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Basic Considerations in Design
Published in Yogesh Jaluria, Design and Optimization of Thermal Systems, 2019
Material selection is not an easy process because of the many considerations that need to be taken into account. These lead to a variety of constraints, many of which may be conflicting. Though cost is an important parameter in the selection, it is not the only one. We want to choose the best material for a given application while satisfying many constraints. However, information on material properties is often not available to the desired detail or accuracy. The range of available materials has increased tremendously in recent years, making material selection a very involved process. However, the choice of the most appropriate material for a given application is crucial to the success of the design in today's internationally competitive environment. With a proper choice of materials, the system performance can be improved and costs reduced. In several cases, material substitution is necessary because of regulations stemming from environmental or safety considerations. For example, the incentive for improvements in gasoline, including addition of ethanol, arises from pollution, availability, cost, and political considerations. Substitution of asbestos by other insulating materials is due to the health risks of asbestos. Obviously, all such considerations complicate material selection and substantial effort is generally directed at this aspect of design.
Protecting the Worker II: Providing Clean Air
Published in Ronald Scott, of Industrial Hygiene, 2018
Replacement of a chemical by a less toxic one is a measure that improves the safety of the plant in many ways. Handling the chemical is less dangerous, spills are less threatening, waste handling is less critical, and levels of air contamination do not have to be controlled as closely. Sometimes such a change is opposed because the substitute chemical is more expensive. If the alternative is an expensive engineering change, however, substitution of another chemical often yields savings when the price of protecting workers adequately against the more toxic chemical is added to the cost sheet.
Alkyl Halides and Substitution Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
A substitution reaction is characterized by one atom or group replacing another atom or group at an sp3-atom (usually carbon). This transformation is made possible by the presence of a polarized bond in an alkyl halide (C—Cl, C—Br, or C—I), where the carbon is electron deficient and has a polarity of δ+. That carbon is most likely to react with an electron donating species. What is a nucleophile?
Hierarchy of contamination control in the fire service: Review of exposure control options to reduce cancer risk
Published in Journal of Occupational and Environmental Hygiene, 2022
Gavin P. Horn, Kenneth W. Fent, Steve Kerber, Denise L. Smith
AFFF has historically been used by firefighters to control and suppress flammable liquid fires such as those from fuel spills (Class B). However, firefighters’ use of AFFF can lead to elevated concentrations of PFAS in firefighter blood and contribute to PFAS contamination of ground and surface water in the general population (Houtz et al. 2013; Hu et al. 2016). Over the past several decades, the formulation of AFFF has evolved to move away from longer chain PFAS (e.g., PFOA, PFOS) and fluorine-free foams have been introduced to the market (Hawthorne and Grant 2022). However, AFFF is still being used for certain types of fires while further evaluation of fluorine-free foams proceeds to determine which foams meet performance requirements. As with any chemical substitution, it is important to choose replacement chemicals that are effective for their intended purpose and do not pose increased or different health and safety risks that cannot be properly managed.
Ten-tier and multi-scale supply chain network analysis of medical equipment: random failure & intelligent attack analysis
Published in International Journal of Production Research, 2022
Kayvan Miri Lavassani, Zachary M. Boyd, Bahar Movahedi, Jason Vasquez
The ‘no substitution’ assumption may not be very realistic at the firm level since firms can switch suppliers, albeit after incurring switching costs and delays. However, the no substitution assumption can be materialised at the higher scales. For example, the substitution may not be feasible at the industry level due to the product specification. The ‘alternate path’ assumption, while possible, may not be feasible, especially at the firm scale, due to a partial or complete lack of compatibility of suppliers that may limit product substitutability and due to available capacity throughout the alternate path.