Process hazard study

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. 

The first 3 levels of process hazard studies align closely with the first three phases of the lEC safety life cycle model. 

Alignment of process hazard studies with lEC safety life cycle... 

This information describes the output response of the SIS as seen by the process hazard study team. 

This guide outlines a typical method for carrying out a process hazard study level 2 for a new or existing chemical process plant. It is based on guidelines originally prepared by IC I in the UK. For a more comprehensive treatment of hazard study procedures reference should be made to the hazard study guides listed in this book. 

As the design of the plant and the control system progresses the details available from the fimctional specification of the control system will permit a more detailed hazard study just as is the case with the process hazard study. ICI and the AECI HAZOP manual suggest a detailed checklist procedure is then applied in a study team format to cover all the potential hazards. 

Chapter 2 Hazards and risk reduction. An examination of basic hazards, the chemical process, hazards studies, the lEC model, protection layers, risk reduction and classification and the important concept of the safety integrity level (SIL). 

Hazard and Operability Study (HAZOP) A systematic qualitative technique to identify process hazards and potential operating problems using a series of guide words to study process deviations. 

The experts are the members providing the technical expertise for completing the study. Depending upon the process, a process hazard analysis could include any or all of the following types of experts. Some can be brought in on an as needed basis ... 

What if Approaches Hazind and Operability (HAZOP) Studies Preliminary Hazard Analysis (PLHA) Process Hazard Analysis (PHA)... 

When derived from handbooks or similar sources, many entries in a checklist may not be applicable to the process being studied. In other cases, process hazards may be so unusual they are not in standard checklists. Thus, it may be difficult to assure that all hazards have been analyzed. Also, checklists may indicate that hazards exist, but not what accident scenarios are associated with them. 

V Process hazard analysis (PHA) must be performed by a team of experts, including engineers, chemists, operators, industrial hygienists, and other appropriate and experienced specialists. The PHA needs to include a method that fits the complexity of the process, a hazards and operability (HAZOP) study for a complex process, and for less complex processes a less rigorous process, such as what-if scenarios, checklists, failure mode and effects analysis, or fault trees. 

The Mond Index (ICI, 1985) has been developed from the 1973 version of the Dow F E Index. The principal modifications to the Dow method include (Lees, 1996) 1) wider range of processes and storage installations can be studied, 2) covers processing of chemicals having explosive properties, 3) improved hazard consideration for hydrogen, 4) additional special process hazards, 5) toxicity included into the assesment. 

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. 

These reviews can be either in addition to or combined with periodic process hazard analyses (PHAs) by using methods such as what-if analysis and HAZOP studies. The latter should consciously focus on identifying scenarios in which intended reactions could get out of control and unintended reactions could be initiated. One means of accomplishing this as part of a HAZOP study has been to include chemical reaction as one of the parameters to be investigated for each study node. Johnson and Unwin (2003) describe other PHA-related approaches for studying chemical reactivity hazards. 

Generally, although not exclusively, a scrubber with a recycle loop of the caustic scrubbing liquor is used cases of once-through scrubbing liquor operation do exist. The scrubber may be operated in batch, semi-batch or continuous mode with respect to the liquid. Process hazards exist in batch and continuous mode, the most significant of which is over-chlorination. Batch-wise operations leads to periodic high loads on the hypochlorite destruction unit. In order to even out these loads, and improve the process safety, a study of alternative treatment options has been undertaken. 

Many different loss event scenarios are possible with intentional chemistry. All of them relate to losing containment or control of the intended reaction, starting another reaction, side reaction or series of reactions that are not intended or expected. A process hazard analysis, using a hazard and operability (HAZOP) study or other appropriate method, should be used to systematically identify and evaluate a full set of loss event scenarios. General causes of uncontrolled reactions include, but are not confined to, the following list ... 

For larger or more complex facilities, a systematic approach to identifying incompatibility scenarios and analyzing their severities and likelihoods may be warranted. A process hazard analysis (PHA) approach such as a hazard and operability (HAZOP) study can be an effective tool to facilitate such an effort, and may be required by regulation if the process falls within the scope of regulations. These methods are discussed in Section 4.5. 

Risk assessment studies can be performed using whatever process information is available (CCPS 1992a). Obviously, the more information and knowledge that is available, the more thorough and valuable the risk study can be. For facilities that must meet regulatory requirements for process hazard analyses, certain process safety information (PSI) is required to be compiled and up to date before starting the analysis. 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

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