Oftentimes when this comes up during class it’s clear that there’s a misunderstanding as to how these three variables can impact the PFDavg calculations. Mission Time is defined as the period of time over which a set of Safety Instrumented Function (SIF) equipment is expected to operate without major…
exida explains Blog
- by Dr. Steve Gandy, CFSP
- Tuesday, November 04, 2025
- Functional Safety
How Does Mission Time, Proof Test Interval and Proof Test Coverage Impact PFDavg?
- by Dr. Steve Gandy, CFSP
- Monday, September 08, 2025
- Functional Safety
How Does A SIF Achieve its SIL Target?
This is a question I’ve been asked many times, with some stating that as long as the PFDavg (or PFH) meets the target SIL then that’s fine. Whereas this statement is partially true, it is not the full answer. IEC61511 defines the criteria for meeting the requirements of an…
- by Alejandro Esparza, CFSE
- Friday, August 08, 2025
- Functional Safety
Más allá de la baja demanda: Entendiendo el verdadero modo de operación de tu SIF (Beyond Low Demand: Understanding Your SIF’s True Mode of Operation)
ESPANOL
¿Se calcula el SIL de una SIF de Demanda Baja igual que el de una SIF de Demanda Alta o Continua?
Es muy importante identificar el modo de operación que es asignado a la Función Instrumentada de Seguridad (SIF). En la industria de procesos lo más común es…
- by Dr. Steve Gandy, CFSP
- Tuesday, July 08, 2025
- CertificationFunctional Safety
What Does IEC 61511 Mean by Competency?
When the latest edition of IEC61511 was published in 2016, one of the key changes was the emphasis on competency and some further guidance on what this means. The relevant clauses in the IEC61511:2016 are 5.2.2.1 to 5.2.2.3 under Clause 5.2.2: Organization and Resources. I am often asked what…
- by Valerie Motto
- Monday, June 16, 2025
- Functional Safety
A Component Reliability Data Source Must Include Useful Life
In exida’s Component Reliability Database (CRD), every component includes a Useful Life expressed in years and/or cycles.
Understanding Useful Life
This post, drawing from exida's whitepaper [1] on how environmental factors impact component reliability, shows how Useful Life, like failure rates, is affected by factors such as temperature…
- by Todd Stauffer
- Tuesday, June 10, 2025
- Functional Safety
Stress vs. Strength: The Foundation of Component Reliability in FMEDA
The So What:
Your product's safety and reliability depend on the constant battle between component stress and strength throughout its useful lifetime. This dynamic is influenced by everything from design and manufacturing to usage and environment. Crucially, without…
- by Dr. Steve Gandy, CFSP
- Tuesday, April 08, 2025
- Functional Safety
What is Prior Use Justification & How To Achieve it?
This is a question I have often been asked in the past. Most people I have spoken with don’t have a good appreciation of what this means and the purpose. From the IEC61511 perspective, designers of Safety Instrumented Systems (SIS) are required to justify the selection…
- by Dr. Steve Gandy, CFSP
- Thursday, January 09, 2025
- Functional Safety
Functional Safety in Mining: Does it Apply?
This is an important question. Mining today is a lot more modernized and automated than in the past, yet there are still accidents occurring. The Impala hoist accident in South Africa in November of 2023 is an example, where there was a tragic loss of life when the hoist…
- by Jonathan Moore
- Tuesday, October 01, 2024
- Functional Safety
FMEA Evolution – Has the essence of FMEA been lost?
Has your FMEA entered the realm of the paperwork exercise that we force ourselves to do for no real reason than someone says we must do it?
I have enjoyed analysis using FMEA. I first learned it existed when I was working for Ford. FMEA was the first Ford…
- by Dr. Steve Gandy, CFSP
- Thursday, September 26, 2024
- Functional Safety
How Does Mission Time Work with Proof Testing to Impact SIL Verification?
I have been asked this question many times by various clients over the years. This comes down to whether a perfect proof test is assumed or not. Let us remember that Mission Time is defined as the amount of time we expect a set of SIF equipment to run until a…
- by Dr. William Goble, CFSE
- Tuesday, September 24, 2024
- Functional Safety
FMEA Mistakes
I find YouTube to be a good source of information on many subjects. Want to know how to fix a widget? There are probably a few videos on that exact subject. Technical subjects are also there. I was searching on “FMEA” and found an interesting looking video on the “Read More...
- by Eman Hamouda
- Wednesday, July 17, 2024
- Functional Safety
Why is Memory Management important for Functional Safety?
What is Memory Mapping?
Memory mapping is a technique used in computer systems to manage memory resources safely, it involves creating a virtual address space that corresponds directly to the physical memory or to a portion of it, this allows programs to access memory in a way that is…
- by Jonathan Moore
- Wednesday, June 12, 2024
- Functional Safety
Have we reached peak C?
The C programming language has undoubtably extremely successful. It consistently ranks highly in the various rankings of most popular programming languages however these studies seem to be measured. C is not a language that is naturally suited to having safety requirements given to it. So, unsuited is it to…
- by Dr. Steve Gandy, CFSP
- Wednesday, January 31, 2024
- Functional Safety
What Does Root Cause Analysis Really Mean?
This is an intriguing question. One that I often ask my classes when I’m teaching our FSE100 Functional Safety course. Very often, they do not know or do not fully understand what this means and why it is important.
The IEC61511 standard requires that any failures that occur within the…
- by Patrick O'Brien
- Tuesday, September 12, 2023
- Functional Safety
Machine Safety Goals
From a machine safety management perspective, what goals are you looking to establish? Building a company safety culture, building awareness of the hazards, building the "buy in" to do things right and do things consistently is very important. It can't be done by a single person. It takes the…