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Introduction: A Review of System Accident Criteria
Understanding the concept of a system accident is important. System accidents may not be the result of a simple single failure, a behavior deviation or a single error, although simple adverse events still do occur. System accidents are the result of many initiators, contributors and combinations of errors, failures and malfunctions. It is not easy to see the system picture or to connect the dots while evaluating multi-contributors within adverse events, and identifying initial events and subsequent events to the final outcome. System risks can be unique, undetectable, not perceived, not apparent and unusual. A novice investigator, analyst or outside party can question the credibility of such diverse events.
When investigating system accidents, a typical question comes to mind: Why was the accident not anticipated? Thinking past simple linear logic is needed, such as a single failure and effect, or cause, single hazard and effect. System accidents can be predicted by inverting design logic, and by considering "what if" logic. Anything that can have an adverse effect on the system must be considered: a poor decision, poor assumption, error in design, calculation error, specification development problem, procedure development error, deviation, management oversight, poor resource planning, cultural influences, behavior, attitude, analysis error or poor judgment.
Designing Accidents
Determining potential event propagation through a complex system can involve extensive analysis. Specific system safety methods, such as software hazard analysis, human interface analysis, scenario analysis and modeling techniques, can be applied to determine system risks, which are the inappropriate interaction of software, human, machine and environment. All of these factors should be addressed when conducting hazard analysis and accident investigation. Consider that hazard analysis is the inverse of accident investigation. An analyst should be able to design prospective accidents, which are potential system accidents and system risks. In order to design a robust system, all the potential accidents associated with the system must be determined.
The objective is to understand the risks associated with the system. Risk knowledge can be gained reactively by conducting accident or incident investigations. It can also be gained proactively by conducting hazard recognition, by considering that hazards, or groups of hazards that define risk, can be identified by inspection, observation, safety review and hazard analysis. A so-called "safe system" is one in which all risks have been identified, eliminated or controlled to an acceptable level throughout the system's life-cycle.
To apply best practices in system safety, the analyst has to be able to identify all potential safety-related risks (system accidents). Thinking is not confined to the logic of a single hazard and linear cause and effect, but extends to multi-causal progression. The analysts should think in terms of being able to design potential accidents, which are unplanned dynamic adverse processes.
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