A process safety event, or PSE, is a term API defines for an actual losses of primary containment, defined under API Recommended Practice 754. It covers any unplanned or uncontrolled release, including non-toxic or non-flammable material, that causes injury, community impact, property damage, or release above a threshold quantity. Built for refining and petrochemical, it’s now used industry-wide.
RP 754 splits PSEs into two tiers. Tier 1 covers the worst outcomes: a fatality, days-away-from-work injury, third-party hospitalization, or $100,000+ in fire and explosion damage. Tier 2 covers smaller losses, like a recordable injury or $2,500+ in damage, and serves as a leading indicator for future Tier 1 events.
Key Points
- Defined by API RP 754; originally for refining and petrochemical, now a common process safety metric.
- Tier 1 covers the highest-consequence losses of containment; Tier 2 covers lower-consequence but predictive ones.
Example
A relief valve that vents several hundred pounds of flammable vapor due to a control malfunction, with no injury or fire, still counts as a Tier 2 PSE if it exceeds the RP 754 threshold quantity.
Cited Sources
- API Recommended Practice 754, Process Safety Performance Indicators for the Refining and Petrochemical Industries
- API — Guide to Reporting Process Safety Events