackout Spearfishing is a favorite among many who live near water. It is considered a sport for some, a pleasurable activity for others, and it is also a good resource for food. While spearfishing can be a fun activity, it also has its dangers, so those engaging in spearfishing should familiarize themselves with safety precautions and diving techniques that will help to assure their safety while in the water. One of the most common causes of injury is known as deep water blackout, and is something that should be very familiar before even considering the dive. Deep water blackout is as much of a danger to new divers as it is to those who are very accustomed to diving. It is unpredictable in most cases, but the following information will offer tips on how to prevent it, explain the deep water blackout itself, and the likely causes for why it happens, so that you can have the information or pass it on to someone else and have the best chance of preventing it. What is Deep Water Blackout? Deep water blackout is a condition described as a loss of consciousness, fainting, or syncope that is typically caused by what is known as cerebral hypoxia. This happens as a result of ascending too quickly from a deep free dive, also known as a breath-hold dive or dynamic apnoea diving. Deep water blackout often occurs with dives that are at least ten or more meters. The immediate cause of deep water blackout is from a rapid drop in the partial pressure of oxygen in the lungs upon rapid ascent from the dive bottom to the top of the water. It typically occurs within the top three meters, and has been known to happen right at the surface of the water as well. What is the Difference between Deep Water Blackout and Shallow Water Blackout? Many people tend to confuse deep water blackout and shallow water blackout as the same problem, and though they are similar, they are not the same. As previously mentioned, deep water blackout happens because of the rapid drop in partial pressure of the oxygen in the lungs upon ascent. Shallow water blackout, on the other hand is caused from hypocapnia, which is due to hyperventilation before diving. Shallow water blackouts can happen in any depth of water, and often occurs in swimming pools during practice. Possible Mechanisms for Deep Water Blackout Because of the nature of this condition, deep water blackout is difficult to figure out. The victims of deep water blackout are typically unable to review the events as they happened, as the very definition of deep water blackout is a loss of consciousness. Often times, divers will remember the events prior to the syncope, and shortly afterwards, but nobody can recall what is happening during the blackout phase. Therefore, scientists, divers and doctors can only guess what causes this condition. There are currently three acceptable possible mechanisms for deep water blackout, and they are constantly being researched and updated as new episodes occur and more information is gathered.

1. Voluntary suppression of breathing: This is considered not to be a primary factor, though it likely plays a part in the process of deep water blackout. Often times, the body’s intrinsic need to regulate breathing will take over when the person is not doing so voluntarily. Many divers are trained to hold their breath for a variety of reasons for an extended period of time. The body may feel as though air is necessary, and it becomes a sudden need to breathe, and the rush can send the body into a deep water blackout.
2. Rapid depressurization: Rapid depressurization happens frequently with divers who are less experienced. Newly trained divers get panicked when they feel they have gone too far, or feel as though they are out of control. When they get this feeling, they often rush to the surface in order to feel safe, which is where the problem occurs. Divers should rise to the top slowly, regardless of their anxiety level. A more serious version of rapid depressurization is known as the bends, which occurs when the nitrogen in the blood expands too rapidly, which can cause pulmonary embolisms.
3. Self induced hypocapnia: One of the widely accepted possibilities for the cause of deep water blackout is a result of trained, well experienced divers. The problem lies because divers are often trained to hold their breath for a long time, and therefore don’t get the urge to breath as often as it may be necessary. Experienced divers, while seemingly ironic, are more likely to experience deep water blackout, as they don’t get the sudden urge to breath, and can fall prey to unconsciousness without warning.