Mar 28, 2010 | Freedive Training, Freediving
Free-diving rescue in water.
The vast majority of loss of motor control(LMC) or blackouts happen on the surface though sometimes on rare occasions they can also occur as the diver nears the surface. In the last ten metres the diver should be accompanied by the safety diver who stays within arm’s length.
The safety should be alert enough to notice any signs of excessive fatigue or overexertion and provide assistance to the tired diver. If blackout occurs before this can happen the safety should come behind the unconscious diver and reach under their armpit and across their chest with one hand while the other arm supports the head, holding it in such a way that the airway remains closed. This is to avoid entry of water into the lungs. The rescue diver should fin towards the surface in a sideways position to the victim. This allows greater freedom of movement for the rescue divers fins. It’s very important that he tries to come up at the safety buoy as this will help lessen the shock to the victim as he comes around.
On the surface the victim should be supported with one hand holding his head well up out of the water in such a way that his airway is fully open. The other hand will very gently slap his face while the rescue diver repeats in a soft voice ‘breath, breath’. The hearing sense is the first to come back after black out and it is very important that the rescue is done in a calm and reassuring manner. The victim may be in a state of disorientation and it is essential that there is nothing done to cause further shock.
Bringing them around gently.
Black out is the last attempt of the body to preserve O2 for the heart and brain as unconsciousness reduces use of O2. Once the body is in a place where respiration is possible i.e. the surface then breathing will resume naturally. We avoid loud noises or abrupt movements because the victim while unconscious is in a vulnerable place and the unconscious mind will react against any situation that seems traumatic by prolonging unconsciousness.
The affected diver should rest and definitely not dive again that day as there is increased risk of black out after having LMC or blackout. Very often the diver will not be aware of having lost motor control or blacked out. In the water there is no need to make a big deal out of it, wait till you get back on the boat or dry land to discuss the matter. It is important that any lessons that need to be learnt are learnt, but we should avoid a situation where the experience becomes something traumatic. There should be no blame or recrimination. It can happen to anyone.
Mar 27, 2010 | Freedive Training, Freediving
How to be a good buddy.
Discussion of shallow water black out(SWB) in the last post brings us to another important part of elementary free dive training; namely buddy skills.
Obviously for a training partner to be reliable, they should be well trained and experienced. They should be aware of the signs of impending SWB or loss of motor control (LMC) and be well versed in correct rescue procedure. They should also trained in CPR and first aid in the very unlikely event of a serious accident. That said training and experience alone are not enough for a good training relationship.
Trust and communication
Trust and communication are also massively important for a good, safe training relationship between buddies. When you are below you really want to know that your surface support is alert and reliable in case of some unexpected incident. It is very difficult to concentrate on your dive, especially a new personal best, if you feel that the guy on the surface is not paying attention or that he won’t be ready if something goes wrong.
Know thy buddy.
You should know your buddies capabilities and mindset, what they can do and what they feel like doing that particular day. Therefore there must be good communication before, during and after dives. Each diver must know what the other plans on doing at each part of the process. Before the dive, the surface buddy should know the expected depth, duration and form the dive will take. It should be agreed beforehand whether the safety diver will remain on the surface or at what depth he should meet the other on his way up.
While the diver starts his dive the safety should be in a state of readiness, wearing fins and having completed his breath up. While waiting to descend to meet the diver he should keep a good watch on the time and continue breathing up.
When he meets the ascending diver the safety should be alert and very observant. He should look for signs of fatigue or panic and make his presence known in a non intrusive way.
As they ascend the last ten metres together, the safety should stay close enough to the diver to grab them should it be necessary.
They should reach the surface at the same time at the safety buoy. If the diver forgets the safety should remind the diver to do recovery breaths immediately upon surfacing. The safety should be able to grab both the buoy and the diver should SWB or LMC occur. He should be close enough to the diver to support his head and gently slap his face, while softly urging him to breath.
After the dive there should be some exchange of feedback before they start preparing for the next dive.
Being supportive and non-competitive.
These are only the basic elements of what a good free-dive buddy should do. Apart from this, they should be supportive and understanding. Ideally buddies don’t compete against each other, but encourage the other to do the best they can on that particular day, respecting always the limits as they are on that particular day.
Varying abilities from one day to another.
These variable limits might be personal i.e. physical or psychological or they might be environmental such as currents or visibility. What is important to understand is that what was easy Monday might be difficult on Tuesday and there is no reason to feel disheartened or de-motivated. That’s sometimes that’s just the way it is and no deep analysis is needed. Our physical and mental energy levels fluctuate and we need to accept how we are feeling on a particular day, without ruthlessly pushing ourselves, even if it means that we don’t do a very impressive days diving.
Environmental conditions can vary from one day to the next and obviously they can also greatly affect what one feels comfortable doing. Even a mildly stronger current makes a big difference on a deeper dive, possibly changing a dive that is relatively easy without currents to a dive that is potentially unsafe with currents.
Obviously currents can negatively affect our abilities, causing more exertion and use of more O2, but other less obvious environmental variables can also greatly affect our capabilities, such as visibility or changes in temperature. Diving to fifty metres in crystal clear waters is a very different thing to diving through fifty metres of near darkness. It can also be very discouraging to dive into a cold water thermo-cline, while trying for a new personal best, especially if there is an accompanying drop in visibility. Another cause of stress can be choppy surface conditions, making it hard to relax and focus before a dive.
Acceptance of what is.
Clearly there are quite a few variable factors that can affect our performance and sometimes it’s not necessary to know exactly why you’re not at the top of your game, sometimes quite simply we have ‘off’ days. The important thing is to accept the limits as they stand in that particular moment and a good buddy should always help you with that, while still encouraging you to do the best that you’re comfortable with.
Mar 26, 2010 | Freedive Training, Freediving
Basic physics as related to free diving and shallow water blackout
To free dive safely an elementary understanding of physics and the effects of pressure is needed. At the basic level to avoid shallow water blackout and in more advanced training to avoid lung squeeze and other pressure related injuries.
When we take a lung full of air at the surface we are breathing at one bar of pressure i.e. 1 ata, one atmosphere, that’s to say that the air we breathe is pressurized by the 10,000 metres of air above us and we use this level of pressurisation as our basic measure of pressure.
Pressure effects on volume of air.
Ten metres depth of saltwater is exerts the same pressure as one atmosphere of air so at a depth of 20 meter there is 2ata of pressure. At 20 metres there is 3 ata of pressure and so on. As air is highly compressible gas when the pressure is increased the volume of the gas will decrease in direct relation to the increase in pressure. This does not mean there is less gas; simply that it occupies a smaller volume in space. In free diving terms if we dive with a full lungful of air of 6 litres, when we reach 10 metres depth the volume shrinks to 3 litres and at 20 it will 2 litres and 30 it will 1.5litres and so on. The amount of air in our lungs in unaffected, only the volume is reduced.
What this means to the free-diver.
The reducing volume of air as we go down affects our dive in many ways, it means that airspaces need more air added to them to maintain the volume, i.e. the ears and mask need to be equalised and obviously it means the deeper we go the less air we have to equalise, tying our depth limit to an ability to equalise.
It also has another less obvious but very important effect. In simple terms the increased pressure of the air in the lungs allows the gases in the air in the alveoli to behave as if there were more of them, i.e. their partial pressure increases. This is also why scuba divers get affected by nitrogen and air cannot be used below 66 metres due to oxygen toxicity. This increase in Partial pressure also affects the free diver in a very real way as it allows the free diver to absorb O2 from the lungs at depth that he would not be able to absorb at the surface. In somewhat simplified terms; at depth the volume of air decreases, increasing the density of gases within the air. This increased density allows O2 to cross the membrane wall into the blood more easily. We can imagine it like this, the lungs shrink and the air in them is squeezed in such a way that gas exchange across the membrane wall is made easier.
Shallow water blackout and how to avoid
All this is fine, except when the breath hold diver spends too long below, while hunting a fish for example. The body still has enough 02 to function at depth because of the increased density of the air, raising the partial pressure of the lung O2, but as the diver ascends the pressure decreases and as he nears the surface the lungs expand and suddenly there is not enough partial pressure/density of O2 to allow it to cross the membrane wall. This can result in a sudden drop in accessible O2 for the body causing unconsciousness to occur, sometimes preceded by loss of motor control (samba). This can happen while getting close to the surface but normally happens on the surface when the diver exhales to take his first breath. This is the most common cause of blackout, the diver exhaling deeply on the surface after overstaying their limit at depth. To avoid this we always use recovery breaths after coming to surface i.e. we only exhale 50 percent of our air then quickly inhale as much as we can, then again exhale half of the air, repeating in this way a few times. In the way we avoid dropping the pressure in our lungs too quickly, which could, in the case of the diver being too close to their limit, induce samba or even blackout.
The cause of shallow water blackout is the change in pressure after the diver uses excessive amounts of O2 at depth. To avoid this we always dive within our limits, we always avoid overexertion particularly in the ascent and we always use recovery breathing upon surfacing.