Preliminary hazard analysis development process

Partial what-if analyses for the two example processes described in Section 4.0 are shown in Tables 4.9 and 4.10. Although for actual, more complex analyses, the what-if tables for each line or vessel would be separate, for these examples, a single table was developed. A preliminary hazard analysis (PHA) would identify that the intrinsic hazards associated with HF are its reactivity (including reactivity with water, by solution), corrosivity (including carbon steel, if wet), toxicity via inhalation and skin contact, and environmental toxicity. The N2 supply system pressure is not considered in this example. The specific effects of loss of containment could be explicitly stated in the "loss of HF containment" scenarios identified. Similarly, the effects of loss of chlorine containment, including the reactivity and toxicity of chlorine, could be specified for the second example. 

Preliminary Hazard Analysis. The next step in the process is the development of a PHA. This analysis is the core of the FSS program and as such is vital in eliminating or reducing the inherent hazards associated with this laboratory operation. The PHA is used to further analyze the data identified in the PHL. This enhances the hazard control data base and provides specific recommended corrective action for the resolution of hazardous conditions. A combination of the informational sources used in the PHL development and any additional design information should be used in PHA development. 

Again the process involves a preliminary hazard analysis to be done very early in the concept stage, followed by subsystem hazard analysis as subsystems are developed, systems hazard analysis that looks at interfaces between subsystems, and, finally, the operating hazard analysis, which tends to add the human element and evaluate procedures. 

The job safety analysis (JSA) [also referred to as the job hazard analysis (JHA)], which is a more simplified form of task analysis, has been a longstanding tool for task and function analysis. JSA has been available and utilized in general industry for many years by the industrial safety community. However, many practitioners do not understand or are simply unfamiliar with the connection between the JSA and the system safety tasks of hazard identification and analysis. It has even been suggested by some in the profession that the JSA itself is a type of oversimplified system safety analysis and, if performed earlier in the job development phase, could be used as the basis of a preliminary hazard analysis for a specific task or set of tasks. However, because JSA is often (if improperly) used to analyze a function only after it has been implemented, much of the data is not factored into the system safety process. The primary purpose of the JSA is to uncover inherent or potential hazards that may be encountered in the work environment. This basic definition is not unlike that previously discussed regarding the various system safety analyses. The primary difference between the two is subtle but important and is found in the end-use purpose of the JSA. Once the job or task is completed, the JSA is usually used as an effective tool for training and orienting the new employee into the work environment. The JSA presents a verbal picture of a specific job. 

In the analysis of system safety, the initial process begins with the development of the preliminary hazard list during the project or system concept phase. Although it is not always compiled in aU cases, an available PHL can become the working foundation for the development of the preliminary hazard analysis during the design phase of the project life cycle. 

The ETBA is an analytical technique that can be of great assistance in preparation of the preliminary hazard list (PHL). It can also be quite useful in the development of a preliminary hazard analysis (PHA), subsystem hazard analysis (SSHA), or the more general system hazard analysis (SHA). The ETBA can also be used, depending on the specific system under consideration, in the development of the operating and support hazard analysis (O SHA), and, of course, during the MORT process from which the ETBA evolved. 

FEED stage At the initial FEED stage, PFDs, certain equipment, etc. are fixed and it is in the process of development of a P. ID. At this stage, preliminary hazard analysis, checklists, etc. are utilized for PHA. Then, slowly instrumentation is developed based on layers of protections desired as a safeguard and interlock. 

However, initially, preliminary hazard analysis is often done for hazard screening processes to assess a major event. This will help in developing an SMS and FSA. Therefore the discussion may be concluded by saying that no potential danger situation is liable for rejection however low the likelihood of its occurrence is. Also if any assumption is considered it must be recorded for further review. 

The scope definition section requires the definition of the boundary of the process and equipment under control being assessed, together with its control system. Since in the majority of cases the input to LOPA is taken from preliminary hazard analysis or HAZOP, the scope is more or less otherwise developed from previous analysis. It is necessary to ensure that equipment under control and its environment are sufficiently understood along with scope and boundary including interface before detailed assessment commences. 

In the previous chapter, it was established that in industry, plant hazards can cause harm to property (plant—machinery, asset), people, or the environment. So, it is important to develop some means of analyzing these and come up with a solution. Unfortunately, it is not as straightforward as it sounds. There are plenty of plant hazard analysis (PHA) techniques and each of them has certain strengths and weaknesses. Also each specific plant and associated hazard has specific requirements to be matched so that hazard analysis will be effective. In this chapter, various hazards (in generic terms) will be examined to judge their importance, conditions, quality, etc. so that out of so many techniques available for PHA it is possible to select which one is better (not the best because that needs to be done by experts specifically for the concerned plant) suited for the type of plant. So, discussion will be more toward evaluation of PHA techniques. Some PHA is more suited for process safety management (PSM) and is sometimes more applicable for internal fault effects [e.g., hazard and operability study (HAZOP)]. In contrast, hazard identification (HAZID) is applicable for other plants, especially for the identification of external effects and maj or incidents. HAZID is also covered in this chapter. As a continuation of the same discussion, it will be better to look at various aspects of risk analysis with preliminary ideas already developed in the previous chapter. In risk analysis risk assessment, control measures for safety management systems (SMSs) will be discussed to complete the topic. 

The DAL is an index number ranking the safety-criticality of the system functions. This ranking implies that in order to make the system safe, greater development rigor must be applied to each successively critical level. Table 2.3 correlates the hardware DALs to the five classes of failure conditions and provides definitions of hardware failure conditions and their respective DALs. Initially, the hardware DAL for each hardware function is determined by the SSA process using a functional hazard analysis (FHA) to identify potential hazards and then the preliminary system safety assessment (PSSA) process allocates the safety requirements and associated failure conditions to the function implemented in the hardware. 

PHA analysis is both a system safety analysis type and technique for identifying for the early identihcation of hazards and potential mishap risk. The PHA provides a methodology for identifying and collating hazards in the system and estabhshing the initial SSRs for design from preliminary and limited design information. The intent of the PHA is to affect the DFS as early as possible in the development process. The PHA normally does not continue beyond the SSHA time frame. 

Another widely used safety analysis method in process industry is the Hazard and Operability Analysis, better known as Hazop (Kletz, 1992). The conventional Hazop is developed to identify probable process disturbances when complete process and instrumentation diagrams are available. Therefore it is not very applicable to conceptual process design. Kletz has also mentioned a Hazop of a flowsheet, which can be used in preliminary process design, but it is not widely used. More usable method in preliminary process design is PIIS (Edwards and Lawrence, 1993), which has been developed to select safe process routes. 

Conception is the most critical step in the development of a new process. Though still done largely on the basis of experience and intuition, it may be implemented with process synthesis. Computerized algorithms may provide for a large number of possible routes to a product. This method, combined with the analysis of raw material costs and DS-51 ASTM tests for process hazardousness, are the best options to speed up the bench-scale development of new chemical processes. Thus, one or a reduced number of routes to the desired product can be identified for preliminary process development. 

STPA is implemented in four steps [6] (1) establish the fundamentals of analysis (2) identify potentially hazardous control actions (3) use the identified potentially hazardous control actions to create safety requirements and constraints and (4) determine how each potentially hazardous control action could occur. In step 1, the safety analyst must identify the accidents or losses which will be considered, hazards associated with these accidents, and specify safety requirements (constraints). After establishing the fundamentals, the safety analyst must draw a preliminary (high-level) functional control structure of the system. In step 2, the analyst has to use the control structure as a guide for investigating the analysis to identify the potentially unsafe control actions. Then he or she translates them to corresponding safety constraints. In step 3, the analj t has to identify the process model variables for each controller (automated controller or human) in the control loop and analyze each path to determine how each potentially hazardous control actions could occur. At the end of the process, a recommendation for the system design should be developed for additional mitigations. 

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