Safer chemicals

S. C. DeVito, ia S. C. DeVito and R. L. Garrett, eds.. Designing Safer Chemicals Green Chemistry for Pollution Prevention, American Chemical Society Symposium Series 640, American Chemical Society, Washington, D.C., pp. 194—223. 

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. 

On December 14, 1977, Trevor Kletz, who was at that time safety advisor for the ICI Petrochemicals Division, presented the annual Jubilee Lecture to the Society of Chemical Industry in Widnes, England. His topic was What you don t have, can t leak, and this lecture was the first clear and concise discussion of the concept of inherently safer chemical processes and plants. 

What do we mean when we speak of an inherently safer chemical process Inherent has been defined as existing in something as a permanent and inseparable element, quality, or attribute (American College Dictionary, 1967). A chemical manufacturing process is inherently safer if it reduces or eliminates the hazards associated with materials and operations used in the process, and this reduction or elimination is permanent and inseparable. To appreciate this definition fully, it is essential to understand the precise meaning of the word hazard. A hazard is defined as a physical or chemical characteristic that has the potential for causing harm to people, the environment, or property (adapted from CCPS, 1992). The key to this definition is that the hazard is intrinsic to the material, or to its conditions of storage or use. Some specific examples of hazards include ... 

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 ... 

The design and implementation of inherently safer chemical processes includes consideration not only of the people operating and maintaining the plant while it is in operation, but also the safety of those who may later use the plant for other purposes. This includes dismantling... 

Can safer chemicals be used (Nontoxic or nonvolatile reactant.) Can quantities be reduced (Careful look at intermediates storage.) Can potential releases be reduced via lower temperatures or pressures, elimination of equipment or by using sealless pumps Can waste be reduced (Regenerable catalyst or recycle.)... 

A collection of databases of chemicals and of functional groups which rank chemicals and groups relative to their reactivity, stability, toxicity, and flammability categories. This would assist in the evaluation of the potential benefits of substituting one, somewhat safer, chemical for another. 

Bodor, N. (1995). Design of Biologically Safer Chemicals. Chemtech (October), 22-32. 

Dale, S. E. (1987). Cost Effective Design Considerations for Safer Chemical Plants. Proceedings of the International Symposium on Preventing Major Chemical Accidents, February 3-5, 1987, Washington, D. C., ed. J. L. Woodward, 3.79-3.99. New York American Institute of Chemical Engineers. 

Englund, S. M. (1990). Opportunities in the Design of Inherently Safer Chemical lants. Advances in Chemical Engineering 15, 69-135. 

Hendershot, D. C. (1991a). Design of Inherently Safer Chemical Processing Facilities. Texas Chemical Council Safety Seminar, june 11,1991, Galveston, TX, Session D. 

Inherently Safer Chemical Processes—A Life Cycle Approach was written by the Center for Chemical Process Safety Inherently Safer Processes Subcommittee ... 

D. A. Crowl (editor). Inherently Safer Chemical Processes—A Life Cycle Approach, AIChE, New York, 1996. 

Promotes pollution prevention, the use of safer chemicals through regulatory and vohmtaiy efforts, risk reduction so as to minimize exposure to existing substances such as lead, asbestos, dioxin, and polychlorinated biphenyls, promotes the public understanding of risks by providing understandable, accessible and complete information on chemical risks. 

Design safer chemicals. Chemical products should be designed to have minimal toxicity. 

Yin H, Anders MW, Korzekwa KR, Higgins L, Thummel KE, Kharasch ED, et al. Designing safer chemicals predicting the rates of metabolism of halogenated alkanes. Proc Natl Acad Sci USA 1995 92 11076-80. 

Reducing the intrinsic hazard of chemicals is the most effective and most fundamental of the risk reduction options available. Intrinsic risk reduction is based on the principle that the structure of a chemical drives hazard and molecular intentional, informed manipulation will result in the design of safer chemicals. Wastewater treatment plants employ large filters packed with granular activated carbon to remove polluted water. Synthetic chemists are... 

Tier III analysis Toxicokinetic/toxicodynamics. The role of ADME in designing safer chemicals... 

An understanding of the role of toxicokinetics and toxicodynamics in the manifestation of hazard is fundamental to designing safer chemicals and can guide early design choices. Toxicokinetics and toxicodynamics use the same principles to study toxicological phenomena as those that are used to study the therapeutic use of chemicals as medicines. Toxicokinetics is concerned with the time course of action of chemicals that involves the disposition of a chemical affected by absorption, distribution, metabohsm and excretion commonly referred to by the acronym ADME. 

Progressing toward the goal of designing safer chemicals requires that the relative safety of chemicals can be compared so that a clear decision process can be identified. The metrics to accomplish this evaluation of the relative hazards of chemicals are well estabhshed but have not been applied to the field of green chemistry, specifically, designing safer chemicals. 

Toxicity is a relative term and to have any usefulness in designing safer chemicals this concept must be clearly articulated to synthetic chemists. For a chemical to be declared a greener alternative there must be a mechanism for comparing the toxicity of one chemical with another. The hterature contains many references to qualitatively and quantitatively evaluating toxicity that can serve as guidance for characterizing the relative reduction in toxicity for a target chemical (see Table 2.3). ... 

A framework for designing safer chemicals using the concepts of green chemistry has been described. The framework is comprehensive because it expands the consideration of hazard... 

The drivers for accepting this new approach must include a mechanism to evaluate the relative greenness of new and redesigned chemicals as well as provide clear directions for advancing towards safer chemicals that is economically viable. 

Lai, D.Y., Woo, Y.T., Argus, M.E., Arcos, J.C. (1996) Cancer Risk Reduction through Mechanism Based Molecular Design of Chemicals. In Designing Safer Chemicals (eds. S. DeVito R. Garrett) 254pp. American Chemical Society, Symposium Series 640, pp. 63-72. 

The Green Screen defines four benchmarks on the path to safer chemicals ... 

THE GREEN SCREEN FOR SAFER CHEMICALS EVALUATING FLAME HETAflOANTS FOR TV ENCLOSURES... 

Figure 8.3 The Green Screen for Safer Chemicals Benchmarks. Reproduced with permission of Clean Production Action.

Benchmark 4 Prefer - Safer Chemical. Only organic chemicals with low inherent toxicity to humans and wildlife, that do not bio accumulate, and rapidly and completely degrade to benign degradation products or metabolites reach Benchmark 4. These are chemicals that would meet the principles of green chemistry that relate to hazard. 

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