Hazard evaluation predictive

Oris, J.T. and Giesy, J.P. (1986). Photoinduced toxicity of antracene to juvenile bluegill sun-fish photoperiod effects and predictive hazard evaluation. Environmental Toxicology and Chemistry 5, 761-768. 

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. 

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. 

This assumption is based on the fact that the polymer-solvent interaction parameter [see Eq. (8)] of the tributyrin-cellulose tributyrate system, as evaluated from melting-point depressions, is nearly zero at about 100° C [Mandelkern and Flory (160)]. It does not follow, however, that the system is athermal, for the parameter generally involves an entropy contribution. Furthermore, the heat and entropy parts of this parameter vary with the concentration in a complicated way, especially in polar systems [see, for example, Takenaka (243) Zimm (22) Kurata (154)]. Thus it is extremely hazardous to predict dilute solution properties from concentrated solution properties such as the melting-point depression, at least on a highly quantitative level as in the present problem. 

In environmental hazard assessment of chemicals, it is necessary to evaluate exposure and effects on humans or ecosystems, and then to perform an assessment. It consists of comparing the predicted environmental concentration (PEC) and the predicted no effect concentration (PNEC) and to make a judgement as to whether the chemical ent ng into environments is hazardous or not. Ultimately, risk management including regulation of chemicals is necessary if a potential hazard is predicted (see also chapter by Motschi). 

Due to the need for premanufacture hazard evaluation and the high costs of field sampling, an increasing emphasis is being placed on predictions of environmental fate and exposure. The methods used to predict the environmental fate of chemicals can be categorized into three basic approaches ... 

To predict the capability of a reaction to runaway requires that someone carries out a hazard evaluation and a risk assessment of the reaction including its reactants, its possible products, and side reactions/products. The hazards of the chemical reactants and products can often be found in the literature. Bretherick s Handbook of Reactive Chemical Hazards provides several examples of reactions that can runaway. These examples include ... 

It is a requirement of any food law that food offered for sale and consumption by the public should be wholesome. Hence any ingredient of food and also any technological additive used in food should be safe when ingested by man. Evidence for the harmlessness of food additives rests essentially on the demonstration that, in the doses in which they are ingested by man, no adverse toxic effects will arise . Since direct experimentation in man is clearly impossible, reliance has to be placed on experiments with laboratory animals. From the observed results, predictions by extrapolation are made of the reactions likely to occur in man, and the eventual hazards from ingestion by man are assessed. Obviously hazard evaluation can be meaningful only on the basis of adequate data. These, in turn, require that the appropriate animal experiments are carried out and conducted in an adequate manner. 

In the first step, a screening process will be applied to separate the major potential hazards these will be addressed in more detail. QRA techniques are used to evaluate the extent of the risk arising from hazards with the potential to cause major accidents, based on the prediction of the likelihood and magnitude of the event. This assessment will be based on engineering judgement and statistics of previous performance. Where necessary, risk reduction measures will be applied until the level of risk is acceptable. This of course is an emotive subject, since it implies placing a value on human life. 

Process Hazards Analysis. Analysis of processes for unrecogni2ed or inadequately controUed ha2ards (see Hazard analysis and risk assessment) is required by OSHA (36). The principal methods of analysis, in an approximate ascending order of intensity, are what-if checklist failure modes and effects ha2ard and operabiHty (HAZOP) and fault-tree analysis. Other complementary methods include human error prediction and cost/benefit analysis. The HAZOP method is the most popular as of 1995 because it can be used to identify ha2ards, pinpoint their causes and consequences, and disclose the need for protective systems. Fault-tree analysis is the method to be used if a quantitative evaluation of operational safety is needed to justify the implementation of process improvements. 

Hazards analysis techniques fall in two broad categories. Some techniques focus on hazards control by assuring that the design is in compliance with a pre-existing standard practice. These techniques result from prior hazards analysis, industry standards and recommended practices, results of incident and accident evaluations or similar facilities. Other techniques are predictive in that they can be applied to new situations where such pre-existing standard practices do not exist. 

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