HAZOP
- Fully qualitative risk assessment
LOPA
- Semi quantitative risk assessment for individual failure modes in a system
How to
- Identify Hazardous Scenario:
Example → Overpressure of a reactor leading to rupture. - Determine Initiating Event Frequency (IEF):
How often could the initiating event (e.g., valve failure) happen? → e.g., once every 1,000 years (1×10⁻³ per year) - Identify Independent Protection Layers (IPLs):
IPLs are safeguards that work independently to prevent or mitigate the consequence. Examples:- Pressure relief valve (PRV)
- High-pressure alarm with operator action
- Emergency shutdown system (ESD)
- Assign Probability of Failure on Demand (PFD) to each IPL:
→ How likely is that safeguard to fail when needed? Example: 1×10⁻² - Calculate Residual Risk:
→ Multiply initiating event frequency by the PFDs of the IPLs
→ Compare residual risk to company or industry tolerable risk criteria.