1. G f GX  ser (G,X) G v Total Common Cause Failures Pr(X = x 1 ) = 1  v, Pr(X = x 2 ) = v

2. Nested Common Cause Groups um(z)um(z) Single element

3. d j (z)d i (z) dj(z)dj(z) di(z)di(z) d m (z) vmvm Operators over d-functions

4. RBD method for nested CCG

5. Limitations of the d-function method Impossible CC groups Impossible nesting

6. Modified UGF 2 1 3 x m =1 protection m is destroyed x m =0 protection m survives U m (z, x) = (1  x 1 x 2 x 3 ) u m (z) + x 1 x 2 x 3 z 0 u m (z)

7. 1 v1v1 v2v2 9 11 10 v2v2 6 7 v2v2 8 512 v1v1 v1v1 A 1 4 2 3 v2v2 9 11 v2v2 10 v2v2 6 7 v2v2 8 512 v1v1 B 1 v1v1 v1v1 3 9 11 10 6 7 8 512 v1v1 v1v1 C 1 4 2 3 9 11 10 6 7 8 512 v1v1 D Multilevel protection solutions

8. Protection against multiple factor impacts Destructive factors Protections Complex protections

9. Different destructive factors 2 1 3 x m =1 protection m is destroyed x m =0 protection m survives U m (z, x) = (1  x 1 x 2 ) (1  x 3 ) u m (z) + (x 1 x 2 +x 3 -x 1 x 2 x 3 )z 0 u m (z)

10. Relevant DFDescription Fire barriers1 Water & foam spray2 3 Extinguishing and neutralization agents release 4 Surge suppressor5 Power conditioner6 Non-organic protecting coating7 Neutralization agents release8 9 5 7 6 3 4 1 2 1 2 3 4 5 6 7 8 9 A A 5 7 6 3 4 1 2 4 2 3 1 5 67 8 9 B Multilevel protection solutions for multiple DF