Appendix 5

Propagation to fatality is 1:2 times 1:5 = 0.1.

Maximum tolerable failure rate leading to single fatality is 10^{−5} pa/10^{−1} = 10^{−4} pa; however the actual process failure rate is 0.05 pa = 5 × 10^{−2} pa.

Thus the protection system should have a target probability of failure on demand (PFD) no worse than:

10^{−4} pa/5 × 10^{−2} pa = 2 × 10^{−3}.

The target is dimensionless and is thus a PFD. the Low Demand column in Table 1.1 is therefore indicated.

Thus the requirement is SIL 2.

Since there are 10 sources of risk (at the same place) the maximum tolerable fatality rate (per risk) is 10^{−5}/10 = 10^{−6} pa.

Target toxic spill rate is 10^{−6} pa/10^{−1} = 10

Start Free Trial

No credit card required