I would like to share my experience which I encountered during my recent safety training to a customer in Malaysia. The topic was on Safety in Machine which the core topic was on the New Standard EN ISO 13849-1 which will be the successor to EN 954-1 ( EN954-1 will be invalid from 28-Dec-2011 )
I realized that 80% of the time I was explaining on the newly introduce Performance Level (PL) and Safety Integrity Level (SIL). During the discussion, there was a question from an engineer.
“In this case, in future we will all use the highest Safety Integrity Level (SIL) say SIL3 or SIL4 and our system will be good and safe”
As I tried to explain in technical terms to the engineer, he seemed to remain unconvinced; therefore I quoted him 2 examples.
For a glass panel installer who is installing a glass panel onto a window at 45 storey high, his safety gear would most likely to consist of Primary Safety Harness, Secondary Safety Harness, Safety Boots, Safety Helmet, Walkie Talkie, Reliable Safety Anchor Point, Reflectively Safety Vest with Distress beacon light etc.
But for a painter who is doing some painting in a ground floor room, he would most likely require a Safety Vest, Safety Boots and Safety Helmet.
It does not make sense to equip the painter with all safety gear like the glass panel installer. The Safety Integrity Level of a process is determine by the design of the process which you are running.
An retired lady would like to purchase a car and she normally travels at 60km/h and she use it only to get to the market alone. She is considering on the following 2 cars:
1st car, comes with 12 air bag, 7 seater, enhance car body for collusion test up to 160km/h. Cost SGD150K
2nd car, come with 4 air bag, 5 seater. Cost SGD SGD75K
In the end, the lady would settle for the second car as she normally travel alone and at a low speed. Using a better safety product which is redundant for your application could be costly and useless.
So with this examples, the engineer understand that through the carefully evaluation of the processes in an application, only then we can decide the correct Safety Integrity Level of the component required for the application.