Chemical inherent safety

The ISI is calculated by Equation 3, where the Total Inherent Safety Index (In) is the sum of the Chemical Inherent Safety Index (Ici) and the Process Inherent Safety Index (IPI). These indices are calculated for each process alternative separately and the results are compared with each other. Table 8 describes the symbols of the subindices. 

The Chemical Inherent Safety Index Ici (Eq.4) contains chemical factors affecting the inherent safety of processes. These factors consist of chemical reactivity, flammability, explosiveness, toxicity and corrosiveness of chemical... 

Chemical inherent safety index, ICi Symbol Score... 

The Chemical Inherent Safety Index deals with the hazards which are related to the chemical properties of substances in the process. The Index has been divided into subindices for reaction hazards and hazardous substances. 

Chemical interaction considers the unwanted reactions of process substances with materials in the plant area. These reactions are not expected to take place in the reactor and therefore they are not discussed in the side reaction subindex. The Inherent Safety Index has utilized EPA s matrix (Hatayama et al., 1980) to classify the hazards of the chemical interaction in a process. The worst interaction that appears between the substances present in the plant area is used in the calculations for the Chemical Inherent Safety Index. 

In this thesis an inherent safety index for evaluating inherent safety in preliminary process design was presented. The inherent safety of a process is affected by both chemical and process engineering aspects. These have been dealt separately, since the index was divided into the Chemical Inherent Safety Index and the Process Inherent Safety Index. These two indices consist of several subindices which further depict specific safety aspects. The Chemical Inherent Safety Index describes the inherent safety of chemicals in the process. The affecting factors are the heat of the main reaction and the maximum heat of possible side reactions, flammability, explosiveness, toxicity, corrosiveness and the interaction of substances present in the process. The Process Inherent Safety Index expresses safety of the process itself. The subindices describe maximum inventory, maximum process temperature and pressure, safety of equipment and the safety of process structure. 

In the second method, the inherent safety index proposed by Heikkila [36] is appHed for safety analysis, which requires less information and covers lots of safety aspects [53]. Table 6.14 shows the results obtained from the inherent safety index method for both the technologies. In the inherent safety index method, the chemical inherent safety index and process inherent safety index are assigned to analyze the hazards caused by chemicals. 

Chemical inherent safety index, Jqj Process inherent safety index, ipj Total inherent safety index, ixi... 

In Eqs. [6.14] and [6.15] Me is the flow rate of chemical C Icj is the score of the chemical inherent safety subindex of chemical C Np is the number of equipment P and Ipi is the score of the process inherent safety subindex of equipment P. Again the dry grind process is found to be superior. In summary, it is observed that the dry grind process is superior to the wet milling process for aU three sustainability measures. 

Total Inherent Safety Index (ISI) Chemical Inherent Safety Index (ICI) Score Process Inherent Safety Index (IPI) Score... 

The Inherent Safety Index developed by Hurme and Heikkila (1998) is a sum of two indices, the Chemical Inherent Safety Index and the Process Inherent Safety Index (see Fig. 8.12). The Chemical Inherent Safety Index contains two subindices, the Reaction... 

The development section serves as an intermediary between laboratory and industrial scale and operates the pilot plant. A dkect transfer from the laboratory to industrial-scale processes is stiH practiced at some small fine chemicals manufacturers, but is not recommended because of the inherent safety, environmental, and economic risks. Both equipment and plant layout of the pilot plant mirror those of an industrial multipurpose plant, except for the size (typically 100 to 2500 L) of reaction vessels and the degree of process automation. 

Inherent safety Inventory reduction Fewer chemicals inventoried or fewer in process vessels. Chemical substitution Substitute a less hazardous chemical for one more hazardous. Fr ocess attenuation Use lower temperatures and pressures. 

Understanding the chemistry of the process also provides the greatest opportunity in applying the principles of inherent safety at the chemical synthesis stage. Process chemistry greatly determines the potential impact of the processing facility on people and the environment. It also determines such important safety variables as inventory, ancillary unit operations, by-product disposal, etc. Creative design and selection of process chemistry can result in the use of inherently safer chemicals, a reduction in the inventories of hazardous chemicals and/or a minimization of waste treatment requirements. 

Storage and receiving are activities that can greatly contribute to a safe and economic operation. It is here that quality control can be achieved at minimal cost. Label verification and other quality assurance measures can increase the confidence level that the correct chemicals have arrived, thereby potentially circumventing the use of wrong chemicals. Wrongly shipped chemicals can be returned to the manufacturer with minimal or no cost to the batch operation owner. As with all processes and activities it is of great importance to apply the principles of inherent safety, in particular the minimization and attenuation principles (CCPS G- 41). 

CCPS G-41. Inherently Safer Processes A Life Cycle Approach. American Institute of Chemical Engineers, Center for Chemical Process Safety, New York. 

Hazards can be reduced or eliminated by changing the materials, chemistry, and process variables such that the reduced hazard is characteristic of the new conditions. The process with reduced hazards is described as inherently safer. This terminology recognizes there is no chemical process that is without risk, but all chemical processes can be made safer by applying inherently safer concepts. This book occasionally uses the term inherent safety this does not mean absolute safety. 

Transportation should be considered when assessing risks associated with planned or existing plants. The design of new chemical processing units should include at the earliest opportunity a qualitative or quantitative risk assessment of the whole system including production, use, and transportation in order to minimize overall risk. A brief discussion of the inherent safety aspects of transportation is included in Chapter 5. 

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 ... 

Rogers and Hallam (1991) provide other examples of chemical approaches to inherent safety, involving synthesis routes, reagents, catalysts and solvents. 

Innovative chemical synthesis procedures have been proposed as offering potential for economical and environmentally friendly routes to a variety of chemicals. These novel chemical reactions also offer potential for increasing the inherent safety of processes by eliminating hazardous materials, eliminating chemical intermediates, or allowing... 

Chemical reactions are sometimes conducted in a dilute solution to moderate reaction rates, to provide a heat sink for an exothermic reaction, or to limit maximum reaction temperature by tempering the reaction. In this example there are conflicting inherent safety goals—the solvent moderates the chemical reaction, but the dilute system will be significantly larger for a given production volume. Careful evaluation of all of the process risks is required to select the best overall system. 

Processing under less severe conditions, close to ambient temperature and pressure, increases the inherent safety of a chemical process. Some examples include ... 

Research chemists have many opportunities to incorporate inherent safety in the choice of chemical synthesis route, including ... 

Dow (Sheffler, 1996 Gowland, 1996a,b) describes the use of the Dow Fire and Explosion Index (Dow, 1994b) and the Dow Chemical Exposure Index (Dow, 1994a) as measures of inherent safety, along with the use of inherently safer design principles to reduce hazards. 

Exxon Chemical (French et al., 1996 Wixom, 1995) has developed an inherent safety review process, and its application at various points in the process life cycle. 

The first major objective for the inherent safety review is the development of a good understanding of the hazards involved in the process. Early understanding of these hazards provides time for the development team to implement recommendations of the inherent safety effort. Hazards associated with flammability, pressure, and temperature are relatively easy to identify. Reactive chemistry hazards are not. They are frequently difficult to identify and understand in the lab and pilot plant. Special calorimetry equipment and expertise are often necessary to fully characterize the hazards of runaway reactions and decompositions. Similarly, industrial hygiene and toxicology expertise is desirable to help define and understand health hazards associated with the chemicals employed. 

Experience has shown that reactive chemistry hazards are sometimes undetected during bench scale and pilot plant development of new products and processes. Reactive chemistry hazards must be identified so they can be addressed in the inherent safety review process. Chemists should be encouraged and trained to explore reactive chemistry of "off-normal operations. Simple reactive chemicals screening tools, such as the interactions matrix described in Section 4.2, can be used by R D chemists. 

Carrithers, G. W., A. M. Dowell, and D. C. Hendershot (1996). It s Never Too Late for Inherent Safety. International Conference and Workshop on Process Safety Management and Inherently Safer Processes, October 8-11,1996, Orlando, PL, New York American Institute of Chemical Engineers. 

Edwards, D. W., D. Lawrence, and A. G. Rushton (1996). Quantifying the Inherent Safety of Chemical Process Routes. 5th World Congress of Chemical Engineering, July 14-18,1996, San Diego, CA, Paper 52d. New York American Institute of Chemical Engineers. 

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