PLC's and Automation Safety

[OkiePC]

When the bigshots find me working on a safety issue, they don't fool with me because they know I'll "lay down on 'em" for two hours with my padlock on the machine and I'll have them fired if they touch it!

I used to be an operator. I would never knowingly violate the rules of safety as I understand them. Thanks for the confirmation on the legality issue. Anyone else got related comments or anecdotes?

 

[hesham]

PLC indeed increase safety

hi all
IMHO PLc indeed increase machines and process safety .this arise from the easy programming mehods we use in programming our applications.PLC programming techniques provide an easy techniques for error and fault handling which can be used within our programs.
For Example what will happen if we output a run command to a motor or a pump without getting a running feedback from the system PLc do this easily in the program.what will happen if the level increase inside a tank without receiving that the feeding pump hase been stopped.what will happen if the motor contactor stuked and many many examples for error and fault handling becomes easier using PLC and very difficult using conventional relay logic.
In the same time many PLC manufactrers produce safety modules fitted in the PLC rack to provide safety shutdowns and fail safe outputs for the process.
BR

 

[leitmotif]

Anyone can get sued at any time for whatever the person filing wants to.
The question is will they win?

Focusing on industrial accidents where it can be clearly shown a persons error was the cause.

Rarely are criminal charges filed in an industrial accident. A prosecuting attorney told me once "yes it is probably reckless manslaughter BUT prove it -- you get me 3 witnesses who will say they saw him touch the tree and heard him say that it was suicide for those kids and I don't care" and I will file charges. In the meantime you are the only agency that has jurisdiction - go get him and hang him high.

People with licenses PE and maybe electrician may be in risk of losing their license.

If an injured person accepts workers compensation they forfeit the right to sue. I beleive that is common in all states.

That does not stop the family thus the 3rd party lawsuit.
Anyone involved with an industrial accident can get sued on a 3rd party law suit.

I don't know all the case law and history but I frequently hear the only reason electricians and engineers are not sued is that they do not have the deep pockets.

Thoughout this whole thread we have been concentrating on the reliability of equipment. The best equipment improperly applied or connected is usesless and likely dangerous. I think we have not been looking at the bigger and more common problem -- mistakes intentional, ignorant or just plain honest mistakes. I know in the Navy and at Trojan we often had a second guy look it over to ensure we got it right. I still do it today on complicated stuff.

Dan Bentler

 

[10baseT]

I think that is important to make a very big distinction - a WELL PROGRAMMED plc can provide additional safety benefits , yet more and more frequently , the tosh that I see written and posing as software only makes equipment more dangerous . There is a very concerning "yee-ha" attitude to software - near enough is good enough , and if the wheels go around , then that's OK . The sooner some people realise that the software we write , and the advice we give can damage your health , the better .

 

[MikeW]

Safety Begins with Careful Design ...

Safety is controlled by how much thought went into each component used in the design and how careful the individual "Risk" was accessed irregardless of the system being hardwired, PLC, safe PLC, etc. For example, all safeties must be powered up reach a safe condition so that a broken wire is the same as a trip and once this is sensed, restarting must be made from a safe condition in a prescribed manner.

PLC outputs and inputs WILL FAIL eventually, probably not as much as hardwired relays, but the result is the same: without careful analysis, life and limb may be in danger. I have even used various personal computers for direct control for over 20 years and even a Window 3.0 can be used safely, provide as you can sense when program has gone south via a watchdog timer, etc. to gracefully terminate execution.

Hardwired safeties have stood the test of time because they help mitigate the chance of failure that a program had a bug in it that did not consider a possible input/ output failure.