PRELIMINARY HAZARD ANALYSIS (PHA)
Bayu Nurwinanto
DESCRIPTION
A preliminary hazard analysis (PHA) produces a line item tabular inventory of non-trivial system hazards, and assessment of their remaining risk after countermeasures have been imposed. this inventory includes qualitative, not quantitative, assessments of risks. also often included is a tabular listing of countermeasures with a qualitative delineation of their predicted effectiveness. A PHA is a early or initial system safety study of system hazards.
It is important to remember that each analytical technique discussed in this article complements (rather than supplants) the others. this is so because each technique attacks the system to be analyzed differently some are top-down, other are bottom-up.
PROCEDURES
- Identify resources of value to be protected, such as personnel, facilities, equipment, productivity, mission or test objectives, environment, etc.These resources are potential tergets.
- Identify and observe the levels of acceptable risks that have been predetermined and approved by management or the client. These limits may be the risk matrix boundaries defined in a risk assessment matrix.
- Define the extent of the system to be assessed. define the physical boundaries and operating phases (Such as shakedown, startup, standard operating, emergency shutdown, maintenance, deactivation, etc). state other assumptions such as whether the assessment is based on an as-built or as designed system, or whether current installed countermeasures will be considered.
- Detect and confirm hazards to the system. Identify the targets threatened by each hazard. A hazard is defined as an activity or circumstance posing potential loss or harm to a target and is a condition required for an undesired loss event. Hazards should be distinguished from consequences and considered in terms of a source (Hazard), mechanism (process) and outcome (Consequence). A team approach to identifying hazards, such as brainstorming, is recommended over a single analyst. If schedule and resource restraints are considerations, then a proficient engineer with knowledge of the system should identify the hazards, but that assessment should be reviewed by a peer.
- Assess worst-credible case (not the worst-conceivable case) severity and probability for each hazard and target combination.
- Assess risk for each hazard using a risk assessment matrix. the matrix should be consistent with the established probability interval and force or fleet size for assessment.
- Categorize each identified risk as acceptable or unacceptable, or develop countermeasures for the risk, if unacceptable.
- Select countermeasures in the following descending priority order to optimize effectiveness: (1) design change, (2) engineered safety system (active), (3) safety devices (passive), (4) warning devices and (5) procedures and training.
- Re-evaluate the risk with the new countermeasure installed.
- If countermeasures are developed, determine whether they introduce new hazards or intolerably diminish system performance. If added hazards or degraded performance are unacceptable, determine new countermeasures and reevaluate the risk.
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| Figure-Preliminary hazard analysis process flowchart |
