Insights

Insights on important topics

"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...
Process Safety
"Proven in use" and "Prior use"
Fault Considerations and Fault exclusion.
A Safety system has to be reliable; but how many faults should be taken into consideration? A redundant system can be designed with two sensors and two redundant final elements but, in case of two faults, we are in trouble! In general, the following ...
Functional Safety
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...
Process Safety
The difference between Route 1H and Route 2H
A brief history of Functional Safety standards
In machinery, one of the first safety standards was BS 5304 “Code of Practice for Safety of Machinery”, first published in 1975
Functional Safety
P1: Reliability data for components used in Safety Systems
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...
Process Safety
Reliability data for components used in Safety Systems
Functional Safety in USA and Canada: the Concept of “Control Reliable”
In Europe, in the 90’s, the reference standard for Functional Safety of Machinery was EN 954-1. At that time, Safety-related Control Systems were classified in 5 Categories: from Category B to Category 4.
UL and CSA Conformity
P2: The Safe Failure Fraction and the Architectural Constraints
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...
Process Safety
P3: Considerations on the Safe Failure Fraction in High and Low Demand
In a previous article we presented an important parameter, used in both high and Low Demand Mode Safety Systems: the Safe Failure Fraction.
Process Safety
P4: Functional Safety - PFD calculation First Part
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 {1.4.2.1}. The bell curve is just an example of a pos...
Process Safety
The three legs of North America product Safety
THE DOUBT: is the knowledge of the NEC, or NFPA 70, important when assessing the electrical conformity of my machinery for export to USA? CONSIDERATION 1: When...
UL and CSA Conformity
The three legs of North America product Safety
P5: Functional Safety - PFD Calculation Second part
In the first part of the article we introduced the concepts of Unreliability function F(t) and of Reliability Function R(t). The former is the base for the parameter PFD(t) and the one used to indicate the reliability of a Safety Instrumented Functio...
Process Safety
P6: The average probability of dangerous failure per hour (PFH)
In the previous articles we explored the Parameter PFDavg: Average Probability of Failure on Demand. It is used to indicate the reliability of a Safety Instrumented System operating in Low demand. We will now explore the domain of Safety-related Cont...
Process Safety