1. A dynamic fault tree analysis (dfta) system, comprising: first processing circuitry including a fault tree module associated with a mission critical system (mcs), wherein said fault tree module includes at least one item characterized by an initial probability density function (pdf); at least one threshold value associated with the mcs; second processing circuitry including a sampling module configured to transform the initial pdf to a heterogeneous pdf (hpdf), wherein the hpdf includes at least one continuous segment and at least one discrete segment; wherein transition between segments is at least partially based on the at least one threshold; and third processing circuitry including a stochastic simulator configured to determine the probability of a mcs failure condition by analyzing the fault tree module using the heterogeneous pdf.