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Introduction Risk expresses the likelihood that the harm from a particular hazard is realized, and is a function of hazard and exposure. More formally it can be defined as: ¡°the possibility that a harmful event (death, injury or loss) arising from exposure to a chemical or physical agent may occur under specific conditions; or alternatively, the expected frequency of occurrence of a harmful event (death, injury or loss) arising from exposure to a chemical or physical agent under specific conditions¡± [1]. Reliability can be defined as: ¡°the probability that an item is able to perform a required function under stated conditions for a stated period of time¡¯ [2]. Human perception, behaviour and reliability A risk assessment is nothing than a careful examination of what, in terms of the work activity, could cause harm to people. This allows the person carrying it out to weigh up whether sufficient and suitable precautions have been taken or whether more should be done to prevent harm. The aim is to make sure that no one gets injured or becomes ill. Accidents and ill health can devastate lives, and affect business if output is lost. It is a legal requirement to access the risks in the workplace. Risk assessment answers the following questions: 1. What are the hazards? 2. What are the potential consequences and effects and these acceptable? 3. What is the likelihood of these consequences/effects occurring? 4. Are the safeguards and controls adequate to maintain the risk as acceptable? The concept of probability is fundamental to the assessment of risk, and the use of statistical database has become a prerequisite. A review of the literature suggests that the process of risk assessment is usually broken down into three stages: (i) Risk identification; (ii) Risk estimation; and (iii) Risk evaluation. Risk management is the practice of managing the resources of the operation in such a way to maintain an acceptable level of risk. This in turn should generate a corresponding level of return that will allow the goals of the operation and management to be achieved. Humans play two roles in risk management. They are a source of risk and they are a resource to mitigate, manage and prosper from risk. Human factors are a broad field and organizations in the past have viewed it in the past as being too complex or difficult to do anything about. The Health and Safety Executive¡¯s definition of human factors, given in HS (G) 48, is: ¡°Environmental, organizational and job factors, and human and individual characteristics which influence behavior at work in a way which can affect health and safety¡± [3]. Human factors focus on human beings and their interaction with products, equipment, facilities, procedures, and environments used in work and every-day living. Investigations following major accidents and incidents have shown that ¡°human factors¡±, in this case resulting in human errors, have frequently played a significant role. ¡°In many domains, human error is evoked as the major contributing factor or cause of accidents. For example, surveys of anaesthesia incidents in the operating room have attributed 70% to the human element¡± [4]. These errors have often occurred as a result of inaccurate perception of a particular risk or combination of risks. To some people the term human error has a connotation of blame or cause. A much more productive approach is to consider human error simply as an event whose cause can be investigated. ¡°Numerous definitions have been proposed for human error, but the following embodies the essence of most of them: Human error is an inappropriate or undesirable human decision or behavior that reduces, or has the potential for reducing, effectiveness, safety, or system performance¡±[5]. Taking risks is a normal part of human behavior but the perception of a particular risk, and the willingness to accept that risk, will vary from one employee to another. The importance of human behavior to the safe and reliable operations is widely accepted. However, the human factor tends to get less attention than technical aspects of safety and reliability. This may be due to a lack of familiarity with available methods and knowledge. Human reliability is inextricably linked to human error and has been used to refer to a methodology, a theoretical concept, and a measure. As a methodology, human reliability is a procedure for conducting a quantitative analysis to predict the likelihood of human error. As a theoretical concept, human reliability implies an explanation of how errors are produced. As a measure, human reliability is simply the probability of successful performance of a task or an element of a task by a human. According to Andrews, J.
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