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PT Notes

Role of Limiting Conditions for Operation in PHA

PT Notes is a series of topical technical notes on process safety provided periodically by Primatech for your benefit. Please feel free to provide feedback.

Process hazard analysis (PHA) practitioners identify safe operating limits for processes, that is ranges of values for critical operating parameters such as flow, temperature, pressure, and level, in order to consider the impacts of deviating from those limits. Such deviations help to identify hazard scenarios for processes so that the possible need for risk reduction measures can be addressed.

Limiting conditions for operation (LCOs) are specifications of critical systems that must be operational and critical resources that must be available to start a process or continue its operation. Critical systems include safeguards, such as fire protection and flares; utilities, such as electric power and instrument air; and support systems such as communications and emergency lighting. Critical resources include staffing levels, fire water supply inventory, etc.

Critical systems must be operating and critical resources must be available to allow a process to operate. Failure of critical systems or lack of critical resources may impact on or affect a release of hazardous chemicals in a process. Loss of these functions may need to be protected by engineering controls, procedures, instrumentation, employee training, etc.

Knowledge of LCOs for a process is essential for PHA practitioners. Failures of critical systems and resources may result in initiating events that trigger hazard scenarios, enable hazard scenarios, or produce safeguard failures. LCOs must be studied by PHA teams to ensure that possible failures of critical systems and resources are considered when identifying hazard scenarios.

In the event that LCOs have not been defined for a process, they should be addressed before a PHA study is started.

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