Quantitative hazard assessment

Structure— Function Relationships. Since PCBs and related HAHs are found in the environment as complex mixtures of isomers and congeners, any meaninghil risk and hazard assessment of these mixtures must consider the quaUtative and quantitative stmcture—function relationships. Several studies have investigated the stmcture—activity relationships for PCBs that exhibit 2,3,7,8-tetrachlorodibenzo-p-dioxin [1746-01-6] (1)... 

Hazard analysis (HAZAN) is a quantitative way of assessing the likelihood of failure. Other names associated with this technique are risk analysis, quantitative risk assessment (QRA), and probability risk assessment (PRA). Keltz [44] expressed the view that HAZAN is a selective technique while HAZOP can be readily applied to new design and major modification. Some limitations of HAZOP are its inability to detect every weakness in design such as in plant layout, or miss hazards due to leaks on lines that pass through or close to a unit but cany material that is not used on that unit. In any case, hazards should... 

Quantitative risk assessment is now used extensively for determination of chemical and microbial risks in food. This concept helps to systematically and scientifically judge whether certain hazardous compounds may reach unacceptable risk levels when ingested. Quantitative risk assessment can support both quality design and quality assurance but, we discuss it from the assurance perspective. In the past decade, much attention has been paid to assessment of microbial risks due to then-typical differences as compared to chemical risks ... 

This chapter provides general information for performing qualitative or quantitative risk assessments on buildings in process plants. For detailed guidance on risk assessment techniques, the user is referred to other CCPS books on this subject, including Reference 3, Guidelines for Hazard Evaluation Procedures, Second Edition, and Reference 4, Guidelines for Chemical Process Quantitative Risk Analysis. 

Passino, D.R.M., Smith, S.B. (1987) Quantitative structure-activity relationships (QSAR) and toxicity data in hazard assessment. In QSAR in Environmental Toxicology-II. Kaiser, K.L.E., Editor, D. Reidel Publishing Co., Dordrecht, Holland, pp. 261-270. 

Hazard Assessment A process used to qualitatively or quantitatively assess risk factors to determine incident operations. 

The dangerous properties of acute toxicity, irritation, corrosivity, sensitisation, repeated-dose toxicity and CMR are evaluated in terms of their potential toxic effects to workers, consumers and man exposed indirectly via the environment, based on the use for each stage in the lifecycle of the substance from which exposure can occur. Risk assessment is also required if there are reasonable grounds for concern for potential hazardous properties, e.g., from positive in vitro mutagenicity tests or structural alerts. The risk assessment involves comparing the estimated occupational or consumer exposure levels with the exposure levels at which no adverse effects are anticipated. This may be a quantitative risk assessment, based on the ratio between the two values, or a qualitative evaluation. The principles of human health risk assessment are covered in detail by Illing (a.30) and more briefly in Chapter 7 of (73). 

The approach described is appropriate for assuring process safety for the preliminary design and is commonly used in industry where hazardous materials are handled. The committee further notes that a full-scale quantitative risk assessment (QRA) will be required in conjunction with the completion of the final design to assure that all process safety issues have been fully addressed. 

Fault tree analysis is based on a graphical, logical description of the failure mechanisms of a system. Before construction of a fault tree can begin, a specific definition of the top event is required for example the release of propylene from a refrigeration system. A detailed understanding of the operation of the system, its component parts, and the role of operators and possible human errors is required. Refer to Guidelines for Hazard Evaluation (CCPS, 1992) and Guidelines for Chemical Process Quantitative Risk Assessment (CCPS, 2000). 

Valschnav, D. "Biochemical oxygen demand data base" Call, D.J. Brooke, L.T. Valschnav, D. AQUATIC POLLUTANT HAZARD ASSESSMENT AND DEVELOPMENT OF HAZARD PREDICTION TECHNOLOGY BY QUANTITATIVE STRUCTURE-ACTIVITY RELATIONSHIPS. University of Wisconsin, Superior research project report (CR809234) 1984. 

Quantitative Stmcture-Activity Relationships (QSARs) are estimation methods developed and used in order to predict certain effects or properties of chemical substances, which are primarily based on the structure of the substance. They have been developed on the basis of experimental data on model substances. Quantitative predictions are usually in the form of a regression equation and would thus predict dose-response data as part of a QSAR assessment. QSAR models are available in the open literature for a wide range of endpoints, which are required for a hazard assessment, including several toxicological endpoints. 

The aim of the risk characterization of a chemical substance under evaluation is to integrate the hazard assessment and exposure assessment in order to evaluate the qualitative and quantitative probability for a health risk likely to occur in a given human population due to actual or predicted exposure to that specific chemical as well as the seriousness of any health risk. 

Major advances have taken place in the last decade in the development of commercially available testing equipment which has greatly improved the quality and reduced the cost of exptl hazard assessment Quantitative data now permit routine kinetic and mechanistic studies of expl and propint reactions. Parenthetically should be mentioned the significant changes which have taken place in gas and liq chromatography which allow the separation of unstable expl process intermediates and reaction products. The identification of such reactive fractions is made possible by on-line mass spectrometers... 

Recommendation 6-1. Quantitative risk assessments and hazard evaluations for both the Newport and Aberdeen facilities should be carried out as early as possible during facility design, and the findings from these assessments should be used in both the design and future operation of the facilities to minimize risk and maximize safety. 

For the purposes of a quantitative risk assessment (QRA) and hazards evaluation (HE), a thorough analysis will be... 

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. 

For non-thresholded contaminants some mechanism is required that will allow the benefits in terms of reduced risks and costs associated with control to be taken into account. The costs of control will include enforcement costs as well as costs to producers in reaching ever stricter standards. Ultimately these costs will be borne by consumers in taxes, increased prices or reduced choice. Economic theory dictates that there must be a point where the extra increase in the cost of control is not justified by the corresponding increase in benefit (reduction in risk). This optimal point will differ for each contaminant according to the technology needed to control it, the nature of the hazard, and the relationship between dose and risk. It is in this latter context that quantitative risk assessment (QRA) becomes critical (see section 2.3.4 of this chapter). 

To be complete, toxicity hazard assessment should consider the specific effects caused by wastewaters to a receiving stream. As applied thus far, the pT-method only provides a quantitative measurement of wastewater toxicity. 

Occasionally the qualitative and intuitive methods of risk assessment fail, and something better is required. For example, a designer may have taken steps to address some hazard, but be unsure whether these are sufficient. There is also the possibility of failure of equipment, control systems or operating procedures which may reduce margins of safety. In these circumstances, quantitative risk assessment may be considered. This is an attempt to put numbers to the risks so that we can judge them objectively. 

The CPSC staff performed quantitative risk assessments on various flame-retardants for both upholstered residential furniture fabrics and foam.89 CPSC addresses chemical hazards under the Federal Hazardous Substances Act (FHSA), which is risk based. For fabrics, five flame-retardants were evaluated, that include antimony trioxide, deca-BDE, HBCD, phosphonic acid, (3- [hydroxymethyl]amino)-3-oxopropyl)-, dimethyl ester (PA), and tetrakis (hydroxymethyl) phosphonium chloride (THPC). These flame-retardants were selected for study because they are used to comply with the U.K. upholstered furniture flammability standard (except THPC) and fabric samples were available for testing. The staff concluded in 2006 that deca-BDE, HBCD, and PA would not present a hazard to consumers and that additional data would be needed to assess antimony trioxide and THPC. 

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