I just finished the Performance Freediving clinic and the first topic we went over was safety during blackouts and sambas. During the class we had students do both (accidentally of course) and we learned how to deal with it effectively and confidently. The reality is that it could certainly happen at any time and for different reasons - hypoxia (low oxygen levels), hypercapnia (high carbon dioxide), and hypocapnia (low carbon dioxide).
A deep water blackout could occur due to hypoxia (excessive hyperventilation at the surface could cause a loss of the urge to breathe and you could simply go too deep or too long), or from turning to fast at the bottom of our descent (low blood pressure then would cause a momentary loss of blood flow to the brain).
Shallow water blackout generally occurs due to hypoxia which could again have been caused by excessive hyperventilation prior to the dive (and the lack of a natural breathing response let us go too deep or too long), because the re-expansion of our lungs has robbed our blood of too much oxygen, and also possibly from a loss of blood pressure and subsequent flow of blood to the brain.
The prevention for these things consisted of proper rest periods between dives (at least twice the time on the surface as the length of the last dive), and limited hyperventilation prior to the dive (only two or three fast exhalations followed by a peak inhalation). During the ascent we were taught to lower the arms 10 to 15 feet below the surface to decrease tension on the chest and to start a slow exhalation at about 6 feet to counteract the re-expansion of our lungs robbing oxygen from the blood. On the surface after ascent we were taught to take three hook breaths (an inhalation followed by a slight chest contraction to keep the blood pressure up) and then three purges (quick exhalations to rid ourselves of excess CO2).
Rescue techniques for blackouts started with simply adjusting our ballast so that we were neutral at 30 feet so that, should we suffer shallow water blackout, we would be positive and rise to the surface on our own. We always dove WITHOUT the snorkel in our mouths!! On dives deeper than 30 feet we would arrange to have our buddy meet us at 30 feet to assist on the ascent should anything happen. When diving with a buddy it was stressed that neither diver should dive deeper than the other could comfortably dive and attempt a rescue.
Rule number one in treatment of a blackout or samba victim: PROTECT THE AIRWAY!! Always make sure that the airway is kept free and clear of water or other obstructions.
Should a blackout occur beneath the surface we were taught to dive to the victim and place the palm of one hand under the the chin with fingers on the mask and the other hand on the back of the head (this would position our elbows on the chest and back) and swim the victim to the surface. The upward force of the palm on the chin would keep the victim's mouth closed and our fingers would keep the mask on (DO NOT grab the victim around the neck). At the surface we would place the victim on their back and support them with one knee. One arm would go over the the victim's arm down through the armpit and then up with our elbow resting under the back and hand reaching from underneath to support the head (easier shown than explained). With the free hand we should remove the victim's mask to allow air to touch the face. The victim should start breathing on their own; if not then the first step is to blow on the victims face, if they still don't breathe then we would start talking to them, and if still nothing, then we would gently tap them on the face with our free hand. If they still don't breath they are probably suffering from a laryngospasm and we should turn their head sideways (do not climb on top of them and push their head under the water) and give a couple of breaths into their mouth (the air on the larynx should trigger it to reopen). The idea here is to become more and more invasive with the treatment without alarming the victim - should they suddenly wake up with someone violently handling them they may panic and only make things worse. The main thing to remember is that there is usually plenty of time and the victim's breathing reflex will eventually take over - as long as you have their airway clear of water and obstruction they will be fine. If the victim is still not breathing after all of the above, then you should try and quickly move them to a place where you can commence artificial respiration and even CPR if necessary.
The treatment of a samba or blackout at the surface is the same except we obviously don't have to dive down to retrieve the victim.
Keep in mind here that I am no expert, but this is what we learned in class and it all made perfect sense to me. I recommend practicing these techniques and becoming very familiar with them so that, should anything go wrong, you will be prepared to deal with it confidently and calmly - one blacked out person and another panicking will not do any good at all.
The danger of a blackout or samba is real (I've now seen it firsthand) and the only way to put the mind at ease about it is to be confident that your buddy knows what to do (PROTECT THE AIRWAY!!) and you will be fine.
I will add one last thing. I only provided this information to help others who may not have access to the class, but I strongly recommend the Performance Freediving classes as the information they provide will undoubtedly make you both a much better and safer freediver. Personally, I think the safety and rescue procedures for freediving should be standardized and made readily available. While growing, this sport should be protected from the bad publicity it will receive from senseless and easily prevented deaths.
