Predictive Hazard Analysis

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. 

Two standard estimation methods for heat of reaction and CART are Chetah 7.2 and NASA CET 89. Chetah Version 7.2 is a computer program capable of predicting both thermochemical properties and certain reactive chemical hazards of pure chemicals, mixtures or reactions. Available from ASTM, Chetah 7.2 uses Benson s method of group additivity to estimate ideal gas heat of formation and heat of decomposition. NASA CET 89 is a computer program that calculates the adiabatic decomposition temperature (maximum attainable temperature in a chemical system) and the equilibrium decomposition products formed at that temperature. It is capable of calculating CART values for any combination of materials, including reactants, products, solvents, etc. Melhem and Shanley (1997) describe the use of CART values in thermal hazard analysis. 

Not all required tasks and hazards can be predicted during the development of a HASP. The plan describes the ongoing hazard analysis and work control process, defines the means of identifying job- or task-based requirements and controls, and discusses ways to inform workers about requirements derived from ongoing job or task hazard analyses. 

Analyses are types of calculations but may be comparative studies, predictions, and estimations. Examples are stress analysis, reliability analysis, hazard analysis. Analyses are often performed to detect whether the design has any inherent modes of failure and to predict the probability of occurrence. The analyses assist in design improvement and the prevention of failure, hazard, deterioration, and other adverse conditions. Analyses may need to be conducted as the end-use conditions may not be reproducible in the factory. Assumptions may need to be made about the interfaces, the environment, the actions of users, etc. and analysis of such conditions assists in determining characteristics as well as verifying the inherent characteristics. (See also in Part 2 Chapter 14 under Detecting design weaknesses.)... 

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. 

More in line with the predictive use of hazards analysis, however, is the experimental and theoretical assessment that the viscosity of the liquid significantly affects this mode of initiation. Such information allows redesign of the process to eliminate handling of low viscosity liquid explosives, and quantitative measurement of the sensitivity of the system to mild shocks as a function of viscosity may allow the optimum level to be selected. This is not necessarily a new concept, only quantified in a different manner. Thirty years ago transporters of neat nitroglycerine in the oil fields were paid 25 a day. The stipend for transporting jellied nitroglycerine was seven dollars, a practical comment on the understood difference in hazard. 

Risk assessment is an essential feature of disaster planning and is in essence a calculation or model of risk, in which a comprehensive inventory is created including all existing and potential dangers, the population most likely to be affected by each danger, and a prediction of the health consequences. Risk analysis uses the elements of hazard analysis and vulnerability... 

Most major chemical and pharmaceutical companies today have developed systematic methods of evaluating new (and in many cases, old) processes and materials for the hazards attendant to their manufacture. The degree of urgency in establishing a chemical process hazard analysis function has often been dictated by some untoward event (usually within the company). It is to the prediction and control or elimination of unplanned reaction events to which the chemical process hazard review must address itself. 

The risk associated with issues of this nature depends on the extent to which the hidden information is relied upon clinically. But there is another factor to consider when information is inappropriately hidden not only do we fail to take it into account but from time to time clinicians will make positive assumptions based on its apparent absence. For example, suppose the system fails to correctly indicate that a CT scan has been carried out when in fact it has. Firstly, by not reviewing the result of the scan we may introduce a delay in care and secondly, we might fail to acquaint ourselves with any clinical activity triggered by the result of the CT scan. Finally we may assume that the original order has failed and issue a new request - unnecessarily exposing the patient to additional ionising radiation. Whilst these user behaviours can be difficult to predict they should at least be considered by the analytical team during hazard analysis. 

Most accidents involve some sort of human error. By its very nature, human error appears to be intractable it is difficult to predict and will vary from person to person. Nevertheless, a hazards analysis team needs to understand the unpredictable nature of human error, and how such error can impact almost any system. 

Figure 15.16 shows an or Gate below the Top Event. Entering the or Gate are two Intermediate Events. The first of these is System Fault —it covers all the equipment, instrument, and human failures that can cause the tank to overflow. The second input to the Top Event is All Other Events. This phrase covers all those events that could cause the Top Event to occur, but which have not been identified. It is a truism that no hazards analysis can ever be complete there will always be scenarios and hazards that were not identified, or not properly understood. Putting an All Other Events gate into the fault tree at this juncture serves as a reminder that no hazards analysis can ever be complete and that predicted risk values are hkely to be overly optimistic. 

In the FEED stage, conduct process hazard analysis, RAM, predictive maintenance, value engineering and constructability studies for accurate scoping of the most profitable revamp option... 

Bommer, J., Scherbaum, F., Bungum, H., Cotton, F., Sabetta, F., Abrahamson, N. A. (2005). On the use of logic trees for ground-motion prediction equations in seismic hazard analysis. Bulletin ofthe Seismological Society of America, 95, 377-389. doi 10.1785/0120040073... 

Seismic hazard analysis which involves collection of seismicity and seismotectonic of the region, selection of predictive relationship to arrive at controlling earthquake... 

In the past 20 to 30 years the use of probabilistic concepts has allowed uncertainties in the size, location and rate of recurrence of earthquakes and in the variation of ground motion characteristics with earthquake size and location to be explicitly considered in the evaluation of seismic hazards. Probabilistic seismic hazard analysis (PSHA) provides aframe-work in which these uncertainties can be identified, quantified, and combined in a rational mannerto provide amore complete picture of seismic hazard. The proper performance of a PSHA requires careful attention to the problems of source characterization and ground motion parameter prediction and to the mechanics of the probability computations. 

The objective of the review of hazard analysis is to determine the adequacy of protection of the nuclear power plant against internal and external hazards with account taken of the actual plant design, actual site characteristics, the actual condition of SSCs and their predicted state at the end of the period covered by the PSR, and current analytical methods, safety standards and knowledge. 

A Failure Mode and Effects Analysis (FMEA) is a sequential analysis and evaluation of the kinds of failures that could happen and their likely effects, expressed in terms of maximum potential loss. The technique is used as a predictive model and forms part of an overall risk assessment study. This analysis is described completely in the MIL-STD-1629A. The FMEA is most useful in system hazard analysis for highlighting critical components (Ridley, 1994). 

Currently, the landslide hazard spatial prediction methods can be divided into qualitative methods and quantitative methods. As we all know qualitative forecasting method mainly depends on the subjective experience and the predicted accuracy of qualitative methods is lower than it of quantitative methods. So the qualitative methods have been gradually replaced by the quantitative methods. Quantitative models can be divided into statistic analysis models, deterministic models, probabilistic model, fuzzy information optimization processing and neurd network models. 

While incident analysis is done after the fact, task analyses can be made after the fact or before the fact. Task analysis may be called job hazard analysis, job safety analysis, or total job analysis. Whatever the name given to the process, the results of task analyses are qualitative and can be predictive. As is said in the Handbook of Occupational Safety and Health, for which Lawrence Slote (1987) was the editor ... 

Risk assessment involves conducting a hazard analysis type of study on the finished product. A prediction of the likelihood of resultant injury compared to the potential severity of such injury can then be used to assess the risk. A further assessment can then be made of which safety systems are adequate for the task and those where further refinements are needed. 

CLASH, Crest level assessment of coastal structures by fuU scale monitoring, neural network prediction and hazard analysis on permissible wave overtopping. Fifth Framework Program of the EU, Contract no. EVK3-CT-2001-00058. www.clash-eu.org. 

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