Risk Evaluation Process for Accidents

A more detailed figure is presented below if the system in question is a chemical plant  

A brief description of the equipment and chemicals used in the plant is needed 

Any hazard in tlie system lias to be identified. Hazards tliat may occur in a chemical plant include  

The event or scries of events that will initiate an accident has to be identified. An event could be a failure to follow correct safety procedures, improperly repaired equipment, or a safety mechanism The probability tliat tlie accident will occur lias to be determined. For e.xample, if a chemical plant has a 10-year life, wliat is the probability that 

Uie temperature in a reaetor will exeeed tlie speeified temperature range The probability ean be ranked from low to high. A low probability means that it is milikely for tlie event to oeeur in the life of the plant. A medium probability suggests that there is a possibility tliat tlie event will occur. A liigh probability means tliat the event will probably occur during tlie life of the plant 

The severity of the consequences of the accident must be determined. This will be described later in detail 

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Risk analysis is a proactive approach in the sense that it makes ns able to identify and assess accident risks before any losses have occurred. It has many similarities to the reactive approaches presented in Part III. It utilises all four sub-systems of the SHE information system, i.e. data collection (risk identification), processing (evaluation of risk), memory (e.g. reliance on historical accident data) and distribution of results for decision-making. 

The risk for other on-site workers (outside the TOCDF and DCD storage area) is evaluated in the same manner as the risk to the public. The probability of one or more fatalities for other on-site workers during the 7.1 years of disposal processing is 5 x 10 (1 in 2,000). With about 100 workers in this category, and assuming that most accidents cause a single fatality, the individual annual risk is 1 x 10 (1 in 1 million per year) for other on-site workers. 

A formal hazard analysis of the anticipated operations was conducted using Preliminary Hazard Assessment (PHA) and Failure Modes and Effects Analysis (FMEA) techniques to evaluate potential hazards associated with processing operations, waste handling and storage, quality control activities, and maintenance. This process included the identification of various features to control or mitigate the identified hazards. Based on the hazard analysis, a more limited set of accident scenarios was selected for quantitative evaiuation, which bound the risks to the public. These scenarios included radioactive material spills and fires and considered the effects of equipment failure, human error, and the potential effects of natural phenomena and other external events. The hazard analysis process led to the selection of eight design basis accidents (DBA s), which are summarized in Table E.4-1. 

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