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Don’t Panic: Understanding the Causes and Remedies of Diver Panic

The “Hitchhikers Guide to The Galaxy” summarized it neatly: Don’t Panic! For good reason: taken together panic/anxiety/stress have been ranked as one the top three risk factors in scuba diving incidents. Here clinical psychologist and scuba instructor Laura Walton dives into the definition and causes of panic, explains why seeking to avoid panic can make matters worse, and offers effective strategies to consider.



by Laura Walton. Header image and photos courtesy of the GUE Archives

54% of experienced recreational divers reported panic while diving (Morgan, 1995)

A handful of studies suggest that as many as a quarter to a half of qualified (i.e. open water or higher) recreational divers have experienced panic or near-panic on at least one occasion (Colvard & Colvard, 2003; Morgan, 1995). 

Incident reports: of those where mental/behavioural state was noted, panic featured in 68% of incidents (Davis, Warner & Ward, 2002).

Taken together panic/anxiety/stress has been ranked as one of the top three risk factors for scuba diving incidents (Buzzacott et al., 2009).

Panic, underwater, risks significant consequences for divers of all levels.  Some research data and professional opinion lists panic as a significant factor in the majority of recreational scuba diving fatalities. Yet, the number of divers who can tell a story of the time they panicked, or almost panicked, suggests that it’s not uncommon.  Avoiding panic seems reasonable.  Paradoxically, however, it is a willingness to approach and understand the risks and experience discomfort may reduce the likelihood of a diver panicking. Successful progression in diving includes exposure to challenging situations that necessitate the development of effective technical and non-technical (See: The Human Diver) skills for responding to stress.  Often less talked about, it is the skills to regulate cognitive and emotional reactions to problems that prevent panic.  For divers seeking to improve their chances, this article highlights the more subtle processes involved in steering away from panic underwater. More experienced divers and instructors may recognize existing practices and be interested in the theoretical underpinnings.

Divers who panic underwater are at significant risk of injury or death, are unable to reason clearly, and cannot consciously control their actions. Their sole focus is to reach safety, and their erratic attempts to do so are usually ineffective and dangerous, often more so than the precipitating event that caused their alarm.

What is panic?

Panic is a physiological and psychological state that can occur when a person is—or perceives themselves to be—under severe stress. Panic interferes with thinking, information processing, and attention to one’s surroundings. It also inhibits one’s ability to consciously control their actions. Panic induces instinctive behavior, leading to survivalist actions which can be effective on land but potentially fatal underwater.

People in a state of panic are also unable to communicate effectively or respond to instructions and are unlikely to form an accurate memory of an event.

Divers are, understandably, warned not to panic. This is probably one of the least controversial opinions in diving; regardless of either one’s training or their experience level, divers will generally agree that panicking at depth can kill. While a range of barriers hamper attempts to gather data on diver panic—including the subjectivity of reporting and innate biases—various formal studies of recreational diving cite panic as a major contributor to dive injuries and fatalities (Buzzacott et al., 2009; Davis et al., 2002; Morgan, 1995). SO DON’T PANIC!  

What makes a scuba diver panic?

Effective risk management for divers’ panic attacks involves understanding, addressing, and managing the factors that cause them.

Various interacting elements can change a diver’s psychological and physiological state, potentially leading to panic. These factors are wide-ranging and can occur at any time—even long after a stressful event. This complex set of factors may be grouped into three broad areas: readiness, regulation, and specific stressor(s). Problems on all three sides of this triangle spark panic: 

“A scuba diver panics when they encounter a stressor(s) that they are: (1) incapable of dealing with due to inadequate level of training, insufficient experience, or improper or deficient equipment (i.e. they lack readiness), and they are (2) unable to regulate their emotions, thoughts, and behaviours to remain sufficiently aware, alert, and stable enough to respond effectively (i.e. difficulty in regulation). In that situation, the scuba diver perceives that the situation is out of their control, the stress levels escalate, and thinking ability deteriorates. Unable to see any available solution, the brain “short-circuits,” with the primitive parts of the brain driving increasingly frantic behaviour in an effort to survive.” (Walton, 2019a)

Avoiding panic and anxiety seems reasonable, but …

Panic is not an action one can choose or not; it is an outcome that arises out of multiple precipitants, and a few drops of discomfort can quickly escalate into a panic storm. An anxious diver knows, rationally, that staying calm and solving their actual problem is the best course of action, but when that anxiety escalates into full-blown panic, the panicked diver is locked in an attempt to escape their own unpleasant experiences, so much so that they are incapable of calm and efficient action. 

Oddly, evidence supports the theory that attempting to prevent panic may inadvertently lead to an escalation of the problem in both the immediate situation as well as over time. After one episode of underwater panic, the diver is often keen to avoid another. Investing time and effort into tackling the problem, one finds creative ways to move away from the internal storm of fearful thoughts and uncomfortable emotions. 

Moving to prevent panic is a good thing, and reflecting upon a panic-inducing dive to develop risk mitigation strategies for the future is wise. Improving skills, upgrading equipment, and diving within more conservative limits can all help divers increase their diving safety. Yet, if these moves are made with a fixed focus on stopping the experience of panic, solution overload can increase anxiety.

Fight or flight fuels panic 

A panic attack can be understood as a cycle (Clark, 1986). Fear is a precursor to panic, and frightening events trigger a cascade of endocrine and neurological processes that are intended to protect us—like the release of adrenaline and nerve signals that increase muscle tension. A fearful diver may start to worry, overthink, or distract from the unwanted emotion as their alarm grows. 

This arousal state colours thoughts with anxiety, generating further neurological and endocrine signals that the body is under threat. Often aided by narcosis, hypercapnia, or both, the reaction tips into panic, a vicious cycle in which the diver becomes more stressed and less capable at an exponential rate. The person is locked in a positive feedback loop: The more they fight against or flee from their own inner experience, the more of a problem it seems, and the more distressed they become.

Entrapped by fear, shame, and guilt: how emotions take over actions

In the early 90s, Jenifer Hunt studied divers’ reactions to decompression injury (Hunt, 1993). Although she didn’t study the role of panic, her research found that shame, guilt, and embarrassment were common reactions to panic, anxiety, and a perceived loss of control. Humans generally dislike and avoid such feelings, and divers are no different. 

Divers often tend to minimize instances of panic or avoid talking about anxiety in diving. But, each time divers become anxious in the future, they’ll still experience their body’s unwanted reactions, including anticipatory fear of embarrassment, also called “experiential avoidance.”

As their willingness to feel certain emotions or sensations decreases, their anxiety increases. This can be a particularly strong motivator for divers because panicking underwater is objectively dangerous, and there are very sound reasons for wanting to prevent it. 

People with a (non-clinical) history of panic report higher levels of experiential avoidance and are more likely to use avoidance strategies when facing emotionally distressing stimuli (Tull & Roemer, 2007). In addition, anticipation of panic itself motivates avoidance of situations and experiences associated with a past panic episode (Craske & Barlow, 1988). For some divers, particularly novices, this may mean avoiding diving entirely. If the person continues to dive, their avoidance tactics will look very different: they will impose restrictions on who they will dive with, where they dive, how deep, or under what environmental conditions.  

Again, placing such limits on oneself to avoid severe consequences is a highly sensible response to panic in diving. However, when enacted in service of experiential avoidance, these restrictions can increase the problem. When a person feels a little more in control of their feelings, they feel better—a neurochemical reward. But, further experiences of discomfort only trigger more avoidance behaviour and, as the restrictions accumulate, the diver’s “safe” opportunities decline. Eventually, they can no longer dive without encountering the unpleasant thoughts and emotions they are trying to avoid. 

Entanglement in language: how our words contribute to the generation of panic 

How humans talk and think about stressful events impacts their reactions to future stimuli. Language has the capacity to shut down awareness and, therefore, drive subtle forms of avoidance that can contribute to future panic. 

Human beings have an awesome ability to create mental representations from verbal knowledge.  Words and stories yield versions of objects and events in the mind without the need for direct experience, activating knowledge, memories, and emotions in response to personal symbolism. This ability is tremendously useful. It can support situational awareness and enhance dive planning, as well as indicate workable solutions such as practicing for potential scenarios. However, the propensity for language to create mental representations and wake up neurological networks can be problematic. 

The human mind can create an imagined, mental construct about a single word. Pause for a moment and watch what your mind does with these three letters: DCI. 

Has your brain ever hit the button underwater?

  Three letters, a series of pixels on your screen—but do they create an image for you? A story? Connect with previous memories? Try OOG (out of gas), CESA (Controlled emergency swimming ascent), AGE (arterial gas embolism), and CAGE (cerebral arterial gas embolism).  

They are just letters. But, words are symbols that stimulate verbal networks in the brain, stirring up emotions and bodily sensations in the process. We react to our thoughts almost as if they were physically tangible. Thinking about a past incident or imagining a future catastrophe can evoke as much (or more) distress than the event happening in reality.

Divers who have experienced panic underwater, or who consciously avoid it, can generate highly aversive mental and bodily reactions (often without actually entering the water!). These reactions are unpleasant, unwanted, and can drive experiential avoidance via language alone, entangling behaviours and reaffirming anxieties. 

Struggling with language 

Clinical psychologist Dr. Steven Hayes’s Relational Frame Theory (RFT) explores links between human language and behavior (Hayes & Hayes, 1992). RFT helps to explain the role verbal behavior plays in psychological disorders such as anxiety, depression, and panic disorders. RFT describes human thought and action in response to verbal stimuli. This complex theory describes the evolution of panic in all settings, including diving. For a detailed primer on RFT, check out: What is Relational Frame Theory (Part One) and part two.

 “Humans can verbally construct a future and plan for it in great detail, thereby increasing the chances of survival. However, RFT also argues that derived relational responding makes verbal self-knowledge emotional and difficult”

― Barnes-Holmes et al., 2004

RFT is about how humans create relational frames between concepts using words. For example, if one dived to 37 m/121 ft in the morning at site A and the maximum depth for the afternoon dive at site B is 25 metres/82 ft, they would detect a relationship between those two dive sites: A is deeper than B, and B is shallower than A. This is a relational frame, where the names of site A and B can be verbal symbols of deep and shallow. If a third option is proposed for a site that is shallower than site A and deeper than site B, site C establishes a triangular frame. Such relational frames provide useful information for dive planning. 

But what happens when discomfort or trauma is added in? If a person with no history of anxiety or panic does their first dive to 35 m/114 ft and has an unfortunate incident—perhaps they accidentally stir up silt and lose visibility—the combination of psychological stress and physical effects of gas density cause anxiety, but they manage to cope with the situation.  

Their next dive is planned to 40 m/130 ft. There is a chance that hearing the depth will trigger bodily stress responses. This stress is a response to verbal stimuli—hearing the words “40 metres.” Why? There was a relational frame generated in the previous experience: 35 meters = deep = panic = “I almost died.” Our relational frame of shallow/deep then automatically connects in with another relational frame: better/worse. If 35 m = panic, then 40 m = worse panic! The low visibility may also impact this frame; the diver may learn to react strongly to low visibility through the association with panic on the first dive. The diver is now experiencing anticipatory anxiety for an event in the future that only exists in their mind as verbal stimuli. 

This is partly because relational frames are bidirectional. During training, an instructor will show a student an object—a BCD, for instance—and tell them what it is called. They see the object, hear the word, and understand that the object is known by that word. 

But, this phenomenon is reciprocal. Immediately, when the student is asked to put on the BCD, they can infer the word’s meaning: If the object is called a BCD, then the word BCD must mean that object. This process is automatic, unstoppable, and irreversible, so using language to escape anxiety can become a problem. What are the unstated reciprocals of each statement below? (Here’s a hint: safe/unsafe; easy/difficult; relax/panic)

“I feel safe when I am close to the guide”

“It will be an easy dive if the visibility is good today”

“When I dive with [name of favorite buddy], I can relax”

When divers encounter discomfort, they may seek to avoid the experience in the future by organising their actions according to the concepts linked in their mind: They create rules, like the statements above. Safety rules may be very helpful. But, if the function of the rules is to avoid unwanted emotions, the diver may get tangled in the reciprocal that they have unconsciously derived. When their favoured buddy cannot equalise or the visibility is not as expected, the reversed story becomes a source of anxiety in and of itself, even when nothing is actually wrong.

By unwittingly creating a neural network to signal danger if the reverse of their rules is to occur, any mental perception of rule-breaking could be enough to set off the panic cycle. Holding tightly to rules as a way to prevent panic becomes the fuel for further episodes. As anxiety increases, the rules increase and become more rigid, creating a restrictive network of relational frames. The diver is then caught up in a struggle with symbols of disaster in their own mind.

“As ideas enter a frame of coordination with “panic” then the specter of panic gets larger and larger while a person’s world gets smaller and smaller as they avoid an increasing number of things.” (Smith, 2008)

The alternative? Approach panic. 

Avoiding emotions or mental images isn’t sustainable. Avoidance can sometimes be healthy; for example, sitting it out when not fit to dive. But, avoiding their own experience is exactly what causes divers to get lost in panic. When they struggle to escape panic, they spiral out of awareness into increasing emotional reactivity and a fusion with language that keeps them stuck in their own minds.  The alternative to avoidance is approach: turning toward experience to become open to learning and accepting of discomfort. Drop the struggle with thoughts. Stay present in an emotional storm.

“I am not fearless. I’m alive today because I’ve learned to embrace fear …”

― Jill Heinerth, Into the Planet: My Life as a Cave Diver

If unaddressed early, a diver’s unhelpful beliefs, thoughts, and emotions may spark panic. By creating space for uncomfortable experiences, instead of shutting down, they can retain situational awareness and more control over their behaviour. Skill at distancing from the words helps maintain calm; the awareness that a thought is a thought tends to decrease the emotional reaction. In responding with openness and space, there is more room to notice the language networks the person may be tangled in. Limiting beliefs and rules may allow a person to feel as if they are controlling stress, but, in the long-term, makes it worse. 

“Between stimulus and response there is a space. In that space is our power to choose our response. In our response lies our growth and our freedom.”

― Viktor E. Frankl

In the panic state, conscious choice is not an option. But, there are many moments in the seconds/minutes/hours/days/weeks/months/years before the cycle spirals when there is a choice. How divers relate to panic is a choice: approach the thought and the fear it generates to think through a useful response (e.g. problem-solve, train in necessary skills, apply risk management); or find ways to avoid the symbolic representation and the emotions it raises (i.e. worry, distract, project). Arguably, that choice makes all the difference in whether a diver is prone to panic.

Plan and make stops 

Making room for uncomfortable experiences is (rather obviously) uncomfortable! It requires stopping and assessing when there is an urge to bolt. It means applying focus on the important task when one is cold, in pain, or frustrated. It calls for putting time and effort into training and practice. It demands admitting fears, communicating needs, and risking rejection. It acknowledges gaps in knowledge and seeks to self-educate, preventing panic through curiosity.

Rather than turning away from panic, it is possible to create more moments to acknowledge its precipitants and choose responses: simple pause points like taking a few minutes to stare at the sea between pre-dive checks and entering the water, setting up points on the descent to stop and offload stress while nothing else is demanding attention, or doing a bubble check of equipment to take note of any psychological leaks (Pacher et al., 2017). Panic is the end of a build-up of stress—a point of no return. The practice of pausing with a willingness to take notice creates opportunities for becoming aware of issues long before reaching the zenith of panic.

Stopping sounds easy. It’s not. A genuine pause to do nothing but be aware of one’s own state can feel vulnerable. It involves exposure to difficult thoughts and sensations. Showing up through fear is more challenging than dissociating. But, it works. Every effective way to address panic or overcome fear involves some form of exposure. By increasing the willingness to experience these, the diver regains control over their actions. 

To illustrate, someone learning to clear their mask may struggle with the aversive experiences of water in their nose and fear of drowning. To avoid these uncomfortable sensations and emotions they could tough it out, mentally disconnect, use distraction to get away from the feeling—rushing to get it over with. Or, they could slow down, notice the sensations, focus on staying present, and being aware of performing the skill. In the second option, there is exposure to the sensations and emotions, and that exposure is important in allowing habituation.2 Being more willing to be uncomfortable makes it easier to become familiar with it. 

Getting help to approach to panic

When someone has been stuck for a while, perhaps due to prolonged avoidance strategies or severe psychological trauma, the problem may be more entrenched. If the issue impacts the person beyond diving, it may even meet criteria for a condition such as post-traumatic stress or an anxiety disorder. Even if the problem only happens in diving contexts, there are evidence-based psychological approaches that are effective in disentangling the person from the problem.  

Therapies for panic, anxiety, and trauma involve turning from avoidance to approach and will include some form of exposure. For example, in Eye-Movement Desensitisation and Reprocessing Therapy (EMDR), patients ponder a distressing scenario and allow themselves to notice the unpleasant reactions they experience (while sitting safely in a comfortable chair). In doing this, the brain gradually gets used to the experience and is finally able to file it away. When the person returns to similar situations, they are no longer so reactive to the stressors and can select a more helpful state—calm, focused or confident.  

Cognitive Behaviour Therapies also tend to involve various forms of exposure, such as mentally rehearsing difficult situations and practicing effective responses in the water. One of the most well-known and effective forms of addressing panic, anxiety, and phobia involves “graded exposure,” where the person gradually faces their fears by doing increasingly challenging versions of it, until it no longer causes them to panic. One of the main reasons this works is because it tackles overt and covert avoidance.  

Greet Discomfort, Avoid Panic

In response to difficult experiences, shoving thoughts and emotions away temporarily works. If anxiety or panic occurs when circumstances trigger unprocessed trauma, then there is a risk of re-traumatisation. It’s like forcing yourself to run on an injured leg—the repetition of intense emotions is painful and feeds cycles of unhealthy avoidance. People can and do work through trauma without formal therapy; like bones and skin, the brain and nerves have innate healing processes. But, sometimes wounds need help to heal. Therapies for trauma and anxiety can help divers to approach panic. PFOs aren’t the only holes in the heart that can be repaired. 

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Panic is an outcome—an unwanted one—and an event we cannot directly prevent or choose. It is an involuntary human process triggered by various factors. Everything about diver panic—from the way it feels to the potential physical and social impacts—is aversive. So, it’s natural to avoid all its aspects. To prevent panic in scuba diving, one needs to be more willing to be uncomfortable—to be less concerned with getting soaked in the precipitants in order to retain focus on finding solutions. 

Panic Survey: Please help us to better understand the experience of scuba divers with panic, and answer questions raised this article by Dr. Laura Walton. Please compete the Panic Survey here.


  1. Behaviourism is a traditional school of psychology that explains all behaviour in terms of stimulus and response; i.e. what we do is learned via interaction with the external environment.  Traditional behaviourism virtually ignored the role of human thought and language and was considered flawed for this reason.   
  2. Habituation: innate reactions to a stimuli decrease when the stimuli is given frequently.  For example, the strong reaction to breathing underwater for the first time lessens as we get used to it. 


Barnes-Holmes, Y., Barnes-Holmes, D., Mchugh, L., & Hayes, S. C. (2004). Relational Frame Theory: Some Implications for Understanding and Treating Human Psychopathology. In International Journal of Psychology and Psychological Therapy (Vol. 4, Issue 2).

Buzzacott, P., Rosenberg, M., & Pikora, T. (2009). Using a Delphi technique to rank potential causes of scuba diving incidents. Diving and Hyperbaric Medicine, 39(1). 

Clark, D. M. (1986). A cognitive approach to panic. Behavior Research and Therapy, 24(4), 461–470. 

Colvard, D. F., & Colvard, L. Y. (2003). A Study of Panic in Recreational Scuba Divers. Undersea Journal

Craske, M. G., & Barlow, D. H. (1988). A review of the relationship between panic and avoidance. Clinical Psychology Review, 8(6), 667–685. 

Davis, M., Warner, M., & Ward, B. (2002). Snorkelling and scuba diving deaths in New Zealand, 1980-2000. South Pacific and Underwater Medicine Society (SPUMS) Journal

Hayes, S. C., & Hayes, L. J. (1992). Verbal Relations and the Evolution of Behavior Analysis. American Psychologist, 47(11), 1383–1395. 

Hunt, J. (1993). Straightening out the bends. aquaCORPS

Morgan, W. P. (1995). Anxiety and Panic in Recreational Scuba Divers. Sports Medicine, 20(6), 398–421.

Pacher, A., Cleveland, S., Muth, T., & Schipke, J. (2017). Fatal Diving Accidents in Alpine Waters: A Series of Triggers Leading to Disaster? Austin Sports Medicine, 2(1), 1014. 

Smith, S. T. (2008). What is Relational Frame Theory (Part Two). Ironshrink. 

Tull, M. T., & Roemer, L. (2007). Emotion Regulation Difficulties Associated with the Experience of Uncued Panic Attacks: Evidence of Experiential Avoidance, Emotional Nonacceptance, and Decreased Emotional Clarity. Behavior Therapy, 38(4), 378–391. 

Walton, L. (2019a). Panic Triangle: What makes scuba divers panic? – YouTube. Fit To Dive Youtube . 

Walton, L. (2019b). PREVENT PANIC in Scuba Diving. In Fit To Dive.  

Additional resources:

Undercurrent (2003) survey of more than 12,000 divers: Panic in Recreational Scuba Divers

Alert Diver.Eu (2011): Psychological reactions and scuba diving, description of a treatment  by Maria Luisa Gargiulo

Alert Diver.Eu (2015): No Panic, we’re Divers! by Andreas Aceranti and Simonetta Vernocchi

What does the absence of panic in face of extraordinarily stressful circumstances look like? Here WKPP co-founder and explorer Bill Gavin reports on a freak incident that resulted in the death of WKPP co-founder and explorer Parker Turner. The report was mandatory reading for Capt. Billy Deans mixed gas courses in the early 1990s: The Incident Report at Indian Springs by Bill Gavin

Check out Dr. Walton’s online course:

Laura Walton is a Clinical Psychologist and scuba diving instructor bringing together psychology and scuba diving to help people with their diving. She provides specialist psychological services for scuba divers in the UK and widely accessible online courses. Laura has been guiding and teaching scuba diving in the UK since 2012 and is currently a PADI Master Instructor at The Fifth Point Diving Centre, Blyth, UK. Find her blog here: Fit To Dive Blog.

Diving Safety

When Easy Doesn’t Do It: Dual Rebreathers in Extended-Range Cave Diving

Rebreather technology has enabled cave explorers to extend their underwater envelope significantly deeper and longer. As a result, a few teams are pushing beyond the practical limits of open circuit bailout and so have turned to bailout rebreathers. But they are not without challenges, as Tim Blömeke, who dives into the latest research and field experience, explains.




by Tim Blömeke. Lead image: KUR divers Bob Beckner and Derek Ferguson in the 124m/407 ft deep Mount Doom chamber in Weeki Wachee Spring, Florida, courtesy of Kirill Egorov.

Dual rebreathers are becoming a thing among the elite of extended-range cave diving. Yet the “Blueprint for Survival” for this type of equipment configuration has yet to be written, and practitioners are faced with difficult trade-offs between competing design goals—like fitness for purpose, logistical feasibility, simplicity, reliability, and ease of use, all of which interact with the peculiarities of human nature. A new research paper proposes a pathway for risk assessment. 

The introduction of rebreathers has considerably extended the range of exploration in cave diving. This is true especially for deeper dives, where open circuit technology faces the combined challenges of greater required gas volumes and higher required helium content, which make such dives both difficult to execute logistically due to the sheer number of cylinders involved, and prohibitively expensive due to the amount of helium in each of these cylinders.

By conserving the metabolically inert components of the breathing gas (most notably the helium), the use of closed circuit rebreathers (CCR) eliminates a good chunk of this problem, but not all of it: Traditional CCR diving procedures require that each diver have enough open-circuit bailout gas available to safely end the dive in the event of a rebreather failure. 

Granted, the amount of bailout gas required for a CCR dive is only a fraction of what would be needed to perform the same dive on open circuit, and if all goes well, the bailout gas will never be breathed by anyone and can be reused for future dives. However, bleeding-edge explorers being who they are and doing what they do, after having used their CCRs to push the range of operations a few miles deeper into the cave systems, they began to encounter an issue very similar to the one that prompted the switch to CCR in the first place: cost and logistics. 

As a real-world example, bailing out from a long-distance cave penetration of 7,500 meters at an average diver propulsion vehicle (DPV) travel speed of 40 m/min takes 187 minutes. Assuming a mean ambient pressure of 6 ATA (50 m depth) and a respiratory minute volume (RMV) of 14 l/min, the amount of bailout gas (not including decompression) required to reach the entrance would be 15,708 liters, or more than seven AL80 cylinders filled to 200 bar. This RMV is likely not conservative enough, given the extreme distance and the possibility of a hypercapnic event being the cause of the bailout so, in practice, a safety margin of at about 50% would be added, giving a total of 10-11 AL80 bailout cylinders. 

The required amount of bailout gas became too large to be carried on the person of the diver, so that cylinders again needed to be staged in a series of set-up dives. Preparations for extended range exploration dives became ever more involved, and logistics became just as difficult to manage as those of old-school open circuit dives–even more so, arguably, due to the considerably greater distance of the staging points from the cave exit. As happens so often, overcoming one obstacle resulted in the discovery of others further down the road.

Corroded stage cylinders.

New safety concerns started to appear as well: For large-scale exploration projects, bailout cylinders needed to remain in a cave system for months at a time, sustaining severe corrosion damage at the tank neck and tank valve interface in the process due to the galvanic reaction between the chrome-plated brass valve and the aluminum cylinder. This isn’t merely a hypothetical concern: On many occasions, the corrosion was so severe that the integrity of the seal was compromised, and explorers found their previously staged bailout cylinders empty when checking them on their way into the cave. While this can be counteracted by installing a magnesium anode on the cylinder (magnesium is lower in the Galvanic series than aluminum and replaces the latter in the reaction), explorers found that the countermeasure only mitigates the issue but does not eliminate it. Long story short, for extreme extended-range dives, open circuit bailout was becoming ever more impractical and problematic.

Enter The  Bailout Rebreather

As a solution to these problems, some explorers began to do away with open circuit bailout altogether and carry a redundant rebreather system—a closed circuit rebreather, or a semi-closed rebreather (SCR) instead. While this practice has gained significant traction recently, the concept itself isn’t new. In his book Into the Unknown, famed Welsh explorer Martyn Farr reports that his German colleague, pioneering cave diver Jochen Hasenmayer, had experimented with a dual unit he dubbed the Speleo-Twin Rebreather (STR-80) as early as 1981. 

Bill Stone flying FRED outside the Wakulla Springs decompression habitat. Photo courtesy of the US Deep Caving Team

In 1987, Dr. Bill Stone delivered a proof of concept by spending 24 hours underwater on a dual CCR, he dubbed “Failsafe Rebreather for Exploration Diving” (FRED), during his visionary Wakulla Springs Project 1987. However, it appears that the first person to utilize redundant rebreathers in actual exploration was Olivier Isler from Switzerland. On August 12, 1990, he first used a triple RI2000 semi-closed unit in his crossing of the Emergence du Ressel (Doux de Coly, France), covering a distance of 1850 m/6070 ft at a maximum depth of 81 m/266 ft. The following year, Isler went on to push through the 4000 m/2.5 mi penetration barrier for the first time. More than a decade later, in 2002, Reinhard Buchaly and Michael Waldbrenner pushed the exploration of the Doux de Coly farther using dual RB80s, which were originally designed by Buchaly and continue to be produced to this day by Halcyon.

Bill Stone spent 24 hours underwater on the fully redundant Cis-Lunar Mk 1, “FRED” during the at Wakulla Springs Project 1987. Here is Stone in the Wakulla deco habitat. Photo courtesy of the US Deep Caving Team

The decision to replace open-circuit bailout with a rebreather is as obvious as it is bold: Obvious because it replicates the successful solution to a past problem and restores the ability of a diver to carry all the gas they need on their person. Bold because… well. Put yourself in the drysuit boots of a cave diver, hours and hours away from the surface, who just survived an assassination attempt by a complex piece of life support equipment. All technical aspects aside, wouldn’t it be reassuring to fall back on a less complex piece of life support equipment whose proper functioning can be ascertained reliably within a few seconds? 

Olivier Isler sporting his triple redundant RI2000 SCR at Doux de Coly. Photo courtesy of O. Isler

Expressed in numbers, a paper by Andrew Fock, Analysis of recreational closed-circuit rebreather deaths 1998-2010, published in 2013, analyzed dive accident statistics for the period from 1998 to 2010 and found that CCR diving is associated with an increase in the risk of death by a factor of up to ten compared with open circuit diving. That ratio essentially applied to CCR dives, which used open circuit bailout. Rebreather technology and diving practices certainly have improved since the time under investigation, but the fact still remains that the complexity of the equipment adds to the overall risk.

With this in mind, taking a closer look at and trying to define the specific risks and benefits of replacing open-circuit bailout with a redundant SCR or CCR seems a reasonable idea. And this is precisely what a team of authors headed by Derek B. Covington did in a recent (March 2022) research paper, asking the question, “Is more complex safer in the case of bailout rebreathers for extended range cave diving?” 

Using a qualitative approach, the authors discuss the reasoning behind bailout rebreather use, its history, different configurations and the various advantages and disadvantages and, finally, the additional potential for human error created by increasing the complexity of the equipment.

Olivier Isler at a deco stop in Doux de Coly

Bailout SCR vs. Dual CCRs

In terms of configurations, there are two main choices for a bailout rebreather: SCR or CCR. With an SCR, the diver still has to carry bailout gas. However, an SCR (such as the side-mounted Halcyon RBK) extends the use of this gas by a factor somewhere between four and ten, thereby drastically reducing the number of cylinders needed while being only the size of a single AL80 cylinder itself. Other advantages of a bailout SCR are that its relative simplicity and lack of sensors or other electronics make it much easier to set up, maintain, and use than a secondary CCR.

These advantages, however, do not come without downsides. With an SCR, the diver does not have the option of adding oxygen into the loop, and the actual oxygen content of the gas breathed is always somewhat lower than the oxygen content of the gas in the cylinders carried. How much lower exactly depends on the portion of the gas vented into the water on each operating cycle of the unit—or the rate of fresh gas supply into the unit—as well as the metabolic needs of the diver. 

Therein lies the crux: For normal operation, the amount of oxygen consumed by the diver, and thus the resulting effective composition of the breathing gas, can be calculated quite reliably. In a bailout scenario, however, it isn’t unlikely for the metabolic needs of the diver to be increased due to higher workload. Without sensors to measure PO2, the precise composition of the breathing gas in the SCR loop becomes unknown, creating a risk of hypoxia, with all the potential consequences that come with it. This risk is unique to SCRs and not present when diving open circuit (where the cylinder sticker tells us what we’re breathing) or while on a CCR (where sensors tell us what we’re breathing).

The other approach is to go for a redundant CCR, as Stone envisioned back in 1987. While seemingly the “purest” in concept—replacing like with like—and optimizing redundancy, the added complexity is significant. Everybody who owns a CCR (especially an eCCR) knows that these machines need lots of love to remain in good working condition. Now multiply that by two: twice the number of sensors, two scrubbers, two sets of primary electronics, two sets of secondary electronics … and that’s just out of the water. 

Some open water explorers are also turning to dual rebreathers. Here is RAID president Paul Toomer in blue water wearing a back mount Divesoft Liberty with a sidemount Liberty bailout. Photo courtesy of Kristof Goovaerts.

To have the redundant system available to them at all times during the dive, divers now need to manage the contents of two breathing loops instead of one. Furthermore, in order to be able to provide assistance in the event of a problem, divers working in a team need to be aware of the failure modes of and emergency procedures for not only their own units, but also the units used by their teammates. Unless everybody on the team is using the same machines for primary and bailout, this considerably adds to the training requirements, as well as to the complexity of the decision-making tree in an emergency situation. Nevertheless, by maximally reducing the required amount of gas to be carried by each diver, a redundant CCR theoretically provides the greatest degree of independence and offers the greatest potential range of exploration.

Approaches to Risk Assessment

To date, the use of dual rebreathers is still too rare for a quantitative, empirical assessment of its safety to be practical, and there is no systematic process in place for collecting data on dual-rebreather dives. “It’s really almost impossible to put a number on it,” said researcher and explorer Andy Pitkin, who co-authored the study. “I think there are only a small number of divers in the world who really need a bailout rebreather, but there are probably quite a few who use them because the idea appeals to them more than using OC bailout. Of course, there is no hard dividing line between the two groups. Where does logistical difficulty become impossible? That’s a very subjective judgment.”

The diversity of configurations and procedures used is another obstacle to objective study. “Are we using identical primary and bailout rebreathers, or is one unit specifically designed as a backup? If the latter, should the bailout unit be another CCR or an SCR? If the former, what are the diving procedures? Does the diver switch between loops at regular intervals, analogous to the procedures for independent doubles or sidemount diving? This would arguably add to task loading. Do the units have separate DSVs or a single, shared one, like that used by Richard Harris and Craig Challen of the Wet Mules? If the diver doesn’t alternate between units, then what other procedures are in place to ensure that both loops remain breathable at all times, especially during depth changes? If using dual CCRs, then what is the approach to ensuring redundancy of the diluent and oxygen supplies?”

The Wet Mules dual Megalodon CCR rebreather connected at the Bail Out Valve (BOV). Photo courtesy of Richard Harris.

The number of open questions and the range of possible, viable answers seem endless. Similar to the situation in the early days of cave diving, the book on bailout rebreathers has yet to be written. While many of the timeless principles from Sheck Exley’s famous booklet, Basic Cave Diving: A Blueprint for Survival continue to apply accordingly, there is no broad consensus yet on best practices, no SOP Manual, no standardized configuration, no published training standards for dual rebreather diving by any training agency. People are still working things out for themselves or their teams.

In consideration of these difficulties, and as a starting point for a discussion, the authors of Is more complex safer… propose a generalized approach to assessing the risks of dual-rebreather diving. Rather than delving into the minutiae of the failure modes of each individual diver’s equipment setup and diving procedures, they outline a method for identifying potential error-producing conditions (i.e., opportunities for human operators to make mistakes) based on a theoretical model originating in risk assessment for nuclear power plants: the WITH/TWIN model (Table 1). The acronym WITH stands for Workplace Design, Individual Capabilities, Task Design, Human Nature. TWIN refers to the same items (Task, Workplace, Individual, Nature).

The underlying idea of this approach is to move beyond merely looking at “human error” prima facie—oh, the diver failed to pack his scrubber properly? How could they! They neglected to monitor their PO2? Pay more attention!—and instead, analyze the conditions that are conducive to such errors. For the purposes of the model, a diver’s equipment configuration is part of their Workplace, their training and fitness belong in Individual Capabilities, the mission, including not only managing one’s gear but also navigation, linework, photography/videography, and surveying fall under Task. 

All these aspects interact with Human Nature. We get stressed when things get exciting, we get complacent when things go smoothly. We are prone to false assumptions, we are terrible at intuitive probability assessment, and our ability to pay attention falls off rapidly once the number of items that need our attention increases significantly beyond the number of voices in our heads. Much like running a nuclear power plant, excellence in cave diving isn’t achieved by sporadic strokes of genius but instead by consistently avoiding mistakes, and an important aspect of the design of equipment and procedures for either is to compensate for the inherent weaknesses of the human mind.

In the words of the study’s authors: 

“Divers and explorers need to consider not just the technical aspects of operating the dual CCR as an equipment-based system, but also the socio-technical aspects and error-producing conditions that adding additional complicated equipment has to the wider system, especially when it comes to training for and executing abnormal operations when workout levels will be high and awareness will be reduced. Nonetheless, as the use of this configuration grows, the risks and benefits will become clearer to investigators and divers alike.”

It will be exciting to observe the future development of dual-rebreather diving as it matures and see where the consensus for best practices will end up… stay tuned and stay safe!


Diving and Hyperbaric Medicine: Is more complex safer in the case of bail-out rebreathers for extended range cave diving? Derek B Covington, Charlotte Sadler, Anthony Bielawski, Gareth Lock, Andrew Pitkin

Fock AW. Analysis of recreational closed-circuit rebreather deaths 1998-2010. Diving Hyperb Med. 2013;43(2):78-85.

NSS-CDS (free download): Basic Cave Diving: A Blueprint for Survival by Sheck Exley

Dive Deeper

InDEPTH: The RB80 Semi-closed Rebreather: A Successful Exploration Tool by David Rhea

Halcyon: Using The RB80 As A Side-mounted Bailout Rebreather by Andy Pitkin, Karst Underwater Research (2018)I

InDepth: Rebreather Holiday Shopping Guide (2020)

aquaCORPS Pioneer Interviews: Stoned: Interview With Dr. William Stone (1994) by Michael Menduno

InDEPTH: Diving Beyond 250 Meters: The Deepest Cave Dives Today Compared to the Nineties by Michael Menduno and Nuno Gomes

Deep Tech: Victory At Last (1998) by John Simenon: Olivier Isler is setting penetration records with a triple-redundant semi-closed rebreather

Tim Blömeke is a cave, wreck and CCR diver who teaches in Taiwan and the Philippines. You can reach him on Facebook:, and Instagram:

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