Formula: PFDavg = ½ λDU × TI
PFDavg = ½ λDU × TI
SIL band (low-demand mode, IEC 61508-1 Table 2): SIL 4 ≤ 10−4, SIL 3 ≤ 10−3, SIL 2 ≤ 10−2, SIL 1 ≤ 10−1.
Formula: STR = λS + λDD
STR = λS + λDD