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The forgotten and underestimated side of diving

Episode 1: The Awakening

Episode 2: Fear

Episode 3: Impairment

Episode 4: Heart Matters

Episode 5: Bubble Trouble

Episode 6: Risk Management

Episode 7: Perception

Episode 8: Task Loading

Episode 1: The Awakening


While we have discovered and conquered nearly every inch of our planet, deep within ourselves still lies the big mystery ...

While technology advances at high speed and we are slowly getting to know the stuff we are made from, the mind still holds so many secrets ...


Maybe biologically we have the same basis but we all differ when thinking about the same issue even when sharing the same ideology.

The amount of energy expenditure on rivalry can be baffling. So much that people are willingly risking their lives to prove the others to be wrong ...

While we believe to be in control, in essence our genes are still driving us.

A dramatic case of rivalry between father and son (both diver) can be read in the book "The Last Dive" by Bernie Chowdhury.

Shock the monkey (over and over again)

History proves that horrible things can be done to achieve what we want. Deep within our brain lies a primal center which responds to primal and basic instincts, mostly driven by fear, we call this now survival ... We think we have everything under control until our life is at danger

This fear is deeply hidden but can emerge. War conflicts and their cruelty are undoubtly proving this, sad but true

We learn how to control it by avoiding it, we developed risk management. Technology can help us, but it does not solve all the problems.


While technology advances at high speed, the human body still has to follow all this ... People are still taking big risks, even today. Technology can kill you.

Episode 2: Fear


Probably the biggest killer is panic. Panic is often the result of fear, fear of getting killed. In diving this means fear of drowning. Most likely proper reasoning is cut off by a number of physiological changes like rapid breathing, higher blood pressure etc .. for more details on various panic symptoms see Ref[1]. Maybe a number of unresolved diver deaths due to a heartattack could be the result of panic ?


Memories of fear are stored in the amygdala, which codes them into signals and transmits those signals to the frontal cortex for action Ref[2] GABA (Gamma-Amino Butyric Acid) is used by higher regions of the brain to tone down some of the lower brain's initial impulses and may function to decrease overly fearful responses to environmental stimuli. Ref[3]

Hit and run response

Reasoning can be blurred so much that we have to rely on instinct like responses. The most primitive response is escape, running away from danger. Signs have been found of divers who lost their way in a cave and tried desperately to crawl their way through tons of rock. Divers who bolt for the surface and hold their breath are clearly indications of this hit and run response.


Another response is halting all activity and self rescue attempt. The person is loosing all hope and total confidence in oneself. Lost divers in a cave have been found dead near the entrance/exit of the cave with empty cylinders. Instead of using their last gas reserve to find their way out they wrote their last words on a slate to their beloved ones.

Episode 3: Impairment


Perceived risk versus real risk

Mental impairment can severely diminish our perception of danger. This inevitably leads to an increase in risk taking due to diminished conciousness, alertness and misjudgment. It is the perception of danger which makes us alert and enables us to prevent a buildup of a series of little incidents into a major disaster.

Risk denial

Risk takers or macho figures are deliberately ignoring danger signals because they believe they can get away with them. They percevere their risk margins as being acceptable while in reality they are almost non-existent. This attitude combined with physiological impairment is a disaster waiting to happen.

Competition/Time pressure

Again, the urge to achieve, to push further explorations in order to beat the competition, can blurr our senses. No one can rule out any mistake. The more humans involved in the exploration project, the more chances for glitches. Any error, no matter how small may have devestating impact when performing extreme exploration projects.


One should stay vigilant at all times. Safety procedures should be rehearsed over and over again regardless whether the dive is simular to the previous one or not. Conditions may look the same but may quickly change. Care should be taken not to rehearse the same thing over and over again. Variation is key, this is important when training safety procedures. Otherwise patterns might emerge and vigilance or discipline might be compromised.



All sport divers diving on air will have experienced the "Martini Effect" due to nitrogen narcosis. For signs and symptoms see Ref[4]. The effect is reversible by just ascending. Susceptibility is different by each individual and may change from day to day. There is no evidence or proof of any adaptation whatsoever.

Other gasses also provide for narcosis. Oxygen, while metabolized, is also believed to be narcotic as well. For the moment the technical diving community is embracing helium to counter the narcotic potential of both oxygen and nitrogen by diminishing those gasses in the mix by replacing them with helium, which is far less narcotic.

Mental lapses

This occurs whenever you surface from a dive and don't recall some parts of your dive. Another typical example is losing your buddy while diving. Losing track of events like gauge monitoring and time is also a common example. Decreased concentration while performing complex dives can be life threatening.

A lack of concentration could be caused by a shortage of oxygen to the brain. The shortage could be caused by having a poor cardiovascular fitness (poor blood transport) or when being susceptible for major C02 buildups like shallow breathers (poor ventilation). Skip breathing facilitates a CO2 buildup and should be avoided at all times during the dive.

Rapid shallow breathing, either by panic, increased anxiety levels (stress) or when doing exercise (swimming against current, high Work Of Breath at depth) all facilitate a CO2 buildup. Again helium is a preferred gas to be breathed at depth since it has low density hence diminishing the WOB to an acceptable level.

Decreased ventilation could also be caused by breathing mixtures having a higher partial oxygen pressure.

Mental lapses could also be caused by blood viscosity increases due to dehydration.

Narcosis also seems to be responsible for facilitating this "memory loss". In fact both Narcosis and CO2 retention seems to act additive.


Fatigue are messages of your body telling you to stop and get some rest. Mental fitness is a requirement for diving and should never be ignored. Concentration diminishes quickly when being fatigued. No wonder that most accidents do happen when people are fatigued.

Sea sickness and dehydration do facilitate fatigue. While vomiting you can force your ears, so much that it is possible not to feel the pressure to equalize and risk an ear injury or ear barotrauma. Inequal pressurarisation of the ears can lead to an alterno baro which induces terrible vertigo symptoms.


There is a wide range of possible side effects both physiological and neurological. Best practice here is when taking medication: don't dive. Otherwise do seek professional help from specialists which do also dive.

Episode 4: Heart Matters


The heart is a very powerful muscle, but we need to take care of it. We all know it takes care of the blood circulation in our body and does this without us thinking about it. Besides the need for oxygen rich (arterial) blood divers equally need a good venous blood circulation to transport the dissolved inert gasses in the blood to the lungs (offgassing). Divers with poor fitness might stress this powerplant by having to work much harder. In addition there are physiological effects of being submerged like blood shifting. Stress, hypertension are also factors to be considered. About 25% of diving casualties are due to a heart attack while being submerged. A sad but clear indication that this factor is greatly overlooked since it can be prevented quite effectively.

Lipid Profile

Cholesterol should be controlled otherwise coronary diseases might develop. It is good to know your lipid profile (LDL,HDL,CHOL/HDL ratio). Exercise will raise HDL while changing food habits might decrease LDL. Omega3 fats are good as they decrease fat concentrations (triglycerides), provide for better blood perfusion, prevent formation of blood cloths and heart rhythm anomalies. In fact a major part of the fat of our brains consists mainly of omega3 fat !

Coach Potato

Cardiovascular health is key to solving the problem. Regular and maintained exercise is the recipe for success. Care should be taken not to overstress the heart in doing so. The target heart rate should be
(220 - age)x.70 Ref[5]. Before starting a training program a medical examination including an Exercise Stress Test is needed. Some information can be found at Ref[6].

Episode 5: Bubble Trouble

The Hole

A PFO (Patent Foramen Ovale) is a hole between the right and left ventricle of the heart. Normally this hole is covered by a "flap" which seals after birth. However in about 30% of the population this flap is not sealed. Increased activity or even a forced valsalva manoeuver can temporarely open this flap. A PFO has been linked to the incidence of decompression illness (DCI): deoxygenated blood bypasses the lung filter and moves to the oxygenated (right side) of the heart. According to DAN (Divers Alert Network) detection of micro bubbles is found on 37% of all dives and on 67% of all repetitive dives. Clearly, people with a PFO still wanting to dive should somewhat restrict their diving, especially repetitive diving. Otherwise micro bubble growth must be controlled by introducing additional stops. UWATEC has developed a new dive computer called "SMART" which allows for 6 levels of micro bubble level stops. They claim reducing microbubbles up to 61%

The Models

Generally speaking there are three kind of models, two of them simulate the ongoing ongas/offgass processes in divers while diving. The third is based on dive profiles having a certain probability of DCI occurrence. These models are called : solution models, bubble models and stochastic models. The most widerspread model in use today is the solution model. A lot of modern dive computers are using modified Haldane or modified Buhlmann solution models. Recently new dive computers are emerging using bubble models. Examples of bubble models are VPM (Varying Permeability Model) and RGBM (Reduced Gradient Bubble model). More info on bubble models can be found at

Size Matters

Bubbles are always present when diving, and right after a dive. They may be perfectly harmless. Controlling their size is paramount. If not, they may cause damage, may lead to DCI, AGE (Arterial Gas Embolism) or CAGE (Cerebral Arterial Gas Embolism). The latter two being fatal. Therefore ascent speed (and control of) is very important. The sport diving community did bring the ascent speed from 18 meters per minute towards 10 meters per minute. Technical divers even ascend slower the last 6 meters (up to 1 meter/min). When deeper, ascent speed is not so much relevant and may be greater (up to 20 meters/min).

Deep Stops

Deep stops is a way of controlling the ascent in a safe manner. To control the expansion of bubbles, deep stops are employed. With the lack of an algorithm the accepted method of halving the depth between the bottom and first stop and then completing a one to two minute stop seems applicable. This process is repeated if the depth between that micro bubble stop and the first real stop is greater than 10 meter.

Episode 6: Risk Management


What is risk anyway ?

There exists a number of definitions. The one I like the most is:

"Risk is the combination of the probability, or frequency, of occurrence of a defined hazard and the magnitude of consequences of the occurrence" (Royal Society Report, 1992).

A commonly used equation for risk is:

Risk = Uncertainty (or Probability) x Impact

The more probably an error or the higher the impact (or both), the higher the risk.

Target risk versus perceived risk

Risk is often underestimated because the perceived risk level can be lower than that of the real risk. The diagram below comes from Target Risk - The theory of risk homeostasis. Ref[10].

The golden six

To dive or not to dive ?

One should determine for himself if he or she is ready to dive. This judgement should be yours only and not be based on someone else's judgement or perception. Several important factors are to be considered. I call them the golden six. I include here two examples.

The following indicates a dive which should not be made


While skills and confidence are more than satisfactory, a serious lack of experience combined with harsh diving conditions and poor fitness however should tell you not to make this dive. It is even not worth the risk regarding the low benefits expected from it.

The following indicates a dive which can be made


Clearly all factors except the condition seems to tell you this dive is possible. While this might be the case, still think about the possibility that environmental factors can get better but can also get worser over time.


Risk margin

There are several ways of dealing with risk. One could be to avoid risk by not making the dive but that is not always an option. In the latter case what needs to be done is minimizing the risk by providing a sufficient margin for error and trying to keep it as large as possible during a contingency.

Greater margins for error allows you to deal with one problem more efficiently hence preventing it from escalating it into a cascade of several other problems, a condition often nicknamed Charlie Foxtrot.

Identifying risks and knowing how to respond swiftly and appropriate is one way of preventing diminishment of your margin for error.

Readiness, contingency planning

Write down all possible scenario's and work out solutions. Do this with your entire dive team, including surface support people. This is often called playing what-if games. Discuss issues, work out solutions and train them routinely so you can perform them swiftly and flawlessly.

For each identified what-if scenario you should specify the following elements:

  • The description of the identified risk
  • The solution to the problem
  • The probability or chance, P (1=unlikely, 2=possible, 3=probable)
  • The impact or life threat imposed, I (0=none, 1=low, 2=medium, 3=high)
  • The calculated risk ( P x I )

Episode 7: Perception

Field of vision

Traditional dive masks limits the perception of potential dangerous situations since the peripheral view becomes severely restricted (tunnel vision). For an explanation of this phenomenom see reference Ref[11].

Compensating for a lack of peripheral view is possible on several occasions. One example is the single file diving in caves. While you do not see the person behind you, you can view the backscatter of his light swaying behind you on the floor, ceiling or walls. This will prevent you from having to look behind you while proceeding and avoiding the risk of hitting things in front of you or accidently swim into a wrong passageway while doing that. For optimum result you can cover your light when doing so.

It is also interesting to note that certain conditions such as nitrogen narcosis (too deep on air) and the onset of oxygen toxicity (too much partial oxygen pressure) do produce tunnel vision.

Women divers do have the advantage of having a better peripheral view than male divers. Men on the other hand have a better spatial insight than women.Ref[12].

Episode 8: Task Loading


Task-loading Basically, this translates as attempting to do too many things at once. An example would be a scuba diver attempting to launch an SMB (Surface Marker Buoy) while trying to maintain depth at a safety stop or deco stop. It is easy to focus on one task to the exclusion of others (perceptual narrowing) when that task is complicated or particularly demanding. In the above example when the diver focuses too much on launching his SMB or on using his reel, he might forget to check for his depth or even forget to make his stop.

In a high stress situation each additional task we add results in a drastic decrease in overall efficiency. Quick example - grabbing a dive knife off your ankles is not a bit of trouble in your livingroom, or even on that easy reef dive in the warm Caribbean last summer. But get tangled in an old fishing line on a deep wreck, in cold and dark waters, with heavy currents and visibility shot to pieces, and that relatively simple task of finding and grabbing that life saving knife on your ankle becomes nearly impossible.

Lack of parallelism

If you are an information technology enthousiast then you probably already heard of multitasking and mutiprocessing. A computer may have several processors (multiprocessor) doing multiple tasks at the same time (parallel processing). We humans on the other hand have only 1 processor: our brain. In order to do several things at the same time our brain will have to prioritize between tasks and switch between tasks to allot each task some amount of time.

Specialized regions

Different regions in our brain handle specific tasks. There is evidence that due to evolution the brain of males is hard wired differently than that of females. While males had one specific task to do, that is hunting, females on the other hand had to perform several tasks like watching the house and children, preparing meals etc... Females clearly have an advantage when it comes to handling several tasks at the same time and can deal better with task-loading.

Contributing factors

In technical diving, task loading is something you should be prepared for. Redundancy for eliminating SPOF's (Single Point Of Failure's) is good but too much redundancy can kill you because of increased complexity and hence inreased risk due to human error.

In recreational diving, a good buddy has also to deal with task-loading since he has to monitor his buddy as well. Diving with a new or unfamiliar buddy will greatly increase this task-loading.

Being unfamiliar with new diving equipment and/or with new procedures.


Prepare and properly train new procedures and/or new equipment.

A same configuration allows the same response by all team members at all times while reducing effective task loading due to unfamiliarity with some equipment and/or positioning thereof.

Reducing to the strict necessary and using a KISS (Keep It Simple Stupid) approach seems to work best.


The way we deal with task loading is threefold. First, we eliminate any task that isn't directly concerned with keeping us alive. Second, we work to reduce the complexity of the tasks we have to do. Finally, we practice, practice, practice the simplified tasks, until they're hammered in so deeply that they don't require excess RAM to perform.

Next Episode

Episode 9: Human Error. To be continued .


Ref[1] The psychology of Diving

Ref[2] Brain's "Fear Center" Identified

Ref[3] Is our tendency to experience fear and anxiety genetic?

Ref[4] Raptures of the (maybe not so) deep

Ref[5] Exercise, Diving and the Heart

Ref[6] ACC/AHA Guidelines for Exercise Testing

Ref[7] Technical background for low bubbling computers

Ref[8] Bubble decompression strategies

Ref[9] Fact fiction and voodoo - The Art of Decompression Diving

Ref[10] Target Risk - The theory of risk homeostasis

Ref[11] Ultra wide view diving masks - how it works

Ref[12] Women take a wider view

Suggested Reading:

The Last Dive by Bernie Chowdhury - ISBN 90-246-0618-7

Technical Diver Encyclopedia - ISBN 0-915539-04-7

Technical Diving from the bottom up by Kevin Gurr - Phoenix Oceaneering Ltd 2002 first ed.

Understanding M-values

Clearing up confusion about deep stops

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