Hazard Analysis Techniques

Ericson, C.A., 2005. Hazard Analyses Techniques for System Safety. Wiley-Interscience, New Jersey. 

While RP14C provides guidance on the need for process safety devices, it is desirable to perform a complete hazards analysis of tlie facility to identify hazards that are not necessarily detected or contained by process sLifety devices and that could lead to loss of containment of hydrocarbons or otherwise lead to fire, explosion, pollution, or injury to personnel. The industry consensus standard, American Petroleum Institute Recommended Practice 14J, Design and Hazards Analysis for Offshore Facilities (RP14J), provides guidance as to the use of various hazards analysis techniques. 

Hazards analysis techniques fall in two broad categories. Some techniques focus on hazards control by assuring that the design is in compliance with a pre-existing standard practice. These techniques result from prior hazards analysis, industry standards and recommended practices, results of incident and accident evaluations or similar facilities. Other techniques are predictive in that they can be applied to new situations where such pre-existing standard practices do not exist. 

You can quickly identify these plant sections by reviewing process flow diagrams and valving arrangements. Isolation points are defined by control valves or powered block valves that can be remotely activated. Process hazard analysis techniques help you identify the maximum credible accident scenarios. (Note that manual valves should not be considered reliable isolation points unless they are located to be accessible following a major accident. However, remotely-activated valves can only be considered reliable isolation points if there are adequate reliability engineering and maintenance programs in place.)... 

The data on probabilities given in this example are for illustration only, and do not represent actual data for these components. Some quantitive data on the reliability of instruments and control systems is given by Lees (1976). Examples of the application of quantitive hazard analysis techniques in chemical plant design are given by Wells (1996) and Prugh (1980). Much of the work on the development of hazard analysis techniques, and the reliability of equipment, has been done in connection with the development of the nuclear energy programmes in the USA (USAEC, 1975) and the UK. 

A number of hazard identification and analysis techniques (e.g., HAZOP), can be applied to identify, analyze, and reduce and/or mitigate the process hazards, which includes handling of reactive chemicals and energetic reactions. Chapter 4 provides an overview of these kinds of techniques as related to reactive chemicals mote detailed reviews of hazards analysis techniques are included in [2,3]. 

In 1993, the Center for Chemical Process Safety (CCPS) published Guidelines for Safe Automation of Chemical Processes (referred to henceforth as Safe Automation). Safe Automation provides guidelines for the application of automation systems used to control and shut down chemical and petrochemical processes. The popularity of one of the hazard and risk analysis methods presented in Safe Automation led to the publication of the 2001 Concept Series book from CCPS, Layer of Protection Analysis A Simplified Risk Assessment Approach. This method builds upon traditional process hazards analysis techniques. It uses a semiquantitative approach to define the required performance for each identified protective system. 

Hazard and operability analysis (HAZOP) A qualitative hazard analysis technique to identify and... 

Determine the critical control points (base investigation on FMEA or other hazard analysis technique). Examples would be ... 

Hazard analysis techniques shall be selected and used that are appropriate for the hazards and complexities of work processes being analyzed... 

FMEA is a prospective hazard analysis technique which is widely used in many domains and increasingly in the service industries [4]. The methodology has its origins in military systems and the aerospace industry in the 1960s. Subsequently the automotive and chemical engineering sectors adopted the tool - indeed in some regulated industries application of the technique is now mandatory. The objective of the tool is to identify what in a product can fail, how it can fail, whether failure can be detected and the impact that will have. The technique can be supplanented with a Criticality Analysis which takes into account the severity of the failure. When this extension is employed, the technique is often called FMECA. 

These four types of inadequate control actions are used in the new hazard analysis technique described in chapter 8. 

Technical Authority (ITA) recommended in the report of the Columbia Accident Investigation Board. The risk analysis itself is described in the chapter on the new hazard analysis technique called STPA (chapter 8). But the first step in the safety or risk analysis is the same as for technical systems to identify the system hazards to be avoided, to generate a set of requirements for the new management structure, and to design the control structure. 

As designed, this safety control structure looks strong and potentially effective. Unfortunately, it has not always worked the way it was supposed to work and the individual components have not always satisfied their responsibilities. Chapter 8 describes the use of the new hazard analysis technique, STPA, as well as other basic STAMP concepts in analyzing the potential risks in this structure. 

The most widely used existing hazard analysis techniques were developed fifty years ago and have serious limitations in their applicability to today s more complex, software-intensive, sociotechnical systems. This chapter describes a new approach to hazard analysis, based on the STAMP causality model, called STPA (System-Theoretic Process Analysis). 

Three hazard analysis techniques are currently used widely Fault Tree Analysis, Event Tree Analysis, and HAZOP. Variants that combine aspects of these three techniques, such as Cause-Consequence Analysis (combining top-down fault trees and forward analysis Event Trees) and Bowtie Analysis (combining forward and backward chaining techniques) are also sometimes used. Safeware and other basic textbooks contain more information about these techniques for those unfamiliar with them. FMEA (Failure Modes and Effects Analysis) is sometimes used as a hazard analysis technique, but it is a bottom-up reliability analysis technique and has very limited applicability for safety analysis. 

STPA (System-Theoretic Process Analysis) can be used at any stage of the system life qrcle. It has the same general goals as any hazard analysis technique accumulating information about how the behavioral safety constraints, which are derived from the system hazards, can be violated. Depending on when it is used, it provides the information and documentation necessary to ensure the safety constraints are... 

Comparison of STPA with Traditional Hazard Analysis Techniques... 

Accident investigations, when the events and physical causes are not obvious, often make use of a hazard analysis technique, such as fault trees, to create scenarios to consider. STPA can be used for this purpose. Using control diagrams of the physical system, scenarios can be generated that could lead to the lack of enforcement... 

Besides the physical system analysis, most hazard analysis techniques and accident investigations consider the immediate operators of the system. Figure C.3 shows the results of a STAMP analysis of the flaws by the lower operations levels at Walkerton that were involved in the accident. 

The first group of hazards analysis techniques covers those that are creative and that encourage out of the box or off the wall thinking. The What-If and HAZOP methods fall into the creative/imaginative category. 

The HAZOP method is probably the most thorough hazards analysis technique, and the one which has the largest number of experienced users and trained leaders. Therefore, it is likely to the method which offers the greatest assurance that major hazards have been identified. 

The checklist approach is generally part of other hazards analysis techniques. The HAZOP method itself is a form of checklist, and FMEAs use a set of checklist questions. 

The What-lf method (spelled here in the same way as it is printed in the OSHA PSM regulation, i.e., hyphenated but with the question mark omitted) is the least structured of the hazards analysis techniques. This method also takes the least amount of time. 

One hazards analysis technique used to analyze equipment items is FMEA. The method examines the ways in which an equipment item can fail (its failure modes) and examinees the effects or consequences of such failures. If the criticality of each failure is to be considered, then the method becomes a Failure Modes, Effects and Criticality (FMECA) Analysis. The consequences can be to do with safety, reliability, or environmental performance. 

The original intent of the preliminary hazard analysis technique was to serve as the initial effort to identify and evaluate hazards in the early stages of the design process. But, in actual practice the technique has attained broader use. The principles on which preliminary hazard analyses are based are used not only in the initial design process, but also in reassessing the safety of existing products or operations. 

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. 

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