Safety System vs. Hardwire / Human Intervention

[Ashereng]

Hello Everyone:

In a previous posting, there was some discussion on the the hierarchy of computer vs. human as the ultimate decision maker in a safety system.

From some of the responses, there seems to be passionate advocates on this issue.

So, I thought I would start a new post on this isssue.

Your comments, experiences and insights is greatly appreciated.



"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[Ashereng]

As stated, most things electrical or mechanical are subject to failure.

I submit most humans are subject to failure also.

I guess my question is, of humans vs. safety system, who is less fallible?

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[IRstuff]

The whole point of redundancy is to not depend on only one thing. Which would be why you should have automatic safeties as well as an E-Stop.

The only issue is to ensure that the automatic safeties are fail-safe, e.g., all failure modes result in no harm to the operator or other bystanders and the E-Stop will kill the machine regardless of whether the safeties are active or not.


Your original question, I thought, was whether the operator should have the ability to countermand the automatic safety. That might be required if the automatic safety winds up leaving the operator 100 ft in the air with no way to get down.

TTFN

 

[Ashereng]

IR,

I agree. A safety system is not just one thing. There is the process equipment, the control system, the physical protection layer, and finally, the safety system layer.

Yes, my OP deals more with whether the operator should be allowd to counternamd the safety system, or whether the safety sysstem should be allowed to countermand the operator.

In many processes, an ESD button/shutdown not only stops the immediate machinery, but also has repercussions that the operator may or may not be aware of. Hence, in an emergency and under stress, an operator may make a poor decision that he/she otherwise would not make without the stress. Then again, as other posters have indicated, sometimes, the safety systems may have blind spots (the safety system is only as good as the designers/inputs) that may need the operator to override it.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?