system safety.pdf

A Brief Overview of Selected System Safety Analytical Approaches R.R. Mohr February 2002 2nd Edition 2 8671 System Safety System safety is… –A management doctrine, and –A family of analytical approaches that support that doctrine The analytical approaches are… –Mutually complementary –Divisible into two broad categories ? Types of analysis and ? Techniques of analysis 3 8671 The Categories of Analytical Approaches Types of analysis address Analytical Techniques address Where, When, or What How to analyze to analyze 4 8671 Some Analysis TYPES Preliminary Hazard Analysis (PHA) System Hazard Analysis (SHA) Subsystem Hazard Analysis (SSHA) Occupational Health Hazard Assessment (OHHA) Software Hazard Analysis Others Where? When? What? 5 8671 Some Analytical TECHNIQUES Preliminary Hazard Analysis* Failure Modes and Effects Analysis* Fault Tree Analysis* Event Tree Analysis* Cause-Consequence Analysis* Sneak Circuit Analysis Probabilistic Risk Assessment Digraph Analysis Hazard and Operability Study (HAZOP) Management Oversight and Risk Tree Analysis (MORT) Many others *Examples of these appear in the following pages. How? 68671 The Techniques are The techniques tend to be mutually complementary. Inductive Deductive Preliminary Hazard Analysis √ Failure Modes Effects Analysis √ Fault Tree Analysis √ Event Tree Analysis √ Cause-Consequence Analysis √ Sneak Circuit Analysis √ Probabilistic Risk Assessment √ Digraph Analysis √ Hazard and Operability Study (HAZOP) √ Management Oversight and Risk Tree Analysis √ 7 8671 Comments on a Few Techniques What they are… How they function… Their advantages… Their shortcomings… 8 8671 Preliminary Hazard Analysis WHAT: Line-item listing of “all” system hazards, with subjective evaluations of severity/ probability/risk for each. HOW: Engineering judgment/intuitive skills/checklists. ADVANTAGES: Provides inventory of “all” system hazards/risks. DISADVANTAGES: Incomplete. Ignores combined hazard effects. Does not sum risk. Non-qu