SYSTEM SAFETY

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SYSTEM SAFETY

• IENG 331 Safety Engineering
• Carter J. Kerk, PhD, PE, CSP, CPE
• Industrial Engineering Department
• South Dakota School of Mines

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System Safety

• Reading Assignment
• Brauer, Chapter 36
• Exercise 1, p. 681
• Review Questions p. 681-3
• Odds

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What is System Safety?

• Accident Prevention!
• Technical / Managerial skills applied to
  systematic, pro-active identification and control
  of hazards throughout the life cycle of a
  system/project/product
• System Safety Society
• http//www.system-safety.org/

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Life Cycle

• Conceptual
• Definition
• Development
• Production
• Deployment
• Disposition

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Example Severity Categories
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Example Probability Categories
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Risk Assessment Matrix
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Evaluation and Use of Risk Matrix
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DOD Approach to System Safety

• MIL-STD-882D
• Provides a framework for applying system safety
  in any organization
• http//www.system-safety.org/
• Products and Services
• Technical Resources
• Links
• Fault Tree Central
• Jacobs Sverdrup

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System Safety Techniques

• Preliminary Hazard Analysis
• System Hazard Analysis
• Subsystem Hazard Analysis
• Operating Support Hazard Analysis
• Fault Hazard Analysis
• Failure Mode Effects Analysis (FMEA)
• Fault-Tree Analysis (FTA)
• Software Hazard Analysis
• Sneak Circuit Analysis
• Simultaneous Timed Events Plotting Analysis
  (STEP)
• Hazard Totem Pole
• Management Oversight and Risk Tree (MORT)

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System Safety Products (Stephans)

• System Safety Program Plan (SSPP)
• Preliminary Hazard Analysis (PHA)
• Subsystem Hazard Analysis (SSHA)
• System Hazard Analysis (SHA)
• Operating Hazard Analysis (OHA)
• From System Safety for the 21st Century,
  Richard A. Stephans, Wiley Sons, 2004.

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Analytical Techniques (Stephans)

• Failure Modes Effects Analysis (FMEA)
• Fault Tree Analysis (FTA)
• Energy Trace Barrier Analysis (ETBA)
• Management Oversight Risk Tree (MORT)
• Project Evaluation Tree (PET)
• Change Analysis
• Common Cause Analysis

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Preliminary Hazard Analysis (PHA)

• ID and evaluate hazards in the early stages of
  the design process
• Has gained broader use
• Hazard identification is the most important
  safety process in that, if it fails, all other
  processes are likely to be ineffective

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Typical PHA

• A hazard description, sometimes called a hazard
  scenario
• A description of the task, operation, system, or
  product being analyzed
• Which exposures are the subject of the analysis
• People (employees, the public) Facility Product
  or equipment loss Operation downtime
  Environmental damage
• The probability interval to be considered unit
  of time or activity events units produced life
  cycle
• A numerical or alpha indicator for the occurrence
  probability
• A risk assessment code, using the RA matrix
• Remedial action to be taken, if risk reduction is
  needed

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PHA Steps

1. Identify known hazards
2. Determine the cause(s) of the hazards
3. Determine the effects of the hazards
4. Determine the probability that an accident will
   be caused by a hazard
5. Establish initial design and procedural
   requirements to eliminate or control hazards

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System Hazard Analysis (SHA)

• As a project is developed and more detailed
  design data are available, a SHA and SSHA may be
  conducted
• Provides more detailed, in-depth risk assessment
  information
• FMEA
• FTA

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Fault-Tree Analysis

• Developed in 1962 at Bell Telephone Labs
• Uses Boolean Logic to evaluate events
• Build a tree structure

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Fault Tree Analysis

• At the top is a principal or undesired event
• Broken down into contributing factors
• Further subdivided into event causes
• Preliminary hazard analyses or other analyses may
  identify major undesirable events
• After the tree is constructed, qualitative or
  quantitative analysis is performed

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Symbols commonly used in FTA.
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Portable electric drill, not double-insulated.
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System Safety

• Reading Assignment
• Brauer, Chapter 36
• Exercise 1, p. 681
• Review Questions p. 681-3
• Odds