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Analysis of recreational closed-circuit rebreather deaths 1998-2010
Abstract
Since the introduction of recreational closed-circuit rebreathers (CCRs) in 1998, there have been many recorded deaths. Rebreather deaths have been quoted to be as high as 1 in 100 users.
Rebreather fatalities between 1998 and 2010 were extracted from the Deeplife rebreather mortality database, and inaccuracies were corrected where known. Rebreather absolute numbers were derived from industry discussions and training agency statistics. Relative numbers and brands were extracted from the Rebreather World website database and a Dutch rebreather survey. Mortality was compared with data from other databases. A fault-tree analysis of rebreathers was compared to that of open-circuit scuba of various configurations. Finally, a risk analysis was applied to the mortality database.
The 181 recorded recreational rebreather deaths occurred at about 10 times the rate of deaths amongst open-circuit recreational scuba divers. No particular brand or type of rebreather was over-represented. Closed-circuit rebreathers have a 25-fold increased risk of component failure compared to a manifolded twin-cylinder open-circuit system. This risk can be offset by carrying a redundant 'bailout' system. Two-thirds of fatal dives were associated with a high-risk dive or high-risk behaviour. There are multiple points in the human-machine interface (HMI) during the use of rebreathers that can result in errors that may lead to a fatality.
While rebreathers have an intrinsically higher risk of mechanical failure as a result of their complexity, this can be offset by good design incorporating redundancy and by carrying adequate 'bailout' or alternative gas sources for decompression in the event of a failure. Designs that minimize the chances of HMI errors and training that highlights this area may help to minimize fatalities.
... Rebreathers are complex devices with more failure points than typical open circuit scuba, and it is not surprising that their use seems associated with a significantly higher accident rate. 2 Such is the importance of rebreather technology to the technical diving community that over several decades this single item of equipment has been the subject of four focused conferences designated Rebreather Forums One through Four. Presentations and discussions at these forums have focussed primarily on technological developments, relevant research, and training and safety issues. ...
... Contextualising narrative: the forum resolved that this statement should be accompanied by citation of relevant supportive medical literature. Various studies have identified the importance of cardiac events as the disabling injury in recreational diving fatalities,2,3 and an expert consensus guideline for cardiac evaluation of divers was recently published.4 ...
Closed circuit rebreathers have been widely adopted by technical divers as tools for reducing gas consumption and extending depth and duration capabilities. Rebreathers are technologically complex with many failure points, and their use appears associated with a higher accident rate than open circuit scuba. Rebreather Forum Four (RF4) was held in Malta in April 2023 attracting approximately 300 attendees and representatives of multiple manufacturers and training agencies. Over two and a half days a series of lectures was given by influential divers, engineers, researchers and educators on topics of contemporary relevance to rebreather diving safety. Each lecture was followed by a discussion session with audience participation. Potential consensus statements were drafted by the authors (SJM and NWP) during the course of the meeting. These were worded to be confluent with some important messages emerging from the presentations and subsequent discussions. The statements were presented one by one in a half-day plenary session of participants, and discussion was invited on each. After discussion and any necessary revision, the participants voted on whether to adopt the statement as a position of the forum. A clear majority was required for acceptance. Twenty-eight statements embracing thematic areas designated 'safety', 'research', 'operational issues', 'education and training', and 'engineering' were adopted. Those statements are presented along with contextualising narrative where necessary. The statements may help shape research and teaching initiatives, and research and development strategies over subsequent years.
... CCR diving also carries an estimated mortality risk of approximately 10 times that of recreational scuba diving, with hypoxia as one of the leading causes of reported CCR diving injuries or fatalities. [1][2][3] One study reported that of the recreational CCR deaths between 1998 and 2010 with a known cause, 17% were due to hypoxia. 2 Like CCR divers, aviators can experience hypoxia with potentially fatal consequences if their cockpit depressurises while in flight or their supplemental oxygen systems fail. Among these aviators, acute hypobaric hypoxia can present with a variety of symptoms including psychomotor (incoordination, tremors), cognitive (concentration, confusion, memory loss), visual impairment (blurred vision, colour/light intensity changes), psychological (anxiety, depression, euphoria), dyspnoea, paraesthesia, headache, dizziness, tachycardia, and loss of consciousness. ...
... [1][2][3] One study reported that of the recreational CCR deaths between 1998 and 2010 with a known cause, 17% were due to hypoxia. 2 Like CCR divers, aviators can experience hypoxia with potentially fatal consequences if their cockpit depressurises while in flight or their supplemental oxygen systems fail. Among these aviators, acute hypobaric hypoxia can present with a variety of symptoms including psychomotor (incoordination, tremors), cognitive (concentration, confusion, memory loss), visual impairment (blurred vision, colour/light intensity changes), psychological (anxiety, depression, euphoria), dyspnoea, paraesthesia, headache, dizziness, tachycardia, and loss of consciousness. ...
Introduction:
Faults or errors during use of closed-circuit rebreathers (CCRs) can cause hypoxia. Military aviators face a similar risk of hypoxia and undergo awareness training to determine their 'hypoxia signature', a personalised, reproducible set of symptoms. We aimed to establish a hypoxia signature among divers, and to investigate their ability to detect hypoxia and self-rescue while cognitively overloaded.
Methods:
Eight CCR divers and 12 scuba divers underwent an initial unblinded hypoxia exposure followed by three trials; a second hypoxic trial and two normoxic trials in randomised order. Hypoxia was induced by breathing on a CCR with no oxygen supply. Subjects pedalled on a cycle ergometer while playing a neurocognitive computer game to simulate real world task loading. Subjects identified hypoxia symptoms by pointing to a board listing common hypoxia symptoms, and were instructed to perform a 'bailout' procedure to mimic self-rescue if they perceived hypoxia. Divers were prompted to bailout if peripheral oxygen saturation fell to 75%, or after six minutes during normoxic trials. Subsequently we interviewed subjects to determine their ability to distinguish hypoxia from normoxia.
Results:
Ninety-five percent of subjects (19/20) showed agreement between unblinded and blinded hypoxia symptoms. Subjects correctly identified the gas mixture in 85% of the trials. During unblinded hypoxia, only 25% (5/20) of subjects performed unprompted bailout. Fifty-five percent of subjects (11/20) correctly performed the bailout but only when prompted, while 15% (3/20) were unable to bailout despite prompting. During blinded hypoxia 45% of subjects (9/20) performed the bailout unprompted while 15% (3/20) remained unable to bailout despite prompting.
Conclusions:
Although our data support a normobaric hypoxia signature among both CCR and scuba divers under experimental conditions, most subjects were unable to recognise hypoxia in real time and perform a self-rescue unprompted, although this improved in the second hypoxia trial. These results do not support hypoxia exposure training for CCR divers.
... However, within technical diving, one of the most important emerging trends is the shift from open circuit diving to close-circuit rebreather (CCR) diving, which is unfortunately associated with a tenfold increased fatality rate compared to open circuit (OC) scuba diving (Fock 2013). Besides the complexity of CCRs, which means that they are more prone to failure than OC equipment, the lack of formal detailed dive planning facilitated by the availability of continuous decompression solutions produced by decompression computers might also explain these figures (Fock 2006). ...
... Since the reconfiguration of Biomarine CCR155, one of the first mixed gas rebreathers to be adopted by sport divers in the early 1990s, the use of CCRs by recreational or technical divers has become increasingly common. This, however, comes with a cost, as the fatality rates for rebreather diving are 8-10 times higher than for open circuit diving (Fock 2013). Although the primary trigger for most of these accidents can be identified as a failure of the 'human-machine interface', two-thirds of fatal dives were associated with a high-risk dive or high-risk behavior such as solo diving, exceeding depth limits, or carrying insufficient gases. ...
PurposeData regarding decompression stress after deep closed-circuit rebreather (CCR) dives are scarce. This study aimed to monitor technical divers during a wreck diving expedition and provide an insight in venous gas emboli (VGE) dynamics.Methods
Diving practices of ten technical divers were observed. They performed a series of three consecutive daily dives around 100 m. VGE counts were measured 30 and 60 min after surfacing by both cardiac echography and subclavian Doppler graded according to categorical scores (Eftedal–Brubakk and Spencer scale, respectively) that were converted to simplified bubble grading system (BGS) for the purpose of analysis. Total body weight and fluids shift using bioimpedancemetry were also collected pre- and post-dive.ResultsDepth-time profiles of the 30 recorded man-dives were 97.3 ± 26.4 msw [range: 54–136] with a runtime of 160 ± 65 min [range: 59–270]. No clinical decompression sickness (DCS) was detected. The echographic frame-based bubble count par cardiac cycle was 14 ± 13 at 30 min and 13 ± 13 at 60 min. There is no statistical difference neither between dives, nor between time of measurements (P = 0.07). However, regardless of the level of conservatism used, a high incidence of high-grade VGE was detected. Doppler recordings with the O’dive were highly correlated with echographic recordings (Spearman r of 0.81, P = 0.008).Conclusion
Although preliminary, the present observation related to real CCR deep dives questions the precedence of decompression algorithm over individual risk factors and pleads for an individual approach of decompression.
... Conversely, the victim of case 18 was a non-experienced diver who drowned at a depth of 5 m. According to studies describing inappropriate breathing of gas, leading to loss of consciousness, water aspiration and drowning, as the most prevalent disabling agent when using a rebreather [21,22], we hypothesized that in case 6, convulsions were triggered by hyperoxia, but without discarding hypercapnia. However, in case 18 the trigger was the diver's inexperience with the rebreather, and the disabling agent was a hypoxia since the oxygen bottle was closed (it was at 200 bar of pressure). ...
... Arterial gas embolism following pulmonary barotrauma (PBt/AGE) was detected as an important cause of death. Cases 1,[3][4][5]14,15,19,22 and 24 had a strongly suggestive history of PBt/AGE based on their technical reports, which described a rapid ascent followed by loss of consciousness immediately after immersion. In cases 1, 3-5, 14, 22 and 24, an autopsy revealed the existence of large volumes of intravascular air, which is typical of AGE [3,17]. ...
To describe the technical characteristics of fatal diving mishaps and to elucidate the causes of death using a sequence analysis and a multidisciplinary investigation of diving-related fatalities. All cases of diving deaths recorded on the coast of Girona (Spain) between January 2009 and May 2018 were analyzed. Most data were obtained from the police technical reports and the forensic pathology service. Each accident was analyzed in order to identify the trigger, disabling agent, disabling injury, and cause of death. During the study period 25 diving-related fatalities were recorded. Most of the victims were males aged 50–69 years, and 11 were experienced divers. Almost all victims were using open-circuit SCUBA to breathe with compressed air as their sole gas supply. None of the victims were diving alone. The most common identified triggers included exertion, panic, buoyancy problems, disorientation and confusion. The main factors identified as disabling agents were rapid ascent, a cardiac incident, panic and entrapment. Asphyxia, lung over expansion, and myocardial ischemia were the most frequent disabling injuries. Finally, drowning represented the main cause of death, followed by arterial gas embolism and natural causes or internal diseases. A differential diagnosis, performed in the setting of a multidisciplinary investigation, is essential for elucidating the cause of death in diving-related fatalities. The proposed sequence analysis allows to clarify underlying problems in these cases and to identify risk factors and unsafe behaviors in diving.
... There is not much literature concerning the diving accidents resulting from the use of CCR, or any other types of rebreather outside the military sector (Louge et al. 2009). Trytkjo andMitchell (2005), Lippman et al. (2011) andFock (2013) examined the matter at different levels of approach. Fock (2013) examined deaths resulting from CCR dives within the period 1998-2010 and concluded that the risk of dying when using rebreathers appears to be 10 times what would be expected when using open circuit. ...
... There is, at present, no evidence to support that the accident rates will change as or if the mean diving depth increases. Fock (2013) suggested that CCR diving risk is reduced significantly when all the rules are respected and the use of the rebreather is well understood by the user. In most of the accident cases reported, the causal factor was human error and not rebreather failure. ...
The closed circuit rebreather (CCR) is not a new diving technology. From the late 1990s CCR units were commercially available in Europe, and increasingly more divers, and among them scientific divers, have been trained to use them. Even if many benefits exist for using CCR for all diving depth ranges, it is in the deep diving zone ranging from 50 m to 100 m of sea water where the main advantages to using this equipment exist. Using rebreathers does carry additional risks, and these must be mitigated to ensure safe usage. A standard for CCR scientific diving has existed for many years in the USA, and the levels of expertise within the European scientific diving community are now sufficient for a European standard to be established. National legislation for occupational scientific diving in many cases excludes CCR diving, which can limit its use for scientific purposes. This paper suggests that, where possible, legislations should be allowed to evolve in order to include this type of equipment where and when its use has direct advantages for both the safety and the efficiency of scientific diving. This paper provides a brief description of the fundamentals of closed circuit rebreather diving and outlines the benefits that its use offers diving scientists. Special attention is given to safety issues with the assertion that the CCR concept is, if strictly applied, the safest available technique today for autonomous deep scientific diving purposes. © 2016, Society for Underwater Technology. All rights reserved.
... -Safety: The risk of mortality while diving a CCR is estimated to be approximately 4-10 times greater than OC diving (Fock, 2013). Rebreather features that may help reduce rebreather accidents include the following: ■ full automation to avoid user errors, ■ reliable O 2 sensor system to avoid a hypoxic or hyperoxic breathing gas composition, ■ O 2 sensor system that can detect sensor failures: current O 2 sensor technology is known to be failure prone and O 2 sensor failures happen frequently, ■ CO 2 sensor to detect a scrubber failure, and ■ low work of breathing -Price: To be successful in the recreational rebreather market, the price of a recreational rebreather should be comparable to a price of an upper-end OC technical diving configuration. ...
... Breathing hoses typically have a connector at each end with one o-ring in each connector. Every additional part increases the risk of system failure, especially when they are connected in series (Fock, 2013). Additionally, the overall work of breathing also depends on the amount of connectors, gas resistance in the loop, length of hoses, etc. ...
Recreational rebreathers are increasingly popular, and recreational diver training organizations now routinely offer training for rebreather diving. Few rebreathers on the market, however, fulfill the criteria of a dedicated recreational rebreather. These remain based on traditional sensor technology, which may be linked to rebreather use having an estimated 10 times the risk of mortality while diving compared with open circuit breathing systems. In the present work, a new recreational rebreather based on two innovative approaches is described. Firstly, the rebreather uses a novel sensor system including voltammetric and spectroscopic validation of galvanic pO2 sensor cells, a redundant optical pO2 sensor, and a two-wavelength infrared pCO2 sensor. Secondly, a new breathing loop design is introduced, which reduces failure points, improves work of breathing, and can be mass fabricated at a comparatively low cost. Two prototypes were assembled and tested in the laboratory at a notified body for personal protective equipment before both pool and sea water diving trials. Work of breathing was well below the maximum allowed by the European Normative. These trials also demonstrated that optical pO2 sensors can be successfully employed in rebreathers. The pCO2 sensor detected pCO2 from 0.0004 to 0.0024 bar. These new approaches, which include a new concept for simplified mechanical design as well as improved electronic control, may prove useful in future recreational diving apparatus.
... . De plus, la mortalité qui y est associée est également plus importante (6). Le haut niveau 23 d'entrainement associé à une sensibilisation particulière aux risques pourrait influencer la 24 planification de ces plongées et les comportements en cas d'incident ou d'accident. ...
Objectives. — The democratization of deep technical diving beyond 50 meters was enabled by the development of rebreather and the use of helium-based breathing mixtures. Dives planification remains a widely debated topic in technical diving community. In addition, accident pattern could differ from what is classically observed in recreational scuba diving and must be largely under-reported. The aim of this investigation was to describe practices and accidentology in mixed-gas rebreather diving.
Methods. — An anonymous survey was conducted on social networks in destination to French residents certified trimix rebreather divers. Demographic data, planification habits and occurrence of post-dive abnormal symptoms were sought. Actions taken regarding onset of symptoms were also investigated.
Results. — In total, 194 questionnaires were analysed. Most of respondents were male (96.4%), mostly aged over 46 years with a high level of certification and for recreational purpose. The dive plans varied depending on the dive profiles with a very high inter-individual variability. Gas density at depth frequently exceeded the recommendations. Among the respondents, 9.8% declared having experienced symptoms suggestive of gas toxicity, mainly linked to nitrogen narcosis. Thirty-four percent reported experiencing evocative symptoms of decompression sickness (DCS) in their trimix dive history for an estimated incidence of 27/10,000 dives and 3.6% described persistent breathing difficulties, which could suggest immersion pulmonary oedema. In case of DCS evocative symptoms, only 42% received normobaric oxygen, 35% sought medical advice
and 29% got hyperbaric oxygen therapy. Three reported having long-term residual symptoms.
Conclusion. — The diversity of practices highlights the lack of strong scientific data supporting them. The accident rate in mixed-gas diving could be higher than in recreational diving, though mostly with mild severity. Treatment seems to be remained neglected despite the high level of knowledge of divers. However, the prognosis seems most often favourable. It appears essential
to continue research into decompression and physiological effects of these dives. Awareness and education efforts in diving first aid must be continued among this exposed community.
... These papers have explored a wide range of topics across several disciplines. These include: identifying sociocultural characteristics of divers (Edney, 2012;Gössling, Lindén, Helmersson, Liljenberg, & Quarm, 2008;Pabel & Cummins, 2017); motivational drivers of RSDT (Giddy, 2018;Wong, Thirumoorthi, & Musa, 2013); the importance of the environment (Dimmock & Musa, 2015;; environmental impacts by divers (Cardwell, 2005;Garrod & Gössling, 2008;Johansen, 2013;Lindgren, Palmlund, Wate, & Gössling, 2008;Lucrezi et al., 2018;Zakai & Chadwick-Furman, 2002); dive site carrying capacity (Dixon, Fallon Scura, & van't Hof, 1993;Hawkins & Roberts, 1997); marine wildlife interaction studies (Cater, 2007;Orams,1999;); economic impact on RSDT Williams & Souter, 2005); destination competitiveness (Neto, Lohmann, Scott, & Dimmock, 2017); marketing (Campbell, 2009), management (Higham & Lück, 2007a,b) and risk and injuries to divers (Cummins,1988;Fock, 2013;Lippman, Walker, Lawrence, Houston, & Fock, 2011;Walker, 2009Walker, , 2018Walker, , 2020. Although this literature contributes to knowledge, there are few studies that identify the major factors impacting the LTS of iconic, globally renowned and economically important RSDT destinations. ...
This research presents an investigation into the major factors impacting the long-term sustainability of recreational scuba diving tourism (RSDT) in the Cairns section of the Great Barrier Reef Marine Park. This section of the GBRMP hosts one of the most iconic, globally renowned and largest agglomerations of RSDT in the world providing significant societal, financial and employment contributions across local and international entities through various linkages ). Cairns is often described by travel writers and the Cairns Regional Council as the Gateway to the Great Barrier Reef, and in scuba diving publications as one of the world’s most desirable RSDT destinations.
... The reported median of 200 dives over a median of six years is similar in scale to the estimated average of 30 dives per year per recreational rebreather diver made in a study of CCR fatalities. 11 We cannot draw inference from Figure 2 regarding when a caustic cocktail may be experienced by CCR divers, other than to conclude they were reported by divers with less than one year of CCR experience through to divers with more than 20 years of experience. There appeared to be no difference in age between divers reporting 1, 2 or ≥ 3 caustic cocktail experiences. ...
Introduction:
Closed-circuit rebreathers (CCRs) are designed to be watertight. Ingressing water may react with carbon dioxide absorbent in the CCR, which may produce alkaline soda with a pH of 12-14, popularly referred to by CCR divers as a 'caustic cocktail'. This study aimed to explore divers' responses to caustic cocktail events and to investigate if CCR diving experience is associated with experiencing a caustic cocktail.
Methods:
An online survey instrument was developed and an invitation to participate was extended to certified CCR divers aged ≥ 18 years. Relationships between number of caustic cocktail events and potential risk factors: age; hours of rebreather diving experience; and number of rebreather dives were explored.
Results:
Of the 413 respondents, 394 (95%) identified as male, mean age was 46 years and median length of CCR certification was six years. Fifty-seven percent (n = 237) of respondents reported having experienced a caustic cocktail. The probability of self-reporting none, one, or more caustic cocktail events increased with experience. Divers reported a variety of first aid treatments for caustic cocktails, with ∼80% citing their CCR instructor as a source of information.
Conclusions:
The more hours or dives a CCR diver accrues, the more likely they will self-report having experienced one or more caustic cocktail events. The majority of CCR divers responded to a caustic cocktail by rinsing the oral cavity with water. A proportion of divers, however, responded by ingesting soda, dairy, juice, or a mildly acidic solution such as a mixture of vinegar and water. The recommendation to immediately flush with water needs reinforcing among rebreather divers.
... Rebreather diving is the activity with the second highest fatality rate in the world per hour of performance, second only to BASE jumping. 2 Hypoxia is the leading cause of fatality for rebreather divers at 38.9% of deaths, while in contrast hyperoxia is responsible for only 9.6%. 5 While hypoxia has signs and symptoms that can be recognizable, studies by the U.S. Air Force have concluded that personnel are likely to notice the symptoms before loss of consciousness only if those personnel have previously undergone hypoxia training in a controlled environment, as 94% of untrained pi-lots experience loss of consciousness despite education about hypoxia's symptoms. ...
Divers who wish to prolong their time underwater while carrying less equipment often use devices called rebreathers, which recycle the gas expired after each breath instead of discarding it as bubbles. However, rebreathers’ need to replace oxygen used by breathing creates a failure mechanism that can and frequently does lead to hypoxia, loss of consciousness, and death. The purpose of this study was to determine whether a pulse oximeter could provide a useful amount of warning time to a diver with a rebreather after failure of the oxygen addition mechanism. Twenty-eight volunteer human subjects breathed on a mixed-gas rebreather in which the oxygen addition system had been disabled. The subjects were immersed in water in four separate environmental scenarios, including cold and warm water, and monitored using pulse oximeters placed at multiple locations. Pulse oximeters placed on the forehead and clipped on the nasal ala provided a mean of 32 s (±10 s SD) of warning time to divers with falling oxygen levels, prior to risk of loss of consciousness. These devices, if configured for underwater use, could provide a practical and inexpensive alarm system to warn of impending loss of consciousness in a manner that is redundant to the rebreather.
... It is therefore essential that comprehensive diving guidelines, including specific fitness to dive prerequisites and CCR diving contraindications will be made easily assessable for reference. Better knowledge of CCR diving is essential given the increased risk of fatality actually estimated to be 10 times higher than recreational opencircuit scuba diving (Fock 2013). However, data regarding the effects of bounce mixed-gas deep CCR diving are still needed. ...
PurposeDeep diving using mixed gas with closed-circuit rebreathers (CCRs) is increasingly common. However, data regarding the effects of these dives are still scarce. This preliminary field study aimed at evaluating the acute effects of deep (90–120 msw) mixed-gas CCR bounce dives on lung function in relation with other physiological parameters.Methods
Seven divers performed a total of sixteen open-sea CCR dives breathing gas mixture of helium, nitrogen and oxygen (trimix) within four days at 2 depths (90 and 120 msw). Spirometric parameters, SpO2, body mass, hematocrit, short term heart rate variability (HRV) and critical flicker fusion frequency (CFFF) were measured at rest 60 min before the dive and 120 min after surfacing.ResultsThe median [1st–3rd quartile] of the forced vital capacity was lower (84% [76–93] vs 91% [74–107] of predicted values; p = 0.029), whereas FEV1/FVC was higher (98% [95–99] vs 95% [89–99]; p = 0.019) after than before the dives. The other spirometry values and SpO2 were unchanged. Body mass decreased from 73.5 kg (72.0–89.6) before the dives to 70.0 kg (69.2–85.8) after surfacing (p = 0.001), with no change of hematocrit or CFFT. HRV was increased as indicated by the higher SDNN, RMSSD and pNN50 after than before dives.Conclusion
The present observation represents the first original data regarding the effects of deep repeated CCR dives. The body mass loss and decrease of FVC after bounce dives at depth of about 100 msw may possibly impose an important physiological stress for the divers.
... In general, there are no CO 2 monitors in CCRs, which is significant because hypercapnia is one of the most common etiologies of injuries and deaths for CCR divers. [3] CCRs also lack fail safe/downstream oxygen safety features, such as limiting the addition of non- deep cave systems in the state of Florida, scientific research concerning marine species and environments beyond the shallow reef habitat, and the discovery and retrieval of artifacts from deep shipwrecks. [5][6][7] As Ed O'Brien, the dive safety officer for the famed Woods Hole Oceanographic Institution (WHOI), says, CCRs are a "…gamechanger for us". ...
... The likely over-representation of rebreathers in 'near-misses' reported by some Australian divers 23 is testament to the greater complexity of these devices, and the increased need for training, maintenance and vigilance. [24][25][26] Many fatal incidents involving rebreather divers appear to result from human error. However, a considerable number have also been attributed to design faults in the devices, something that is being progressively identified and addressed. ...
Introduction:
We aimed to identify the possible chain of events leading to fatal scuba diving incidents in Australia from 2001-2013 to inform appropriate countermeasures.
Methods:
The National Coronial Information System was searched to identify scuba diving-related deaths from 2001-2013, inclusive. Coronial findings, witness and police reports, medical histories and autopsies, toxicology and equipment reports were scrutinised. These were analysed for predisposing factors, triggers, disabling agents, disabling injuries and causes of death using a validated template.
Results:
There were 126 known scuba diving fatalities and 189 predisposing factors were identified, the major being health conditions (59; 47%), organisational/training/experience/skills issues (46; 37%), planning shortcomings (29; 23%) and equipment inadequacies (24; 19%). The 138 suspected triggers included environmental (68; 54%), exertion (23; 18%) and gas supply problems (15; 12%) among others. The 121 identified disabling agents included medical-related (48; 38%), ascent-related (21; 17%), poor buoyancy control (18; 14%), gas supply (17; 13%), environmental (13; 10%) and equipment (4; 3%). The main disabling injuries were asphyxia (37%), cardiac (25%) and cerebral arterial gas embolism/pulmonary barotrauma (15%).
Conclusions:
Chronic medical conditions, predominantly cardiac-related, are a major contributor to diving incidents. Divers with such conditions and/or older divers should undergo thorough fitness-to-dive assessments. Appropriate local knowledge, planning and monitoring are important to minimise the potential for incidents triggered by adverse environmental conditions, most of which involve inexperienced divers. Chain of events analysis should increase understanding of diving incidents and has the potential to reduce morbidity and mortality in divers.
... Divers should not touch underwater animals, including corals. This is not only to protect the diver from injury, but also to protect marine life [11]. Respondents formulated there are seven element of diving risk control on human factor that is: a. Have a documented environmentally friendly dive monitoring program b. ...
Indonesia is one of the most popular scuba diving destinations in the world. The popularity of recreational scuba diving has increased in recent decades. But despite its popularity, this recreation has a high potential danger. The risk of diving hazard must be managed to eliminate or minimize the risk of death, injury, or illness. The purpose of this study is to develop the minimum requirements criteria of the dive industry based on risk management. This study identifies three factors that cause dive risks: workplace environment, human factors and the natural environment. Results of focus group discussion with 108 respondents dive industry included both big and small businesses, locally and foreign owned in Bali, Yogyakarta, Labuan Bajo, Bogor, Depok and Bekasi are arranged 12 elements of risk management of dive hazards which will become the criteria for minimum requirements of the diving industry in Indonesia
... It is a risk that may be encountered more frequently by divers who use a closed-circuit rebreather (CCR). For those who use this type of equipment, hypoxia is usually the most frequent cause of death [1]. ...
Hypoxia is one of the main problems an underwater diver may have to face. The probability of experiencing hypoxia is related to the type of dive and the equipment used. Hypoxia in diving is a potentially fatal event for the diver, as it can lead to the loss of brain functions and consequently to the loss of breathing control, all in the absence of specific premonitory symptoms. It is a risk that may be encountered more frequently by divers who use a closed-circuit rebreather (CCR). For those who use this type of equipment, hypoxia is usually the most frequent cause of death [1].
Our study was aimed at the detection of peripheral oxygen saturation in order to identify, in the future, a preclinical hypoxic condition. We combined the use of pulse oximetry with two forehead sensors on an underwater diver subject who was using an electronic closed-circuit rebreather (ECCR). Despite the known limits of this
method and the preliminary status of these findings [2], the recorded data show a clear validity in the use of pulse oximetry in immersion for the detection of peripheral oxygen saturation. In the future, the pulse oximeter could become part of the instrumentation of the diver who uses CCR gear. The device could easily be implemented in these rebreathers.
The possibility of being able to perform a basic instru- mental analysis means that the diver can become more quickly aware of imminent hypoxia, characterized by the absence of clearly identifiable warning symptoms, and can put in place all the correct procedures for an emergency ascent, avoiding serious consequences.
... These data, combined with fatality data from the UK and elsewhere, support the assertion that, because of their greater complexity, there is a higher risk of mechanical failure and indeed death with CCRs compared to open-circuit scuba. 24 Despite the ubiquitousness of generally accurate pressure gauges, breathing gas supply problems persist, contributing to 12-18% of the near misses in this series and being a suspected trigger in an alarming 41% of US diving deaths. 7 Although the unpredictable can occur and catch a diver unawares, good dive preparation, including gas consumption planning and monitoring, can prevent many 'out of air' emergencies. ...
Introduction:
This study aimed to compare the results from three Australian scuba diver surveys. As the surveys differed in recruitment methods, the expectation was that respondents would differ in some important characteristics.
Methodology:
Anonymous, online, cross-sectional surveys of the demographics, health, diving practices and outcomes were distributed to: (1) Divers Alert Network Asia-Pacific (DAN AP) members; (2) Professional Association of Diving Instructors (PADI) Asia-Pacific members; and (3) divers who had received any PADI non-leadership certification within the previous four years. Only data from divers resident in Australia were analysed.
Results:
A total of 2,275 responses were received from current Australian residents, comprising 1,119 of 4,235 (26.4%) DAN members; 350 of 2,600 (13.5%) PADI members; and 806 of 37,000 (2.2%) PADI divers. DAN and PADI members had similar diving careers (medians 14 and 15 years, respectively). PADI members had undertaken more dives (median 800) than DAN members (330) and PADI divers (28). A total of 692 respondents reported suffering from diabetes or a cardiovascular, respiratory, neurological or psychological condition and included 34% of the DAN members and 28% of each of the PADI cohorts. Eighty-four divers had been treated for decompression illness (approximately 5% of DAN and PADI member groups and 1% of the PADI divers). Eighty-seven of 1,156 (7.5%) PADI respondents reported a perceived life-threatening incident while diving.
Conclusions:
Despite low response rates, this study indicates clear differences in the characteristics of the divers in the three cohorts. Therefore, a survey of a single cohort may represent that diving population alone and the findings may be misleading. This bias needs to be clearly understood and any survey findings interpreted accordingly.
... 9−12 The added risks of using mixed gases are largely unknown, but studies of diving deaths show that using a closed-circuit rebreather possibly carries a four-to ten-fold increase in the risk of dying while diving. 13 The combined additional risks of diving wrecks using rebreathers, while also in remote locations with limited medical support, are the reasons that many tour groups will employ physicians with practical experience in emergency medicine. ...
Injuries suffered as a result of a rebreather oxygen explosion and fire occurred to a diver on vacation in the island state of Chuuk, Micronesia. The medical and logistical management of the diver in a remote location are described. The mechanism of both the fire and the subsequent blast and burn injuries are discussed. Prevention of and preparation for such incidents are discussed in the context of the increasing frequency of dive and adventure travel to remote areas.
... There are various types of CCR available today and hazards associated with them have been described previously. 6 In this paper 'rebreather' refers to any form of scuba that recycles exhaled gas, including semi-closed rebreathers, CCRs, electronic and manual rebreathers. ...
Introduction:
Cave divers enter an inherently dangerous environment that often includes little visibility, maze-like passageways and a ceiling of rock that prevents a direct ascent to the surface in the event of a problem.
Methods:
Reports of cave diving fatality cases occurring between 01 July 1985 and 30 June 2015 collected by Divers Alert Network were reviewed. Training status, safety rules violated, relevancy of the violations, and root causes leading to death were determined.
Results:
A total of 161 divers who died were identified, 67 trained cave divers and 87 untrained. While the annual number of cave diving fatalities has steadily fallen over the last three decades, from eight to less than three, the proportion of trained divers among those fatalities has doubled. Data regarding trained cave divers were divided into two equal 15-year time periods. Trained cave divers who died in the most recent time period were older but little else differed. The most common cause of death was asphyxia due to drowning, preceded by running out of breathing gas, usually after getting lost owing to a loss of visibility caused by suspended silt. An overwhelming majority of the fatalities occurred in the state of Florida where many flooded caves are located.
Conclusion:
Even with improvements in technology, the greatest hazards faced by cave divers remain unchanged. Efforts to develop preventative interventions to address these hazards should continue.
... Bad behavior such as diving without bailout, disregarding alarms, omitting checklists and even entering the water with a closed valve or electronics shutdown is often associated with accidents. A bias in comparing the CCR to OC accident rate is that CCRs are frequently used for deep mixed-gas dives thereby exposing the divers to dangerous environments, which can be the real cause of accidents independent from the diving apparatus used (Fock, 2013). ...
Any activity one wishes to pursue will have a certain degree of risk. It is up to the person performing the activity to correctly identify and quantify the extent of such risk, and to define if possible, a mitigation strategy aiding in the decision of whether or not one is willing to accept the residual risk. Diving is a potentially dangerous activity. Proper risk assessment and management is therefore mandatory, especially for the more complex operations such as those required for scientific diving. Risk Assessment Matrixes (RAM) are based on the identification of hazards, the probability of their occurrence, the gravity of their consequences and the level of the resulting risk. Such procedures have been developed in a variety of operational situations including aerospace, industry, military and commercial diving. Human and Organizational Factors (HOF) are involved in the vast majority of diving accidents. Maintaining good Situational Awareness (SA) is a key factor for the safety and proficiency of divers. The use of checklists should be enforced as they will greatly reduce the occurrence of human errors. The risk of diving equipment failure can be reduced by proper maintenance and correct use. A diving-related accident is seldom the result of a single mistake. More often accidents result from a chain of events that may begin with a relatively minor problem that escalates to an uncontrollable situation. Defining consistent diving and contingency plans is the cornerstone of risk management.
... Although there are higher inherent risks when using CCR rather than OC (Fock 2013), the accident analysis research related to both training and manufacturing has led to a greatly improved safety record. Rebreather training courses regularly emphasize constant monitoring of the CCR unit, and involve extensively practicing drills to simulate possible unit failures. ...
... There are special populations outside of medicine who are also routinely exposed to HBO 2 , including military, commercial and recreational divers, and subterranean workers. 37,49,118 The risk of O 2 toxicity is increased when the ratio of O 2 to inert gas is raised in the hopes of minimizing deleterious gas effects. Combat divers use pure O 2 via a rebreather apparatus for clandestine purposes (to avoid bubbles). ...
INTRODUCTION: The use of hyperbaric oxygen (O2) as a therapeutic agent carries with it the risk of central nervous system (CNS) O2 toxicity.
METHODS: To further the understanding of this risk and the nature of its molecular mechanism, a review was conducted on the literature from various fields.
RESULTS: Numerous physiological changes are produced by increased partial pressures of oxygen (Po2), which may ultimately result in CNS O2 toxicity. The human body has several equilibrated safeguards that minimize effects of reactive species on neural networks, believed to play a primary role in CNS O2 toxicity. Increased partial pressure of oxygen (Po2) appears to saturate protective enzymes and unfavorably shift protective reactions in the direction of neural network overstimulation. Certain regions of the CNS appear more susceptible than others to these effects. Failure to decrease the elevated Po2 can result in a tonic-clonic seizure and death. Randomized, controlled studies in human populations would require a multicenter trial over a long period of time with numerous endpoints used to identify O2 toxicity.
CONCLUSIONS: The mounting scientific evidence and apparent increase in the number of hyperbaric O2 treatments demonstrate a need for further study in the near future.
Manning EP. Central nervous system oxygen toxicity and hyperbaric oxygen seizures. Aerosp Med Hum Perform. 2016; 87(5):477–486.
... Unfortunately, the limited endurance of human physiology and life support systems (i.e., breathing gases supply) require that cave divers conduct inherently dangerous explorations and many have lost their lives, making cave diving one of the highest risk exploration activities (Fock, 2013). ...
In this field note, we detail the operations and discuss the results of an experiment conducted in the unstructured environment of an underwater cave complex using an autonomous underwater vehicle (AUV). For this experiment, the AUV was equipped with two acoustic sonar sensors to simultaneously map the caves' horizontal and vertical surfaces. Although the caves' spatial complexity required AUV guidance by a diver, this field deployment successfully demonstrates a scan-matching algorithm in a simultaneous localization and mapping framework that significantly reduces and bounds the localization error for fully autonomous navigation. These methods are generalizable for AUV exploration in confined underwater environments where surfacing or predeployment of localization equipment is not feasible, and they may provide a useful step toward AUV utilization as a response tool in confined underwater disaster areas.
Closed-circuit rebreathers offer several advantages over open-circuit systems, but at a cost of increased complexity. While manufacturers have made great strides in improving equipment safety, this is enabling technology associated with greater risk than that of basic open-circuit systems. Core hazards include hypoxia, hyperoxia, hypercapnia, respiratory loading, gas supply, caustic ingestion, buoyancy management, decompression stress, and human factors. Rebreathers can expand the diving range, but they are demanding in design, training needs, monitoring requirements, and operation. Some issues cannot be engineered out, and some solutions can create their own problems. Users must accept responsibility for both risks and management demands. Ongoing commitment is required to maintain best practice, considering both collective experience and evolving knowledge to make changes when appropriate.
Nowhere is redundancy more indispensable than extended range cave diving. Training and practice in this discipline ensure divers are equipped with backup regulators, gauges, lights, and adequate breathing gas for a safe exit, emergencies, and decompression. Depending on penetration distances and depth, open circuit cave diving may require carrying more gas cylinders than can be logistically managed by the diver themselves while maintaining safe gas supply margins. Consequently, divers are forced to either stage cylinders in the cave prior to the dive or rely on resupply from support divers. Both scenarios have significant drawbacks. Due to the improved efficiency of breathing gas utilisation and other advantages, closed circuit rebreathers (CCR) have enabled extended range cave diving. With increasing depths, penetration distances, and bottom times, these divers must also plan for an increasing amount of open circuit bail-out gas in the event of CCR failure. Staged cylinders have traditionally been utilised, but this strategy has limitations due to the advanced dives needed to place them and equipment degradation due to prolonged water immersion, which can often result in cylinder and regulator corrosion with consequent leakage of contents over time. Consequently, a growing number of CCR divers are foregoing open-circuit bailout altogether by carrying an additional CCR system for bailout. Although these bailout rebreathers may facilitate further exploration and have certain advantages, the risks of diving with two complex machines remain to be clearly defined.
The vast majority of recreational dives are performed by divers using single cylinders of compressed air and open-circuit breathing systems, typically to a maximum depth of 40 m of seawater (msw). More extreme dives (in terms of depth and duration) are performed by a small subgroup of recreational divers who refer to their activity as ‘technical diving’. Technical divers substitute helium for nitrogen in gas mixes for deep diving to reduce the narcotic effect of nitrogen respired at high partial pressures and to reduce the density of the gas. These mixes also contain less oxygen than air in order to manage the risk of cerebral oxygen toxicity. Adequate gas supplies for long dives are carried in multiple cylinders, or divers may utilise ‘rebreather’ devices that recycle expired gas through a carbon dioxide (CO2) absorbent and which include a system for maintaining a safe inspired pressure of oxygen (PO2) as oxygen is consumed. These devices are complex and error-prone, and there is some evidence for relatively high accident rates in their use. Using these techniques, compressed gas dives between 40 and 100 msw are now relatively ‘routine’, and more extreme dives to depths in excess of 300 msw have been completed. A challenge of deep technical diving is the effect on respiratory physiology. There are multiple factors (including increased density of the respired gas) that increase the work of breathing during deep dives. This, in turn, may cause significant perturbation of normal respiratory control. In particular, there is a tendency for divers to hypoventilate and retain CO2 which can produce a number of dangerous secondary effects. Another significant challenge is uncertainty over the optimal protocol for decompression from deep dives. Technical divers utilise progressively more oxygen-rich breathing mixes during ascent in order to accelerate inert gas elimination, but there is uncertainty over how to plan the duration and depths of the ‘decompression stops’ that are completed during the ascent to allow time for this elimination to occur.
Humans in extreme environments, regardless of whether in space or deep in the oceans of the Earth, rely on life support systems to be kept alive and perform their exploration missions. Diving is similar to extravehicular activities in its duration and the need for human respiratory sustaining. This thesis presents the development of an analytical rebreather model, which is the system that recirculates and conditions the air the diver is breathing during a dive. The capability of simulating rebreather performance is currently lacking in the diving commercial and military industry. We believe that the advantages of having such a model are multi-fold: it can be used for mission planning, evaluating the impact of adding a new technology or modifying existing parameters or operational regime on an hardware configuration without performing expensive and time consuming hardware tests. An analytical model, like the one developed in this thesis, can also be used in complement with hardware testing to fine tune systems and increase resource endurance through the application of different electronic control strategies. The developed Matlab/Simulink model of this rebreather is modular and can be generalized to study open, semi-closed or closed circuits, in which the breathing gas used is air, oxygen, nitrox or heliox. The system's operational environment can be the ocean's surface (1 atmosphere), space (less than 1 atmosphere pressure) or deep underwater (more than 1 atmosphere pressure). After introducing the analytical modeling process for the rebreather, this thesis goes on to explore the model's applications for the study of different oxygen control strategies in order to maximize the oxygen lifetime during a dive, as well as the model's applicability as an aid in accident investigations. We aim to determine what is the maximum endurance of a rebreather system, given a particular, set configuration of components, as well as to study the reverse problem: if we set a mission endurance, what architectures would be able to achieve this level? Additionally, we are interested in studying how the tradespace of diving depth versus the diving systems's endurance looks like and how more complex control methods can help in pushing the existent boundary toward higher endurance limits. We show that more complex control algorithms can extend the duration of the oxygen tanks in a rebreather by a factor of 6.35, and, when given a set endurance level, control can help lower the tank sizes by a factor of 4.
Technical divers use gases other than air and advanced equipment configurations to conduct dives that are deeper and/or longer than typical recreational air dives. The use of oxygen-nitrogen (nitrox) mixes with oxygen fractions higher than air results in longer no-decompression limits for shallow diving, and faster decompression from deeper dives. For depths beyond the air-diving range, technical divers mix helium, a light non-narcotic gas, with nitrogen and oxygen to produce 'trimix'. These blends are tailored to the depth of intended use with a fraction of oxygen calculated to produce an inspired oxygen partial pressure unlikely to cause cerebral oxygen toxicity and a nitrogen fraction calculated to produce a tolerable degree of nitrogen narcosis. A typical deep technical dive will involve the use of trimix at the target depth with changes to gases containing more oxygen and less inert gas during the decompression. Open-circuit scuba may be used to carry and utilise such gases, but this is very wasteful of expensive helium. There is increasing use of closed-circuit 'rebreather' devices. These recycle expired gas and potentially limit gas consumption to a small amount of inert gas to maintain the volume of the breathing circuit during descent and the amount of oxygen metabolised by the diver. This paper reviews the basic approach to planning and execution of dives using these methods to better inform physicians of the physical demands and risks.
The author participated in a technical diving expedition to the South China Sea primarily to dive several deep World War Two wrecks. During the expedition, diving practices and diver health were observed, and a diver health survey was completed by six of the seven divers at the end of each diving day. This survey showed a slight worsening of health scores during the first half of the expedition, which then returned to baseline levels. However, no diver reached a health score of a level (six) associated with clinical decompression sickness (DCS) in a previous study. No clinical DCS was detected or treated; however, a high level of pre-existing musculoskeletal complaints prevalent in this group made clinical diagnosis difficult for marginal symptoms. A high proportion (50%) of divers reported symptoms consistent with pulmonary and ocular oxygen toxicity. The use of closed-circuit rebreathers for 74 dives in the depth range of 50 to 70 metres' sea water, with total dive time 100.4 hours, was associated with few technical problems for a suitably trained and experienced group of technical divers.
Closed-circuit rebreathers (CCR) have been used for many years in military diving but have only recently been adopted by technical leisure divers, media and scientific divers. Rebreather divers appreciate the value of training, pre-dive checks and equipment maintenance but it is often difficult to visualise just how important these factors are and how they inter-relate for a rebreather. In this paper, the well-known technique of fault tree analysis (FTA) is used to identify risk in a rebreather. Due to space constraints, only the branch of the tree for unconsciousness as a result of hyperoxia is considered in detail but, in common with the whole tree, end events are shown to be human-factor related. The importance of training to the emergency situation, the use of formal pre-dive checklists and the value of good design to prevent accident escalation are discussed further.