Hazard analysis methods

TABLE 26-1 Process Hazard Analysis Methods Listed in the OSHA Process Safety Management Rule... 

A critical assembly is a split bed on which fissionable material used to mock up up a separated reactor core that is stacked half on each half. One half is on roller guides so that the two halves may be quickly pulled apart if the neutron multiplication gets too high. Use the Preliminary Hazards Analysis method described in section 3,2.1 to identify the possible accidents that may occur and the qualitative probabilities and consequences. List the initiators in a matrix to systematically investigate the whole process. Don t forget human error. 

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 HAZARD ANALYSIS METHODS WITH EXAMPLES... 

Theorem. No hazards analysis method exists that is both complete and whose running time is bounded by a polynomial in the number of initial species present in the plant. 

The date on which the proposed changes would become effective and, if a temporary change, the date on which the modified process would revert to the original process. If the changes are to be permanent, the Pre-Startup Review procedure should be implemented. Many companies require that the modified process be analyzed for hazards, prior to startup, using a Process Hazards Analysis method that would be consistent with the inherent or demonstrated hazards. 

This chapter is divided into two sections. The first section, 4.1, contains a consolidation of requirements for hazard analysis and hazard communication associated with the general use of chemicals. Section 4.2 details consolidated requirements for analyzing hazards when certain hazardous operations are involved. This section is similar to section 4.1, but contains more specificity and additional rigor regarding hazard analysis methods and dociunentation. 

ANALYSIS TEAM. A list of the team members, their roles, and brief biographical sketches are included here. Because the PSM Rule requires a team approach, this section should demonstrate that the PSM team requirements were met. These requirements include expertise in engineering and process operations, experience and knowledge specific to the process being analyzed, and knowledge of the specific hazard analysis method. 

SWIFT, as with many hazard analysis methods has its origins in industry and manufacturing. The guidewords originally conceived lend themselves to the management of raw materials, environmental release of chemicals, etc. In HIT the technique holds true but guidewords need to be modified. Card, Ward and Clarkson propose an alternative set of guidewords for SWIFT [1] ... 

The most common form of inconsistency occurs when one or more process models is incomplete in terms of not defining appropriate behavior for all possible process states or all possible disturbances, including unhandled or incorrectly handled component failures. Of course, no models are complete in the absolute sense The goal is to make them complete enough that no safety constraints are violated when they are used. Criteria for completeness in this sense are presented in Safeware, and completeness analysis is integrated into the new hazard analysis method as described in chapter 9. 

The following are two examples of causal factors identified using STPA step 2 as potentially leading to the hazardous state (violation of the safety constraint). Neither of these examples involves component failures, but both instead result from unsafe component interactions and other more complex causes that are for the most part not identifiable by current hazard analysis methods. 

STPA as currently defined provides much more useful information about the cause of human errors than traditional hazard analysis methods, but augmenting STPA could provide more information for designers. Stringfellow has suggested some additions to STPA for human controllers [195]. In general, engineers need better tools for including humans in hazard analyses in order to cope with the unique aspects of human control. 

Was the most appropriate hazards analysis method used ... 

Some hazards analysis methods, particularly FTA, lend themselves to an understanding of multiple contingencies. However, the more commonly used methods, particularly the HAZOP technique, do not do so because it is hard to discuss complex logic in a team environment. 

The Checklist Method uses a set of prewritten questions to stimulate discussion and thinking, often in the form of a What-If discussion. The questions are developed by experts who have conducted many hazards analyses and who have extensive experience to do with the design, operation, and maintenance of process facilities. Checklists are not comprehensive—no hazards analysis method can make that claim. Nevertheless, they should make sme that a complete range questions is asked and that nothing that would be regarded as obvious is overlooked. 

In the introduction to this section it was suggested that fault trees are best used to analyze and better define the hazards that have already been identified by one of the more creative hazards analysis methods, such as HAZOP. However, fault trees can also be used just to identify hazards. When used in this manner the method is known as Qualitative FTA (QFTA). Using this approach, the hazards analysis team leader, using a whiteboard develops the tree in conjunction with the team. He or she postulates the Top Event, such as Tank T-lOO overflowing, and asks the team members to suggest ways in which this may happen. As the discussion develops, the leader sketches out the OR and AND Gates of the Tree, showing the combinations of events that need to occm for the Top Event to occur. 

Figure 18.3 identifies some of the hazards analysis methods that are used at different stages of the project. 

Proper application of hazard analysis methods and PHA (What-if, HAZOP, FMEA) in pre-FEED and FEED stages is very important to develop safer and cost-effective designs... 

To communicate with decision makers, terms must have been defined and agreed upon. While identical terms may be used in the several hazard analysis methods described in the literature, those terms may be given different meanings in the text material describing them. 

What-lf Hazard Analysis. This hazard assessment method utilizes a series of questions focused on equipment, processes, materials, and operator capabilities and limitations, including possible operator failures, to determine that the system is designed to a level of acceptable risk. Users of the What-If method would identify possible unwanted energy releases or exposures to hazardous environments. Bulletin 135 contains procedures for use of a What-If checklist. For some hazards, a What-If checklist will be inadequate and other hazard analysis methods may be used. 

This section identifies the methods used to identify and characterize hazardous materials and energy sources associated with the fadlities, operations, and inventory. Several sources of information and hazard analysis methods were used to identify the hazardous material inventory and potential energy sources at the HCF. 

Safety analysis (hazard analysis) The entire complex of safety (hazard) analysis methods and techniques ranging from relatively informal job and task safety analyses to large complex safety analysis studies and reports (SSDC). 

The fault hazard analysis (FHA)—also referred to as the functional hazard analysis—method follows an inductive reasoning approach to problem solving in that the analysis concentrates primarily on the specific and moves toward the general (TAI 1989). The FHA is an expansion of the FMEA (Stephenson 1991). As demonstrated in the previous chapter, the FMEA is concerned with the critical examination and documentation of the possible ways in which a system component, circuit, or piece of hardware may fail and the effect of that failure on the performance of that element. The FHA takes this evaluation a step further by determining the effect of such failures on the system, the subsystem, or personnel. In fact, when a FMEA has already been completed for a given system and information on the adverse safety effect of component or human failures is desired for that system, the safety engineer can often utilize the data from the FMEA as an input to the FHA. 

Checkhsts. These have a varied degree of detail and are often used to verify compliance with standards. The output of this analysis is mainly only as good as the checkhst it is based on, and the use of checklists is ffequendy combined with other hazard analysis methods. 

MORT provides an excellent hazard analysis method for the post incident element of the practice of safety. 

Applioation to Offshore Operations Hazards Analysis Methods... 

It is prudent that a few terms associated with PHA, mainly for PSM systems, are discussed. In Table II/2.1.2-1, a few hazard analysis methods have been highlighted such as the Dow FEI and the Mond Index, etc. for quick risk assessment in process plants. 

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