Saturday, January 17, 2009

Overview Hazard Analysis


Under the PSM Rule, the PrHA element requires the selection and application of appropriate hazard analysis methods to systematically identify hazards and potential accident scenarios associated with highly hazardous chemicals. The components of a PrHA are summarized and explained below.

Process Safety Information

The PSM Rule requires that up-to-date process safety information exist before conducting a PrHA, with the exception of technology information that can be created in conjunction with the PrHA. Complete and accurate written information about process chemicals, technology, and equipment is essential to the team that performs a PrHA. It is also needed by personnel developing training programs and operating procedures, subcontractors whose employees work with the process, teams conducting pre-startup reviews, and local emergency preparedness planners.

Information About Highly Hazardous Process Chemicals

Information about the chemicals used in a process, as well as chemical intermediates, must be comprehensive enough for an accurate assessment of fire and explosion characteristics, reactivity hazards, safety and health hazards to workers, and corrosion and erosion effects on process equipment and monitoring tools. Information must include, at a minimum: (1) toxicity information; (2) permissible exposure limits; (3) physical data such as boiling point, freezing point, liquid/vapor densities, vapor pressure, flash point, autoignition temperature, flammability limits (LFL and UFL), solubility, appearance, and odor; (4) reactivity data, including potential for ignition or explosion; (5) corrosivity data, including effects on metals, building materials, and organic tissues; (6) identified incompatibilities and dangerous contaminants; and (7) thermal data (heat of reaction, heat of combustion). Current Material Safety Data Sheets (MSDSs) may be used to help meet this requirement. Where applicable, process chemistry information should be included about potential runaway reactions and overpressure hazards and hazards arising from the inadvertent mixing of incompatible chemicals.

Information About Process Technology

Process technology information must include at least: (1) block flow diagrams or simplified process flow diagrams such as the type shown in Figure 4.1; (2) process chemistry; (3) DOE contractor-established criteria for maximum inventory levels for process chemicals; (4) process limits that, when exceeded, are considered an upset condition; and (5) qualitative estimates of the consequences of deviations that could occur if established process limits are exceeded. If the original technology information is not available, it can be created in conjunction with the PrHA.

Block flow diagrams may be used to show major process equipment and interconnecting process flow lines, flow rates, stream composition, temperatures, and pressures. When necessary for completeness, process flow diagrams should be used to show all main flow streams including valves; pressures and temperatures on all feed and product lines within all major vessels; and points of pressure and temperature control. Construction materials, pump capacities, pressure heads, compressor horsepower, and vessel design pressures and temperatures are shown when necessary for clarity. Major components of control loops are usually shown along with key utilities. Piping and instrumentation diagrams (P&IDs), which are required under process equipment information, may be more appropriate to show some of these details.

Information About Process Equipment

Process equipment information must include at least: (1) materials of construction; (2) P&IDs; (3) electrical classification; (4) relief system design and design basis; (5) ventilation system design; (6) design codes and standards; (7) material and energy balances for processes ; and (8) safety systems.

Process equipment design and materials must be documented by identifying the applicable codes and standards (e.g., ASME, ASTM, API). If the codes and standards are not current, the DOE contractor must document that the design, construction, testing, inspection, and operation are still suitable for the intended use. If the process technology requires a design that departs from the applicable codes and standards, the contractor must document that the design and construction are suitable for the intended purpose.

Process Hazard Analysis

A PrHA is an organized and systematic method to identify and analyze the significance of potential hazards associated with processing or handling highly hazardous chemicals. A PrHA helps employers and workers to make decisions for improving safety and reducing the consequences of unwanted or unplanned releases of hazardous chemicals. It is used to analyze potential causes and consequences of fires, explosions, releases of toxic or flammable chemicals, and major spills of hazardous chemicals. It focuses on equipment, instrumentation, utilities, routine and non-routine human actions, and external factors that might impact a process.

The PSM Rule specifies that a PrHA be performed on every process covered under the rule. If several processes require PrHAs, the PrHAs must be prioritized. A preliminary hazard analysis (PHA) may be used to determine and document the priority order for conducting PrHAs. At a minimum, the PSM Rule requires the prioritization to consider the potential severity of a chemical release, the number of potentially affected employees, and the operating history of the process, including the frequency of past chemical releases and the age of the process.


Covered chemical processes must comply with the following:

  • The PrHA must be in place prior to process startup.
  • Each PrHA must be updated and revalidated at least every 5 years to assure that it is consistent with the current process.


To help assure that all hazards are identified and evaluated, PrHAs must address the following.

  • The hazards of a process. These hazards may be identified by performing a PHA.
  • Previous incidents that had the potential for catastrophic consequences in the workplace.
  • Engineering and administrative controls applicable to the hazards and their interrelationships.
  • The consequences of failure of engineering and administrative controls.
  • The influence of facility siting.
  • Human factors.
  • A qualitative range of possible safety and health effects on employees in the workplace caused by failure of controls.


PrHAs must be performed by a team. Teams can vary in size and in operational background, but must have expertise in engineering and process operations. Individuals may be full-time team members or may be part of a team for only a limited time. That is, team members may be rotated according to their expertise in the part of the process being reviewed.

The team conducting a PrHA must understand the method being used. In addition, one member of the team must be fully knowledgeable in the implementation of the PrHA method. The PSM Rule also requires that at least one team member be an "employee" with experience and knowledge specific to the process being evaluated. Some organizations have interpreted the term "employee" to mean an hourly employee such as a senior operator.

The ideal PrHA team has an intimate knowledge of the standards, codes, specifications, and regulations applicable to the process. Team members must be compatible, and the team leader must be able to manage the team and the study.

Findings and Recommendations

DOE contractors should establish a system to:

  • promptly address the team's findings and recommendations;
  • assure that recommendations are resolved in a timely manner and that resolutions are documented;
  • document actions to be taken;
  • develop a written completion schedule for the action steps;
  • complete actions as soon as possible;
  • communicate the actions to all affected personnel.

DOE contractors must retain PrHAs and updates for each process covered by the PSM Rule, along with documented resolutions of recommendations, for the life of the process.

Acceptable Methodology

The PSM Rule specifies that DOE contractors use one or more of the following methodologies, as appropriate, to determine and evaluate the hazards of the process being analyzed:

  • What-If
  • Checklist
  • What-If/Checklist
  • Hazard and Operability Study
  • Failure Mode and Effects Analysis
  • Fault Tree Analysis
  • An appropriate equivalent methodology.

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