LOPA is a simplified form of risk assessment. It assists in compliance with PSM and RMP regulations and with the ANSI/ISA S84.00.01-2004 / IEC 61511 standards, Functional Safety: Safety Instrumented Systems for the Process Industry Sector.
LOPA is often used as an extension of process hazard analysis (PHA). PHA teams use engineering judgment to decide if additional safeguards are needed to protect against accident scenarios they identify. This subjective approach can lead to disagreements and possibly inappropriate measures to reduce risk. A more rational and objective approach is needed, at least when considering risk remediation measures for high risk scenarios or those that are expensive to implement. Layers of Protection Analysis (LOPA) was developed for this purpose.
LOPA is also used to comply with the S84 / IEC 61511 standards. S84 / IEC 61511 requires the allocation of safety functions to protection layers, the determination of required Safety Instrumented Functions (SIFs) and the determination of their Safety Integrity Levels (SIL). LOPA is one method used for this purpose. The required SIL of a SIF is derived by taking into account the required risk reduction to be provided by that function. S84 / IEC 61511 notes that this is best accomplished as part of a process hazards and risk analysis (i.e. a PHA) to benefit from possible synergies and the information developed.
LOPA is used to evaluate scenario risk and compare it with risk tolerance criteria to decide if existing safeguards are adequate, and if additional safeguards are needed. Without risk tolerance criteria, there is a tendency to keep adding safeguards in the belief the more the safer. This can be a false assumption. Eventually safeguards will be added that are unnecessary and may add complexity that can result in new unidentified hazard scenarios. LOPA helps focus limited resources on the most critical safeguards.
This course describes each step in performing LOPA and provides experience in its use. A detailed manual is provided for use as a reference after you have completed the course. Also provided are Microsoft Excel and PHAWorks® templates for conducting LOPA studies.