Circuit design justification.

mk42 said:

Interesting. I had always heard that on your side of the ocean, if the machine builder followed the proper standards and provided that Declaration of Conformity, they were off the hook for anything that happened.

Click to expand...

But there are no procedures tthat if you follow them you will precisely and 100% always make any machine safe. There will always be an interpretation aspect, and if you interpret wrongly you may still be brought to court. For example, a lot of safety is down to user instructions. Remove the risk, cover the risk, actively guard the risk, and if there are still risk signage and user instructions will be the last line of defence.
When you start looking at a machine in order to make the risk assesment and decide safety measures, boy can you get into some discussions !
But the more effort you put in, the safer the maschine will be, and you will be better covered.

Dirt said:

The risk is never going to be zero. Are you supposed to be responsible for a life time when there's a calculated risk if something happens?

Click to expand...

If there is an accident, and the user was not negligent, then either the manufacturer was negligent or the risk was so difficult to anticipate that the manufacturer is excused for not anticipating it. If the manufacturer has put a dedicated and honest effort into the safety, then there will be no jail sentence, and if there is a fine, then it will not be severe. It is recognized that risks can never be brought completely to zero.

JesperMP said:

If there is an accident, and the user was not negligent, then either the manufacturer was negligent or the risk was so difficult to anticipate that the manufacturer is excused for not anticipating it. If the manufacturer has put a dedicated and honest effort into the safety, then there will be no jail sentence, and if there is a fine, then it will not be severe. It is recognized that risks can never be brought completely to zero.

Click to expand...

Agreed, that's how it is here.

Was asking towards the other side of the pond.

Dirt said:

Interesting discussion!

Around here, the proper way of doing a risk assessment:

* Identify risks
* Identify/calculate probability
* State your accepted risk probability (supposed to be stated by plant owner, which will be responsible for safety of workers, environment and the public)
* Calculate what SIL/other precautions needed to achieve an accepted risk probability

The risk is never going to be zero. Are you supposed to be responsible for a life time when there's a calculated risk if something happens?

Click to expand...

The usual design cycle I see over here is "Sil 3 is the best, I need a SIL 3 safety system." And then you buy a safety PLC, safety IO, wire it up, and see if it works.

Note that nowhere in there did you see a proper risk analysis or reading the safety IO manuals to check for proper wiring methods.

mk42 said:

The usual design cycle I see over here is "Sil 3 is the best, I need a SIL 3 safety system." And then you buy a safety PLC, safety IO, wire it up, and see if it works.

Note that nowhere in there did you see a proper risk analysis or reading the safety IO manuals to check for proper wiring methods.

Click to expand...

Have customers thinking like that as well! Always a challenge to explain the concept. Especially that if you add a bunch of SIL3 equipment it's not sure you have a SIL3 classed safety function..

Originally Posted by mk42 View Post
The usual design cycle I see over here is "Sil 3 is the best, I need a SIL 3 safety system." And then you buy a safety PLC, safety IO, wire it up, and see if it works.

Note that nowhere in there did you see a proper risk analysis or reading the safety IO manuals to check for proper wiring methods"
_______________________

Haha. Couldn't have said this any better myself.
P.s.
(I do not know how to quote)