Qualitative Hazard Risk Analysis

Obviously, hazard risk information can be presented eidier qualitatively or quantitatively. This Section provides qualitative risk procedures and information. Several of these approaches are given below. 

Low Tile probability of occurrence is considered unlikely during the 

High Tlie probability of occurrence is consido ed sufficiently high to 

Medium The chemical is eiqiected to move into the surroundirig 

Definitions of severity regarding tlie consequences are as follows  

Medium The chonical is expected to move into the surrounding 

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Section 18.2 Risk Cliaracterization Section 18.3 Cause-Consequence Analysis Section 18.4 Qualitative Hazard Risk Analysis Section 18.5 Quantitative Hazard Risk Analysis Section 18.6 Uncertainties/Limihitions Section 18.7 Public Perception of Risk Section 18.8 Risk Communication... 

Fusible Link a mechanical release device actiwited by the heat effects of a fire. It usually consist of two pieces of metal joined by a low melting solder. Fusible links are manufactured as various incremental temperature ratings and are subjected to varying normal maximum tension. When installed and the fixed temperature is reached, the solder melts and the two metal parts separate, initiating the desired actions Hazard Analysis the systematic identification of chemical or physical characteristics and/ or processing conditions and/or operating conditions that could lead to undesired events Hazardous Area, Electrical a US classification for an area in which explosive gas/air mixtures are, or may be expected to be, present in quantities such as to require special precautions for the construction and use of electrical apparatus HAZOP an acronym for Hazard and Operability study, which is a qualitative process risk analysis tool used to identify hazards and evaluate if suitable protective arrangements are in place if the process were not to perform as intended and unexpected consequences were to result... 

In the past, qualitative approaches for hazard evaluation and risk analysis have been able to satisfy the majority of decision makers needs. In the future, there will be an increasing motivation to use QRA. For the special situations that appear to demand quantitative support for safety-related decisions, QRA can be effective in increasing the manager s understanding of the level of risk associated with a company activity. Whenever possible, decision makers should design QRA studies to produce relative results that support their information requirements. QRA studies used in this way are not subject to nearly as many of the numbers problems and limitations to which absolute risk studies are subject, and the results are less likely to be misused. 

The Chemical Process Industry (CPI) uses various quantitative and qualitative techniques to assess the reliability and risk of process equipment, process systems, and chemical manufacturing operations. These techniques identify the interactions of equipment, systems, and persons that have potentially undesirable consequences. In the case of reliability analyses, the undesirable consequences (e.g., plant shutdown, excessive downtime, or production of off-specification product) are those incidents which reduce system profitability through loss of production and increased maintenance costs. In the case of risk analyses, the primary concerns are human injuries, environmental impacts, and system damage caused by occurrence of fires, explosions, toxic material releases, and related hazards. Quantification of risk in terms of the severity of the consequences and the likelihood of occurrence provides the manager of the system with an important decisionmaking tool. By using the results of a quantitative risk analysis, we are better able to answer such questions as, Which of several candidate systems poses the least risk Are risk reduction modifications necessary and What modifications would be most effective in reducing risk ... 

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. 

In the final phase of risk analysis—risk characterization—one integrates outputs of effects and exposure assessments. Risk is expressed in qualitative or quantitative estimates by comparison with reference values (e.g., hazard quotient). The severity of potential or actual damage should be characterized with the degree of uncertainty of risk estimates. Assumptions, data uncertainties and limitations of analyses are to be described clearly and reflected in the conclusions. The final product is a report that communicates to the affected and interested parties the analysis findings (Byrd and Cothern, 2000). 

As Hendershot (1995) has pointed out, most process options will be inherently safer with respect to one type of hazard, but may be less safe from a different viewpoint. In some cases the overall balance is readily apparent and it is easy to get general agreement on which option offers the safest overall balance. In other cases that balance is less apparent, and more sophisticated tools including qualitative ranking schemes, quantitative risk analysis and formal decision making tools may be needed. 

Logic Model Methods The following tools are most commonly used in quantitative risk analysis, but can also be useful qualitatively to understand the combinations of events which can cause an accident. The logic models can also be useful in understanding how protective systems impact various potential accident scenarios. These methods will be thoroughly discussed in the Risk Analysis subsection. Also, hazard identification and evaluation tools discussed in this section are valuable precursors to a quantitative risk analysis (QRA). Generally a QRA quantifies the risk of hazard scenarios which have been identified by using tools such as those discussed above. 

Layers-of-protection analysis (LOPA) is a semiquantitative methodology for analyzing and assessing risk. It is typically applied after a qualitative hazards analysis has been completed, which provides the LOPA team with a listing of hazard scenarios with associated safeguards for consideration. LOPA uses simplified methods to characterize the process risk based on the frequency of occurrence and consequence severity of potential hazard scenarios. The process risk is compared to the owner/operator risk criteria. When the process risk exceeds the risk criteria, protection layers are identified that reduce the process risk to the risk criteria. 

Risk analysis is a term that is applied to a number of analytical techniques used to evaluate the level of hazardous occurrences. Technically, risk analysis is a tool by which the probability and consequences of accidental events are evaluated for hazard implications. These techniques can be either qualitative or quantitative. 

Several qualitative approaches can be used to identify hazardous reaction scenarios, including process hazard analysis, checklists, chemical interaction matrices, and an experience-based review. CCPS (1995a p. 176) describes nine hazard evaluation procedures that can be used to identify hazardous reaction scenarios-checklists, Dow fire and explosion indices, preliminary hazard analysis, what-if analysis, failure modes and effects analysis (FMEA), HAZOP study, fault tree analysis, human error analysis, and quantitative risk analysis. 

At this point in the example, the eompany-wide reviews eompleted in Chapters 2 and 3 are replaeed with a first-level qualitative risk analysis foeused on the transportation aetivities of a single XYZ Cheinieal faeihty. To eontinue the example, a single XYZ Chemical facility is selected. This facility will continue to be evaluated as the level of analysis detail increases from qualitative to semi-quantitative in this chapter to quantitative risk analysis (Chapter 5). As the level of detail increases, the analysis will be directed at specific questions that remain following each level of analysis. This facility will continue to be the focus of Chapter 6 where the security vulnerabihty of the hazardous materials in transit is evaluated. Chapter 7 where risk reduction options are evaluated, and Chapter 8 where the ongoing management of risk continues in the future. 

The site-level health and safety manager was given notice from corporate for the need to conduct the qualitative risk analysis of the plant s hazardous material transportation operations. The safety manager was provided with a questiotmaire regarding all chemicals of concern, shipping quantities, modes of transit, and the route characteristics (similar to the checklist found in Table 4.2). This information was transmitted back to corporate for analysis, which included a corporate-level comparison to the other XYZ Chemical facihties risk results. Based on the information collected at the site level, the following was determined and reviewed by corporate for this facility ... 

Qualitative Risk Analysis Based primarily on description and comparison nsing historical experience and engineering jndgment, with httle quantification of the hazards, consequences, likelihood, or level of risk. 

A safety professional is a person engaged in the prevention of accidents, incidents, and events that harm people, property, or the environment. They use qualitative and quantitative analysis of simple and complex products, systems, operations, and activities to identify hazards. They evalnate the hazards to identify what events can occur and the likelihood of occnrrence, severity of results, risk (a combination of probability and severity), and cost. 

HSE assessments have a long tradition within the oil-and gas industry. These assessments use a wide range of methodologies, from the strict quantitative methods such as QRA (Quantitative Risk Analysis) and FMECA (Failure Mode Effect and Criticality Analysis) to the more qualitative methods such as HAZOP (HAZard OPerability analysis). Most methods combine qualitative and quantitative data and approaches. For example, an FMECA basically uses generic failure data, expert judgments are likewise important. 

According to the ISO/IEC Guide 51 1999, risk evaluation is defined as a wide process of estimation and analysis. In its terminology risk analysis is defined as the systematic use of information to identify hazards and estimate risk, and the risk estimation is defined as a procedure to determine if the risks are tolerable or not. In this manner ISO/IEC Guide 51 1999 presents a iterative process model to evaluate and reduce risks that can be applied to qualitative and quantitative risk evaluations, as shown in Fig. 1. 

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