Specific Reaction Hazards

D. R. Stull11 developed a rating system to establish the relative potential hazards of specific chemicals the rating is called the reaction hazard index (RHI). The RHI is related to the maximum adiabatic temperature reached by the products of a decomposition reaction. It is defined as... 

On the basis of the test and calculation results illustrated in Table 3.6, it is possible to make an energy appraisal for the specific reaction under investigation. Generally speaking, the potential for a worst-case decomposition becomes greater when the hazard class is high as listed in Table 3.6. The worst case should be assumed instead of the credible case, in general, as follows ... 

The wise chemist consults the material safety data sheet (MSDS) before handling any new chemical in the laboratory. The reaction hazards posed by chemicals must be thoroughly assessed before any reaction is run on scale. The MSDS also includes information that has been compiled about the toxicological hazards of specific chemicals. An MSDS may be found with the shipment of a chemical, in databases within a company, or in databases accessible through the Internet [2],... 

Besides, the use of organic and inorganic chemicals employed as reactants, catalysts, medium of reaction, purifying substances etc., are not only harmful but also hazardous in nature. Nevertheless, the various conditionalities of critical and specific reactions are sometimes articulated and spelled out so meticulously that one has to follow them just like gospel truth , to accomplish the right synthesis, and hence, the right product. 

The format of the first edition has been retained for this second edition with the addition (by popular demand) of two appendices. One gives summaries of 100 incidents illustrating their causes and indicating what can happen if appropriate procedures as described in the guide are not followed. The other provides a practical example of a typical chemical reaction hazard assessment, from consideration of the process description, through experimental testing to the specification of safety measures. 

The book does not focus on occupational safety and health issues, although improved process safety can benefit these areas. Detailed engineering designs are outside the scope of this work. This book intends to identify issues and concerns in batch reaction systems and provide potential solutions to address these concerns. This should be of value to process design engineers, operators, maintenance personnel, as well as members of process hazards analysis teams. While this book offers potential solutions to specific issues/concerns, ultimately the user needs to make the case for the solutions that provide a balance between risk... 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

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 ... 

Hazardous reactions are pointed out in specific cases. In addition general safety rules for work with fluorine and fluorinated agents are thoroughly discussed on pages 25 and 26 of this book and on pages 13 and 14 in the 1976/1992 editions. 

Provision of information and instruction to personnel as to the hazards with the specific chemical, including possible reactions. 

Hazard, i.e. the potential of the material to cause injury under certain conditions (flammability, explosion limits in air, ignition and autoignition temperatures, static electricity (explosions have occurred during drying due to static electricity), dust explosion, boiling point, fire protection (specification of extinguishers, compounds formed when firing), R S (nature of special risk and safety precautions). Table 5.2-5 lists hazards associated with typical chemical reactions. 

A process is inherently safe in a rigorous sense, when no fluctuation or disturbance can cause an accident. To search for synthetic routes that avoid hazardous reactants, intermediates, and reaction mixtures, is an impetus to be seriously considered by chemists and process designers. Nevertheless, there will always be a need to cope with potentially hazardous materials and reaction mixtures in future process design work, the more so because process streams are expected to become potentially more dangerous in the future. The process streams will be more concentrated to increase energy efficiency, to ease purification, and to decrease the load of wastewater and spent acids. More concentrated process streams have a higher specific content of latent energy and are hence less stable. 

Professor Martel s book addresses specifically some of the more technical eispects of the risk assessment process, mainly in the areas of hazard identification, and of the consequence/effect analysis elements, of the overall analysis whilst where appropriate setting these aspects in the wider context. The book brings together a substantial corpus of information, drawn from a number of sources, about the toxic, flammable and explosive properties and effect (ie harm) characteristics of a wide range of chemical substances likely to be found in industry eind in the laboratory, and also addresses a spectrum of dangerous reactions of, or between, such substances which may be encountered. This approach follows the classical methodology and procedures of hazard identification, analysing material properties eind... 

Chemical oxidation typically involves reduction/oxidation (redox) reactions that chemically convert hazardous contaminants to nonhazardous or less toxic compounds that are more stable, less mobile, or inert. Redox reactions involve the transfer of electrons from one compound to another. Specifically, one reactant is oxidized (loses electrons) and one is reduced (gains electrons). The oxidizing agents... 

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