Process hazard analysis selection

For every new tolling situation a process hazard analysis should be conducted using one of several acceptable methodologies in common use. The goal is to select a methodology appropriate to evaluate the hazards of the toll process in question. 

The toller and their client can work together to identify the appropriate method and detail required for the process hazard analysis. Consider adding a brief statement in the final PHA report documenting why the method was selected. 

One of the most important elements of the PSM Rule is the process hazard analysis (PrHA). It requires the systematic identification of hazards and related accident scenarios. The PSM Rule allows the use of different analysis methods, but the selected method must be based on the process being analyzed. The PSM Rule specifies that PrHAs must be completed as soon as possible within a 5-year period. However, one-fourth of the PrHAs must have been completed by May 26, 1994, with an additional one-fourth completed each succeeding year. The highest risk processes were to be done first. A schedule for PrHAs must be established at the outset of a process safety management (PSM) program to give priority to the highest risk processes. PrHAs must be reviewed and updated at least every 5 years. 

The process hazard analysis can be a starting point for the selection of fire scenarios. The process hazard analysis can be reviewed to develop a list of scenarios that result in fire as a consequence. Generic release sizes for small, medium, and large releases have been proposed as shown in Table 5-1 (Spouge, 1999). This saves time by eliminating the need to develop a detailed scenario. The analyst can use these release sizes to perform fire modeling calculations and determine the impact by moving the release point locations. The release criteria are considered to be representative of scenarios that could reasonably be expected to occur. 

If a recommendation asks for a change in the process, the action must undergo a formal process hazard analysis (PHA) study, such as a HAZOP or other methodology, before implementation. This systematic and formal approach identifies and evaluates hazards associated with the proposed revisions. The study may uncover failure scenarios, adverse consequences, and obscure relationships that are not immediately apparent. The CCPS publication Hazard Evaluation Procedures i is an excellent guide to selection and proper application of PHA methodologies. 

Identifying the potential hazards (PHA, process hazard analysis, or HAZOP, hazard and operability analysis) during operation must be done from a wide-angle approach dangerous situations can occur due to many root-cause situations other than those specified by, for instance, ASME or PED. Based on the results of the risk assessment, the pressure equipment can be correctly designed and the most effective safety system selected. 

Select analysis method for each process hazard analysis to be performed... 

F Choose team leader and team members to conduct process hazard analysis and train team members in analysis method selected for this process... 

Recent regulatory requirements make hazard analysis part of the PPE selection process. Hazard analysis procedures should be used to assess the workplace to determine if hazards are present, or are likely to be present, which may necessitate the use of PPE. As part of this assessment, the employees work environment should be examined for potential hazards that are likely to present a danger to any part of their bodies. If it is not possible to eliminate workers exposure or potential exposure to the hazard through the efforts of engineering controls, work practices, and administrative controls, then the proper PPE must be selected, issued, and worn. The checklist found in Figure 24.3 may be of assistance in conducting a hazard analysis. 

To develop the risk-management strategy, start with a process hazards analysis (PHA) and review the process design and its control, operation, and maintenance practices. Select a multidisciplinary team with expertise in these areas, and use an accepted hazard-evaluation procedure, such as a hazard and operability (HAZOP), what-if, or checklist analysis, to determine how process deviations from intended... 

Alternative release scenario. Alternative release scenarios must be more likely to occur than the worst-case scenario, and must reach an off-site endpoint. The EPA says owners should also consider these factors in selecting alternative release scenarios five-year accident history and failure scenarios identified by a process hazard analysis (PHA) or Program Level 2 hazard review. The alternative release scenario analyses may be performed using somewhat more flexible modeling approaches and parameters than specified for worst-case scenario analyses. For example, active mitigation credit can be given. 

There are a large number of standard methods suitable for each stage in the hazard analysis and risk assessment procedure. The selection of the proper method depends on several factors. Some of these are the type of process, the stage in the lifetime of the process, the experience and capabiUties of the participants, and the step in the procedure that is being examined. Information regarding the selection of the proper procedure is available in an excellent and comprehensive reference (1). 

With the PHA methodology selected, the team assembled and the process safety information gathered, the analysis of chemical and process hazards, and the consequences and deviations associated with those hazards are identified. 

More in line with the predictive use of hazards analysis, however, is the experimental and theoretical assessment that the viscosity of the liquid significantly affects this mode of initiation. Such information allows redesign of the process to eliminate handling of low viscosity liquid explosives, and quantitative measurement of the sensitivity of the system to mild shocks as a function of viscosity may allow the optimum level to be selected. This is not necessarily a new concept, only quantified in a different manner. Thirty years ago transporters of neat nitroglycerine in the oil fields were paid 25 a day. The stipend for transporting jellied nitroglycerine was seven dollars, a practical comment on the understood difference in hazard. 

Use hazard analysis findings to identify potential high-impact events and the process safety barriers intended to prevent such incidents. Select metrics that indicate the health of these barriers. This is a direct recommendation in HSG254, and the BP plant in Hull, England, is piloting this approach (see Appendix II). This perspective is seen as a leading indicator. 

Hazard analysis techniques shall be selected and used that are appropriate for the hazards and complexities of work processes being analyzed... 

Lastly, in the nineteen nineties, OSHA s Process Safety Standard was introduced as 29 CFR 1910.119, requiring hazard analysis and process safety assessment of selected hazardous substances. For example, use of methanol in dye and pigment syntheses now requires an extensive process safety analysis and audit. 

In order to save time, the leader and scribe may preselect the nodes. In a very simple process, this decision may make sense. Generally, however, the team as a whole should decide on the nodes, partly because all hazards analysis decisions are team decisions, and partly because the definition and selection of a node often is affected by the discussions that have taken place with regard to earlier nodes. Also, if the leader and scribe are from outside the local organization, they may not fully understand all the process parameters that could affect node selection. 

A formal hazard analysis of the anticipated operations was conducted using Preliminary Hazard Assessment (PHA) and Failure Modes and Effects Analysis (FMEA) techniques to evaluate potential hazards associated with processing operations, waste handling and storage, quality control activities, and maintenance. This process included the identification of various features to control or mitigate the identified hazards. Based on the hazard analysis, a more limited set of accident scenarios was selected for quantitative evaiuation, which bound the risks to the public. These scenarios included radioactive material spills and fires and considered the effects of equipment failure, human error, and the potential effects of natural phenomena and other external events. The hazard analysis process led to the selection of eight design basis accidents (DBA s), which are summarized in Table E.4-1. 

At least one bounding accident from each of the major types has been selected unless the bounding consequences are low. Accident categories are internally initiated operational accidents (fires, explosions, spills, and criticality) natural phenomena events for the site (e.g. earthquakes, tornadoes) that could affect the facilify and externally initiated, man-made events (e.g. airplane crashes, transportation accidents, and adjacent facility events). Criticality assessments have indicated that criticality is an incredible event for isotope processing operations. Based on these evaluations, criticality has not been included in the hazard analysis and will not be included in the accident analysis. 

More important, over 90% of the guideline is generic. Thus, it is a basic document on hazard analysis and risk assessment providing guidance on reducing risks according to a prioritized procedure and on the selection of appropriate design and protective measures. When the process is complete, a tolerable risk level will be achieved. 

Because of the complexity of chemical processes, the response selection should be tailored to the characteristics and requirements of each plant and safety function. A hazard and risk analysis defines for each hazard scenario when action should be taken, giving the initiating causes, consequence severity, and protection layers. The potential for common cause should also be evaluated to ensure the actions can be implemented in the presence of the initiating cause and the SIF device fault. 

When no hazard exists, continued operation of the process is generally preferable to initiating an unnecessary shutdown. Shutdown can cause additional hazards, such as large flaring events or cascade shutdowns of other process units, and does result in the need to restart the process unit with all of its potential hazards. The decision to shut down versus continued operation is made by balancing the risk posed by the potential process hazard if a process demand occurs and the risk associated with shutdown and start-up. This decision is greatly influenced by the relative robustness of the SIS architecture and system utilities. The path can be selected at the channel, sub card, card, or CPU level of the system. The device safety manual may contain specific requirements that should be followed, unless a detailed analysis of the final system architecture demonstrates that deviation from the safety manual is acceptable. 

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