Hazards predictive hazard evaluation procedures

Predictive hazard evaluation procedures may be required when new and different processes, designs, equipment, or procedures are being contemplated. The Dow Fire and Explosion Index provides a direct method to estimate the risks in a chemical process based upon flammability and reactivity characteristics of the chemicals, general process hazards (as exothermic reactions, indoor storage of flammable liquids, etc.) and special hazards (as operation above the flash point, operation above the auto-ignition point, quantity of flammable liquid, etc.). Proper description of this index is best found in the 57-page Dows Fire and Explosion Index, Hazard Classification Guide, 5 th ed., AIChE, New York, 1981. 

Fig. 5. Steps in a predictive hazard evaluation. (From Guidelines for Hazard Evaluation Procedures. Copyright 1985 American Institute of Chemical Engineers.)...

The AIChE s Guidelines for Hazard Evaluation Procedures, Second Edition (1992) [5] offers a wide variety of alternates to review systems for hazards. These review procedures can be used to evaluate some plant modifications. No single identification procedure can be considered the best for all companies or all situations. Two basic categories of evaluations are (1) adherence to good engineering practice and (2) predictive hazard evaluation. 

The degree of confidence in the final estimation of risk depends on variability, uncertainty, and assumptions identified in all previous steps. The nature of the information available for risk characterization and the associated uncertainties can vary widely, and no single approach is suitable for all hazard and exposure scenarios. In cases in which risk characterization is concluded before human exposure occurs, for example, with food additives that require prior approval, both hazard identification and hazard characterization are largely dependent on animal experiments. And exposure is a theoretical estimate based on predicted uses or residue levels. In contrast, in cases of prior human exposure, hazard identification and hazard characterization may be based on studies in humans and exposure assessment can be based on real-life, actual intake measurements. The influence of estimates and assumptions can be evaluated by using sensitivity and uncertainty analyses. - Risk assessment procedures differ in a range of possible options from relatively unso-... 

The enormous cost of multiple-species, multiple-dose, lifetime evaluations of chronic effects has already made the task of carrying out hazard assessments of all chemicals in commercial use impossible. At the same time, quantitative structure activity relationship (QSAR) studies are not yet predictive enough to indicate which chemicals should be so tested and which chemicals need not be tested. In exposure assessment, continued development of analytical methods will permit ever more sensitive and selective determinations of toxicants in food and the environment, as well as the effects of chemical mixtures and the potential for interactions that affect the ultimate expression of toxicity. Developments in QSARs, in short-term tests based on the expected mechanism of toxic action and simplification of chronic testing procedures, will all be necessary if the chemicals to which the public and the environment are exposed are to be assessed adequately for their potential to cause harm. 

Computers are now used in the design and development of new chemicals, and their employment in toxicity prediction could lead to improved products that present a reduced hazard to humans. Although computers are useful for performing routine calculations, they do not usually possess insight or rationalization. Therefore, they should represent only one of a number of test procedures used to formulate a full safety evaluation in a given chemical. Where they are used, their results should be interpreted by a panel of expert toxicologists capable of providing an overall view of the likely toxic risk in the human environment. 

DSC ts widely used to predict the potential explosive hazard of materials in an ASTM method. The basis of the method, developed by Committee E 27, is the determination of the reaction kinetics using Ozawa s procedure (206). Ozawa employs a ploi of the logarithm of the DSC heating rate versus the peak maxima temperatures E. Z, k. and t can be calculated from this plot. The ASTM method has been used to evaluate the thermal stability of irinitrotoluene (207). nitrocellulose (208). and many other substances. 

Conventional instructions assume that workers or machinery can operate according to well-defined tasks and procedures to produce controlled and predictable results. In hazardous environments, workers must observe and evaluate a constantly changing stream of information so that they can adjust practices as conditions warrant in highly specific problems in the mine. 

Accident figures are the core data for most safety approaches. Accidents are screened to compare and evaluate safety standards and practices of different nations, industries, companies, and work places. They serve as figures for insurance companies to predict the expected risk of work activities. They lead to better safety standards by localizing hazards at work places, and are employed to initiate safe working procedures, working equipment and environment, and safe working behavior. 

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