Edition No. 6
Risk Assessment for Potential Hazards:
A Short Tutorial on Hazard and Operability Analysis
Hazard analysis is a systematic examination of design intent to assess the hazard potential of system mis-operation or malfunction. A hazard analysis is part of “risk assessment” where Hazard is a characteristic of the system/plant/ process representing a potential undesired event, and Risk is the combination of probability that an undesired event will occur and the severity of the consequences of that undesired event.
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Hazard analysis applications are used to meet various regulatory requirements such as the Process Safety Management Standard, Risk Management Programs and in some cases, local Fire Department requirements. Hazard analysis techniques can also be applied during equipment/ system design as well as to mature equipment and processes. When applied to identify design flaws and lack of controls early on in the design phase of a new system, tool or process, one is able to realize the benefits of:
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Less re-engineering
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Reduces need for administrative controls
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Clarifies interaction of equipment & facility
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Aids in preparing operating manuals
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Most cost effective at this phase
When applied to existing or installed equipment, the benefits include assisting with emergency planning, assessing the need for additional controls, identification of supplemental training requirements and recognizing opportunities for operability improvement.
There are several hazard analysis methods that are described by the American Institute of Chemical Engineers (AIChE) Center for Chemical Plant Safety (CCPS) “Guidelines for Hazard Evaluation Procedures” (1985); they include:
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“What If?” Analysis
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Hazard and Operability (HazOp) Studies
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Failure Modes, Effects and Criticality Analysis (FMECA)
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Fault Tree Analysis
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Event Tree Analysis
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Cause-Consequence Analysis
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Human Error Analysis
From EORM’s perspective, there are three basic “Rules of Thumb” in choosing a hazard analysis method. First, there is no universally appropriate method for all applications, second, there is no uniquely correct method for a given application and third, there is a most appropriate method for a given application.
For those who are interested, the remaining portion of this write up and follow-on link is focused on introducing one of the various hazard analysis methodologies, Hazard and Operability or Haz-Op and how it could be applied to systematically break down a system, equipment or process into a series of nodes for careful examination thereby, providing a logical and thorough means of identifying a multitude of process hazards.
Applying Hazard and Operability Methodology
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The first step in preparing a Haz-Op is to define the system to be analyzed. Once the system is defined, then nodes (boundaries) are selected that provides a logical breakdown of major subsystems (or components) for examination.
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Once the nodes are selected, the analyst should obtain all available documents necessary, including drawings, specifications, schematics, component lists, etc to complete the analysis. Piping and instrumentation drawings (P&ID) are critical to a thorough examination where process piping and chemical distribution systems are part of a node(s).
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A team of interdisciplinary experts should be assembled so that a competent examination of each node is performed. For a process intensive system, the team should be comprised of representatives from Product Safety, Process Engineering, Product Development and Field Service. At the heart of the effort, the team identifies the means through which deviation from the design intent can occur. It further determines whether these deviations, collectively or individually, might create a hazard(s). The team should be led by an individual acting in a facilitation role as well as another who serves as technical scribe. At the start of the session, the facilitator should remind the team of the analysis boundaries and recommended nodes and ensure that this focus is kept throughout the analysis session.
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Steps used to examine each node include:
Developing the “intention(s)” and associated parameters (design intent) for each element;
Brainstorming deviations from the design intent (parameter) using guideword identifiers, for example, “high”, “low" or “none” for the parameter “pressure.” (Once the guide word is applied, then the deviation is identified, for example, “high pressure” or “low pressure”;
Determining causes and consequences of the deviating elements;
Recommend effective mitigation or protection(s) to eliminate the consequences of identified single point hazards; and
Lastly, a column should added to capture comments and Action Items. -
The results of the analysis are recorded on a worksheet.
Helpful Hints
These helpful hints will enhance the usefulness of the analysis and make the analysis effort more manageable.
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When determining nodes, select a portion of the process or equipment that is anticipated to be similar acting with regard to applicable parameters and potential important consequences.
Examples:A tank, its pump and associated piping within a given containment area might be one node (with regard to chemical leak).
The above-atmospheric section of gas piping might be a different node than the sub-atmospheric section (with regard to breach of containment).
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As the study progresses, if potential consequences are determined to be different within a node, you may want to simplify the analysis by reducing the scope (bringing in the boundaries) of that node.
Examples:A leak to containment vs. a leak to environment
Leaks which may result in chemical incompatibility based on manifolding
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The facilitator should be disciplined in reminding the team of the analysis boundaries (physical, operating, and scope).
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The facilitator may save the analysis team considerable time and effort by determining appropriate nodes prior to session and gaining team consensus in advance of the session.
For an example of this hazard analysis technique, please refer to the following article: http://www.sematech.org/public/docubase/abstracts/3846aeng.htm
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