Compliance with IEC 61511 What do we have to do to be compliance with IEC 61511? This Standard introduces the concept of Safety Life Cycle and, therefore, the answer is associated with the fulfillment of each phase of this cycle. Our intention is to explain it, in a simple way, for the not so expert. …
Failure Probability Is it very important to calculate very precisely the average probability of failure “PFDavg” of a Safety Instrumented Function? The short answer is “NO“, and we will try to explain it below. The first thing to say is that Functional Safety is much more than meeting the probability of failure. IEC 61511 defines …
Complex Architectures in the final element (I) Calculating the probability of failure (PFDavg) in a complex architecture is not usually easy, especially if we do not know the concepts well. Let’s see in this case a complex architecture in the final element. Example: Logic 4oo4 in the final element From time to time we find …
Most common errors in the SIS The aim of this article is to review some of the most common errors in the SIS (Safety Instrumented System) that can serve as a guide and reason for reflection for all those involved in its design, implementation and maintenance. Both IEC 61508 and IEC 61511 indicate the great …
Systematic Failures IEC 61511 defines systematic failures as those “related to a “pre-existing” fault, which can only be eliminated by removing the fault by a modification of the design, manufacturing process, operating procedures, documentation or other relevant factors”. The peculiarity of systematic failures is that they are “hidden” and may never manifest or be detected, …
Partial Valve Stroke Test (PVST) The Partial Valve Stroke Test is used in the Safety Instrumented Function (SIF) to diagnose valve failures without having to stop the process. The problem of the shut-off valves in low demand SIFs is that they remain in a position (open or closed) for many months, without knowing if they …
Why invest in Functional Safety A common perception in many industrial plants is that Safety is more an expense than an investment. If we have not had a serious accident in the Plant in the last 10 or 20 years, we may have difficulty finding arguments to invest in Functional Safety. Implementing in the Plant …
Compare SILcet with exSILentia To perform the SIL verification in process industry, according to IEC 61508 and IEC 61511, there are several software tools such as “exSILentia” by Exida, our SILcet software and others. In the process industry “exSILentia” is, without a doubt, the reference software with great international recognition. It is a great suite …
Transmitter Diagnostics In the previous post we have explained in a brief way what are the failures of transmitter that affect the calculation of PFDavg / PFH and MTTFS of the Safety Instrumented Function (SIF). We will go deeper into the transmitter diagnostics and explain it with some example. Recall that the “Fail High” and …
Transmitter Failures (4-20 mA) In the following table we see an example of the types of transmitter failures and which we should consider when verifying the Safety Instrumented Function (SIF). The rates in the example correspond to the Rosemount model 3051 pressure transmitter. Type of failure Example of Failure Rates per hour (FITS) Notes Fail …
Logic Solver (PLC versus relays) The Logic Solver is the SIS subsystem where the logic of the safety functions resides, that is, what are the interlocks of the sensors and how they act on the final elements. We do not always refer to a Safety PLC when we talk about the Logic Solver, because the …
