Chemical process, basic hazards

NFPA-325 Guide to Fire Hazard Properties of Flammable Liquids, Gases and Volatile Solids, (1994 ed.), NFPA-321 Basic Classification of Flammable and Combustible Liquids (1991 ed.), NFPA-497A, Classification of Class 1 Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas (1992 ed.), and NFPA-497B, Classification of Class II Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas (1991 ed.), National Fire Protection Association, Quincy, MA. 

The purpose of this handbook is to facilitate, within the DOE, the performance of chemical process hazards analyses (PrHAs) as required under the PSM Rule. It provides basic information for the performance of PrHAs, and should not be considered a complete resource on PrHA methods. Likewise, to determine if a facility is covered by the PSM rule, the reader should refer to the handbook, "Process Safety Management for Highly Hazardous Chemicals" (DOE-HDBK-1101-96). 

In addition to the importance of combustion reactors in chemical processes, mcon-troUed combustion reactions create the greatest potential safety hazard in the chemical industry. Therefore, all chemical engineers need to understand the basic principles of combustion reactors to recognize the need for their proper management and to see how improper management of combustion can cause unacceptable disasters. 

After an introduction that considers the place of chemical industry in society, the basic concepts related to risk analysis are presented. The second section reviews the steps of the risk analysis of chemical processes discussed. Safety data are presented in the third section and the methods of hazard identification in the section after that. The chapter closes with a section devoted to the practice of risk analysis. 

Many fundamental concepts of human health risk assessment from chemical and biological hazards have been described in Risk Assessment in the Federal Government Managing the Process (NRC, 1983). The basic paradigm developed in that report is shown in Figure 6-1, and it captures the two key components—risk assessment and risk management—that apply equally well to building protection situations. 

Training can also be a problem area. Most companies only provide basic hazard communication (HAZCOM) training to contractor employees and then rely on the contract company to provide any job-specific training to their own employees. In many instances this leaves the contract employees with gaps in their training, especially when it comes to unique issues and concerns related to the process or chemicals handled at the facility. When outsourcing functions which impact process safety, the details of the training provided to the contract employees should be carefully reviewed and customized or enhanced as needed. 

The safety of a process can be achieved by inherent (internal) and external means. Inherent safety focuses on the intrinsic properties of a process and attempts to design out hazards rather than trying to control hazards through the application of external protective systems. Inherently safer processes rely on chemistry and physics (properties of materials, quantity of hazardous materials) instead of control systems (interlocks, alarms, procedures) to protect workers, property, and the environment. It would be inappropriate to talk about an inherendy safe process, as an absolute definition of safe is difficult to achieve in this context since risk cannot be reduced to zero. However, one can talk about a process or chemical being inherently safer than other(s). For instance, water can be an extremely hazardous chemical under certain conditions (e.g., floods), but in the context of a chemical process, water is an inherently safer solvent than other chemicals. Trevor Kletz has postulated some basic principles of inherent safety [79,80] that process systems engineers can follow when designing or retrofitting chemical processes. Kletz s inherent safety principles can be summarized as follows ... 

The basic concept of inherently safer process design is to reduce the hazard of a process by reducing or eiiminating the hazards associated with materials and operation of the process. This approach is described in detaii in the CCPS book, Inherently Safer Chemical Processes, A Lifecycle Approach, 2nd edition, 2008. in brief, there are four major strategies for inherently safer design ... 

One of the most frequently encountered problems in chemical process operations is that of separating two materials from a mixture or a solution. Distillation is the most frequently used method of making such a separation. Another useful separation method is extraction, a process that separates two materials in a mixture by introducing a third material that will dissolve one of the first two materials but not the other. In liquid-liquid extraction, all four materials are liquids, and the mixture is separated by allowing them to layer out by weight or density. There are basically three steps in the liquid-liquid extraction process (1) contact the solvent with the feed solution (2) separate the raffinate from the extract and (3) separate the solvent from the solute. The solvent must be able to dissolve the solute but not the raffinate must be insoluble so that it will layer out must be separable from the solute should be inexpensive and readily available and should not be hazardous or corrosive. 

Chemical Hazard Analysis (CHA)— A CHA is derived from HAZOP methodologies and can be considered a precursor to a PHA. It is applicable to analyzing petrochemical or chemical processing hazards. The same seven basic HAZOP guidewords are used no, more, less, part of, reverse, as well as, and other. While CHA assumes the proposed chemical reaction is basically safe when conducted as specified (should... 

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). 

Included ia the OSHA regulations are standards for safe work practices such as lock-out/tag-out and confined space entry, personal protective equipment, storage of hazardous materials, welding process, forklift operation, and requirements for fire protection. Basically, all activities within a chemical facihty are covered by OSHA standards. 

Basic process chemistry using less hazardous materials and chemical reactions offers the greatest potential for improving inherent safety in the chemical industry. Alternate chemistry may use less hazardous raw material or intermediates, reduced inventories of hazardous materials, or less severe processing conditions. Identification of catalysts to enhance reaction selectivity or to allow desired reactions to be carried out at a lower temperature or pressure is often a key to development of inherently safer chemical synthesis routes. Some specific examples of innovations in process chemistry which result in inherently safer processes include ... 

Today the chemical industry is involved in a broad spectrum of manufacturing processes tliat range from biological preparations to plastics and e.vplosives. Altliough the basic plans and designs for tliese processes may be similar, each individmil plant will have its own unique set of potential hazards. 

Surampalli, Ong, Seagren, and Nuno compiled and edited a book by the American Society of Civil Engineers (ASCE) called Natural Attenuation of Hazardous Wastes.97 In addition to a discussion of the regulatory framework, this book covers major pollutants and basic scientific principles on physical, chemical, and biological processes involved in natural attenuation. It also contains an extensive review of literature, examples of applications of natural attenuation, and site characterization and monitoring requirements and procedures. 

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