Human factors are the physical or cognitive properties of individuals, or social behavior which is specific to humans, and influence functioning of technological systems as well as human-environment equilibria. The safety of underwater diving operations can be improved by reducing the frequency of human error and the consequences when it does occur. Human error can be defined as an individual's deviation from acceptable or desirable practice which culminates in undesirable or unexpected results.
Dive safety is primarily a function of four factors: the environment, equipment, individual diver performance and dive team performance. The water is a harsh and alien environment which can impose severe physical and psychological stress on a diver. The remaining factors must be controlled and coordinated so the diver can overcome the stresses imposed by the underwater environment and work safely. Diving equipment is crucial because it provides life support to the diver, but the majority of dive accidents are caused by individual diver panic and an associated degradation of the individual diver's performance. - M.A. Blumenberg, 1996
Human error is inevitable and most errors are minor and do not cause significant harm, but others can have catastrophic consequences. Examples of human error leading to accidents are available in vast numbers, as it is the direct cause of 60% to 80% of all accidents. In a high risk environment, as is the case in diving, human error is more likely to have catastrophic consequences. A study by William P. Morgan indicates that over half of all divers in the survey had experienced panic underwater at some time during their diving career. These findings were independently corroborated by a survey that suggested 65% of recreational divers have panicked under water. Panic frequently leads to errors in a diver's judgment or performance, and may result in an accident. Human error and panic are considered to be the leading causes of dive accidents and fatalities.
Only 4.46% of the recreational diving fatalities in a 1997 study were attributable to a single contributory cause. The remaining fatalities probably arose as a result of a progressive sequence of events involving two or more procedural errors or equipment failures, and since procedural errors are generally avoidable by a well-trained, intelligent and alert diver, working in an organised structure, and not under excessive stress, it was concluded that the low accident rate in commercial Scuba diving is due to this factor. The study also concluded that it would be impossible to eliminate absolutely all minor contraindications of Scuba diving, as this would result in overwhelming bureaucracy and would bring all diving to a halt.
A dive team may be considered as a system which is influenced by the following factors:
There are considerations associated with each of these factors relating specifically to diving.
Humans function underwater by virtue of technology, as our physiology is poorly adapted to the environment. Human factors are significant in diving because of this harsh and alien environment, and because diver life support systems and other equipment that may be required to perform specific tasks depend on technology that is designed, operated and maintained by humans, and because human factors are cited as significant contributors to diving accidents in most accident investigations
Professional diving is a means to accomplish a wide range of activities underwater in a normally inaccessible and potentially hazardous environment. While working underwater, divers are subjected to high levels of physical and psychological stress due to environmental conditions and the limitations of the life support systems, as well as the rigours of the task at hand.
Unmanned remotely operated vehicles (ROV's) allow performance of a variety of tasks at almost any depths for extended periods, but there are still many essential underwater tasks which can only be performed or are most effectively performed by a diver. A diver is still the most versatile underwater tool, but also the most unpredictable, and his own behaviour may threaten his safety.
Recreational, or sport divers, including technical divers, dive for entertainment, and are usually motivated by a desire to explore and witness, though there is no distinct division between the underwater activities of recreational and professional divers. The primary distinction is that legal obligations and protection are significantly different, and this is reflected in organisational structure and procedures.
Recreational diving has been rated more risky than snow skiing, but less risky than other adventure sports such as rock climbing, bungee jumping, motorcycle racing and sky diving. Improvements in training standards and equipment design and configuration, and increased awareness of the risks of diving, have not eliminated fatal incidents, which occur every year in what is generally a reasonably safe recreational activity.
Both categories of diver are usually trained and certified, but recreational diving equipment is typically limited to Self Contained Underwater Breathing Apparatus (Scuba), whereas professional divers may be trained to use a greater variety of diving systems, from Scuba to surface supplied mixed gas and saturation systems. A recreational diver may use some ancillary equipment to enhance the diving experience, but the professional will almost always use tools to perform a specific task.
Since the goal of recreational diving is personal enjoyment, a decision to abort a dive, for whatever reason, normally only affects the diver and his companions. A working diver faced with the same decision, must disappoint a client who needs and expects the diver's services, often with significant financial consequences. Therefore, the working diver often faces greater pressure to provide the service at the cost of reduced personal safety. An understanding of the human factors associated with diving may help the diving team to strike an appropriate balance between service delivery and safety.
Human factors are the influences on human behavior, and the resulting effects of human performance on a process or system. Safety can be improved by reducing the frequency of human error and the consequences when it does occur. Human error can be defined as an individual's deviation from acceptable or desirable practice which culminates in undesirable or unexpected results.
These error categories relate to three levels of human performance:
Three error mechanisms can be defined which correlate the error categories with human performance levels:
Violations are a special category of mistakes where someone intentionally fails to apply a good rule, or deviates from acceptable or desirable practice.
Four categories of violations may be identified:
Age and gender are factors in the tendency to violate rules: Young men are more likely to violate rules than most older women, but men and women of all ages are similarly prone to error.
These error mechanisms explain the psychological basis for errors, but the mechanisms are not readily observable.
Stress has been defined as "the result of an imbalance between the demands placed upon an individual and the capacity of that individual to respond to the demands" 
A person will respond to stress by taking actions to change the situation in order to reduce the stress When the actions are successful the result is described as 'coping', when unsuccessful the level of stress will increase and may lead to panic.
The person exposed to a stressful situation (beyond skill based response), cognitively appraises the situation and compares it to previous experience using rule based or knowledge based assessment. The perception of stress is an individual reaction based on learned behaviour and available information and can vary dramatically between subjects. Perceived stress levels can in many cases be reduced by a reduction in uncertainty, which may result from education, training and experience, and a stressor which is perceived by one person as a threat, may be regarded as a challenge by someone else, or an inconvenience by a third person. These perceptions all evoke a response, but they indicate a very different level of tolerance and ability to cope with the situation.
Once stress is perceived, the person must decide how to respond to the stressor. The situation must be assessed, memory interrogated, options evaluated, and an appropriate response chosen.
Ability to perform the chosen response may be affected by the stress situation, and once the response has been attempted, the subject will review how the response has affected the situation, and judge whether the response has been effective.
Depending on the perceived residual stress, the process may be stopped or repeated indefinitely until the situation has been resolved, or the stress level increases until the subject is no longer able to cope.
The level of perceived stress can affect performance. When there is little stress there is a tendency toward carelessness that may result in poor performance, but sufficiently high stress can overwhelm capacity and cause degraded performance due to inability to cope. Optimum performance occurs when the stress levels are less than the person's ability to respond, but sufficient to keep them alert. This varies with the individual and the situation, and can not be maintained continuously, but performance can be improved through personnel selection  and training.
The benefits of training may include an increase in performance at a given stress level and improvement of coping skills by developing response reactions to given stress situations. These are patterns of action which have been learned by experience and can be applied to similar situations, when the person operates on Reason's rule-based performance level, and reduce the need for a long and error prone cognitive process, thereby saving time, reducing stress and improving the ability to cope.
The objective of training should be to improve ability to continue the normal coping process when presented with unforeseen circumstances. A possible danger of training is over-reliance on learned procedures, as each stress situation is in some way unique and therefore no learned procedure will be a perfect match. The individual must retain the ability to assess whether the learned procedure is appropriate and adapt it to the specific situation. Therefore, training should include situational assessment and decision making under stress.
Appropriate stress response, or coping, is a cognitive process which evaluates a stress situation and the available options, then selects an appropriate course of action to respond. A diver needs to retain the ability to process information and make decisions while under stress, especially when confronted with unforeseen events.
It is important for the diver to retain the ability to process information and make appropriate decisions while under stress. A sense of control and competence while under stress is crucial. An over-stressed person will tend lose control and truncate the coping process, and become indecisive, losing the ability to analyze and act. As the situation overcomes the individual's ability to cope, panic sets in and creates a barrier in the stress response that blocks the decision process. A lack of action or continuation of an inappropriate action may lead to errors and accidents.
The diver's maxim, "stop, breathe, think, act", is a widely taught method for working through unexpected events underwater. The intention is to calm the diver and maintain an ability to cognitively appraise a stress situation.
The dive maxim, "stop, breathe, think, act" is generally a good response, but it is not appropriate for all diving emergencies. This response assumes that both time and an adequate supply of breathing gas are available, and though this is often true, some situations require immediate learned responses which must be habituated by education, training and repetitive practice to overcome inappropriate instinctive and natural reflexive responses. For example, a diver should exhale whenever ascending to prevent lung overexpansion injuries, and if the diver is subject to a collision or sudden upwelling underwater, the natural reaction may be to tense up and hold his breath, particularly if the breathing gas supply is interrupted at the same time. This reaction could prove fatal if the diver is lifted sufficiently to cause lung overexpansion. Only through education training and practice, and perhaps proper selection, will the diver reflexively exhale as a response to a pressure reduction.
Other factors suggested by Bachrach to prevent panic are listed below:
The most frequently cited cause of diver injury or death is panic, or a loss of control  Analysis of the human factors associated with diving can identify the primary influences which lead to panic, and suggest methods to promote safety.
Dive safety is primarily controlled by the individual diver and his ability to cope with stress underwater. The development of a diving accident may begin with a diver in a normal psychological and physiological state. The presence of a stressor may alter the diver's psychological and physiological state, and if the stress becomes excessive the diver's skills will diminish. Stressors may arise from human factors, the environment, equipment, procedures, organizational factors, or interactions between any of these, and these stress effects are cumulative.
A diver is normally able to cope with applied stressors and perform the dive safely, and while the diver has sufficient capacity for coping, the stress is relieved or controlled and the operation can continue, but If the stress exceeds the diver's capacity, then the stressor is beyond the diver's control and an accident may result.
An accident is an event leading to injury, occupational illness, death, or material loss or damage. A "near accident" is an event which had the potential to cause injury, occupational illness, death, or material loss or damage, but did not due to some corrective action.
Three critical stages can be identified in the development of an error into an accident:
Equipment, procedures, organization, environment, individual factors and interactions between them are the sources of contributing and compounding events and conditions. Analysis of near accidents can be of great value to identify sources of error and allow planning to reduce or eliminate contributing and compounding conditions.
A safety study estimated about a million shortcuts taken per fatal accident.
The fatality is the peak of the accident pyramid. The base of the pyramid is the shortcuts, and in between are escalating levels of near-accidents which could (but too often do not) serve as lessons learned. Blumenberg, 1996
Accident investigations typically focus on the end event, and attempt to erect barriers to similar accidents, such as personal protection equipment, backup equipment or alarm systems. These are intended to prevent the recurrence of similar accidents, and are often effective in this limited goal.
Accidents continue to occur because the majority of the contributing and compounding factors are not addressed. Human behavior and the systems in which people work are too complex to analyse all possible interactions. A more effective route to accident prevention is to reduce or mitigate the occurrence of human error by focusing on the contributing and compounding human factors that create an environment in which accidents are likely to occur.
Accidents frequently appear to happen unexpectedly because people failed to recognize the indications of developing crisis which resulted in the accident. A crisis can be defined as a rapidly developing sequence of events in which the risks associated with the system rapidly increase to a hazardous state. The interaction of system factors is complex and often unpredictable, and hazard can accumulate at a rate which varies depending on the system, until corrective action is taken, the hazard dissipates without intervention, or an accident occurs.
Although the individual operator is most often responsible for committing errors that cause accidents, it is also often the individual operator who is best placed to recognize the development of a dangerous situation and take corrective action, and this usually happens before the situation escalates into an accident.
The ability of the operator to recognize potentially dangerous situations can be improved by incorporating warning mechanisms into systems, and training can significantly improve their ability to recognize the development of a hazardous situation and take appropriate corrective action in time to return the system to an acceptable level of safety.
Diving equipment can be grouped into four general categories:
Manufacturers are continuously improving diving equipment to allow deeper, longer and safer diving operations, but the equipment still has ergonomic limitations and can exert significant stress on the diver:
Proper ergonomic engineering can reduce the physical demands on the diver due to the equipment, but it also important for equipment design to consider psychological aspects. Research by Morgan and others has shown that anxiety states may be a response to disordered breathing caused by use of breathing apparatus, and that some people experience respiratory distress or panic behaviour while doing physical exercise wearing scuba. Morgan has also recommended that more research be done on psychological aspects of human-respirator interface.
Diving procedures are promulgated in many forms, including:
Among the organisations publishing diving procedures, the US Navy, British HSE and NOAA are notable for funding published scientific research on diving safety.
Separate dive procedures are developed for each type of diving, such as air and mixed gas diving, inshore and offshore diving, or recreational and professional diving. Decompression tables, programs and algorithms that prescribe depth and time limitations are also a subset of procedures, and highlight the unique nature of the hyperbaric work environment.
The underwater work environment exposes divers to physical, psychological and pathological stresses. No other industrial working environment alters normal worker physiology more than diving. Blumenberg 1996
Environmental influences include pressure, cold, currents, surge, and limited visibility, and underwater conditions can change rapidly, often without warning. Dive teams must anticipate environmental conditions and their effects, and plan accordingly. The diving environment cannot be controlled, but the diving team can control when and how the diver enters the underwater environment.
Not everyone has the physical and mental capacity to dive safely. Professional diving can be physically demanding work, and some diving tasks require considerable strength and stamina, and a sufficient reserve of physical and psychological strength to cope with unexpected situations. The requirements for recreational diving may be less rigorous, but any diver, whether professional or recreational, should have some minimum capabilities in order to dive safely. Physical screening standards which take into account anticipated work demands are commonly used by commercial and military divers, and detailed lists of physical contraindications to diving have been published. These standards can vary widely, but the need for physical screening is generally accepted.
Behavioral problems may be more important than physical problems because 'no amount of physical screening can protect a diver from his own stupidity' and 'the majority of diving accidents are caused by poor judgment or inattention to the basic rules of diving safety... ' Mental fitness may be at least as important as physical fitness for divers. and maturity and responsibility should be evaluated as carefully as physical health and fitness.
Selection of divers should match the individual's mental and physical abilities to job demands, but although research has successfully developed a unique psychological profile for divers, psychological screening is seldom applied. According to Morgan, divers are "characterized by low scores for measures of anxiety, and high scores for measures of aggression, assertiveness, confidence and sensation-seeking; they also tend to possess an internal locus of control." Morgan has also successfully used Spielberger's State-Trait Anxiety Inventory to predict with 88% accuracy which divers amongst a class of new recreational divers would experience panic.
The organizational factor is the dominant controllable factor affecting behavior of the individual diver. The organization can be analysed at several levels ranging from a two-man buddy team through the dive team, the whole organization and up to the whole diving industry, and all organizational levels influence the individual diver's behavior and performance.
Interactions between the other factors is the most unpredictable factor. Some interactions are linear and relatively easily predicted, but others are complex. Unanticipated interactions between factors can be critical when a diver is working in an isolated hyperbaric environment. Thorough planning and preparation can help to minimize unanticipated interactions, and effective coping skills may be necessary to control interactions when they occur.
The simplistic statement that most diving accidents are due to diver error does not address the underlying reasons for the diver making the mistake. Errors are inherent in human nature, and it is more useful to consider all levels of influence on the behaviour of the diver as this may throw light on the reasons why the same errors are repeated so often.
Analyses of aviation accidents show that 60 to 80% of aviation accidents are at least partly due to human error. The techniques of Human Factor Error Analysis can be applied to diving at all levels of the industry and sport, and can provide insight into why incidents occur and divers die. Industrial accident analysis indicates a ratio of around 1 in 600 of fatalities to reportable accidents, and the British Hyperbaric Association indicates that approximately 3.5 times the number of divers are recompressed as are reported through the BSAC incident reporting system.
A four layered model for defense against human error has been described, which attributes error to three levels of latent failure and one of active failure, and posits that in general an accident is due to failure of all four levels of defence. These levels are:
The failures associated with these levels are labelled:
Unsafe actions can be categorised as errors or violations.
Errors are events where the outcome is not that which was intended or hoped for, or expected, and the precipitating action is unintentional.
Skill based errors refer to skills learned during training. These should generally be sufficiently well learned to be done without much conscious thought, as an almost automatic reaction to the circumstances. This makes them more reliable in a stressful situation, but also makes them more susceptible to performance loss with retention interval (when not practiced often enough). The rate of performance degradation depends on degree of overlearning, skill type and personal differences.
Other skill based errors involve incorrect technique. This can be a result of incorrect training or inadequate assessment and feedback during training, or learning bad habits after training. Skill based errors are prevented by practicing skills and ensuring that they are effective.
These are errors where the actions proceed according to intention, but prove to be inappropriate.
These errors occur when a situation is either not recognised, or misdiagnosed, or the diver has forgotten the correct reaction. These are all more probable if the stress level is already high unless the procedures have been well entrenched in memory by regular training and practice. Regular training with multiple scenarios and honest debriefings are recommended as mitigation for this class of error.
When a problem is not fully understood and learned procedures do not fit the situation the diver is more likely to make errors in problem solving.
The suitability of the process for making decisions depends to a large extent on the time available. Immediately life-threatening problems must be dealt with immediately, but other problems allow some time for considering the situation before reacting. As available time increases, the applicability of knowledge based processes and analytical processes also increases.
Errors of decision can be mitigated by ensuring that the diver has experienced a wide variety of reasonably probable scenarios, preferably as live simulations, or if this is not practicable, as mental exercises. Having considered the scenario and worked on problem solving provides a pattern of thought which can assist in solving similar problems in real incidents, and the diver is more likely to work on problem solving and less likely to panic. Instructors with varied, relevant and current diving experience are more likely to provide this sort of training experience.
Depth and visual perception errors are easily made underwater as we are not optimised for the environment, and lack of recent experience can aggravate the problem. This can easily lead to disorientation. Nitrogen narcosis can compound this effect and make reasoned judgements considerably more difficult below 30m, but this can be reduced by the use of helium. Colour discrimination is also diminished with depth and darkness, and colour-coding becomes an unreliable method of identifying equipment at the times when it is most critical and an error can be fatal.
Violations are events where the consequences are foreseeable, and the action is taken with knowledge of the possible consequences, and knowledge that the risk is not generally considered acceptable within the organisational environment of the agent.
Routine violations occur when policy violations are made due to a history of "getting away with it", so the perception develops that the risk is lower than it really is and the violation can become the norm. Accident analysis suggests that most accidents are caused by violations of teaching or agency recommendations.
Exceptional violations occur when the procedures or policies are intentionally violated without need or good cause.
Situational violations occur when the consequences of the violation are understood, but the violation is honestly assessed to be the best course of action available under the circumstances.
Some examples of violations:
Good communication and team or buddy skills are necessary to limit the risk of a recoverable incident deteriorating into an accident. A good team has more capacity to deal with an emergency than a solo diver in most circumstances, but in the absence of adequate team or buddy skills, a solo diver may be safer
Team and communications skills are relevant at the planning and preparation stages as well as in the water. A team must be familiar with each other's equipment, and the gas planning of all members must be compatible. Constructive debriefing after the dive can help the team members make the most of the learning opportunities of the dive.
There are a large range of circumstances, some within the control of the dier, some not, which can temporarily degrade the ability of the diver to dive safely. Some of these are purely physical, others have a psychological influence. Many are to some extent self-inflicted.
Divers should not be deterred by peer pressure from declining a dive when they are ill prepared, and they should not allow themselves to be pressured by service providers such as boat skippers and divemasters into accepting responsibility for the safety of another diver if they do not feel confident that both they and the other diver can deal adequately with any reasonably foreseeable problem that may occur during the dive.
Divers need to be aware of their surroundings as they operate in an alien environment and inattention can result in missing a critical cue which could have allowed early response to a problem. Any mental state which is likely to reduce the situational awareness of the diver will increase risk.
Diving while in a sub-optimal physical condition reduces the reserves available for dealing with a problem. Clearly not all divers are equal in their physical strength and fitness, but people learn to compensate for personal differences, and become accustomed to dealing with situations from their ground state. Any reduction in capacity from the normal status is likely to present unfamiliar challenges in a crisis, and may precipitate an unrecoverable chain of events, as normally adequate reactions are found to be insufficient, and fail to rectify the situation as expected.
Furthermore, some conditions such as injuries, dehydration or illness may physiologically predispose the diver to other conditions such as decompression sickness, hypothermia or barotraumas.
Personal strength and fitness vary amongst people. Furthermore, they vary with time for the same person, and although the underwater environment reduces the effects of gravity, there are other factors which can make activity more strenuous, such as viscous drag, increased work of breathing and adverse water movements.
Mental abilities also affect a diver's capacity to deal with unexpected situations. Two common factors influencing a diver's accurate and objective assessment of situations and their ability to cope with conditions are ignorance of the realities, and the tendency to overestimate personal competence which is most notable in those with the least ability to make an accurate judgement. Both of these factors can be mitigated by continued study and training. In effect, the best way to learn how to accurately judge competence in a skill set, is to be competent at those skills. In the absence of personal competence, the person must rely on the objective judgement and accurate feedback of instructors, supervisors and other persons in perceived positions of authority. Failure to provide this feedback is not a kindness, it is a dereliction of responsibility, as it may lead to potentially dangerous misjudgements of ability to seal with the rigour of the underwater environment, particularly where the specific circumstances are outside the experience of the diver.
The influence of experience on the accurate self-assessment of competence is not so clear cut. Some incompetent people are able to go through a wide range and depth of experience without discovering their incompetence or improving their skills.
Kruger and Dunning suggest that those with limited knowledge in a field suffer a double burden: "Not only do they reach mistaken conclusions and make regrettable errors, but their incompetence robs them of the ability to realize it."
Causal factors go beyond the operator, and extend to supervision.
In the context of recreational diving, supervision refers to dive leaders, dive guides, instructors, topside dive marshals and dive boat skippers, and in the club environment, also to the diving officer or training officer and experienced divers acting as mentors to less experienced divers. In the professional context, ir refers to the dive supervisor and other on-site management personnel.
Supervisors have a moral duty to their charges,and may have a legal duty as well. These duties may include giving guidance, providing training or learning opportunities, leadership by example and direction, information and motivation.
The duty to act as a good role model is important as although the supervisor may advise or instruct charges to do things in an appropriate way, it is what the role model actually does that often has the most lasting impression.
Poor technique and incorrect information passed on by a person in a supervisory position may perpetuate the use of unsafe or inefficient procedures. Failure to correct poor technique or skills has a similar effect, whether it is due to indifference or ignorance on the part of the supervisor.
A further manifestation of poor supervision may occur when the supervisor does not have the experience appropriate to the current environment.
Unsafe supervision can be split into four categories?
The influence of an organisation are less immediately obvious, and may be difficult to quantify. Many latent unsafe conditions originate with decision makers who are at a distance from the dive site and may be unaware of the full consequences of their directives. They may be biased by economic or political pressures and outdated knowledge and experience. Often decisions are made without full consideration of the possible consequences, not necessarily intentionally, and some unsafe policy decisions can not be avoided, so there should be measures to identify them and mitigate them before they have adverse consequences.