Process Safety, Health, Environment and Risk Management
What the exam tests
Hazard identification (HAZID, HAZOP), risk ranking (LOPA, SIL), relief and flare systems, flammability and toxicity, dispersion, environmental control and regulatory compliance.
Core rules
- HAZOP applies guide words - no, more, less, reverse, as well as, part of, other than - to nodes defined by design intent.
- LOPA: mitigated frequency = initiating frequency × product of PFDs of independent protection layers; compare with the tolerable risk target.
- SIL from PFD: SIL 1 = 10⁻¹–10⁻², SIL 2 = 10⁻²–10⁻³, SIL 3 = 10⁻³–10⁻⁴.
- Flammability: LFL/UFL in air, inerting below the limiting oxygen concentration, flash point versus autoignition temperature.
- Relief devices: API 520/521 sizing, set pressure at or below MAWP, back-pressure limits, fire and two-phase cases.
- Exposure limits: TLV-TWA over 8 h, STEL over 15 min, IDLH for escape decisions.
Worked example
An initiating event has frequency 0.1/yr. Protection layers are a BPCS loop with PFD 0.1, an operator response to alarm with PFD 0.1, and a pressure relief valve with PFD 0.01. Mitigated frequency = 0.1 × 0.1 × 0.1 × 0.01 = 1×10⁻⁵/yr, exactly meeting a 10⁻⁵/yr target. Adding an independent high-pressure trip with PFD 0.01 takes it to 1×10⁻⁷/yr; shared sensors, however, cannot be credited twice as separate layers.
Traps
- Counting one transmitter as both BPCS and SIS protection.
- Using a 25 °C LFL for a hot stream; LFL widens as temperature rises.
- Setting relief pressure above MAWP.
- Confusing TLV-TWA with STEL or ceiling limits.
- Ignoring domino effects and plot layout when assessing risk.