Hazard study

This chapter takes a closer look at those aspects of hazard studies that have a bearing on the development and specification of safety instrumented systems. It is important to understand that in general, hazard studies are a part of the overall task of safety, health, and environment management for any industrial activity, particularly in large industrial plants. Functional safety is just one part of the safety management task and hence the lEC functional safety standard supports some of the tasks of safety management but does not cover the overall task. 

Examples of procedures for conducting hazard studies are shown but these serve only as an introduction to the subject and do not cover the depth of knowledge needed by an individual to conduct such studies. Specialized textbooks and training courses exist for this work, which are largely the responsibility of a process or chemical engineer. The objective here is to show how such studies are used to provide a means of identifying hazards and specifying the requirements for risk reduction. 

There are four sections located towards the end of this chapter that provide additional information of value to those wishing to pursue hazard study and analysis in greater detail. 

The starting point for an SIS is the safety requirements specification or SRS. If we look at the input requirements for developing an SRS, we will see that much of the information needed stems from a good knowledge of the manufacturing process, its normal operations, and its potential hazards. 

ANSI/ISA S84.01-1996 provides an excellent summary of the specification requirements. Section 5.2 of the standard shows the input requirements of the standard that are expected to be generated from the hazard analysis activities. 

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The primary issue is to prevent groundwater from becoming radioactively contaminated. Thus, the property of concern of the long-lived radioactive species is their solubility in water. The long-lived actinides such as plutonium are metallic and insoluble even if water were to penetrate into the repository. Certain fission-product isotopes such as iodine-129 and technicium-99 are soluble, however, and therefore represent the principal although very low level hazard. Studies of Yucca Mountain, Nevada, tentatively chosen as the site for the spent fuel and high level waste repository, are underway (44). 

Fire and uncontroUed polymerization are a concern in the handling of chloroprene monomer. The refined monomer is ordinarily stored refrigerated under nitrogen and inhibited. This is supported by routine monitoring for polymer formation and vessel temperature. Tanks and polymerization vessels are equipped for emergency inhibitor addition. Formalized process hazard studies, which look beyond the plant fence to potential for community involvement, are routine for most chemical processes. 

Adequate engineering design for the duty intended Hazard studies ( What if ) carried out ... 

Hazard studies carried out to identify normal and abnormal hazards and circumstances leading to such hazards ... 

A laboratory pressure safety program [223] presents a list of questions helpful in evaluating the problem of hazard studies in the open laboratory... 

The way of using the index is flexible. Comparisons can be made at the level of process, subprocess, subsystem, or considering only part of the factors (e.g. only process oriented factors). Different process alternatives can be compared with each other on the basis of the ISI. Also the designs of process sections can be compared in terms of their indices in order to find the most vulnerable point in the design. Sometimes a comparison based on only one or two criteria is interesting. E.g. a toxicity hazard study can be done by considering only the toxic exposure subindex. Because its flexibility the total inherent safety index is quite easily integrated to simulation and optimization tools. 

Weinstein, N.D. 1986. Public Perceptions of Environmental Hazards Study 1 Final Report Statewide Poll of Environmental Perceptions. Trenton, NJ New Jersey Department of Environmental Protection, Office of Science and Research. 

Although some of the words used above have an intuitive, if slightly fuzzy meaning, we need to be fairly precise about their definitions in the context of Hazard Studies and Risk Assessment. 

The first step in risk assessment in any project is to identify the potential hazards involved. This is done using Hazard Studies, which have been developed as a means of identifying and managing hazards in the design, building and early stages of operation of chemical plant. They are adaptable and may address both process and non-process hazards. 

Hazard Study 1 aims to ensure that the understanding of the project, process and materials involved is sufficient to enable safety, health and environmental issues to be properly addressed. It also contributes to key policy decisions and establishes contacts, both internally and with external authorities. In essence it asks the question do you know what you re doing It is carried out early in the project when the scope is reasonably well understood, but there may still be alternative routes or processes or competing avenues for investment. 

Hazard Study 4 is a check that the plant has been constructed to the intended design, all actions from previous studies have been carried out, operating and emergency instructions are satisfactory and the training of appropriate people has been executed and validated. 

Hazard Study 5 ensures that the project, as implemented, meets Company and legal requirements. 

Hazard Study 6 checks that all actions in Hazard Studies 1-5 have been completed and reviews them in the light of operational experience on the plant. This study is carried out after the plant or process has been running for a few months. As well as providing feedback to improve or modify the process and its operation, it forms a useful guidance for possible improvements in future designs. 

In practice, Hazard Studies 1, 2 and 3 are used in a broadly similar pattern across the whole of the chemical process industries. However, the content and application of studies 4, 5 and 6 varies considerably between different companies and organisations, and indeed extra studies are often inserted. Since this chapter is aimed primarily at the design of process plant, the latter three studies will not be considered beyond this brief mention. 

It has been found that well executed Studies 1 and 2 result in a plant design that is right first time , and reduce the stress and amount of work needed at the HAZOP (Hazard Study 3) stage (see the A brief history of Hazard Studies box-out). 

We will now look at the first three Hazard Studies in more detail. 

A brief overview of the history of Hazard Studies, as experienced by one major UK chemical company, may be of help in setting this chapter in context. 

HAZOP study remains one of the best ways of seeking out process hazards, and it is seated firmly at the heart of the Hazard Study framework. 

The output of Hazard Study 1 is a formal report with the following sections ... 

The answers to much of this will he in the work already completed in Sections 2, 3, 4, 5, 8 and 10 of the Hazard Study 1 report, but the information is viewed in a different perspective. 

When a process flow diagram for a plant is available, but before detailed design commences, Hazard Study 2 may be carried out. This is a much more creative exercise than Hazard Study 1 (which is largely concerned with data collection). The purpose of this study is to look at the process area by area and identify the particular hazards and operating situations which the process engineer must take account of in his or her design. 

In some circumstances a Hazard Study 2 will include factors affecting the construction of the plant and its eventual demolition, as well as the demolition of any existing redundant structures. 

Recording Hazard Study 2. Each organisation will have its own favourite way of recording the output from Hazard Study 2, but typically this will be in a tabular format under headings such as ... 

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