Intrinsic safety approaches

With regard to hazardous substance substitution, the guiding principle of the intrinsic safety of chemical substances, products or application systems was examined within the scope of the SubChem project. An essential approach for implementation of the guiding principle of the intrinsically safe substance or the intrinsically safe application system, especially with regard to the health and ecological consequences, would be the use of chemicals of short ranges (chemicals with low environmental persistence and transport distance) e.g. by ... 

Again and again, testing houses, manufacturers and users of intrinsically safe products have put the question, how could the narrow borderlines of classic intrinsic safety concerning available power be passed over These borderlines are determined by reference curves as well as by installation rules. The following approaches are dealt with in more detail below ... 

Table X/3.7.1-3 Pros and Cons of Different Approaches to an Intrinsic Safety (IS) Circuit ...

An innovative approach based on broad implementation of the intrinsic safety features and passive safety technology was adopted in the design of SMART reactor. All primary... 

Moreover, we have to cope with one of the biggest dreams/nightmares of industrial chemists the high productivity AND selectivity AND safe oxidation of organic substrates by oxygen/air in the presence of suitable oxidation catalysts. Usually, this approach does not give fully acceptable results either with respect to the intrinsic safety of the process, or to its performances quite often deep oxidation takes place or difficult safety constraints must be considered. 

French railways have from the outset pursued a deterministic approach, known as intrinsic safety, which requires comprehensive knowledge of failure modes of the components, this being possible as long as ... 

From 1975 to 1990, scientists at the University of Kansas utilized a rational synthetic design for the definition of a new excipient, the SBE derivative of P-CD (SBE7-P-CD CAPTISOL ). Designing renal safety into the CD was approached by introducing anionic substituents onto the CD structure. This approach capitalized on the increased water solubility that would be realized with the introduction of an ionic substituent. Higher intrinsic water solubility was expected to help minimize the potential precipitation of the CD, if concentrated in the kidney cell, and the charged substituent was expected to capitalize on the ability of the kidney to efficiently excrete ionic compounds into the urine, thus reducing residence time and exposure of the kidney cells to the CD. 

The major advantage of (fractional) oral clearance as a phenotypic trait is that its value is linearly related to the enzyme s catalytic activity, provided that first-order conditions are present. This requirement, along with any safety considerations, is the main reason the dose of an in vivo probe should be as low as possible, consistent with analytical considerations. Furthermore, it is possible to directly extrapolate this type of trait measure to the disposition of other drugs whose metabolism is mediated by the measured enzyme and also to place the trait value within a therapeutic context. On the other hand, estimation of oral clearance requires multiple blood and urine collections, often over many hours, that are an inconvenience for the study subject and require considerable amounts of analytical time and effort. Because of this, simpler and less time-consuming approaches have often been used. However, it is not always appreciated that such phenotyping tests provide only an indirect measure of metabolizing activity and may be affected by factors other than the enzyme s intrinsic clearance. In addition, it is difficult to relate an indirect trait measure to parameters that are of clinical importance, such as the drug s clearance. 

In recent years a number of groups have developed compounds that serve as single precursors for specific binary materials 133, 134, 135,136,137,138,139,140,141,142). In this approach, the objective is to synthesize precursor molecules that are easy to handle with low toxicity and that intrinsically contain not only the desired stoichiometry of the material but also a low energy decomposition pathway. When successful these rational precursors have the desired properties of convenience and safety but, as important, create opportunities for preparing films of presently known stoichiometry with new properties as well as for exploring systems of unknown stoichiometry and properties. 

A key danger in the retrospective approach is to fall into the trap of conveniently building the safety argument around selective evidence which happens to be at hand. To do so runs the risk of forcing the safety case to articulate an artificially rosy picture of the world. It can be easy to assume that a much-loved system that has been in operation for many years must be intrinsically safe. That is not to say that it is unsafe but one should actively question whether the data which happens to be available can truly and objectively substantiate the safety case s claims. In some circumstances it may be appropriate to undertake the hazard assessment in a virtual vacuum of operational knowledge perhaps involving personnel who are somewhat removed from its day-to-day business. In this way appropriate controls can be developed and more objectively be tested to determine whether they can be traly validated. 

Many causality algorithms and categorisation systems have been proposed but none has gained universal acceptance, and the value of assessing this for each individual report of a suspected ADR now seems to be doubtful. It is certainly much more efficient to reserve such assessment for a series of cases which might represent a new and/or important safety issue. Systematic assessment of causality in individual cases occurring in clinical trials is intrinsically a weaker approach to assessing causality than comparison of numerical cormts. 

Safety engineers identify the approach of using "intrinsically safe" hardware as being "preventive." This approach assumes that an ignition can be prevented and seeks to do just that. 

The debate about "containing" vs. "intrinsically safe" design is for safety engineers, and outside the scope of the book. This author has successfully used both approaches. Fires in vapor degreasers using flammable solvents are nonexistent, or occur with an extremely low incidence, or are well-concealed. 

Operating systems (OS) are common to almost all computing platforms including those used in safety related systems (SRS). OS are commercial components and, as with other off the shelf components, there can be significant difficulties in assessing their dependability cost-effectively. An OS provides a broad range of support services to application software, hence it cannot easily be assessed independently of the services of the application it supports. Also many of the functions of the OS are at a low level, but are so influential to the operation of the system that they become an intrinsic aspect of deployment risk for those systems. Thus we require a specialised approach to assessing dependability of OS. 

To deal with more stringent requirements in terms of energy consumption requires a shift from heat loss minimization toward novel intensified process concepts that intrinsically require less energy. Safety should now be considered as an intrinsic plant property rather than a responsive action, and the plant needs to be flexible to be able to respond quickly to changes in the market. Last but not least, new concepts will be required to provide a basis for sustainable future developments, that is, the use of renewable resources and processes based on green solvents. As a result of this changing focus, a shift toward a multidisciplinary approach can be observed. 

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