The ETBA

As stated earlier, the ETBA has great utility in determining the specific breakdowns in energy barriers during an accident/incident investigation. The ETBA is also quite useful in the analysis of new or existing systems to examine the adequacy of energy barriers currently in place. 

The following example will evaluate an existing oxygen supply system installed at a fictitious hospital Memorial General Hospital). 

The ETBA begins with an identification of fhe types of energy involved in this case. For the purpose of this example, only the two primary sources shall be examined here. Obviously, the very first concern is the presence of an extremely high pressure in a confined sysfem. The gas in fhis example (oxygen) is highly combustible and, thus. 

DRAWING NUMBER ENERGY AMOUNT TYPE BARRIERS (CONTROLS) POTENTIAL TARGETS RAC NO. ANALYSIS OF BARRIER EFFECTIVENESS RECOMMENDED ACTIONS CONTROLLED RAC APPLICABLE STANDARDS 

MQHS CMV-051834 High Pressure Gas Isolation valves Personnel 1C Barriers adequate to prevent exposure Ensure proper procedures are es ished and followed IE ASME OSHA 29CFR 1910.134 

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The HazOp study is also similar to the ETBA in that it traces energy flows through a facility, studies barriers to control energy flows, and identifies the targets of unwanted energy flows. 

This particular analytical technique can be used to aid in preparing preliminary hazard lists (PHLs), conducting preliminary hazard analyses (PHAs), subsystem hazard analyses (SSHAs), or system hazard analyses (SHAs). The ETBA may be helpful in performing operating hazard analyses (OHAs) and accident analyses and in other situations. The ETBA seems to be particularly well-suited to facility system safety programs. 

Collect the necessary input documents and reference resources, including applicable codes, standards, and regulations, list of consultants, lessons learned information, examples of ETBAs on similar projects, other analyses and/or a PHL on this project, and other materials that may aid in the ETBA effort). List the types of energy associated with this project, which may include... 

Complete the ETBA worksheets (Fig. 13-2) for each energy type. Use the completed ETBA worksheets to complete the appropriate type of analysis (PHL, PHA, SSHA, SHA) worksheets and report (see Chapter 8). 

The PHA (Figure 6.2) is perhaps the most critical analysis that will be performed because it is usually the first in-depth attempt to isolate the hazards of a new or, in some cases, modified system. The PHA will also provide rationale for hazard control and indicate the need for further, more detailed analyses, such as the subsystem hazard analysis (SSHA) and the system hazard analysis (SHA). The PHA is usually developed using the system safety techniques known as failure mode and effect analysis (FMEA) (Chapter 9) and/or the ETBA. Data required to complete... 

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. 

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. 

The ETBA is one of the fundamental tools of system safety analysis and, when used, can not only document the adequacy of hazard barriers and controls but also identify those energy flow areas within a system that may have been overlooked as potential risk hazards during the concept or design phase of the project. 

It should be understood that the performance of an FHA is not always a requirement. Other analytical methods such as, but not limited to, the FMEA and the ETBA, if performed, should have already evaluated most, if not all, of the same hazards that would be identified in the FHA. However, the FHA is a powerful tool in hazard identification and control, and the benefit of its performance should not be overlooked. The FHA is an excellent system safety engineering method that can be used to ensure system operational integrity. 

Once the various types of energy affecting the system have been identified, the ETBA worksheet should be completed. Figure 9.1 shows a sample ETBA worksheet. The information recorded on the completed ETBA worksheet can then be used to perform subsequent analyses (PHL, PHA, etc.) along with their related reports. In some cases, depending upon the level of detail desired, the ETBA itself may provide an adequate amount of information to be included in the final PHA. In fact, since hazardous events can usually be associated with some type of energy transfer and, since accident causal factors typically involve the absence of controls or the failure of existing barriers and. 

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