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Process Safety Index: Is Good, GOOD ENOUGH?

October 16, 2017

Process Safety Performance Indicators (PSPI) are an effective tool for monitoring and analysing the success of risk control measures both in terms of Leading (to provide advance warning of potential events) and Lagging (to record and evaluate these events when they occur).


High reliability organisations (HRO) utilise these indicators to improve performance and increase engagement, however with so many indicators to choose from, it is likely that different sites, companies, countries and industries will have different sets of indicators and it is therefore more challenging to identify and analyse wider trends in similar applications to maximise shared knowledge.

A good set of performance indicators may indicate that operations are 'safe' but are they safe enough?

A standard approach (called the Process Safety Index) is proposed which is based on established industry principles to objectively and consistently evaluate the fine balance between Threats and Protection in order to assist duty holders to determine if they have sufficient (or indeed excessive) protection in a way that can be anonymously compared across businesses without revealing sensitive process information.

In simple terms, the Process Safety Index is an arithmetic evaluation of the overall Protection against the Threat(s) being addressed.

Contributions are determined from the Properties (Chemical) and Process (Conditions) i.e. WHAT is handled/stored and HOW it is handled/stored. This is inspired by the Dow Fire & Explosion Index which considers Material Factors, General & Special Process Hazards.

A simple Properties classification could be based on the NFPA 704 "Fire Diamond":

This considers the Flammability, Health, Instability & Special factors. A more detailed classification could be based on the 9 elements of the Globally Harmonized Systems of Classification & Labelling of Chemicals (GHS):

The Process contribution to the Threat is based on the operating conditions & location:


Pressure: includes vacuum
Temperature: includes cryogenic & considers boiling & flash/autoignition points
Inventory: includes regulatory thresholds e.g. Seveso, OSHA etc
Exposure: includes site personnel, public, vehicles and the environment

The first 3 reflect the potential effects of a loss of containment i.e. the greater the pressure, temperature or mass/volume, the more severe the consequences are likely to be. Exposure reflects the vulnerability of the process to external impact/influences (e.g. extreme weather) as well as the vulnerability of local or remote personnel to the process. Admittedly, Pressure is less straight forward to categorise compared to Temperature & Inventory (see caveats later).

Contributions are determined by the Prevention (Leading) and Performance (Lagging) metrics.

There are a number of Process Safety Management (PSM) systems adopted including the UK Energy Institute & OSHA PSM and within these there are components which can be monitored both proactively and reactively. There are also several publications relating to Leading & Lagging Process Safety Indicators including the IChemE Safety Centre and CCPS.

From one of the above systems, 8 leading components are selected which can be monitored both at a unit/operation level but also at a site/cultural level to reflect equipment specific & general trends. The short list is still under development (see caveats later) but could for example consider the following:

Process Safety Information
Process Hazard Analysis
Operating Procedures
Training & Employee Participation
Mechanical Integrity
Management of Change
Emergency Planning & Response
Compliance Audits

In terms of lagging indicators, a 3 tier system based on API 754 could be adopted plus a 4th factor which monitors the execution & conclusion of incident investigations e.g.:

Tier 1 LOPC events of Greater Consequence
Tier 2 LOPC events of Lesser Consequence
Tier 3 Challenges to Safety Systems
Post Event Investigations

The method simply combines scores as follows:

Threats = Σ (Properties) * Σ (Process)
Protection = Σ (Prevention) * Σ (Performance)
Process Safety Index = Protection - Threats

This provides a range of scores from -256 to +255 which could be ranked as follows:

An example is given below which indicates an Index of -79 based on a Threat score of 117 and a Protection score of 38:

Obviously the calibration of this method will determine its accuracy and therefore its success or failure and it is acknowledged that there is still some work to do (see caveats later).


The index is applied to a Unit Operation or Major Equipment which could be aggregated up the business hierarchy i.e. Unit → Area → Site → Region → Enterprise.

At the lower levels (Unit/Area/Site), a colour coded Block Flow Diagram (similar to OSHA PSM Appendix B) could be adopted as both a Control Room & Board Room dashboard for both Operators/Supervisors & Managers/Directors:

The index could also be displayed at the site entrance (similar to the Lost Time Incidents score/days that many companies use) as a reminder of the current state of the plant(s). Something similar to the (now obsolete) Homeland Security Advisory System (HSAS) could be adopted to simply show the potential for an incident (rather than a Terrorist Attack):

Maybe this is too dramatic & disproportionate but it would certainly grab attention! Instead of your intranet displaying your stock price, it could show the local & corporate Process Safety Index.


"Men more frequently require to be reminded than informed" ― Samuel Johnson

Perhaps a more productive use of the index would be to track performance within the business and across industries in a way that can be anonymised so that you can gauge performance against your peers (competitors) to help drive improvement - similar perhaps to the Dow Jones Index.


Future performance might also be predicted (extrapolated - within reason) based on anticipated degradation to forecast when a lower threshold may be breached e.g. index becomes negative.

This method is still under development and this article is intended to gauge industry interest. Current challenges include:

Determination of appropriate pressure parameters/thresholds
Leading performance indicators which provide suitable granularity at unit level
General calibration i.e. parameter ranges & criteria

All contributions are welcomed - many thanks.

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