Chapter 2 Preliminary Hazard Analysis

Chapter 2 Preliminary Hazard Analysis - Sverdrup R R Mohr...

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Unformatted text preview: Sverdrup R. R. Mohr September 1993 5 th Edition REVISED for UC System Safety I 1 PRELIMINARY HAZARD ANALYSIS 2 BACKGROUND — THE PROBLEM… PREMISE: You own, operate, design, or are responsible for a system/process/activity. It may be small or large, simple or complex. It may no longer exist, be presently in operation, or be a future plan. QUESTIONS: 1. What are the associated Hazards and their Risks? 2. Is it “safe?” Are the Risks under acceptable control? APPROACH: Do a Hazard Analysis. Identify the Hazards. Assess their Risks. There are many Types and Techniques of analysis. Examples: • Preliminary Hazard Analysis (PHA) • Energy Flow / Barrier Analysis • Failure Modes and Effects Analysis (FMEA) • Fault Tree Analysis (FTA) • System Hazard Analysis (SHA) • Subsystem Hazard Analysis (SSHA) • Operating & Support Hazard Analysis (O&SHA) • Occupational Health Hazard Analysis (OHHA) • Software Hazard Analysis • …many others... 3 SOME DEFINITIONS… • PRELIMINARY : (adj.) coming before and usually forming a necessary prelude to something. (The PHA can be done in the design or pre-operation phase, or it can be the first analysis done on a mature system.) • HAZARD : (n.) an activity or condition which poses threat of loss or harm (“A condition that is prerequisite to a mishap”—MIL-STD-882C/¶3.2.4) • ANALYSIS : (n.) an examination of the elements of a system, separation of a whole into its component parts. • PHA = An early or initial system safety study of potential loss events. It is a list or inventory (PHL) of system hazards and includes qualitative, not quantitative, assessments of risk for the individual hazards. • mishap: (n.) an undesired loss event • threat: (n.) a potential for loss • target: (n.) a thing having worth threatened by a hazard • risk: (n.) long-term rate of loss—the product of loss severity and loss probability • severity: (n.) how bad? • probability: (n.) how likely? — how often? A Preliminary Hazard List (PHL) is simply a line item inventory of system hazards, with no evaluation of Probability/Severity/ Risk. 4 PHA USES… A well done Preliminary Hazard Analysis: • Identifies hazards and their potential consequences. • Assesses risk to develop an expected loss rate. Risk = Probability x Severity (R = P x S) = (loss event / unit of time) ($ lost / loss event) = $ lost / unit of time • Guides cost-effective resource deployment. If you know areas of weakness (unacceptable risk), you know where to concentrate resources and problem-solving efforts. The PHA is a line-item inventory of “ all ” system Hazards and their risks. It may be carried out at any point in system life cycle (preferably beginning with design concept formulation.) 5 5. Do the countermeasures introduce NEW hazards? . . . or, DEVELOP COUNTERMEASURES AND REEVALUATE ACCEPT (WAIVER) ABANDON OR AND AAA 1. Identify TARGETS to be protected: Preliminary Hazard Analysis Process Flow 6. Do the countermeasures...
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Chapter 2 Preliminary Hazard Analysis - Sverdrup R R Mohr...

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