ISA TR84.00.02 PART 2

ISA-TR84.00.02-2002 - Part 2 is informative and does not contain any mandatory requirements. This part of the technical report is intended to be used only after a thorough understanding of ISA-TR84.00.02-2002 - Part 1, which defines the overall scope. ISA-TR84.00.02-2002 - Part 2 provides:

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

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

c) failure rates and failure modes of SIF components;

d) diagnostics, diagnostic coverage, covert faults, test intervals, redundancy of SIF components;

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

ISA-TR84.00.02-2002 - Part 2 provides one possible technique for calculating PFDavg values for Safety Instrumented Functions (SIF) installed in accordance with ANSI/ISA-84.01-1996, "Application of Safety Instrumented Systems for the Process Industries".

ISA-TR84.00.02-2002 - Part 2 provides the engineer(s) performing design for a SIF with a relatively simple technique generally following the simplified equation approach for assessing the capability of the designed SIF.

The procedures outlined in ISA-TR84.00.02-2002 - Part 2 provide the engineer with steps to follow in estimating a mathematical value for PFDavg for typical configurations of SIF designed according to ANSI/ISA-84.01-1996. This procedure is appropriate for SIL 1 and SIL 2 SIFs. This procedure should not be used for SIL 3 SIFs unless the User has a thorough understanding of the SIL Verification mathematics and fully understands the limitations of the simplified equations.

ISA-TR84.00.02-2002 - Part 2 does not cover modeling of external communications or operator interfaces. The SIL analysis includes the SIF envelope as defined by ANSI/ISA-84.01-1996 (see Figure I.2).