System Safety Engineering

System safety is the use of a combination of management and systems engineering techniques that is integrated into the evaluation and reduction of risk in a system, operation, or process. The overall purpose is to identify hazards, eliminate or control them, and mitigate any remaining risk. It should be a comprehensive approach to managing risk. Many techniques have been developed for this purpose. A number of these are listed in the following:

  • • Time loss analysis: Time loss analysis evaluates emergency response performance.
  • • Human factor analysis: Human factor analysis identifies elements that influence task performance, focusing on operability, work environment, and management elements.
  • • Integrated accident event matrix: An integrated accident event matrix illustrates the time-based interaction between the victim and other key personnel prior to the accident and between the emergency responders and the victim after the accident.
  • • Failure modes and effects analysis: This method is most often used in the hazard analysis of systems and subsystems; it is primarily concerned with evaluating single-point failures, probability of accidents or occurrences, and reliability of systems and subsystems.
  • • Software hazard analysis: This analytic technique is used to locate software- based failures that could have contributed to an accident.
  • • Common cause failure analysis: Common cause failure analysis evaluates multiple failures that may be caused by a single event shared by multiple components.
  • • Sneak circuit analysis: A sneak circuit is an unanticipated energy path that can enable a failure, prevent a wanted function, or produce a mistiming of system functions. Sneak circuit analysis is mainly performed on electronic circuitry, but it can also be used in situations involving hydraulic, pneumatic, mechanical, and software systems.
  • • Materials and structural analysis: Materials and structural analysis is used to test and analyze physical evidence.
  • • Design criteria analysis: This method involves the systematic review of standards, codes, design specifications, procedures, and policies relevant to the accident.
  • • Accident reconstruction: Although not widely used in accident investigations, accident reconstruction may be useful when accident scenes yield sketchy, inconclusive evidence.

Scientific modeling: Scientific modeling models the behavior of a physical process or phenomenon. The methods, which range from simple hand calculations to complex and highly specialized computer models, cover a wide spectrum of physical processes (e.g., nuclear criticality, atmospheric dispersion, groundwater and surface water transport/dispersion, nuclear reactor physics, fire modeling, chemical reaction modeling, explosive modeling).

These more sophisticated analyses become the realm of science and engineering or those having specific training or expertise and should not be undertaken lightly or as a cure to all existing problems. This is an occasion when complexity becomes more than simple occupational safety and health (OSH) and usually requires the use of outside expertise.

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