Diving safety

Open circuit

In the case of a single cylinder scuba set with a single first stage, and a single second stage, each of these items has a low but non-zero probability of failure. The components work in series - if any one of them fails, the system fails. It is equivalent to a single chain in which if any link fails, the chain breaks. When the dive is very shallow, the diver can safely escape to the surface, and when there is another diver right there with spare gas at the time of failure, they can share gas. At other times, a failure of a single item can kill the diver. ^[61]

Assuming independence of failure events, each item that can cause failure of the combined system is a critical point of failure and increases the probability of system failure. For the system not to fail, all items must not fail according to the formula:

   ${\displaystyle {p}=1-\prod _{i=1}^{n}(1-p_{i})}$

where:

• ${\displaystyle n}$ – number of components
• ${\displaystyle p_{i}}$ – probability of component i failing
• ${\displaystyle p}$ – the probability of all components failing (system failure)

As a purely illustrative example, if there is a 1 in 100 probability of a regulator failure, and a 1 in 1000 probability of a scuba cylinder failure then

${\displaystyle p_{reg}=0.01}$, and ${\displaystyle p_{cyl}=0.001}$

Therefore:

${\displaystyle P_{fail}=1-(1-p_{reg})\times (1-p_{cyl})}$

Substituting values:

${\displaystyle P_{fail}=1-(1-0.01)\times (1-0.001)}$

    ${\displaystyle =1-0.99\times 0.999}$

   ${\displaystyle =1-0.98901}$

   ${\displaystyle =0.01099}$ which is close to the sum of the two probabilities.

The example shows that each critical point of failure increases the probability of system failure by approximately that item's probability of failure.

If there are two completely independent scuba sets at the diver's disposal, either one of which is sufficient to allow the diver a safe return, then both sets must fail during the same dive to cause a fatal outcome. These items work in parallel - all must fail for the system to fail. The probability of this happening is extremely low for reliable equipment. ^[61]

Assuming independence of failure events, each duplicate redundant item added to the system decreases the probability of system failure according to the formula:-

   ${\displaystyle {p}=\prod _{i=1}^{n}p_{i}}$

where:

• ${\displaystyle n}$ – number of components
• ${\displaystyle p_{i}}$ – probability of component i failing
• ${\displaystyle p}$ – the probability of all components failing (system failure)

Taking two independent sets with the same probability of failure calculated in the example above:

${\displaystyle p_{left}=0.01099}$, and ${\displaystyle p_{right}=0.01099}$

Therefore:

${\displaystyle P_{fail}=(p_{left})\times (p_{right})}$

Substituting values:

${\displaystyle P_{fail}=0.01099\times 0.01099}$

    ${\displaystyle =0.00012078}$

It is clear from the example that redundancy reduces the risk of system failure very rapidly, and conversely, that disregarding a failure of a redundant item increases the probability of system failure equally rapidly.

Closed circuit

Open circuit scuba has a small number of fairly rugged and reliable components, each with a small number of failure modes and a low probability of failure. Most of these components remain present in closed circuit scuba, but there are also a number of additional items which could fail. Therefore, the rebreather architecture is inherently more likely to fail, and it is necessary to provide redundancy of critical components to provide reliability even approaching that of open circuit scuba. It is also more important to provide full redundancy of breathing gas supply as some rebreather failure modes do not allow safe ascent. Bailout to open circuit is the simplest and most robust option, but for dives where a long return under an overhead, or long decompression are necessary, open circuit can be impractically bulky. There is a point at which closed circuit bailout becomes a more manageable option, and the requirement for ability to return safely from any point on the planned dive profile makes it necessary for the breathing loop and gas supplies to be fully independent, though the ability to make use of the primary gas supply in the bailout rebreather can considerably extend the range for a small added complexity, using highly reliable components, but adding to the task loading of the diver. ^[61]

A hazard specific to closed circuit rebreathers is failure of the oxygen partial pressure control system. The breathing gas mixture in a diving rebreather loop is usually measured using electro-galvanic oxygen sensors, and the output of the cells is used by either the diver or an electronic control system to control addition of oxygen to increase partial pressure when it is below the chosen lower set-point, or to flush with diluent gas when it is above the upper set-point. When the partial pressure is between the upper and lower set-points, it is suitable for breathing at that depth and is left until it changes as a result of consumption by the diver, or a change in ambient pressure as a result of a depth change.^{[ citation needed ]}

Accuracy and reliability of measurement is important in this application for two basic reasons. Firstly, if the oxygen content is too low, the diver will lose consciousness due to hypoxia and probably die, ^[62] or if the oxygen content is too high, the risk of central nervous system oxygen toxicity causing convulsions and loss of consciousness, with a high risk of drowning becomes unacceptable. ^[62] Secondly, decompression obligations cannot be accurately or reliably calculated if the breathing gas composition is not known. ^[62] Pre-dive calibration of the cells can only check response to partial pressures up to 100% at atmospheric pressure, or 1 bar. As the set points are commonly in the range of 1.2 to 1.6 bar, ^[62] special hyperbaric calibration equipment would be required to reliably test the response at the set-points. This equipment is available, but is expensive and not in common use, and requires the cells to be removed from the rebreather and installed in the test unit. To compensate for the possibility of a cell failure during a dive, three cells are generally fitted, on the principle that failure of one cell at a time is most likely, and that if two cells indicate the same P_O2, they are more likely to be correct than the single cell with a different reading. Voting logic allows the control system to control the circuit for the rest of the dive according to the two cells assumed to be correct. This is not entirely reliable, as it is possible for two cells to fail on the same dive. ^[62]

Legislation, codes of practice and organisational procedures

Professional diving is generally regulated by occupational safety and health legislation, which can vary between jurisdictions, but tends to have some common features.

• Some form of statutory law protecting persons at work. ^[40]
• Regulations empowered by the statutory law referring specifically to occupational diving activities and defining their scope. ^[40]
• Codes of practice for diving activities approved or recommended in terms of the regulations. ^{[14] [2]}
• A requirement for employers of occupational divers to provide a safe working environment to the extent reasonably practicable, and to provide specific guidance for them in the procedures and equipment to be used by way of an operations manual. ^{[14] [2]}
• Training standards specifying the minimum competences required for occupational diving in various circumstances, generally associated with diving mode and depth range, and for the minimum competences of other specified members of a dive team. ^{[14] [2]}
• Medical standards of fitness to dive, and persons authorised to perform medical examinations on divers to assess their fitness to dive. ^[14]
• Formal registration of personnel assessed as competent to perform in specified roles as members of a professional diving team, and their legal responsibilities in terms of occupational health and safety. ^[14]

In most jurisdictions, recreational diving is unregulated, and an entirely untrained person is not legally hindered from scuba or freediving at their own risk in public access bodies of water. There is to some extent industry self-regulation, and most service providers will require customers to show evidence of competence appropriate to the service requested. This is usually a matter of presenting a recognised C-card, and is intended mainly to limit liability. The other instrument commonly used to limit liability is a waiver signed by the customer as part of the conditions of service.

Medical screening

Fitness to dive, (also medical fitness to dive), is the medical and physical suitability of a diver to function safely in the underwater environment using underwater diving equipment and procedures. Depending on the circumstances it may be established by a signed statement by the diver that he or she does not suffer from any of the listed disqualifying conditions and is able to manage the ordinary physical requirements of diving, to a detailed medical examination by a physician registered as a medical examiner of divers following a procedural checklist, and a legal document of fitness to dive issued by the medical examiner.

The most important medical is the one before starting diving, as the diver can be screened to prevent exposure when a dangerous condition exists. The other important medicals are after some significant illness, where medical intervention is needed, and has to be done by a doctor who is competent in diving medicine, and in these cases fitness can not always be established by prescriptive rules. ^[72]

Psychological factors can affect fitness to dive, particularly where they affect response to emergencies, or risk taking behaviour. Overconfidence and trait anxiety are both undesirable characteristics in a diver. The use of medical and recreational drugs, can also influence fitness to dive, both for physiological and behavioural reasons. In some cases prescription drug use may have a net positive effect, when effectively treating an underlying condition, but frequently the side effects of effective medication may have undesirable influences on the fitness of diver, and most cases of recreational drug use result in an impaired fitness to dive, and a significantly increased risk of sub-optimal or inappropriate response to emergencies.

Fitness to dive can be modified to some extent by training. Physical fitness can be improved to give the diver better capacity to deal with physical challenges, and properly conducted stress exposure training can improve situational awareness and the ability to focus on relevant responses under stress.

Pre-dive preparation and planning

Dive planning is the process of planning an underwater diving operation. The purpose of dive planning is to increase the probability that a dive will be completed safely and the goals achieved. ^[48] Some form of planning is done for most underwater dives, but the complexity and detail considered may vary enormously. ^[73]

Professional diving operations are usually formally planned and the plan documented as a legal record that due diligence has been done for health and safety purposes. ^{[14] [27]} Recreational dive planning may be less formal, but for complex technical dives, can be as formal, detailed and extensive as most professional dive plans. A professional diving contractor will be constrained by the code of practice, standing orders or regulatory legislation covering a project or specific operations within a project, and is responsible for ensuring that the scope of work to be done is within the scope of the rules relevant to that work. ^[14] A recreational (including technical) diver or dive group is generally less constrained, but nevertheless is almost always restricted by some legislation, and often also the rules of the organisations to which the divers are affiliated. ^[73]

The planning of a diving operation may be simple or complex. In some cases the processes may have to be repeated several times before a satisfactory plan is achieved, and even then the plan may have to be modified on site to suit changed circumstances. The final product of the planning process may be formally documented or, in the case of recreational divers, an agreement on how the dive will be conducted. A diving project may consist of a number of related diving operations. ^{[15] [14]}

A hazard identification and risk assessment procedure is the basis of a large part of dive planning. The hazards to which the divers will be exposed are identified, and the level of risk associated with each is evaluated. If the risk is deemed to be excessive, control methods will be applied to reduce the risk to an acceptable level, and where appropriate, further controls will be set in place to mitigate the effects if an incident does occur. ^{[14] [15]}

A documented dive plan may contain an overview of diving activities, a schedule of diving operations, specific information on the dive plan, contingency plans, emergency plans, and a budget. ^[48]

Following the plan

A basic strategy of risk management is to plan an operation and then conduct it, as far as reasonably practicable, according to the plan. If this is done, the risks will have been assessed and the equipment chosen will be suitable. Deviation from the plan brings in unassessed factors. In professional diving where a diving operation plan must be drawn up, variation from the plan generally requires reassessment of risk and recording of the deviation and any measures that were found necessary to manage the changed circumstances, but diverging to an existing contingency plan is not normally considered deviation from the plan. ^{[14] [13]} In recreational diving, the diver is free to plan or not, and to change the plan on whim, but technical diving certification agencies generally encourage divers to "plan the dive and dive the plan", as this is considered good practice for safety, and is the same strategy used by professionals. ^{[42] [74]}

Standard operating procedures {SOPs) and codes of practice (CoPs) are used to reduce the amount of detail required in dive planning. These documents provide much of the necessary detail of how frequently encountered tasks should be performed, using methods which have been tested and found to be effective, efficient and acceptably safe. When standard procedures are used, it is not necessary to detail those procedures in the dive plan, as the team members should be familiar with them already. ^[15]

Standard operating procedures are the procedures identified by the diving contractor as the recommended or required way of performing a range of routine activities and codified in a document. Following SOPs is generally a condition of employment for the diving team, and the provision of SOPs may be a requirement of health and safety regulations. The document is often called the operations manual, diving manual or something similar. For example, the U.S. Navy Diving Manual, ^[50] and NOAA Diving Manual, ^[48]

Codes of practice are procedures identified by a larger population as preferred methods for a similar range of activities. They may be a set of industry best practice recommendations, such as the IMCA Code of Practice for offshore diving, ^[75] a government regulated set of recommendations, ^[15] or a regulated set of requirements which must be followed. ^[76]

In recreational diving there are also some procedures that are widely recognised and common to most training agencies, but there are some procedures that differ between agencies, and divers may therefore differ in their expectations in some contingencies. Ideally any two divers intending to dive together in the buddy system, should use the same or compatible responses to emergencies where prompt and effective response could be a matter of life or death. This ideal does not always map well onto the common practice of buddy pairs being allocated more or less arbitrarily by the divemaster or charter boat skipper. The consequence is that some divers accept that the buddy system is degraded by this practice, and they amend their expectations by assuming that the buddy may not be of any practical assistance, and plan to be self-sufficient. Other divers refuse to dive with anyone who is not trained to the same system. ^[42] Many divers simply accept the status quo and do not even question the safety implications.

Use of checklists

Studies have shown that the use of written checklists can significantly reduce the number of critical human errors in occupations and procedures where a small number of critical checks can make a proportionately large effect on the risk of the operation. These are reminders to make critical checks for people who are well aware of the need, and highly skilled and responsible posts such as airline cockpit crew and operating theatre staff, who nevertheless occasionally fail to complete the necessary preparations in the absence of a checklist. The concept has been tested on a group of recreational divers and the reduction in undesirable incidents was highly significant. ^{[77] [78] [79]} Checklist systems are more common in professional diving, where the code of practice or operations manual may mandate recording that each checklist has been applied. ^[80] The checklist is effective when all critical checks are listed. Additional detail may be counterproductive as distraction. ^{[79] [81]} More detailed checklists may be appropriate where equipment is set up and tested. The pre-dive check mnemonics advocated by diver training agencies are less reliable, as they rely on memory, vary considerably, using different terms to refer to the same or similar set of checks and the order of checks is highly variable and can cause divers trained by different agencies to become confused when diving together. In some cases the same initial has been reused in the same mnemonic for several groups of checks. A written checklist covering the safety-critical checks in a logical order avoids the distraction of trying to remember what the next item to be checked should be, and ensures that all the checks are covered, even if the checks are interrupted. ^[77] There are several stages at which the use of a checklist is appropriate. These include during dive planning, risk assessment, equipment setup (particularly assembly and function testing of rebreathers), preparing the diver for the water, and in emergencies for which there is a planned response. A commonly used special case of a checklist in scuba diving is the decompression schedule for a planned dive profile, often carried by each diver in written format on a wrist slate or wet notebook. ^[82]

The pre-dive equipment safety checks are an application where the use of a written checklist has been shown to reduce the incidence of mishaps which could potentially escalate to incidents with significant adverse consequences. ^[77]

The use of checklists for pre-dive checks is generally considered good practice by recreational diver training agencies, but is seldom applied in practice. Pre-dive procedures include planning and organisation of the dive and preparation of equipment, which generally includes function tests of safety critical equipment and assembly of the scuba set. Occasionally a buoyancy check may be made for unfamiliar equipment. An effective pre-dive checklist would reduce the probability of failing to kit up correctly and completely before entering the water. Divers are trained to apply mnemonics to conduct pre-dive checks in training, but there is little or no follow-up to encourage their use outside of the training environment. Each training agency has its own "buddy check" mnemonic recorded in its training manual, but there is very little common ground between them, and two divers trained by different agencies to equivalent certification, are unlikely to be familiar with each other's buddy check system, while in theory they have equivalent qualifications and are considered competent to dive together. ^[77] Solo divers avoid this problem by taking sole responsibility for their pre-dive checks, at the expense of losing the hypothetical double check of the buddy.

Most of the memorised checklists rely on mnemonics, which are all short and very unspecific, covering a wide range of checks, surveys and preparations, usually using a single word each to represent a series of checks on several important aspects of preparation. These checklists do not provide focused instructions, and important details of the actions to be taken may be forgotten or overlooked, or missed due to distractions. It is not known to what extent these mnemonic checklists are used in the field, and none of them have been evaluated for effectiveness. The use of a written checklist which provides sufficient detail to ensure that all necessary pre-dive checks are completed is experimentally associated with a significant reduction in unsafe conditions before a dive, and mishaps during a dive. In some cases the identification of unsafe conditions during the checks allows corrective measures to be taken, after which the dive may proceed, without associated mishap, and in some cases the dive is cancelled and the possibility of associated mishaps avoided. ^[77]

Reasons cited for failure to properly complete pre-dive checks include:

• not using a written checklist,
• the checklist being over-complicated, in too much detail or in an inconvenient order,
• time pressure
• peer pressure
• distractions and interruptions
• lack of space
• overconfidence and complacency, often influenced by outcome bias

and combinations of these. ^[39]

Breaking pre-dive checks into groups which are done at different stages of preparation may require some of the checks to be repeated, but can still be more effective than doing everything at the last minute, when the conditions in which the checks are done are more conducive to attention, comfort and making any necessary adjustments to the equipment. This can apply particularly to diving from small boats, when assembly of the breathing set and partial kitting up in the diving suit before launch may be necessary due to space constraints and a wet bumpy ride to the site. ^[39]

Training, practice and experience

To make effective use of standard procedures, the diving team must be competent in the procedures, particularly the diving and emergency skills. These skill sets are the basis of the standard operating procedures, and have themselves been standardised to a degree where they are largely internationally accepted, and are portable between organisations without requiring much re-learning. ^[45] A large part of the variation is associated with different equipment and equipment configurations, and operators need to become familiar with new equipment under controlled conditions before using them in the field. This is the realm of formal training for diving certification, which is normally done by registered diving schools and instructors, and equipment rating and familiarisation, which may be done by the employer or by diver training schools, depending on the risks and complexity of the training, and how much unfamiliar equipment is involved. For example, basic operation of an unfamiliar mode of life support equipment like surface supplied diving or a rebreather is likely to be learned at a school, while the details of operating a different model of non-diving equipment, like a hydraulic bolt-tensioner is likely to be learned from a skilled operator of that equipment, or at a manufacturer's familiarisation workshop. It is common practice to record such training and the associated assessment in the diver's logbook, as well as any certificate which may be issued. ^{[14] [76]}

Appropriate response to minor life-support equipment malfunctions which can be corrected by the diver is very important for diving safety. The diver is expected to deal with a number of small problems promptly and correctly before the situation escalates. Dealing with such problems as a dislodged or flooded mask, or free-flowing regulator, or correctable buoyancy fault should be done before the situation deteriorates to an emergency. A basic understanding of the physics and physiology of diving should give the diver the ability to predict the consequences of possible responses to unfamiliar contingencies. A diver with inadequate understanding may respond inappropriately to an emergency outside of their training and experience, which though unlikely remains possible. Repeated practice beyond initial competence of standard responses to the more likely contingencies develops a "muscle memory" response, which helps the diver perform the correct response under stress, and when more than one problem occurs simultaneously. It is possible to never experience one of these problems, and some divers may never need the skills in practice, but divers who do not practice the skills are more likely to be overtaken by circumstances if something does go wrong. The practice of stress exposure training in controlled conditions, where the diver is task loaded with an increasing level of simulated problems and must deal with them, is thought to develop the diver's confidence in their ability to manage an emergency effectively, which may give them the ability to avoid panic and continue to respond usefully to the situation, giving a better chance of survival. ^{[83] [84]}

Continued occasional practice of emergency procedures after initial training ensures that the skills are not lost due to lack of use. Divers who have not practiced their skills for several months or years are at higher risk of accidents when first returning to the water, and refresher courses and checkout dives in benign conditions are available to get the skills back to standard and thereby reduce risk of an accident. ^[85]

Stand-by diver

The stand-by diver's job is to wait until something goes wrong, and then be sent in to sort it out. For this reason a stand-by diver should be one of the best divers on the team regarding diving skills and strength, but does not have to be expert at the work skills for the specific job. The stand-by diver is usually required to remain ready for deployment at very short notice during the entire working dive, and will usually be fully dressed ready to deploy, except for helmet or mask. When deployed, the stand-by diver will normally follow the umbilical of the diver who is in trouble, as unless it has been severed, it will reliably lead to the correct diver. The stand-by diver must maintain communications with the supervisor throughout the dive and is expected to give a running commentary of progress so that the supervisor and surface crew know as much as is reasonably practicable about what is happening underwater to be able to plan accordingly, and must take the necessary steps to resolve incidents, which may involve supply of emergency air or locating and rescuing an injured or unconscious diver. In bell diving, the bellman is the stand-by diver when the working diver is out of the bell, and may have to recover a distressed diver to the bell and give first aid if necessary and possible. There will generally be a surface stand-by diver in addition to the divers in the bell. ^{[90] [13]} The stand-by diver and working diver are generally interchangeable, unless specialised skills are required for the task of the specific dive, and professional divers are trained in rescue procedures appropriate to the equipment they are qualified to use. ^[45] Rescue skills are not included in the minimum training standards for entry level recreational divers according to RSTC and ISO publications, ^{[43] [44]} and a diver cannot be obliged to perform procedures for which they are not qualified.

Incident management

In professional diving, the incident manager will be the supervisor, who should be trained and competent to handle procedures for the reasonably foreseeable incidents that may occur during diving operations for the range of diving operations they are licensed to control. ^[2] The supervisor will advise and coordinate efforts by other participants until the affected diver or divers are handed over to a competent agency, or the casualty is assumed dead. The master of the vessel will be advised by the supervisor regarding safety of diving personnel, but remains responsible for the overall safety of the vessel and occupants. ^[14]

In recreational diving, the skipper of the dive boat is likely to be responsible for the safety of the divers on or near the boat, and to ensure that everyone who left the boat to dive is back on the boat before it leaves the site. Unless there is another person specifically appointed as responsible for incident management, the skipper will generally have this responsibility by default. Competence requirements for dive boat skippers will vary depending on the jurisdiction. There is no international standard. There is no specific post for incident management for recreational shore dives. If a diving instructor is involved they will have a duty of care for their learners, and may be the best qualified person to advise emergency services, but it is likely that any emergency services contacted will have to do their best according to their code of practice. Divers Alert Network will be available to advise on best practice if one of their clients is involved, and have been known to do so as a pro bono service even when they have no direct involvement.

Buddy or team divers

A buddy or team diver is simultaneously the diver and the stand-by diver for the buddy or other members of the team. Since it is increasingly difficult to keep track of a larger number of divers, and the benefits of larger groups are small, teams are usually of three divers. Larger groups are generally split up into three diver teams and pairs.

When using the buddy system, members of the group dive together and co-operate with each other, so that they can help or rescue each other in the event of an emergency. ^[91] This is most effective if the divers are both competent in all the relevant skills and are sufficiently aware of the situation to be able to respond in time, which is a matter of both attitude and competence, both of which may vary with circumstances. ^[92]

In recreational diving, a pair of divers is usually the best combination in buddy diving; with threesomes, one of the divers can easily lose the attention of the other two. The system is likely to be effective in mitigating out-of-air emergencies, non-diving medical emergencies and entrapment in ropes or nets. When used with the buddy check it can help avoid the omission, misuse and failure of diving equipment, though the use of a written checklist is more reliable. ^[77]

In technical diving activities such as cave diving, threesomes are considered an acceptable practice. ^[93] This is usually referred to as team diving to distinguish it from buddy diving in pairs. Diving in a three person team requires a higher level of situation awareness regarding the disposition of team members, but also provides a considerably enhanced support system if anything goes wrong. As a way to reduce peer pressure on the least confident or experienced diver, some certification organisations suggest making that diver the executive leader of the team, with primary responsibility for decisions regarding terminating the dive or venturing into areas of increased difficulty or risk, while retaining the general rule that any diver can terminate the dive at any time without argument. ^[94]

When professional divers dive as buddy pairs their responsibility to each other is specified as part of the standard operating procedures, code of practice, or governing legislation. This may range from equal mutual support to one of the divers being appointed as the safety diver, with no task responsibilities, to the task specialist. ^[95]

Support divers

A technical diving support team is a group of people organised to provide support to the divers in a similar way to a professional diving team, but without the same legal constraints. Support divers are recreational divers who are members of the support team who have made themselves available to provide in-water assistance to the primary diving team, and are typically used for a particularly complex or hazardous dive, such as in depth record attempts and major cave and wreck explorations, where the lead divers may need to spend several hours under the water, and the dive is logistically complicated. They may be chosen for useful support skills other than diving, but must be competent for the dives they are expected to do. ^{[42] [96] [97]}

Such support may include deploying and recovering stage cylinders, monitoring and escorting the primary team divers during decompression, providing additional breathing gas when requested, and providing assistance in an emergency. In some cases they may function as standby divers, and not be required to enter the water during the dive unless something goes wrong. ^{[42] [96] [74] [73] [97]}

Personal protective equipment for mitigation

Analysis of rebreather diving incidents shows that full-face masks and mouthpiece retaining straps are effective for protecting the airway if a diver loses consciousness underwater due to breathing an inappropriate gas mixture, the most common disabling agent. This increases the chances of a successful rescue. Full face masks are more effective, bit more complex and expensive. Mouthpiece retaining straps are not as effective but are inexpensive and simple to use. These measures have not been widely adopted by the recreational diving community. ^[98]

Recreational diver and service provider perceptions

A survey on the perceptions of recreational divers and recreational diving service providers in 2018 showed that both groups considered the personal surface marker buoy and the dive computer to be the most important safety accessories. Dive centres also considered a backup mask, cutting tool, whistle and reel important, whereas divers generally did not. ^[102]

The most important safety aspect that should be provided by a diving service provider was considered to be breathing gas quality, followed by staff competence, training provision, and availability of oxygen for first aid. Local availability of a recompression chamber was considered of lower importance, possibly because it is beyond the control of the diver or the service provider. ^[102]

Dive centres considered that recommendations of the instructors was an important factor in allocating buddy pairs, an opinion not shared by most divers. Both groups agreed that gender, age, family connection or existing friendship were not significant factors, and divers and service providers both considered experience, buoyancy skills and emergency skills important. ^[102]

About 30% of the dive centres had experience with scuba incidents and accidents, about 60% of them with decompression illness. Drowning and equipment failure each accounted for 11%, followed by boat accidents at 9%, and staff perceived these to be the highest risks. About 30% of divers had experience with a diving accident or incident, and about 60% had witnessed an accident or incident, including equipment failures and buddy separation, but also changes in weather conditions and interactions with dangerous animals. ^[102]

Divers considered the greatest risks as being lost at sea, decompression illness and equipment failure, and did not consider drowning or hazardous animals to be a high risk. The population sample was considered representative of the actual members of DAN Europe, being characterised by mostly middle aged males. The study focused on perceived risk, which does not necessarily correspond to actual risk, and the correlation between diver experience and risk perception was not investigated. ^[102]

The study concluded that recreational diving safety might be improved by raising awareness of risk and working towards accident prevention by training and attempting to create a culture of safety in the recreational diving industry. A hazard identification and risk assessment (HIRA) protocol and a diving safety officer programme which are similar to systems used with some success by professional divers have been developed by DAN Europe and are being offered to the recreational diving public. ^[102]