Indicates whether to perform only qualitative analysis. When this checkbox is selected, any failure and/or repair properties entered for quantitative analysis is ignored. When this checkbox is cleared, both qualitative and quantitative analysis are performed. For qualitative analysis, results include a list of cut sets and the propagation of True/False conditions. For quantitative analysis, failure and/or repair properties entered for lowest-level events are used to calculate the likelihood of occurrence of the top event.

Indicates whether to use exact calculations. When this checkbox is cleared, cut sets are used to calculate an approximation based on properties you supply on the FTA > Advanced page. For more information, see Advanced Page. When this checkbox is selected, gate logic is used to calculate an exact solution.

The gate at which to begin the calculation for the selected tree. Choices are:

A cut set identifies which unique combination of component failures and/or events can cause the top event to occur. A minimal cut set is the smallest set of events, which, if they all occur, cause the top event to transpire. When this checkbox is selected, minimal cut sets are generated, although they are referred to simply as cut sets in the application.

Reliability importance measures rank the basic events in the tree to show how consequential they are in regard to causing the top event to occur. When this checkbox is selected, importance measures are calculated for the events that are inputs to gates. For more information, see Reliability Importance Measure Calculations.

The probability that, at a given time, the system will not function. When this checkbox is selected, unavailability is calculated.

The frequency of failures over a given time period. When this checkbox is selected, failure frequency is calculated. The frequency value shown on the gate is affected by the failure rate multiplier, which is specified by General > Failure Rate Multiplier General in the System file properties. For more information, see General System File Properties.

When selected, the calculated failure probability is compared to the maximum allowable probability to see if safety criteria are met. If the failure probability is equal to or less than the value specified for maximum allowable probability, Meets safety criteria is set to Yes. Otherwise, it is set to No. If Qualitative analysis only is selected at the top of the page, the checkbox for this property is cleared and unavailable.

When selected, uncertainty analysis is performed. This checkbox is present for all three types of fault trees. Uncertainty analysis is used for trees with top events that rarely occur, which is frequently the case for safety analyses. Failure properties, such as failure rate, are specified using statistical distributions or confidence bounds. A standard error is then entered to indicate the uncertainty associated with the resulting failure rate. If Qualitative analysis only is selected at the top of the page, the checkbox for this property is cleared and unavailable.

When selected (default), calculation results are generated for only the top gate.

When selected, calculation results are generated for all gates.

The probability value that determines whether to use a cut set in calculations. Choices are: 0, 1e-30, 1e-25, 1e-20, 1e-15, 1e-10, and le-5. The default is 0. You can also type a probability value in this field.

The number of events to use to determine whether to use a cut set in calculations. The default for this field is a number sign (#), which indicates that no limit exists on the number of events. You can enter any integer greater than or equal to 1 to set a limit.