Mishap risk

The MIL-STD-882D standard practice describes a system safety approach that is useful in the management of Environmental, Health of Safety mishap risks encountered in the life cycle of Department of Defense (DOD) systems, subsystems, equipment, and facilities. To paraphrase the standard, mishap risk must be identified, evaluated, and mitigated to a level acceptable (as defined by the system user or customer) to the appropriate authority, and compliant with federal laws and related rules. Further, residual mishap risk associated with an individual system must be reported to and accepted by the appropriate authority. These basic requirements are fundamental to system safety. 

Require an assessment of mishap risk be presented as part of any program evaluation or review, and as a part of all decisionmaking milestones. 

This undesired event can result from personnel error, environmental conditions, design inadequacies, and procedural deficiencies. It can also relate to system, subsystem, or component failure or malfunction. System safety methods require acceptance of some level of mishap risk, determine mishap probability, establish severity threshold, and create appropriate documentation procedures (Table 1.25). 

Different organizations have variations for the appUcation of system safety methods and procedures. Military Standard 882 (MIL-STD 882) addresses an approach for mishaps and risks encountered during the development, testing, production, use, and disposal of systems, subsystems, equipment, and facilities. Those engaged in military acquisitions have used the procedures in MIL-STD 882 for a long time to identify, evaluate, and mitigate mishap risks to an acceptable level. 

System safety the application of engineering and management principles, criteria, and techniques to achieve acceptable mishap risk, within the constraints of operational effectiveness and suitability, time, and cost, throughout all phases of the system life cycle. 

Five examples of risk assessment matrices follow. First, an adaptation is shown in Table 7 of the Mishap risk categories and mishap acceptance levels as in the working draft of MIL-STD-882E, the Department of Defense Standard Practice For System Safety. A comment in Appendix A of 882E is pertinent here A mishap assessment matrix allows classification by mishap severity and mishap probability and assists in managing the decision-making to achieve the necessary risk elimination or reduction to an acceptable level. ... 

Element 3—risk assessment. For each identified hazard, the mishap severity and probability or frequency are estabhshed. A mishap risk assessment matrix is used... 

In 882E, Appendix A provides Guidance For Implementation Of A System Safety Effort, It runs 43 pages long. It is good reading. Item A.4.1.2.1.3 speaks of Mishap risk assessment matrix and scaling as follows ... 

To emphasize It is not necessary to adopt a complicated and costly risk assessment system when the situations at hand can be resolved with a qualitative (subjective) and simpler system. Item A.7 in Appendix A, Example Mishap Risk Assessment Matrices, is truly educational. In several places in this book, readers are advised to develop risk assessment matrices suitable to the hazards and risks with which they deal and to keep them simple. That idea is supported in A.7, where it is said that ... 

Mishap risk assessment matrices should be tailored to each system or class of systems based on the expected range of severity of potential mishaps and the range of probability or frequency of these mishaps. 

Reduce mishap risk through design alteration. 

If unable to eliminate or adequately mitigate the hazard through design or ESFs, reduce mishap risk by using protective safety features or devices. 

For hazards that cannot be eliminated, consideration is to be given to safety devices that will minimize mishap risk (e.g., interlocks, redundancy, fail safe design, system protection, fire suppression, and protective measures such as clothing, equipment, devices, and procedures). 

Safe design attempts to achieve an acceptable mishap risk through a systematic application of guidance obtained from standards, specifications, regulations, handbooks, checklists, and other sources. Safe-design needs derive from the selected parameters and associated acc eptanc e criteria. The life cycle of systems includes design, research, development, evaluation, production, inventory, operational support, and disposal. Probabilistic fault tolerance adds redundancy to equipment and systems. 

Design and develop a system presenting minimal mishap risk... 

Since many systems and activities involve hazard sources that cannot be eliminated, zero mishap risk is often not possible. Therefore, the application of system safety becomes a necessity in order to reduce the likelihood of mishaps, thereby avoiding deaths, injuries, losses, and lawsuits. Safety must be designed intentionally and intelligently into the system design or system fabric it cannot be left to chance or forced-in after the system is built. If the hazards in a system are not known, understood, and controlled, the potential mishap risk may be unacceptable, with the result being the occurrence of many mishaps. 

We live in a world surrounded by hazards and potential mishap risk hazards, mishaps, and risks are a reality of daily life. One of the major reasons for... 

Systems have become a necessity for modern living, and each system spawns its own set of potential mishap risks. Systems have a trait of failing, malfunctioning, and/or being erroneously operated. System safety engineering is the... 

Presents an acceptable level of mishap risk under abnormal operation... 

Example 1 The pilot decided to abort the intended mission and return to base after one of the two engines on the aircraft failed. In this case, aircraft safety is reduced, and preestablished contingency plans require the pilot to terminate the mission rather than expose the aircraft to higher mishap risk and loss of the aircraft. In this situation, the pilot is the authorized entity. 

System safety is a mishap risk management process, whereby mishap risk is identified through hazards, and if the risk does not meet the established level of acceptability, design action is taken to reduce the risk to an acceptable level. For various reasons, it is often impossible to eliminate mishap risk in many systems. System safety should be involved in establishing the criteria and constraints for acceptable risk for system programs. Military standard (MIL-STD)-882 identifies the criteria for four levels of risk high, serious, medium, and low, each of which is accepted by a different level of decision authority. 

Stating that mishap risk for a particular hazard is acceptable can be misleading if not thoroughly defined. If a high-ranking authority accepts a high-risk hazard because a lower-ranking person cannot, does that really make the system suitably safe, or does it discount the risk It may be more ethical and cost-effective to state that the potential mishap risk presented by a particular... 

See As Low as Reasonably Practicable (ALARP), Hazard, Mishap Risk, Residual Risk, and Risk for additional related information. 

System safety is generally involved in the acceptance test process. Safety may review test results to ensure safety concerns are adequately resolved and that design safety requirements are met. Safety may also review acceptance test procedures to ensure that no test hazards exist and that the potential mishap risk of a test is acceptable. It may be necessary for safety to be present as a witness to the conduct of certain acceptance tests, generally on safety-critical components. 

In system safety, the terms accident and mishap are synonymous, and no distinction should be made between the two terms. Under the definition of a mishap, MIL-STD-882C equates accident and mishap as synonymous. In system safety parlance, the term mishap has become the preferred term (rather than accident) primarily to maintain a consistency of terminology when discussing mishap risk. The term incident is related to accident and mishap but has a shghtly different meaning. 

An AUR is a completely assembled ammunition intended for delivery to a target or configured to accomplish its intended mission. This term is identical to the term all-up-weapon. System safety is concerned with weapons and munitions in the final AUR configuration (i.e., as a system). The AUR configuration provides a system architecture and design that can be analyzed for hazards and potential mishap risk. 

System safety performs HAs and risk assessment on system architectures in order to identify hazards and potential mishap risk. A system hazard analysis (SHA) is essentially an HA of the overall system architecture, including its components and functions. System safety influences system architecture design by requiring the implementation of safety design features, such as redundancy, to reduce the overall mishap risk potential. 

The most critical question that must be answered is, will the COTS item contribute to any system hazards when integrated into the new system The COTS item must be an integral part of all HAs performed on the system to determine if it can contribute to causing any significant hazards. This means that design information, reliability information, and previous HAs data must be available. If this information is not available to the safety analyst, then a comprehensive HA of the system cannot be performed, and total system mishap risk is not fully known. 

The compliance-based safety approach is effective and useful however, its major drawback is that it does not ensure that all system potential mishap risk is reduced to the lowest effective value practical. Prescriptive safety provides a known basic level of safety, but it may fall short if further safety features are necessary for a particular system. Prescribed safety requirements only address a known set of hazards. Even for a compliance-based safety program, it is still necessary to perform HA to ensure that all hazards have been identified and the risk mitigated to the lowest level practical. 

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