Hazard Analysis - Hazards and Risk

Hazards and Risk

A hazard is defined in FAA Order 8040.4 as a "Condition, event, or circumstance that could lead to or contribute to an unplanned or undesirable event." Seldom does a single hazard cause an accident. More often, an accident occurs as the result of a sequence of causes. A hazard analysis will consider system state, for example operating environment, as well as failures or malfunctions.

While in some cases safety risk can be eliminated, in most cases a certain degree of safety risk must be accepted. In order to quantify expected accident costs before the fact, the potential consequences of an accident, and the probability of occurrence must be considered. Assessment of risk is made by combining the severity of consequence with the likelihood of occurrence in a matrix. Risks that fall into the "unacceptable" category (e.g., high severity and high probability) must be mitigated by some means to reduce the level of safety risk.

IEEE STD-1228-1994 Software Safety Plans prescribes industry best practices for conducting software safety hazard analyses to help ensure safety requirements and attributes are defined and specified for inclusion in software that commands, controls or monitors critical functions. When software is involved in a system, the development and design assurance of that software is often governed by DO-178B. The severity of consequence identified by the hazard analysis establishes the criticality level of the software. Software criticality levels range from A to E, corresponding to severities of Catastrophic to No Safety Effect. Higher levels of rigor are required for level A and B software and corresponding functional tasks and work products is the system safety domain are used as objective evidence of meeting safety criteria and requirements.

Recently a leading edge commercial standard was promulgated based on decades of proven system safety processes in DoD and NASA. ANSI/GEIA-STD-0010-2009 (Standard Best Practices for System Safety Program Development and Execution) is a demilitarized commercial best practice that uses proven hostistic, comprehensive and tailorable approaches for hazard prevention, elimination and control. It is centered around the hazard analysis and functional based safety process.

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