Process Safety Event (PSE)

This definition follows that of the Process Safety Event (PSE) as defined in the 2nd edition of American Petroleum Institute's Recommended Practice 754 (API RP754).

Below you will see references to "Table 1" and "Table 2." These tables define material threshold quantities for reporting PSE Tiers 1 and 2 and appear in Appendix A of the PDF file API Guide to Report PSE, Version 3.1. You will also find more information and resources regarding Recommended Practice 754 and PSE on the API web site.

Tier 1 Indicator: Definition and Consequences

A Tier 1 Process Safety Event (T-1 PSE) is a loss of primary containment (LOPC) with the greatest consequence as defined by API RP754. A T-1 PSE is an unplanned or uncontrolled release of any material, including non-toxic and non-flammable materials¹ (e.g. steam, hot water, nitrogen, compressed CO2, or compressed air), from a process that results in one or more of the consequences listed below:

• an employee, contractor or subcontractor “days away from work” injury and/or fatality;
• a hospital admission and/or fatality of a third party;
• an officially declared community evacuation or community shelter-in-place, including precautionary community evacuation or community shelter-in-place;
• an engineered pressure relief² (e.g., PRD, SIS, or manually initiated emergency depressure) discharge, of a quantity greater than or equal to the threshold quantities in Table 1 in any one hour period, to atmosphere whether directly or via a downstream destruction device that results in one or more of the following four consequences:
  • fire or explosion³ damage greater than or equal to $100,000 of direct cost;
  • rainout;
  • discharge to potentially unsafe location;
  • an on-site shelter-in-place or on-site evacuation, excluding precautionary on-site shelter-in-place or on-site evacuation;
• public protective measures (e.g. road closure) including precautionary public protective measures.
• an upset emission from a permitted or regulated source of a quantity greater than or equal to the threshold quantities in Table 1 in any one hour period, that results in one or more of the following four consequences:
  • rainout;
  • discharge to potentially unsafe location;
  • an on-site shelter-in-place or on-site evacuation, excluding precautionary on-site shelter-in-place or on-site evacuation;
  • public protective measures (e.g., road closure) including precautionary public protective measures.
• a release of a material greater than or equal to the threshold quantities described in Table 1 in any one-hour period.

You will only enter T-1 PSE counts, but the formula to compute T-1 PSE Rate = [Total T-1 PSE Count/Total Work Hours] x 200,000

Tier 2 Indicator: Definition and Consequences

A Tier 2 Process Safety Event (T-2 PSE) is a LOPC with lesser consequence. A T-2 PSE is an unplanned or uncontrolled release of any material, including non-toxic and non-flammable materials (e.g. steam, hot water, nitrogen, compressed CO2, or compressed air), from a process that results in one or more of the consequences listed below and is not reported as a Tier 1 PSE:

• an employee, contractor or subcontractor recordable injury;
• an engineered pressure relief⁴ (PRD, SIS, or manually initiated emergency depressure) device discharge, of a quantity greater than or equal to the threshold quantities in Table 2 in any one-hour period, to atmosphere whether directly or via a downstream destructive device that results in one or more of the following four consequences:
  • a fire or explosion⁵ damage greater than or equal to $2,500 of direct cost;
  • rainout;
  • discharge to a potentially unsafe location;
  • an on-site shelter-in-place or on-site evacuation, excluding precautionary on-site shelter-in-place or on-site evacuation;
• public protective measures (e.g., road closure) including precautionary public protective measures.
• an upset emission from a permitted or regulated source, of a quantity greater than or equal to the threshold quantities in Table 2 in any one-hour period, that results in one or more of the following four consequences:
  • rainout;
  • discharge to potentially unsafe location;
  • an on-site shelter-in-place or on-site evacuation, excluding precautionary on-site shelter-in-place or on-site evacuation;
  • public protective measures (e.g., road closure) including precautionary public protective measures.

You will only enter T-2 PSE counts, but the formula to compute T-2 PSE Rate = [Total T-2 PSE Count/Total Work Hours] x 200,000

Tier 3 Indicator: Definition and Consequences

Tier 3 Process Safety Events (T-3 PSEs) are company or site defined performance indicators that provide information about the strength (or lack thereof) of barriers and weaknesses in equipment and hazard control systems. A Tier 3 indicator represents a challenge to the barrier system that progressed along a path to harm but stopped short of a Tier 1 or 2 LOPC consequence. Examples of Tier 3 indicators include:

• Safe Operating Limit Excursions (i.e., a process parameter deviation hat exceeds the safe operating limit applicable to the phase of operation);
• Primary Containment Inspection or testing Results Outside Acceptable Limits (i.e., an inspection or test finding that indicates primary containment equipment has been operated outside acceptable limits);
• Demands on Safety Systems (EXCLUDING intentional activations during periodic testing or manual activation as part of normal shutdown process; SIS activation configured for equipment protection with no LOPC consequence);
• Other LOPC events (i.e., a loss of primary containment with a consequence less than Tier 2 events).