Worst credible hazard

A worst-credible hazard is a hazard that is credible and where the hazard risk parameters are taken at the maximum, or worst-case values. For example, the hazard probability is taken at worst-case possibility, and the hazard severity is taken at worst-case scenarios. 

Capital Project Review and Design Procedures (for new or existing plants, expansions, and acquisitions) Appropriation request procedures Risk assessment for investment purposes Hazards review (including worst credible cases)... 

The rates of reaction (energy release in the form of heat or pressure) which depend on the temperature, pressure, and concentrations. In any hazard evaluation process, the rates of reaction during normal and abnormal operations (including the worst credible case) must be considered in order to design an inherently safe process. 

This same model is used to calculate the maximum credible event (MCE) which is defined as that unintended, unplanned, or accidental adverse occurrence which causes release of agent from an ammunition item, bulk container, or process. It must be realistic with a reasonable probability of occurrence. It is necessary to hypothesize an MCE to enable calculation of the magnitude of a worst case hazard. The hypothetical MCE for any given situation will be based upon the nature and characteristics of the agent involved, ammunition, container, configuration, and... 

Learned speculations are to be made on the consequences of an occurrence the number of fatalities, injuries, or illnesses the value of property or equipment damaged the time for which productivity will be lost and the extent of environmental damage. Historical data can be of great value as a baseline. On a subjective basis, the goal would be to decide on the worst credible consequences should an incident occur, not the worst conceivable consequence. When the severity of consequence is determined, a hazard analysis will have been completed. 

Severity is defined as the worst credible consequence should a hazard-related incident occur. 

Hazard severity is defined as the aggregate of the worst credible outcomes of a hazards-related incident, considering the exposure. 

The unit inherent hazard index UHI), is introduced to consider the safety scores of the equipment, expressed by the credit factors cfi,k)- Thus, the UHI is mostly determined by the estimated impact area of the worst credible scenario ... 

Hazard severity An assessment of the worst credible mishap that could be caused by a specific hazard (MIL-STD-882). 

Assess hazards for severity and probability based on worst-credible (not worst-possible) cases. 

Hazard severity, in Table 5.2, is a qualitative measure of the worst credible mishap resulting from the particular hazard cause. For more granularity, the hazard severity table can be quantified. For example, the safe distance or exclusion zone of an expanding toxic vapor cloud could be used to categorize hazard severity. You may also wish to expand the severity definitions and customize them to fit your particular operation. 

It is the assessed consequences of the worst credible mishap that could be caused by a specific hazard. Severity can be stated in various terms, such as death, injury, system loss, system damage, environmental damage, and dollar loss. It should be noted that mishap severity and hazard severity are really the same entity, just viewed from two different perspectives. 

These functions are the basis for the Functional Hazard Assessment (FHA), for the identification of possible hazards. In workshops with experts - to combine technical, domain and safety know-how - various techniques are applied. This includes brainstorming, use of historical data and functional failure modes and effects analysis to identrfy possible failure modes, their operational effects and the respective severity of the worst credible outcome. Based on the safety-relevant failure modes, potential hazards are determined and respective risks are allocated according to the risk matrix. The FHA leads to derivation of top level hazards. 

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. 

HA is qualitatively performed in both narrative and matrix formats. The common matrix used across most disciplines nses Categories of Severity and Levels of Probability. Hazard Severity Categories from I to TV provide a measure of the worst credible mishap resulting from personnel error, environmental conditions, design... 

The subsequent step is to identify the various scenarios which could cause loss of control of the hazard and result in an accident. This is perhaps the most difficult step in the procedure. Many accidents have been the result of improper characterization of the accident scenarios. For a reasonably complex chemical process, there might exist dozens, or even hundreds, of scenarios for each hazard. The essential part of the analysis is to select the scenarios which are deemed credible and worst case. 

Calculates the vulnerability zone based on the maximum quantity present for screening Calculations are based on credible worst case a.ssumptions identified in the Technical Guidance for Hazards Analvsis. 

On the basis of the test and calculation results illustrated in Table 3.6, it is possible to make an energy appraisal for the specific reaction under investigation. Generally speaking, the potential for a worst-case decomposition becomes greater when the hazard class is high as listed in Table 3.6. The worst case should be assumed instead of the credible case, in general, as follows ... 

Inherently safe maintenance of a system in a non-hazardous state after the occurrence of any credible worst case deviations from normal operating conditions. 

Define the release This step may be based on a worst possible case based on the maximum amount of material within a process loop, or a worst probable (credible) case selected from a hazards review. 

Much discussion could be presented as the most credible worst case event at the facility. Obviously a multitude of unbelievable events can be postulated (industrial sabotage, insane employees, plane crash impacts, etc.). Only the most realistic and probable events should be considered. In most cases, historical evidence of similar facilities is used as a reference for the worst case events. Alternatively, the effect of the most probable high inventory hydrocarbon release could be postulated. The worst case event should be agreed upon with loss prevention, operational and senior executive management for the facility. The worst case credible event will normally define the highest hazard location(s) for the facility. From these hazards, suitable protection arrangements can be postulated to prevent or mitigate their effects. 

A worst-case scenario is the most credible and reasonable overall effect of the hazard occurring on the system. A credible assessment is based on the engineering judgment of the safety engineer. 

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

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