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Pre-dive CCR checks and checklists do not always prevent accidents due to equipment failure

“One of the key things I teach is to understand that safety does not necessarily mean the absence of failures or accidents, rather it is the existence of rules and safeguards and the capacity of a system or organisation to survive a failure safely.” This is a quote by Todd Conklin, a researcher and practitioner
Published: May 5, 2020 - 09:30
Updated: July 22, 2023 - 19:38
Pre-dive CCR checks and checklists do not always prevent accidents due to equipment failure

“One of the key things I teach is to understand that safety does not necessarily mean the absence of failures or accidents, rather it is the existence of rules and safeguards and the capacity of a system or organisation to survive a failure safely.” This is a quote by Todd Conklin, a researcher and practitioner in the security and performance industry in the United States. The point is that we develop technical and non-technical skills and design equipment, procedures and training and manage the environment so that risk can be managed at an acceptable level. But we can’t design or manage everything, not everything can be predicted, so we need to be able to deal with those ‘unplanned events’ and then make the story of what happened available so others can learn from it.

In closed circuit diving, one of the best ways to ensure dive safety is to make sure that the unit assembly and control tests have been done correctly before diving. However, even if you do your due diligence on the surface, including packing the canister and then carrying out a full set of control tests, there is always a chance that something will go wrong. An example is the incident caused by elevated CO2 levels, during a cave dive 400 metres from the entrance. The only reason the participants survived the incident was because of effective teamwork and a high level of situational awareness, which allowed the participants to understand that not everything was OK and that action was required.

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The following report written by Phil Short is about an instructor evaluation dive in the French cave system. The dive involved three students, a trainee instructor and an Instructor Trainer (IT). Phil (IT) carried out the instructor evaluation during the dive.


Rebreathers were assembled and tested on site in accordance with both the unit checklists provided by the manufacturer and checklists in accordance with training standards, prior to diving. The bailout cylinders were stacked in the lake prior to entering the cave, before the pre-dive checking procedures were carried out. The divers entered the water at a point where the water was up to their waist to put on their fins and strap on the cylinders. In the lake, the water was stagnant, with no flow, and there was fines and organic debris floating on the surface. All divers closed the loops in the CCR while carrying out the last activity, which was putting on the fins. When the divers bent down the mouthpieces of the breathing loops were under water, which is normal.

The observed diver (the trainee instructor) put the mouthpiece in his mouth, blew air to clear it of water, then switched the DSV to CCR mode and breathed normally, monitoring the primary and backup pO2 readings to confirm correct operation of the device. When all divers were ready the dive began.

Initial part of the dive

The divers descended to a depth of 30 m, passed the bend in the corridor beyond the entrance, and then slowly ascended to a passage at a depth of 20 m, then at 18 m, and then at 15 m, all the while swimming at about 10 m per minute. At P.300 (300 m into the cave) the diver described felt a slight tremor and a slight tingling and stinging sensation in his arms and hands, but his perception was that the way he breathed remained the same. The instructor switched to the OC automaton he had strapped around his neck for two or three ‘rescue’ breaths, checked the indicators and readings on the monitoring equipment as he felt better and returned to the CCR closed loop. Instructor Trainer (sailing behind) noticed the rescue procedure performed by the instructor, swam over to him and asked if everything was ok. The instructor replied “Ok” and the dive continued. Everyone swam at a calm speed of 10m per minute.


At P.400 (400m from the cave entrance) the Instructor on placement again felt tingling and local stinging, but this time he also noticed an increased breathing rate and breathing discomfort. The diver performed the open circuit surge procedure again and after approximately 6-10 breaths his breathing rate began to normalise and the diver felt better. The IT noticed the re-rescue procedure, approached the evaluated instructor and asked if everything was alright. The evaluated instructor replied “yes”, IT turned the team around completing the dive, confirming with the trainee instructor and each of the three trainees. The Trainee Instructor also signalled for the instructor to remain on the back-up open circuit until they left the cave.

During the controlled ascent, one of the 7-litre bailout cylinders, with a pressure of 300 bar, was emptied to 70 bar and the other remained full, with a pressure of 300 bar.

After leaving, the trainee instructor calculated that the average gas consumption during breathing was about 18-20 l/min, compared to normal at 12 l/min.

For the next 2-3 days the diver experienced a severe and prolonged headache.

The trainee instructor explained that he felt fine throughout the dive but had a feeling that something was wrong.


Technical Approach

After the instructor’s dive, the CCR was disassembled and a detailed inspection revealed that a small piece of wood, similar to a splinter from a match, had stuck to the one-way inspiratory control valve (mushroom valves). When pressed under the inspiratory valve it held the valve in the open position. This trinket must have entered the valve through the mouthpiece when the cylinders and fins were pinned in the lake. Otherwise a check of the one-way valves would have revealed a leak. The level of hypercapnia during the dive was at a relatively low level, this allowed the frequency and breathing rate to return to ‘normal’ as quickly as it had. However, had IT not stepped in, it is likely that the trainee instructor would have continued the dive by swimming deeper into the cave. This could have led to a situation that would probably not have ended so happily. Let’s not be fooled by the biased results… Technical solutions, such as using a fabric barrier on the mouthpiece, may prevent such contaminants from entering, but functionality will be affected. In this case on resistance and breath work.

Non-technical Approach

Situational awareness: the evaluated instructor had limited situational awareness due to the narcotic effects of CO2. The trainee instructor observed events unfolding during which ‘abnormal’ incidents occurred. The trainee instructor was also concentrated and under psychological pressure due to the attention he was giving to the assessment and supervision of the trainees, compared to being ‘more rational’ and with greater awareness.

People notice things when they are dangerous, interesting, enjoyable or important (DIPI). Through his experience, the Trainer Instructor recognised that this situation was interesting, potentially dangerous and therefore important and required appropriate action.


Messages were communicated correctly, when IT took the lead and ensured the communication loop was closed, everyone completed the dive. Direct communication with trainee instructor with clear message to remain on open circuit.


It is very difficult to make correct decisions when we do not have all the data. Furthermore, CO2 is a known narcotic agent that reduces clarity of thought. A victim under the influence of this agent may be the worst person to make critical decisions because they are focused on moving on, especially during this type of activity. The trainer has made an executive decision. It is not known whether the trainees noticed what happened and what their decision-making processes were. However, a conflict of authority would likely have made it more difficult for the trainees to finish the dive earlier (see the ‘How Safe is Your Diving’ blog on ‘The Human Diver’ for more information).


Teamwork is one of the most important non-technical skills. I often hear that teamwork won’t help when you are diving in the open sea and you are alone. My answer is that effective team members can help detect situations that a single person may not notice, for whatever reason, whether through cognitive load or due to physiological problems such as anaesthesia, hypoxia or hypercapnia. The team can help to prevent adverse events. As long as there is psychological safety, it can also help to regain control of the situation when something goes wrong. The team will shift the decision-making process away from the person in this stressful situation, providing additional resources (cognitive and physical) to help resolve the problem. However, for teamwork to be effective, there must be a common set of standards, behaviours and goals. As the interdependence of the team increases, so does the need for higher levels of competence within the team to perform tasks.


The Instructor Trainer took the lead on the situation and moved from a coaching and evaluating role to a direct leadership role. Situational leadership and the ability to move between different leadership styles are essential in high risk environments. Finally, both the IT and the trainee instructor demonstrated an appropriate level of leadership by sharing an account of the incident so that others could also learn from the events.

Feedback and discussion

The team discussed what they would do differently to prevent a recurrence of this problem at a technical level. Their view was that a ‘risk assessment’ of the environment should be carried out and if there is a reservoir of static water, with a high potential for contamination and debris, it was felt that one should enter the water with a mask on and a closed loop in the mouth. This is not always easy and there is a question of trade-off between one risk and the other.

Non-technical capabilities do not stand alone. As Sully (Captain Chesley Burnett “Sully” Sullenberger) said after the Airbus was embedded in the Hudson River in 2009:

“One way you can look at it is that for 42 years I made small regular deposits in the experience bank: education and training and on 15 January the balance was sufficient for me to make a very large withdrawal.”

Divers don’t dive enough to experience all the possible failures that can happen, so sharing these types of stories allows the community to know what can happen and provide a level of chronic anxiety about what might happen. This doesn’t mean you should be paranoid, as only a certain amount of events can be prepared for, but you can certainly increase the odds in your favour if you start planning for safe failures in whatever you do.


Editor’s note

In both the UK and USA, there is increasing pressure within the diving community to be transparent and build a knowledge base based on events that have taken place. With the right culture of non-judgementalism to look for causes rather than blame, and negative judgement from the community and authorities of any actions that seek to suppress or fail to provide full information, regarding incidents, data collection and analysis is made possible in a transparent manner. With a sense of safety for those directly involved in an incident and an appropriate culture of incident reporting, the diving community has the opportunity to self-analyse the causes of situations. This allows new training procedures, regulations or guidelines to emerge that can effectively prevent certain situations from recurring or, if they do occur, to keep them under control.

This approach results in new training procedures, new training requirements and new technical and non-technical skills being introduced into training programmes. It is the analysis of accidents that have happened and the accounts of such events in the spirit of Just Culture – the descriptions of these events have allowed the analysis and then the creation of such basic training procedures as the OOA procedure or the more advanced checklists for CCR divers. Only by promoting a Culture of Justice, without judging and without blaming, do we have the opportunity to gather information, learn, draw conclusions and prepare for the future. Also in our own backyard.

Link to original: CCR, decision making, leadership, non-technical capability, Teamwork, Gareth Lock 09 March 2020

From the author:

When I started my adventure with technical diving more than 15 years ago, my instructor said “position, trim, buoyancy, configuration and ability to react to the situation is only 20%. The other 80% is the head”.

Over the years of training myself and other divers on numerous courses, acting as an instructor and being a psychologist by education, I cannot underestimate the impact of human factors on the quality and safety of diving. The vast majority of diving accidents in recent years, is a result of neglecting or neglecting the widely understood influence of the human factor on diving safety. This does not just apply to the accident situation itself, but more importantly to the culture, science, information, blame and capacity of the environment to share information in a factual way, without placing blame. In 2019, I read the book Under Pressure Diving Deeper With Human Factors. I developed a closer relationship with the author – Gareth Lock, owner of The Human Diver. I decided to promote the Just Culture philosophy and try to raise awareness of the importance of human factors in diving. I present an article that appeared on thehumandiver.com, and a book “Under Pressure” is also in preparation.

Andrzej Górnicki

Accident analysis, decision making, cognitive errors, Gareth Lock 24 August 2019 Original title: Why ‘They should have’, ‘…could have’ or ‘I would have…’ do not improve diving safety

the human diver Gareth Lock, He spent 25 years with the Royal Airforce as an aircraft instructor, navigator and engineer. Gareth founded The Human Diver In January 2016, in response to knowledge and training gaps related to human influence and assumptions Just Culture in the diving industry. He has taught over 350 courses and 20 presentations on human factors in diving. Published in March 2019, the book Under Pressure: Diving Deeper with Human Factors has sold nearly three thousand copies to date. Gareth runs The Human Diver website, and blog, as well as training and webinars. More information and original versions of articles can be found at The Human Diver.



Andrzej Górnicki Andrzej GórnickiSport and technical diving instructor. Co-author of workshops on safe closed circuit diving. Trained as a psychologist and coach, associated with soft skills training. Graduate of postgraduate studies in Underwater Archaeology at the University of Warsaw. He has worked as an instructor, guide and dive base manager in Portugal, Croatia, Norway, Malta, Egypt, Sweden and Poland. Translates training materials for the largest organisations training and certifying divers. Author of articles related to diving. For years, he has been involved in disseminating the latest knowledge and trends in diving. Actively supports the Baltictech technical diving conference.


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About author

Andrzej Górnicki jest absolwentem psychologii. Trener i wykładowca, szkoleniowiec. Prowadzi szkolenia z zarządzania i kierowania zespołami oraz zasobami ludzkimi. Nurkuje od 2004 roku. Nurek rekreacyjny i techniczny z doświadczeniem przekraczającym dwa tysiące nurkowań. Od 2005 roku jest instruktorem Nurkowania. Ponad 100 licencji wystawionych w federacji SSI oraz ponad 100 w TDI i SDI.
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