Fire, generally scenarios

A general treatment of fires in mines must deal with the general scenarios under which they are likely to occur. The origin of fires maybe a diverse field, but the basic manifestations can be hmited to a few variables. The first of these will be the consideration of the basic fire presentation. Next will be the state of the fire with respect to the combustion chemistry. The method of ignition will be considered also, particularly in respect to self-ignition. Finally, some discussion is warranted with respect to the general behavior of fire-related phenomena. 

Consequence Phase 3 Develop Detailed Quantitative Estimate of the impacts of the Accident Scenarios. Sometimes an accident scenario is not understood enough to make risk-based decisions without having a more quantitative estimation of the effects. Quantitative consequence analysis will vary according to the hazards of interest (e.g., toxic, flammable, or reactive materials), specific accident scenarios (e.g., releases, runaway reactions, fires, or explosions), and consequence type of interest (e.g., onsite impacts, offsite impacts, environmental releases). The general technique is to model release rates/quantities, dispersion of released materials, fires, and explosions, and then estimate the effects of these events on employees, the public, the facility, neighboring facilities, and the environment. 

True fire hazard can be determined only in a specific scenario. Therefore, it is necessary to determine which fire properties are most relevant to the scenario in question. These fire properties will then have to be measured and combined in order to obtain an overall index of fire hazard. As a general rule, it is clear that the most important individual property that governs levels of fire hazard is the rate of heat release the peak rate of heat release is proportional to the maximum intensity a fire will reach. 

Fire risk assessment is made in order to determine the overall value of decreasing fire hazard in a particular scenario. The level of fire risk that is acceptable for a situation is, normally, a societal, and not a technical, decision. Therefore, fire hazard assessments are generally more common than fire risk assessments. The NFPA Research Foundation has undertaken a project to develop a methodology for fire risk assessment. It has done this by studying four cases in detail upholstered furniture in residential environments, wire and cable in concealed spaces in hotels and motels, floor coverings in offices and wall coverings in restaurants. 

No general rules-of-thumb are available for plastic tanks/containers failure criteria should be based on available test data (SINTER, 1997). FRP is used offshore for fire water lines in order to reduce weight. Wet pipe FRP systems may be effective in afire scenario because water is flowing, allowingthe heatto be carried away. If the pipe is dry, failure may rapidly occur. 

An integral part of defining the fire-scenario envelope is determining the appropriate dimensions for use in planning fire protection. For liquid hydrocarbon fuels, a frequently used frame of reference is a fire-scenario envelope that extends 20-40 ft (6-12 m) horizontally, and 40 ft (12 m) vertically, from the source of liquid fuel. For pool or spill fires, the source is generally considered to be the extent of the fire as defined by containment such as dikes and curbs. 

The difference between the crash rates per mile in the first two reports is due to the use of a bounding rate (using general data) in the first report and a carrier-specific rate in the second report. The third report derived a truck crash rate per billion ton-miles, based on Federal Motor Carrier Safety Administration data for the number of commercial vehicle hazmat crashes divided by the number of commercial vehicle ton-miles. The commercial vehicle accident rate per ton-mile value was multiplied first by 0.59 and then by 0.013 to account for the number of ton-miles for for-hire commercial vehicles and for Class 6 poisons, respectively. These adjustments to the accident rate are inappropriate without consideration of the corresponding hazmat crashes, for which no data were used. The total accident scenario probabilities may be conservative (too high), however, when the probabilities of fire occurring, impact forces sufficiently high, etc. are considered. These probabilities do not appear to have been addressed, and the committee did not review the reports at that level of detail. 

It is necessary to perform the review with an open mind set to identify the risks and consequences. A major accident would generally occur from one of these three categories -a fire or an explosion or a toxic release. These three major hazard categories are further subdivided in Table 3.1 that could be helpful in developing relevant scenarios. 

At sites for which an aircraft crash scenario is postulated, the crash event is generally associated with the release of significant amounts of fuel, which most probably wiU be ignited, and this may lead to subsequent explosions. The design measures for such an event generally envelop the provisions necessary to handle other external fire scenarios as mentioned above. 

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