Chapter 4 – Process Hazard Analysis (PHA)
The PHA is extremely important since it is an effort to identify and analyze the possible hazard scenarios within a process.
The PHA will basically look for:
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Potential causes and consequences of fires, explosions and toxic releases.
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Equipment failures, human errors and external events that may cause accidents.
OSHAs PSM standard dictate that the following methodologies can be used to identify and analyze the possible hazards:
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What-If – Uses “What If” questions, such as “What if water enters the process?”
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Checklist – Prepared questions to stimulate discussion about the hazards of the process. A question could be “Where can water enter the process?”
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What-If/Checklist – combination of What If/Checklist
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Hazard and Operability Study (HAZOP) - Investigates each element of a system for all of the ways in which important parameters can deviate from the intended design conditions to create hazards and operability problems.
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Failure Modes and Effects Analysis (FMEA) - looks at all the components of a system to see how it can fail and what would the effect of this failure have on downstream of this system.
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Fault Tree Analysis - A graphical, model, which shows an undesired top event and then all the lower level events that have to occur in order to achieve the undesired top event. It uses Boolean logic to combine these lower level events to lead up to the undesired top event.
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Other Methods are Acceptable with OSHA approval.
According to OSHAs PSM standard, the PHA must address the following:
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Hazards of the process – examples are fire and explosion, toxic releases, etc.
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Identification of any previous incidents – lessons learned from incidents can be analyzed. Could use incidents from similar processes.
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Engineering controls – examples could be ventilation, exhausts, etc.
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Administrative controls – examples could be minimizing the number of personnel in the vicinity of a hazardous operation.
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Consequences of failure of engineering and administrative controls – what happens when these controls fail?
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Facility siting – looks at the impacts to structures, equipment, and nearby personnel if a fire and explosion or the release of toxic substances.
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Human Factors – looks at operator intervention with the process
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Qualitative evaluation of range of the possible safety and health effects of failure of controls on employees in the workplace
A severity, likelihood and risk-ranking scheme could be used.
Therefore, the PHA must identify:
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All credible causes and consequences for hazard scenarios
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Include the causes of previous incidents
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All safeguards for the process
OSHA requires that a team approach be used when performing a PHA. For a PHA team:
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One member must have knowledge of the methodology used,
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One member must have experience and knowledge specific to the process,
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One member must have expertise in engineering and process operations.
The PHA team could also generate recommendations to make the process safer. If this happens, then the employer must establish a system to:
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Address and resolve recommendations in a timely manner
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Document resolutions and actions taken
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Written schedule for completion of actions
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Communicate actions to employees whose work may be affected
In order to keep the PHAs current, they must be revalidated every 5 years and will:
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Use same team approach as when PHA was initially completed
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Ensures PHA is still consistent with the current process and that should include modifications.
NOTE: All revisions of the PHA must be kept on file for the entire life of the process.
