The influence of physical, cognitive and behavioral characteristics of divers on safety
Human factors are the physical or cognitive properties of individuals, or social behavior which is specific to humans, and which 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.
Human factors include both the non-technical skills that enhance safety and the non-technical factors that contribute to undesirable incidents that put the diver at risk.
[Safety is] An active, adaptive process which involves making sense of the task in the context of the environment to successfully achieve explicit and implied goals, with the expectation that no harm or damage will occur. – G. Lock, 2022
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 professional scuba diving is due to these factors. The study also concluded that it would be impossible to eliminate absolutely all minor contraindications for scuba diving, as this would result in overwhelming bureaucracy and would bring all diving to a halt.
Human factors engineering (HFE), also known as human factors and ergonomics, is the application of psychological and physiological principles to the engineering and design of equipment, procedures, processes, and systems. Primary goals of human factors engineering are to reduce human error, increase productivity and system availability, and enhance safety, health and comfort with a specific focus on the interaction between the human and equipment.
Factors influencing the performance of a diving team.
A diving team may be considered as a system which is influenced by equipment, environment, procedures, organisation, individuals, and interactions. There are considerations associated with each of these factors relating specifically to diving. The diving environment and equipment are external influences with which the diver interacts, and their effects are partly independent of human factors, but procedures, organisation and individuals are primarily human factors.
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 underwater vehicles (ROUVs ot ROVs) and autonomous underwater vehicles (AUVs) 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 some 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. Legal constraints are more necessary to protect the employee under these conditions, and are applied with variable levels of effectiveness. 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.
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.
 ;templatestyles src="Template:Visible anchor/styles.css" / ;Human factors engineering has also been defined as "the science of people at work". It is mainly concerned with understanding human capabilities, and applying that knowledge to the design of tools, equipment, systems, and processes. Input from various disciplines may be used and the field is considered a mix of engineering and psychology, with four main goals: enhancing safety, comfort and productivity, and reducing and managing errors. Human factors have also been equated to non-technical skills, the interpersonal skills, which include communication skills, leadership skills, team-work skills, decision-making skills, and situation-awareness skills.
 ;templatestyles src="Template:Visible anchor/styles.css" / ;Non-technical skills can be defined as "interpersonal skills which include: communication skills; leadership skills; team-work skills; decision-making skills; and situation-awareness skills." They do not include the technical skills required to get the job done. However, they complement these technical skills making them more efficient and effective:
Situation awareness is the continuous cycle of perception, comprehension, and prediction of the near future developing situation. It is a critical foundation for successful decision-making where conditions are evolving and there is little room for error. Attention is a limited resource and must be shared among the current situations, with due consideration of their importance. The part of the diver's attention focused on physical skills is high with new skills, but decreases with experience as the skills become internalised and more automatic, making more attention available for monitoring the environment and the dive, giving a broader awareness of the situation. Focus of attention may change with noticing a hazard, an interesting event, a need to make a decision, or a distraction, reducing the attention available for other matters. In some situations the combined attention of team members can significantly broaden the overall awareness of a team. Factors of delegated responsibility and team redundancy are relevant to achieving a good balance between excessive overlap and gaps in awareness.
Diver communications are a safety-critical skill for both professional and recreational divers, as a large number of emergency procedures depend on conveying the problem to the team member who is expected to help. Voice communications follow a specific protocol to minimise confusion, and recreational divers communicate mostly by hand signals, which must be intelligible to the dive buddy to avoid inappropriate response.
Communication between divers and between surface personnel and divers is imperfect at best, as a consequence of the physical characteristics of water. This prevents divers from performing at their full potential. Voice communication is the most generally useful format underwater, as visual forms are more affected by visibility, and written communication and signing are relatively slow and restricted by diving equipment.
Decision making is an essential component of diving operations from the dive planning stage through preparation, during the normal conduct of the dive, and particularly where contingencies, emergencies, and rescues may occur. Decisions are made based on information provided by communication and personal observation of the environment and developing situation.
Effective teamwork requires the members of the team to each be familiar with, and competent at, their allotted tasks, to communicate effectively with each other, and to be able to trust that the others will perform their tasks and communicate all necessary information at the appropriate times. In a commercial diving team this is facilitated by explicit and familiar job descriptions for each member, and the use of standard procedures, so that a team assembled from strangers can start work at a reasonable level of effectiveness.
Effects of human factors on diving safety.
Two ways of analysing the effects of human behaviour on safety are applied. One attempts to identify who was involved in a deviation from the recommended procedure, and the other attempts to identify why deviation from the recommended procedure seemed to be a good idea at the time. The first approach tends to apportion blame, on the assumption that the recommended procedure was, in fact, optimum, and the other aims to learn why the recommended procedure was not considered appropriate at the time. This second approach has been shown to be more productive of learning from the experience, but can only work within a just culture in which the people involved feel safe to discuss the details.
Categories of error.
Reason categorizes how errors occur by analysing what causes a plan to fail. 
Levels of performance.
These error categories relate to three levels of human performance:
Error mechanisms.
Three error mechanisms can be defined which correlate the error categories with human performance levels:
Violations.
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.
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 to reduce the stress. When the actions are successful the