Consequence Severity Categories

The consequence criterion presents some advantages when compared to the others. When applying this approach, all HAZOP scenarios must be assigned a consequence severity category, which guarantees a thorough analysis, since all scenarios will be classified. Besides that, this criterion is less time-consuming than the risk criterion, since the team is requested to... 

The scenario tolerable frequency associated to each consequence severity category indicates the frequency in which the organization tolerates an event with such impact. To provide an example, according to CCPS (2001), a maximum tolerable risk for workforce of 10 per year is a typical criteria used with LOPA, considering any one scenario affecting an individual (with potential to cause a fatality within a unit or local area). These values are used during LOPA to define how much risk reduction a scenario needs to achieve a tolerable frequency of occurrence. 

After selecting a HAZOP scenario and assigning the consequence severity category, the LOPA team had to establish the initiating event frequency. For the out-ofservice coke drum safety rehef valve leaking scenario, a frequency of 10 per year was assigned. All other scenarios were related to operator error. 

The level of management which is responsible for safety risk acceptance is based on the qualitative ranking of the risk being accepted. Ranking is achieved by taking into account hazard consequence severity categories, whether the hazard is characterised as unresolved or controlled, and the number of safety critical items associated with the risk being accepted. 

The consequence severity category = 2 Overall frequency (as estimated before) = C The estimated SIL (from Table 4.20) = 2... 

Cause-consequence analysis serves to characterize the physical effects resulting from a specific incident and tlie impact of these physical effects on people, tlie environment, and property (causes are discussed tluoughout Cliapter 16). Some consequence models or equations (see Chapter 17) used to estimate the potential for dniiuige or injury fall into several categories. ... 

The only available study involved exposure of rabbits to considerably lower amounts of the test substance than the standard protocols for this endpoint recommend. Relatively severe (e.g. conjunctival redness grade 3) but reversible effects were seen. It is predictable that under standard test conditions, the effects on the eye would be very severe and consequently GHS Category 1 (irreversible effects on the eye) would be justified. 

It is important to additionally account for differences in potential toxicological consequences (severity, damage, or impact) in the comparison. Characterization factors can be expressed in terms of metrics such as DALYs (disability adjusted life years) for human health, for example. The results for toxicological impacts can be directly cross-compared with those of DALY-based indicators for other impact categories, such as for climate change. 

The fire behaviour of polymer foams is largely dependent on their exposure to air and is dominated by the characteristic low thermal inertia which permits the surface to respond very rapidly to any imposed heat flux and consequently ignition maximum rates of burning can be achieved very quickly. Approaches toward reducing the flammability of polymer systems, in general, can be grouped in several categories [25,142,155-176] ... 

Examples follow in Tables 1-5 to show variations in the terms and their descriptions as used in a variety of applied risk assessment processes for the probability of occurrence and severity of consequence. There is no one right method in selecting probability and severity categories and their descriptions. 

The checklist that follows contains some additional features that require explanation. One method of deciding whether a method statement will be required is to put a numerical value on the size of the perceived risk. In this case the parameters used to estimate the size of the risk are the consequences (severity of the outcome), the numbers exposed to the hazard and the probability of harm occurring with the stated control measures in place. Values for the first and last categories can be supplied in advance of the use of the form if desired. The formula used for deriving the risk rating is not based upon any particular piece of research it shows only one possible view of the relative importance of the three categories selected. 

A CSI is essentially the same as an SCI except that systems required to identify CSIs have additional statutory and regulatory requirements that the contractor must meet in supplying those CSIs to the government. For systems required to have a CSI list, HA and mishap risk assessment is used to develop that list. The determining factor in CSIs is the consequence of failure, not the probability that the failure or consequence would occur. CSIs include items determined to be life-limited, fracture critical, fatigue-sensitive, and so on. Unsafe conditions relate to hazard severity categories I and II of MIL-STD-882. A CSI is also identified as a part, subassembly, assembly, subsystem, installation equipment, or support equipment for a system that contains a characteristic, failure mode, malfunction, or absence of which could result in a Class A or Class B accident as defined by DoDINST 6055.7. 

PreUndnary Consequence Anafysis, PCA, is used to assess the consequences of a release in terms rtf severity categories. It is onfy carried out for some releases as others can normally be estimated fipom the results. If members of the public or escalation Ity domino effects are involved it is necessary to carry out a full consequence analysis to ascertain societal risk and additional information is received befwe the evaluation of harm and damage can be estimated. 

Fuzzy sets are well suited to characterizing linguistic variables by fuzzy memberships to the defined categories for a particular situation. Failure likelihood, consequence severity and failure consequence probability could all be characterised using the same set of categories but different membership functions. In this way, the safety associated with a failure mode may also be modelled using fiizzy sets. 

Each identified hazard is allocated severity classification according to the defined safety criteria. Accident severity categories are defined to provide a qualitative measure of the consequences resulting from personnel error, environmental conditions, design inadequacies, procedural deficiencies or system, sub-system or component failures. The severity is the worst credible consequence of a hazard (i.e. the worst accident) and is independent of random or systemic failure modes. 

Accident severity category Qualitative description of worst-case credible consequences of hazard. 

There are several steps which iadividuals and corporations can and should take to minimi2e the consequences of ha2ard occurrence, as well as risk to employees and the pubHc. Much of the legislation has adopted a hierarchy of controls that essentially fall iato two categories, ie, engineering and administrative (43,44). 

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