Risk assessment likelihood analysis

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... 

The approach used in an FHA is to assume ignition of releases. In reality, not all releases result in afire. The likelihood of ignition can be addressed in the quantitative risk assessment process. However, in an FHA it is important to identify if ignition sources are present for the fire scenarios to occur. In some instances, fire scenarios can be eliminated from analysis because of the lack of a credible ignition source. 

In some cases, after completing the consequence portion of the analysis, the impact of the consequences is deemed so severe that the company may decide to provide fire protection that will provide mitigation without completing the likelihood analysis. It is important to take the time to analyze the consequences (conduct an FHA) and determine if reasonable mitigation measures can be applied before continuing with the fire risk assessment. Credit for additional mitigation measures can be taken in the fire risk assessment. 

Risk assessment starts with risk identification, a systematic use of available information to identify hazards (i.e., events or other conditions that have the potential to cause harm). Information can be from a variety of sources including stakeholders, historical data, information from the literature, and mathematical or scientific analyses. Risk analysis is then conducted to estimate the degree of risk associated with the identified hazards. This is estimated based on the likelihood of occurrence and resultant severity of harm. In some risk management tools, the ability to detect the hazard may also be considered. If the hazard is readily detectable, this may be considered a factor in the overall risk assessment. Risk evaluation determines if the risk is acceptable based on specified criteria. In a quality system environment, criteria would include impact on the overall performance of the quality system and the quality attributes of the finished product. The value of the risk assessment depends on how robust the data used in the assessment process is judged to be. The risk assessment process should take into account assumptions and reasonable sources of uncertainty. Risk assessment activities should be documented. 

The fourth core element, the maximin principle, is not implemented at all. On the contrary, there is a strong reliance in TSCA and in the implementation of the act on formal risk assessments and cost-benefit analysis, which more or less completely blocks complementary approaches, such as decision-making aiming at reducing the likelihood of the worst case becoming a reality. 

Identifying a hazard is only a small part of the risk assessment process. Hazard must be differentiated from risk. Assessing risk involves an analysis of the likelihood that adverse effects to human health or the environment after exposure to a chemical may occur. For risk management, exposure assessments therefore play equal (if not more) important parts as evaluations of hazard. The following sections discuss how toxicology, exposure assessments, and risk characterisations contribute to the central scientific definition of risk as probability versus consequence [93-95]. 

Risk analysis of accidents serves a dual purpose. It estimates tlie probability tliat an accident will occur and also assesses the severity of the consequences of an accident. Consequences may include damage to tlie surrounding environment, financial loss, injury to life and/or deatli. This Part of the book (Part IV) is primarily concerned witli tlie metliods used to identify liazards and causes and consequences of accidents. Issues dealing with healtli risks have been explored in tlie previous Part (III). Risk assessment of accidents provides an effective way to help ensure eitlier tliat a inisliap will not occur or reduces tlie likelihood of an accident. Tlie result of tlie risk assessment also allows concerned parties to take precautions to prevent an accident before it liappens. 

The risk assessment process can be conducted by examining record types to see if they are GxP or non-GxP, and then applying severity checks, likelihood, and probability of detection criteria, as illustrated in Figure 15.2. The most severe scenarios shonld be linked to direct patient/consnmer impact. GxP noncompliance and broken license conditions are severe in their own right bnt not as critical as patient/consumer health in this analysis." Its likelihood will be influenced by the degree of human error in how the record is input and used. The probability of detection needs to take into account the probability of the impacted record being used. Once failure modes are understood, then the appropriate design controls can be introduced. These should be documented and validated as part of the computer system life cycle discussed earher in this book. 

A quantitative risk assessment (QRA) is an integrated, quantitative analysis (including uncertainty) of accident scenarios, their likelihood, and possible consequences. Current QRAs examine human actions as well as systems failures, external events as well as internal failures, and worker risk as well as public risk. A salient feature of a QRA is that it is integrated, in that it ... 

Vulnerability is a measure of the likelihood of adversary success (Las) in causing the desired consequences (mathematical complement of protection system effectiveness). Vulnerability, or Las, is an estimate of the likelihood that the existing security countermeasures will be overcome by the attempted attack. This factor represents a qualitative surrogate for the quantitative conditional probability of success used in some government risk assessment models (U.S. Department of Justice, 2002). There are numerous subfactors involved in the analysis of Las, so this factor may be difficult to quantify. Alternatively, the TSVA team can assess the vulnerabilities and existing countermeasures to determine the defined adversary s ability to succeed. 

These criteria and others were converted into a numerical scheme so they could be combined and used in an early risk assessment of the changes being contemplated and their potential likelihood for introducing significant new risk into the system. The criteria were weighted to reflect their relative importance in the risk analysis. 

The goal of human error quantification is to produce error probabilities, building on task analysis and error identification techniques to provide a probabilistic risk assessment (PRA). This provides numerical estimates of error likelihood and of the probability of overall likelihood of system breakdown. Quantification of error is the most difficult aspect of HRA, often heavily reliant on expert judgement, rather than the more rigorous approach of actual observation and recording of error frequencies. Such techniques are little used in healthcare but have been successfully applied to anaesthesia (Pate-Cornell and Bea, 1992). Nevertheless, some hospital tasks, such as blood transfusion, are highly structured and the quantification of errors probabilities would seem to be eminently feasible (Lyons et al, 2004). 

Major elements of an occupational safety and health program address recognition, evaluation, and control of hazards. The activities may include risk assessment and charting of probability and severity of potential incidents. The activities may deal with routine functions as well as non-routine functions. Changes in operations and conditions or equipment may also trigger these activities. Inspections, reviews, and other analysis methods will help identify the hazards, the likelihood of occurrence and the potential severity. For example, there should be inspections of repair and maintenance work to ensure that guards and other protections are in place or an area is clear of flammable and combustible materials and sources of heat and fire. Previous chapters offered several methods for hazard recognition and control. 

Risk Assessment The identification and analysis, either qualitative or quantitative, of the likelihood of the occurrence of a hazardous event or exposure, and the severity of injury or illness that may be caused by it... 

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