Preliminary hazard analysis example

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. 

Table 3.3 Example of what-if worksheet for preliminary hazard analysis. 

For example, the hazard analysis and risk assessment requirements of the European Standard ISO 14121, Safety of Machinery—Principles for risk assessment (formerly EN 1050), have been adequately met in some companies in the design or redesign stages by applying an adaptation of the preliminary hazard analysis technique. 

A communication accompanies the analysis, explaining the assumptions made and the rationale for them. Comment would be made on the assignment of responsibilities for the remedial actions to be taken, and when. An example of a preliminary hazard analysis worksheet appears as Addendum A in this chapter, courtesy of Sverdrup Technologies, Inc. This form requires entry of severity, probability, and risks codes before and after countermeasures are taken. 

Prior hazard analyses (for example, preliminary hazard list, preliminary hazard analysis, and failure mode and effects analysis) should also be... 

In an effort to demonstrate the utDity of the preliminary hazard list and the preliminary hazard analysis in the initial evaluation of system risk, an example of a simple vapor degreaser in a manufacturing facility will be examined. This illustration will utilize the PHL in the development of the PHA in the method discussed earlier in this chapter. However, it must be noted from the outset that this example is intended... 

The SSHA evaluates hazardous conditions, on the subsystem level, which may affect the safe operation of the entire system. In the performance of the SSHA, it is prudent to examine previous analyses that may have been performed such as the preliminary hazard analysis (PHA) and the failure mode and effect analysis (FMEA). Ideally, the SSHA is conducted during the design phase and/or the production phase, as shown in Chapter 3, Figure 3.4. However, as discussed in the example above, an SSHA can also be done during the operation phase, as required, to assist in the identification of hazardous conditions and the analysis of specific subsystems and/or components. In the event of an actual accident or incident investigation, the completed SSHA can be used to assist in the development of a fault tree analysis by providing data on possible contributing fault factors located at the subsystem or component level. 

This example will develop a hardware FMEA for a proposed system that is well into the design phase of the product life cycle. For informational purposes, it is assumed that a preliminary hazard analysis was previously performed during the early stages of the design phase of this system. The information from the PHA will be used to assist in the development of the hardware FMEA. It should also be noted that the nature of a FMEA requires evaluation of subsystems, subassemblies, and/or components. For this reason, more detailed and specific descriptive information is provided here than that supplied for previous examples discussed in this text. 

For example, from a safety perspective someone needs to compute the water supply requirements for fire protection and other uses. Someone needs to identify which spaces or operations need emergency lighting or power. A safety specialist may need to conduct a preliminary hazard analysis or other analysis for some or all operations or spaces. The results will give the design team information to incorporate into the design. 

Figure 36-2. Example of a chart for use in conducting a preliminary hazard analysis.

Figure 36-2 provides an example of a preliminary hazard analysis chart. Referring to the chart, one can see that PHA can capture a lot of details for each hazard. 

System Structure Analysis. After the identification of subsystems to be examined and the definition of undcsired events within the context of preliminary hazard analysis, events which lead to incidents are investigated. These event sequences can be represented as logic structure in a block diagram, a flow diagram, a fault tree, or a decision table. In the presentation which follows (Table 4.9.). a decision table was used. It contains, column by column, the combinations of system states which lead to the undesired event. The presentation permits qualitative identification of weak points in the system. In general, for example, the probability of a system state will decline with the growing number of failed components. The logic structure presentation could form the basis for further quantitative analyses. 

The GPCA safety requirements were designed on the basis of a preliminary hazard analysis for the controller of the pump. We found that almost half of the requirements can be related to user interface functionalities, and correctly capture basic human factors concerns. However, a hazard analysis specifically addressing user interface functionalities is needed to cover a more complete set of aspects related to human factors. We are currently starting this hazard analysis. Some examples of safety features and constraints that are currently not considered in the GPCA safety requirements and can potentially make the user interface design safer follows. 

While a preliminary functional decomposition of the system components is created to start the process, as more information is obtained from the hazard analysis and the system design continues, this decomposition may be altered to optimize fault tolerance and communication requirements. For example, at this point the need... 

In order to utilize the ETBA in the performance of the system safety analyses listed above, certain essential data are required for evaluation. For example, if the ETBA is to be performed on a specific manufacturing facility, then the analysis should begin with an examination of completed facility drawings. If the ETBA is concerned with a specific project, or a newly designed piece of manufacturing equipment, the project plans and schematics must be evaluated. It should be noted that the level of detail required is dependent on the analysis itself. Development of a preliminary hazard list will not require extensive detail and evaluation, whereas an ETBA in support of a subsystem hazard analysis will meticulously analyze the project to the component level and detailed drawings will, therefore, be required. 

All of the hazard analysis techniques discussed in this chapter follow this hazard analysis process. The remainder of this chapter describes the most coimnonly used hazard analysis techniques and gives some concrete examples of their applications. However, the first step in using hazard analysis is to create a preliminary hazard list (PHL). 

---