Process Safety

The safety of chemical and petrochemical processes

GT Engineering is member of the Technical Committees of the following Standards: IEC 61508 series, IEC 61511-1, IEC 62061 and ISO 13849-1. We support users in the reliability assessment of Safety and Production Systems. From a Hazard and Operability (HAZOP) study, we move to a Layer of Protection Analysis (LOPA) to a SIL allocation. We can than help designing each Safety Instrumented System and calculate the Sil level reached. We organise training on all the aspects of Functional Safety and we are lecturers on Functional Safety at Brescia University and at the Milan Polytechnic (School of industrial and Information Engineering).
The Failure Rate λ
The failure rate is the basis of the Functional Safety theory.
Example of PFDAvg Calculation
We want to calculate the PFDavg for a low demand mode Safety Loop involving a pressure transmitter, an analogue barrier, two electronic safety modules and the STO (Safe Torque off) of a Variable Speed Drive.
"Proven in use" and "Prior use"
THE DOUBT: What is the difference between a Proven in Use and a Prior Use Device?   Actually the two terms are quite similar and it is very easy to mix t...
"Proven in use" and "Prior use"
The Maclaurin series and the Failure in Time (FIT)
Mathematically, it can be shown that certain functions can be approximated by a series of other functions. In particular, ex can be developed as a so called Maclaurin series:
Reliability of a Safety Function in Low Demand mode.
In low demand mode, the Reliability of a safety function is defined with the parameter PFDavg. IEC 61508 divides the requirements into four safety integrity levels, SIL1, SIL2, SIL3, and SIL4, with SIL4 being the most reliable and SIL 1 being the le...
The difference between Route 1H and Route 2H
THE DOUBT: What is the difference between Route 1H and Route 2H? Let’s try to place the subject into the main picture. When you hear about Route 1H and 2...
The difference between Route 1H and Route 2H
Reliability data for components used in Safety Systems (P1)
THE DOUBT: What are the main reliability data for components used in Safety Applications? When you deal with components used in Safety Critical Systems yo...
Reliability data for components used in Safety Systems
Reliability Functions in Low and High Demand mode
Functional safety was born having in mind the Reliability aspects of Safety-related Control Systems, designed to be activated upon hazardous process deviations; the latter is a process demand generating a Demand Rate of the safety system that protect...
The Safe Failure Fraction (SFF): what is it and how to use it (P2).
A Safe failure is the failure of an element, inside a component that plays a part in implementing a safety function, that results in a spurious operation of the safety function. That means, it places the machine into a safe state (it generates and em...
Considerations on the Safe Failure Fraction in High and Low Demand (P3)
In a previous article we presented an important parameter, used in both high and Low Demand Mode Safety Systems: the Safe Failure Fraction.
The PFD(t) is the unreliability function F(t) used in low demand mode. Hereafter its definition, supposing a constant failure rate λ:
Functional Safety - PFD calculation First Part (P4)
A continuous probability distribution is indicated with f(x) and is usually called Probability Density Function (PDF). It is expressed by an equation and it can be represented as in the Figure 1.5 {}. The bell curve is just an example of a pos...
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