Tier 1 / Tier 2 PSE Rate Calculator
Formula Reference (API RP 754)
PSE Rate = (Total PSE Count ÷ Total Work Hours) × Base Hours — calculated separately for Tier 1 and Tier 2.| 200,000-hour base | Matches standard OSHA TRIR convention |
| 1,000,000-hour base | Per-million-hours convention |
| Basis for choice | Should match your company's occupational injury rate convention |
Tier 1 vs Tier 2 — Quick Reference
Both tiers begin with an unplanned or uncontrolled loss of primary containment (LOPC). Tier 1 covers the most severe outcomes — injury/fatality, hospital admission of a third party, fire/explosion damage ≥ $100,000, community impact (e.g. evacuation), or a release at or above the Table 1 threshold quantity. Tier 2 covers lesser-consequence LOPCs not already counted in Tier 1 — a recordable injury, fire/explosion damage ≥ $2,500, or a release at or above the (lower) Table 2 threshold quantity.Methodology, interpretation & sources
Purpose. Calculate Tier 1 and Tier 2 Process Safety Event (PSE) rates in line with API RP 754 methodology — standardizing your loss of primary containment (LOPC) event counts against total work hours, using either the 200,000 or 1,000,000-hour convention.
How to use the result. Start with source data you can verify, enter values on a consistent unit and time basis, and record the assumptions used. The main inputs on this page include Reporting Standard / Base Hours API RP 754 allows either a 200,000 or 1,000,000 man-hour multiplier — the choice should match your company's occupational injury rate convention., Tier 1 PSE Count LOPC events with the greatest consequence (e.g. injury/fatality, ≥$100k fire/explosion damage, community impact, release ≥ Table 1 threshold)., Tier 2 PSE Count LOPC events with lesser consequence (e.g. recordable injury, ≥$2,500 fire/explosion damage, release ≥ Table 2 threshold)., Total Work Hours Total hours worked by all employees and contractors in the same reporting period., Your Name, Email. Re-run the calculation when those assumptions change rather than carrying an old result forward.
Decision use. Use this calculator as a structured process-safety screening aid. It does not replace a formal PHA, QRA, LOPA or competent engineering review when those methods are required.
Limitations. Event definitions, consequence assumptions, exposure frequencies, safeguards and uncertainty should be documented so that the result can be independently reviewed.
Primary references. Use the current edition/version that applies to your jurisdiction and organization:
Editorial note. Prepared and maintained by Impact Tech Solutions. Editorially updated 28 September 2026. No individual professional credential is claimed on this page; high-consequence, statutory, tax, engineering or health decisions should be independently verified against the current primary source and, where required, a qualified professional.