Safety

Question 1

Root Cause Analysis (RCA)

Answer 1

• focus of traditional accident analysis
• often converges to “human error” as the root cause
• system designers tend to ignore how humans interact with the system and punish humans when they make the system fail
• RCA is not a helpful model

Question 2

Reliability vs Safety

Answer 2

• Reliability: a measure of time between failures
• high reliability is neither necessary nor sufficient for safety

Question 3

Systems Theory

Answer 3

• systems have emergent properties that only exhibit themselves when the system is analyzed as a whole –> interaction of discrete components
• safety is an emergent property of a complex system
• emergent properties are controlled by imposing constraints on the interactions of system components

Question 4

STAMP

Answer 4

Systems Theoretic Accident Model & Processes
- safety is a control problem
- goal: apply controls that enforce safety constraints
- accidents (unintentional losses) happen when controls are inadequate or non-existent
- losses happen b/c component interactions and properties can lead to hazardous states

Question 5

STPA

Answer 5

Systems Theoretic Process Analysis
- STAMP-based hazard analysis process
1. Analyze system for hazards
2. Check if controls exist for each
3. Address problems in design
4. Prevent accidents