AAOM Handbook

flow sheet (down to Productive Unit level). The two Pareto diagrams shall rank the processes based on

HSE Criticality,

Business Criticality.

The processes and risks that have Criticality Ratings beyond the acceptable threshold shall be identified.

The criticality rating (CR) shall be calculated based on the formula;

CR = Sum of Consequences × Probability of Threat During Functional Life × Probability of Exposure

NB: For threats where the probable time to occurrence is short compared to the Functional Life the Probability of Failure during the Functional Life will be 100% and the formula becomes;

CR = Sum of Consequences × Probability of Exposure

The consequence matrix contained in Appendix 1 shall be used as a guide in calculating the Criticality Rating while the ORM Risk Matrix shall be applied to risks within the scope of the ORM Baseline Risk Management Process. The consequences used in determining the criticality rating shall be based on the worst probable scenario (that with the highest value for consequence rating × probability of occurrence × probability of exposure) for any of the identified risks. The likelihood of process risk indicates the probability that the failure event will occur at least once during the Functional Life, on the basis that no control action is in place to prevent it – i.e. the probability if we do nothing. For example, for a plant with a 10 year Functional Life the Probability of Failure for; a v-belt on a continuously operated pump drive is likely to be 100%, and for the concrete base on which the pump set is mounted it is likely to be 0%. The Probability of Exposure indicates the percentage of risk events from which the full consequences are likely to arise. For example the probability of exposure to environmental damage in the event of a mine fuel storage tank leak is; almost 100% if there is no secondary containment structure around the tank and, is almost 0% if there is a secondary containment structure.

When evaluating the Criticality Rating of a process consider; • the common causes of unwanted events. • Safety margins employed during design.

• Construction materials, techniques and practices. • The environment in which the process is located. • Operating practices. • Modification of design, use or operation. • The probable frequency of an unwanted event. • The health, safety or environmental consequences of the unwanted event.

© McAlear Management Consultants 2006

Operational Planning: Set Service Strategy

Updated: August 2018

Page 17