Preliminary Hazard Analysis PHA

TABLE 15.6.1 Summary Tabic to Be Completed for Preliminary Hsizard 

As indicated above, the PHA may ser e as a precursor to further liazjird analyses. It is included in tliis chapter because it can pro ide a cost effective, early-on plant nieiliod for hazard identification. As its title indiaitcs. the PHA is really intended for use only in the preliniiimry pliase of plant development for cases where past experience provides little or no insight into any potential safety problems, e.g.. a new plant with a new process. 

Preliminary Hazard Analysis (PHA) is a widely used method during the concept design phase. This is an unstructured approach that is used when there is a lack of definitive information such as functional flow diagrams and drawings. The mefhod has proved to be an effechve tool to take early measures to identify and eliminate possible hazards when all the necessary data are unavailable. Its findings are also considered useful to serve as a guide in potential detailed analysis. 

PHA requires the formation of an ad hoc team of individuals with appropriate familiarity with items such as equipment, materials, substances, and/ or the process in question. The team members review the occurrence of hazards in the area of their expertise and experience, and as a group they play the devil s advocate. Additional information on this method is available in Hammer and Price [4]. 

Preliminary Hazard Analysis (PHA) was introduced in 1966 after the Department of Defence of the United States of America requested safety studies to be performed at all stages of product development. The Department of Defence issued the guidelines that came into force in 1969 (Military Standard (1969,1999)). 

Preliminary Hazard Analysis is performed to identify areas of the system, which will have an effect on safety by evaluating the major hazards associated with the system. It provides an initial assessment of the identified hazards. PHA typically involves  

Determining hazards that might exist and possible effects. 

Determining a clear set of guidelines and objectives to be used during a design. 

Creating plans to deal with critical hazards. 

This approach is generally used during the conceptual design phase and is relatively an unstructured tool because of the lack or unavailability of definitive information such as functional flow diagrams and drawings [23]. PHA has proven to be an effective method to take appropriate early steps to identify and eliminate/minimize hazards when the required data are not available. The findings of PHA serve as an effective guide in potential detailed analysis. 

---

Figure 15.6.1. Logic diagram lo couiplele for Preliminary Hazard Analysis (PHA).

If several processes require PrHAs, the PrHAs must be prioritized. A preliminary hazard analysis (PHA) may be used to determine and document the priority order for conducting PrHAs. At a minimum, the PSM Rule requires the prioritization to consider the potential severity of a chemical release, the number of potentially affected employees, and the operating history of the process, including the frequency of past chemical releases and the age of the 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. 

Assessment. An analysis of the hazards present in this laboratory show the most significant hazard to be the release of vapor CSM from engineering controls and into the workplace. The significance of this hazard mandates further efforts in system safety in the form of a Preliminary Hazard List (PHL) and a Preliminary Hazard Analysis (PHA). The user must in this instance take an active role in the design review process. 

Other possible preliminary safety analysis methods are concept safety review (CSR), critical examination of system safety (CE), concept hazard analysis (CHA), preliminary consequence analysis (PCA) and preliminary hazard analysis (PHA) (Wells et al., 1993). These methods are meant to be carried out from the time of the concept safety review until such time as reasonably firm process flow diagrams or early P I diagrams are available. 

Once the set of accidents has been agreed upon, hazards can be derived from them. This process is part of what is called Preliminary Hazard Analysis (PHA) in System Safety. The hazard log is usually started as soon as the hazards to be considered are identified. While much of the information in the hazard log will be filled in later, some information is available at this time. 

Two types of analytical methods are used to evaluate hazards 1) preliminary hazards analysis (PHA), and 2) failure modes and effects analysis (FMEA). PHA is an accident scenario-based form of analysis. The FMEA is a complementary type of evaluation that utilizes a system failure-based form of analysis. Generally, FMEAs were only accomplished for equipment which was perceived to have a significant safety role, i.e. SSCs which were anticipated to be designated as safety significant in accordance with DOE-STD-3009. Unlike PHA, the first objective of FMEA is to subdivide the facility into several different (and, to the maximum extent possible, independent) system elements. Failure modes of each system element are then postulated and a structured esramination of the consequences of each failure mode follows. However, similar to PHA, FMEA. documents preventive and mitigative features (failure mechanisms and compensation) and anticipated accident consequences (failure effects). This appendix documents the FMEA for the HCF. 

The DECRIS RVA has two phases Phase 1 consists of a risk screening of undesired events, and is similar to a preliminary hazard analysis (PHA). Phase 2 consists of the following steps ... 

The preliminary hazard analysis (PHA) is an initial look at the entire system. A PHL, if available, is expanded by adding new hazards that may be identified as more project information is developed, as well as more information about each hazard. If a PHL has not been prepared, the PHA serves as the primary hazard identification tool as well as the initial hazard analysis. The methods used for conducting a PHA are basically the same as for a PHL, even though occasionally more advanced techniques may be appropriate. 

Hazard identification is continued throughout the design stage and documented in the preliminary hazard analysis (PHA), subsystem hazard analysis (SSHA), and the system hazard analysis (SHA). Even though the primary purpose of these products is to analyze previously identified hazards and to determine the adequacy of controls, every effort should be made to continue to identify new hazards, especially those associated with interfaces and changes. 

The major hazard analysis and control effort is concentrated in the design phase (or phases). The first and in many ways the most important hazard analysis is the preliminary hazard analysis (PHA). 

The preliminary hazard list (PHL) dcKuments and provides initial assessment of hazards identified very early in the life cycle. The PHL is a feeder document for the preliminary hazard analysis (PHA) and provides the first information to aid in scaling the system safety effort. 

The preliminary hazard analysis (PHA) expands the preliminary hazard list by identifying additional hazards, analyzing identified hazards, recommending hazard controls, and determining the level of risk after the controls are... 

---