Tier 1 and 2 both apply the concept of an acute release to differentiate a PSE from other LOPCs which occur over a prolonged period (such as fugitive emissions) and are unlikely to constitute a major incident risk of a fire or explosion. An acute release of material is defined as LOPC which exceeds the reporting threshold for a Tier 1 or Tier 2 PSE within any period of one hour during the event. Acute releases include but are not limited to equipment and piping failures due to corrosion, overpressure, damage from mobile equipment, sabotage, etc. For example: valves being left open; tanks being overfilled; flare or relief systems not operating as intended; process upsets or errors that result in process materials entering other process containment systems with no provisions or design considerations; corrosion of a pipe or a gasket failure where the release over an hour exceeds thresholds.
Source: OGP Report No. 456, Process Safety – Recommended Practice on Key Performance Indicators, International Association of Oil & Gas Producers, November 2011. Global Standards