Tuesday, February 3, 2009

Process Hazard Analysis

Process Hazard Analysis (PHA)

Process Hazard Analysis (PHA) is a method to evaluate and identify credible hazardous scenarios. PHA is a thorough, orderly, systematic approach for identifying, evaluating, and controlling the hazards of processes involving hazardous chemicals. Based on most U.S. state and federal standards, an initial PHA must be performed on all covered processes. Thereafter all PHAs must be updated and revalidated, based on their completion date, at least every 5 years.

The process hazard analysis methodology selected must be appropriate to the complexity of the process and must identify, evaluate, and control the hazards involved in the process. One or more of the following methods is used, as appropriate, to determine and evaluate the hazards of the process being analyzed:

  • What-if,
  • Checklist,
  • What-lf/checklist,
  • Hazard and operability study (HAZOP),
  • Failure mode and effects analysis (FMEA),
  • Fault tree analysis, or
  • An appropriate equivalent methodology.

The PHA must address the following:

  • The hazards of the process;
  • The identification of any previous incident that had a potential for catastrophic consequences in the workplace;
  • Engineering and administrative controls applicable to the hazards and their interrelationships, such as appropriate application of detection methodologies to provide early warning of releases. Acceptable detection methods might include process monitoring and control instrumentation with alarms, and detection hardware such as hydrocarbon sensors;
  • Consequences of failure of engineering and administrative controls;
  • Facility sitting;
  • Human factors; and
  • A qualitative evaluation of a range of the possible safety and health effects on employees in the workplace if there is a failure of controls.

The PHA is performed by a team with expertise in engineering and process operations. The PHA team should include at least one employee who has experience with and knowledge of the process being evaluated. One member of the team must be knowledgeable in the specific analysis methods being used.

In performing a PHA, the first step is to define the purpose, scope and objectives of the study. The purpose defines why the PHA is being performed, e.g. to identify hazardous scenarios, to meet a regulatory requirement, etc. The scope defines the boundaries of the process being studied. The objectives define the expectations of the PHA results.

Next step is amass all the pertinent Process Safety Information (PSI) [see “The more you know: Process Safety Information (PSI)”] and appropriate Standard Operating Procedures. To plan the PHA, the process is divided into smaller manageable sections.

The PHA is conducted by identifying deviations from the design intent. The design intent includes values for operating conditions (e.g. temperature, pressure, flow, etc.), equipment (e.g. materials of construction, etc.) or external events (e.g. general loss of electrical power, etc.). There may be one or several causes of deviations. Causes are categorized as: 1.) Human Error, 2.) Equipment Failure or 3.) External Events. The team brainstorms and decides the credible causes of these deviations. If one of these deviations may occur, there are consequences that may result. The consequences may impact operability, quality or may be hazardous. Each scenario (deviation/cause – consequence combination) is evaluated further, particularly the hazardous scenarios. In evaluating these scenarios, existing safeguards are documented that prevent, detect or mitigate the scenarios. The team then determines if a recommendation is appropriate to prevent, detect or mitigate the scenarios.

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