Hazard identification measurement

The acronym for chemical process quantitative risk analysis. It is the process of hazard identification followed by numerical evaluation of incident consequences and frequencies, and their combination into an overall measure of risk when applied to the chemical process industry. It is particularly applied to episodic events. It differs from, but is related to, a probabilistic risk analysis (PRA), a quantitative tool used in the nuclear industry... 

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-... 

This chapter will review the application of these methods for the hazard identification and characterization of chemical allergens and, where appropriate, for the measurement of relative potency in the context of risk assessment. 

Thus, for hazard identification, only the measurement of one or two temperatures is necessary. Actually, for equipment without a heating or cooling system, evaluation of the term (d2T/dt2) greater than zero is sufficient. The method is independent of detailed process knowledge and, generally, of human judgment. 

In general, hazard identification criterion represents the deviation of one or more measured variables from specified values. This is the basis upon which a significant percentage of risk analyses are done. For a chemical process, a number of measurable variables, physical properties, and states or positions of various parts of the overall equipment, e.g., pumps, valves, and motors, can be specified for every time or phase of the process. Certain deviations from the "standard" recipe or settings can then be defined in advance as hazardous, and thus can be used for initiation of an alarm at the early stage of a runaway or upset condition. 

The What-if, the checklists and Hazop are well publicized hazard identification tools. But as Bollinger et al. (1996) have pointed out the use of any of these techniques demands knowledge, experience and flexibility. No prescriptive set of questions or key words or list is sufficient to cover all processes, hazards and all impacted populations. Bollinger et al. find that refinement of the quantitative measurement techniques such as safety indices and convergence to a single set of accepted indices would be beneficial. 

Also indices such as the Dow Fire and Explosion Hazard Index and the Mond Index have been suggested to measure the degree of inherent SHE of a process. Rushton et al. (1994) pointed out that these indices can be used for the assessment of existing plants or at the detailed design stages. They require detailed plant specifications such as the plot plan, equipment sizes, material inventories and flows. Checklists, interaction matrices, Hazop and other hazard identification tools are also usable for the evaluation, because all hazards must be identified and their potential consequences must be understood. E.g. Hazop can be used in different stages of process design but in restricted mode. A complete Hazop-study requires final process plans with flow sheets and PIDs. 

Before any mitigation measures can be designed, an effective hazard identification study must be conducted. The results of such a study (a set of release scenarios) can be used to develop a coherent set of mitigation strategies. In the process industries, these studies are most commonly conducted using hazard and operability (HAZOP) studies, what-if checklists, failure modes and effects analyses (FMEA), and several other comparable techniques (CCPS, 1992). 

DNA repair can be detected by the same assays (alkaline elution and Comet) that are used to detect DNA damage, but with various time intervals between the end of exposure and the time of sampling. An additional assay for assessing DNA repair has been utilized for many years, namely the unscheduled DNA synthesis (UDS) assay. The endpoint measured is the uptake of tritiated thymidine into DNA repair sites following exposure. The sensitivity of the assay is relatively low, especially in vivo, and this limits its predictive value for hazard identification. Thus, a negative response in a UDS assay has very limited value because of this low sensitivity. 

The basic objective of hazard analysis is to identify and assess potentially hazardous situations, and their possible consequences and associated risk, in order to provide a rational basis for determining where risk reduction measures are needed. Hazard identification always has been an integral part of design and operational practice. However, it is to a large degree still an informal process depending on the experience of those directly involved. 

Many other cell lines have been used to address specific types of toxicity. Some of these have reached a level of validation that is sufficient for in vitro screening purposes. For example, the 3T3 NRU assay was regarded as an acceptable screen for hazard identification of potential phototoxicity [27,28], This assay utilized the in vitro 3T3 cell line as a generic cell line and Neutral Red uptake as a cytotoxicity measurement. The compound in question is subjected to UV irradiation to assess the effect of UV rays on compound induced toxicity to 3T3 cells. Another example is the use of the MCF-7 cell proliferation assay as an in vitro screen for endocrine disrupters [29],... 

However, hazard identification alone does very little to protect human health—it is only the start of the process. When a chemical has been identified as a potential skin sensitizer, then unless it is banned from use, the risk that it presents must be assessed and managed. To achieve this, it is vital to characterize the relative potency of the identified sensitizer, not least since the currently available evidence indicates that this may vary over perhaps five orders of magnitude [25, 26]. As mentioned earlier, this has been successfully achieved using the LLNA EC3 value [27-34], Consequently, various workers have begun to compare the predictions from in vitro methods to this potency measure (e.g., [82, 85]). It would be preferable though to develop predictive systems in vitro which deliver information on the relative potency of skin sensitizers in humans rather than in mice. To this end, a... 

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