Severity of occurrence

Methodology— The multidisciplinary team should represent leadership from throughout the organization and provide oversight for the patient safety program. All patient care and nonpatient care departments must report safety events and potential occurrences. The report will contain aggregated information related to the type of occurrence, severity of occurrence, number and type of occurrences per department, and impact on the patient. The team will... 

Determine the severity of occurrence - The severity of a human error should take into account the consequences of the error on the system, operation, environment and operator. This can be quantified in monetary terms or downtime. 

Accident investigation indicates that there are often many individual causes to an accident, and that a series of incidents occur simultaneously to cause the accident. The following figure is called the safety triangle", and shows the approximate ratios of occurrence of accidents with different severities. This is based on industrial statistics. 

To predict the properties of a population on the basis of a sample, it is necessary to know something about the population s expected distribution around its central value. The distribution of a population can be represented by plotting the frequency of occurrence of individual values as a function of the values themselves. Such plots are called prohahility distrihutions. Unfortunately, we are rarely able to calculate the exact probability distribution for a chemical system. In fact, the probability distribution can take any shape, depending on the nature of the chemical system being investigated. Fortunately many chemical systems display one of several common probability distributions. Two of these distributions, the binomial distribution and the normal distribution, are discussed next. 

Criticality Mnalysis. The criticaUty assessment provides a figure-of-merit for each failure mode. This figure of merit is based on the likelihood of occurrence of the failure mode (Occ), the criticaUty (severity) of the failure mode on system performance (Sev), and the detectabiUty of the failure mode by the user prior to occurrence (Det). 

The most popular scheme among commercial companies is the assignment of a risk priority number (RPN) based on probabiUty of occurrence, detectabihty, and severity of a particular failure mode. The factors (Occ, Sev, and Det) are each rated on a 1 to 10 scale and then an RPN is based on the product of the three rating values. 

We can demonstrate the notions of risk and risk assessment using Figure 1.18. For a given probability of failure occurrence and severity of consequence, it is possible to map the general relationship of risk and what this means in terms of the action required to eliminate the risk. 

For example, if both occurrence and severity are low, the risk is low, and little or no action in eliminating or accommodating the risk is recommended. ITowever, for the same level of occurrence but a high severity, a medium level of risk can be associated with concern in some situations. The level of occurrence, for some unknown reason, changes from low to medium and suddenly we are in a situation where the risk requires priority action to be eliminated or accommodated in the product. 

FMEA can be used to provide a quantitative measure of the risk for a design. Because it can be applied hierarchically from system through subassembly and component levels down to individual dimensions and characteristics, it follows the progress of the design into detail. FMEA also lists potential failure modes and rates their Severity (S), Occurrence (O) and Detectability ( )). It therefore provides a possible means for linking potential variability risks with consequent design acceptability and associated costs. Note that the ratings of Occurrence and Detectability are equated to probability levels. 

While 30 ppm may be acceptable as a maximum probability of occurrence for a failure of low severity, it is not acceptable as severity increases. An example table of FMEA Severity Ratings was shown in Figure 2.20. In the definite return to manufacturer (a warranty return) or violation of statutory requirement region (S = 5 or S = 6), the designer would seek ways to enhance the process capability or else utilize some inspection or test process. Reducing d will reduce occurrence, as indicated by equation 2.11, but inspection or test is of limited efficiency. 

Figure 2.21 is a graph of Occurrence against Severity showing a boundary of the acceptable design based on these criteria for the case when d = 1 and Pof = 1. The graph is scaled in terms of FMEA ratings for Occurrence, equivalent probabilities and parts-per-million (ppm). 

Total frequencies of environmental illness are difficult to measure. When causes can be identified, however, scientists observe that frequencies of occurrence of a particular illness vary directly with the severity and extent of exposure. Particularly frequent in the workplace are skin lesions from many different causes and pulmonary diseases related to the inhalation of various dusts, such as coal dust (black lung), cotton dust (brown lung), asbestos fibers (asbestosis), and silica dust (silicosis). Environmental agents can also cause biological effects without overt clinical illness (for example, chromosome damage from irradiation). 

Frequency with the dimensions of per unit time, ranges from zero to infinity and means the number of occurrences per time interval. Probability is dimensionless, ranges from zero to one, and has several definitions. The confusion between frequency and probability arises from the need to determine the probability that a given system will fail in a year. Such a calculation of probability explicitly considers the time interval and, hence, is frequency. However, considerable care must be used to ensure that calculations are dimensionally correct as well as obeying the appropriate algebra. Three interpretations of the meaning of probability are ... 

A simple example of fault tree analysis applied to an internal combustion engine (Figure 3.4.4-2) is the Figure 3.4.4-3 fault tree diagram of how the undesired event "Low Cylinder Compression" may occur. The Boolean equation of this fault tree is in the caption of Figure 3.4.4-3. Let the occurrence of these events be represented by a 7, non-occurrence by 0, and consider that there may he a long history of occurrences with this engine. Several sets of occunrence.s (trials) are... 

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 report documents the development of data on the severity as well as the frequency of accidents involving truck, rail, and air transport. Volume 1 includes a summary giving the probability of occurrence of accidents as a function of accident severity. Subsequent Volumes give supporting data, calculations and analysis. 

If the probability of the accident and tlie severity of its consequences are low, then die risk is usually deemed acceptable and the plant should be allowed to operate. If die probability of occurrence is too high or die damage to the surroundings is too great, dien the risk is usually unacceptable and die system needs to be modified to minimize these defects. 

Each cell in tlie matrix (Table 18.4.2) is assigned a risk ranking as indicated by the letters. In this approach, an A level risk corresponds to a very severe consequence with a high likelihood of occurrence. Action must be taken, and it must be taken promptly. At tlie other end of the scale, a E level risk is of little or no consequence witli a low likelihood of occurrence, and no action is needed or justified. For example, a level C risk might warrant mitigation witli engineering and/or administrative controls or may represent risks tliat are acceptable with controls and procedures. 

There are three common protocols for barbiturate detoxification. In all approaches, the goal is to prevent the occurrence of major symptoms and to minimize the development of intolerable minor symptoms. The first procedure is based on protocols described by several authors (Ewing and BakeweU 1967 Isbell 1950 Wilder 1968) (see Table 3 ). The first step is to determine the severity of tolerance. If the patient is intoxicated, no additional barbiturate should be given until the symptoms of intoxication have resolved. If there is substantial evidence or strong suspicion of chronic barbiturate use, it is not necessary or desirable to wait until withdrawal symptoms appear. A 200-mg oral dose of pentobarbital may be given on an empty stomach to a... 

Van der Linden PW, Hack CE, Struyvenberg A, van der Zwan JK Insect sting challenge in 324 subjects with a previous anaphylactic reaction current criteria for insect venom hypersensitivity do not predict the occurrence and severity of anaphylaxis. J Allergy Clin Immunol 1994 94 1512-1519. 

Cyperus rotundus L. is a weedy species, native to India, but widely distributed in countries on the Pacific Rim and islands in the Pacific Basin. Commonly referred to as purple nut sedge, it has been known in the Hawaiian Islands since the middle of the nineteenth century. In addition to its weedy nature, the taxon has attracted attention because of the antifebrile activity of its rhizomes. Chemical studies have disclosed the presence of several sesquiterpene derivatives, some of which have been implicated in the plant s medicinal use (cyperene and cyperinerol) (Wagner et ah, 1990, p. 1399). Our interest in this species is the existence of several chemotypes with interesting patterns of occurrence involving Pacific Rim countries and several oceanic islands, including the Hawaiian Islands, islands in the southern Pacific, and the Philippines. 

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