Single contingency

Single Contingency - A single abnormal event causing an emergency. 

While generally only a single contingency is considered for design purposes, there may be situations where two or more simultaneous contingencies should be taken into account e.g., if there is some remote interrelationship between them, and pressures or temperatures developed could result in catastrophic failure. Such contingencies are also considered, and the 1.5 Times Design Pressure rule may be applied in this situation. 

Normal Individual and Process Unit Basis for PR Sizing Considerations -The following single contingencies should be considered as the normal basis for evaluating overpressure that can result from electric power failures ... 

Other Utihties - Failure of other uOhties, such as inert gas to seals and pinge systems, or compressed air (when used by the process) may in some cases determine pressure relief requirements. These cases are evaluated on a single contingency failure basis similar to the above. 

Car-Sealed Open Valve - Car-sealed open block valves are permissible in pressure reheving escape paths, provided that the single contingency of closing the CSO valve does not cause any equipment to be subjected to more than 1.5 times its design pressure. (Note Use of CSO valves is not recognized in all local codes.) The requirements for CSO valves are as follows ... 

PR valves normally in vapor service, but which under any single contingency may discharge flammable, corrosive or hazardous liquids. 

The single contingency which results in the largest accumulation (B-E) of liquid safety valve releases during 30 minutes, regardless of any associated vapor rate. The level at point E is used for pumpout pump sizing. 

The single contingency which results in the largest vapor load regardless of any associated liquid load, is used to determine the maximum required vapor space C-F, and a high level alarm is placed at point C. 

Vapor load considerations must include all safety valve, emergency vapor blowdown and vapor stream diversion sources which release as a result of a single contingency. 

Liquid loads are considered from all safety valves that discharge as a result of a single contingency, plus in each case an allowance for knockout drum liquids (fuel gas knockout drums, absorber overhead knockout drums, and compressor suction and interstage knockout drums) equal to the inventory of all drums which discharge to the blowdown drum, at their LHA point. 

The maximum vapor load on the drum is based on the largest release from safety valves discharging as a result of a single contingency. Vapor velocities in the drum are based on 100% of critical velocity (refer back to Equation 1). However, a velocity of 175% of critical is permitted when one is applying the 1.5... 

Gas pilots must be provided with a reliable source of gas which will remain available under any single contingency such as power or air failure. Pilots should be designed for the anticipated gas composition, which should be reasonably constant. 

A design pressure of 345 kPa at the lowest possible operating temperature of the entering vapors resulting from a single contingency. 

Olsen Neale made an effort to suppress his worry and formulate some kind of coherent response to the situation—one he didn t have a single contingency plan for. No one at CNIS ever believed she could actually escape. "I ll leave for Trafalgar right away. Our first priority is to inform Admiral Lalwani that Mzu s gone, so she can start activating our assets to find her. Then the First Admiral will have to beef up Omuta s defences. Damn, that s another squadron which the navy can t spare, not now."... 

Condition p = 0 points on the single contingencies, superposed on the SARW trajectories any among their steps cannot be returned due to the... 

The evaluations show that, for these limits, the calculated effective multiplication factor, keff, of any and all configurations (allowing for bias and uncertainties in reactivity due to any single contingency) is < 0.95. Normal operations are all considerably lower [Mitchell and Romero, 1999, Section 6, Evaluation and Results]. Thus,... 

ANS-8.10 allows facilities that meet its protection criteria to base criticality prevention on certain single primary methods of control that have a low probability of failure. This is single-contingency control. Examples of acceptable primary criticality controls include ... 

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