ISA TR84.00.02 PART 3

W/D S/D BY ISA TR84.00.02

ISA-TR84.00.02-2002 – Part 3 is intended to be used only afterachieving a thorough understanding of ISA-TR84.00.02-2002 – Part 1,which defines the overall scope. This technical reportaddresses:

a) technical guidance in Safety Integrity Level (SIL)Analysis;

b) ways to implement Safety Instrumented Functions (SIF) toachieve a specified SIL;

c) failure rates and failure modes of SIF components;

d) diagnostics, diagnostic coverage, covert faults, testintervals, redundancy of SIF components; and

e) tool(s) for SIL verification of SIF.

ISA-TR84.00.02-2002 – Part 3 is considered informative and doesnot contain any mandatory requirements. The User should refer toISA-TR84.00.02-2002 – Part 1, which defines the generalrequirements for the verification of SIL for SIF.

ISA-TR84.00.02-2002 – Part 3 is intended to provide guidance onthe application of Fault Tree Analysis (FTA) to SIF. FTA is onepossible technique for calculating SIL for a SIF installed perANSI/ISA-84.01-1996.

ISA-TR84.00.02-2002 – Part 3 covers the analysis of a SIFapplication from the field sensors through the logic solver to thefinal elements.

Common cause failure and systematic failure are an example ofimportant factors readily modeled in FTA.

Part 3 assumes that the complex analysis of the failure rate fora programmable logic solver is done by another method (see Part 5)or is provided by a vendor as an input PFD_L orMTTF^spurious into this analysis (per Clause 7.3.2 ofANSI/ISA-84.01-1996, the failure rate of the logic solver should besupplied by the logic solver vendor). Calculation of thePFD_avg and MTTF^spurious ofelectrical/electronic/programmable electronic systems can beperformed using FTA by applying the techniques presented in thispart.

This part does not cover modeling of external communications oroperator interfaces. The SIL analysis includes the SIF envelope asdefined by ANSI/ISA-84.01-1996 (see Figure I.2).

The ultimate goal for the FTA is to determine the following:

• The PFD_avg, Safety Integrity Level (SIL), and

• The MTTF^spurious of the SIF

This analysis aids in the design of an effective SIF by allowingthe User to determine where weaknesses exist within the SIF. Thistechnique is applicable when the failure of the SIF can be causedby more than one pathway, when strong interactions exist betweenmultiple SIF, or when several support systems (instrument air,cooling water, power, etc.) are involved.

Edition:

02

Published:

06/17/2002

Number of Pages:

72

File Size:

1 file , 340 KB