Hazard Analysis Sidebar

Hazard analysis can be defined as a process for utilizing all known safety data on a system (1) to identify all possible hazards, (2) to develop controls that mitigate or eliminate the hazards, and (3) to verify that selected controls actually will reduce the dangers associated with the hazards to an acceptable level. When developing and documenting a system for the evaluation of identified hazards, the rail transit agency should address the following issues, at a minimum:

• Hazard severity.  Hazard severity categories are defined to provide a qualitative measure of the worst credible mishap resulting from personnel error; environmental conditions; design inadequacies; procedural deficiencies; or system, subsystem or component failure or malfunction as shown in the Table below.

HAZARD SEVERITY CATEGORIES

• Hazard probability.  The probability that a hazard will be created during the planned life expectancy of the system can be described in potential occurrences per unit of time, events, population, items, or activity.  Assigning a quantitative hazard probability to a potential design or procedural hazard is generally not possible early in the design process.  A qualitative hazard probability may be derived from research, analysis, and evaluation of historical safety data from similar systems.  Supporting rationale for assigning a hazard probability shall be documented in hazard analysis reports.  An example of a qualitative hazard probability ranking is shown in the Table on the next page.