AAOM Handbook

SS.07 Identify Threat Characteristics

Context

The purpose of a Service Strategy is to identify and manage potential risks related to a process. Some of the common hazard types related to historic and probable risks are; • Stress - materials science subdivides this into catastrophic overstress that produces sudden failures (e.g. fracture), prolonged high stress that produces creep deformation and prolonged cyclic stress that produces fatigue failure. Similar types of results can be produced in people. Some examples of potential forms of stress are; physical/mechanical, thermal, voltage, radiation, mental, etc. • Chemical - in materials science terms this would be due to the (re)action of chemicals such as oxygen, acids, alkalis, but in a broader context could also include drugs, alcohol etc. • Wear - materials science subdivides wear into different mechanisms for the removal of material, e.g. abrasion, erosion, fretting etc. • Fouling - accumulation of material, e.g. silting, scaling, contamination etc. • Obsolescence - this is not a category used in materials science but reflects a type of hazard that arises from the loss of support for either the products or services of a process, e.g. due to innovation or competition, the imposition of constrictions to the process, e.g. imposition of new standards/laws, or the loss of essential resources for the continued operation of the process, loss of people, skills or knowledge, loss of parts sources etc. The above hazards may act either alone or in combination, and when acting in combination may produce an unwanted event that does not occur with either of the mechanisms absent, e.g. stress corrosion cracking, the result of a combination of highly alkaline environment and high physical stress levels. • A failure mechanism classification of 'Random' is sometimes applied to electronic components. However, this is a situation where the unwanted event is visible (the failure), but the underlying mechanism is usually not readily identifiable. Analysis of electronic failures most commonly reveals evidence of overstress, fatigue or chemical reaction. However, the evidence for the hazard release mechanism is usually masked by either the small scale of the issue, or by the packaging of the component, or by the damage caused by the failure. Overstress usually results in random catastrophic failure of electronic components. Fatigue is typically thermal or mechanical in origin, and hence evident in the operating environment (heat or vibration), and exhibits a wear out pattern. Chemical action is also typically evident in the operating environment and also exhibits a wear out pattern. Hence, a reasonable estimate can be made of the likely hazard release mechanisms applying to electronic components.

Some aspects to consider when trying to identify the types of hazards that may arise in or around a Process are: