Control System Upgrade Safety

I've heard mixed opinions on this matter but if a machine is to go through a control system upgrade to what extent are you liable for reviewing the safety and design aspects?

Common sense and all the studying I've been doing over the last few days say it should be reviewed and upgraded to the latest standards however what if the upgrade is purely control hardware based?

I'll give an example... A customer has a PLC which is now redundant and spares are becoming hard to find. They don't want a full machine retrofit. They just want a new PLC running the same code as before.

What are your thoughts on this?

Rules are different in different places.

In the US, basically, if you've ever touched it, you're responsible. If something goes wrong or someone gets hurt, most parties settle as soon as possible. Actually defending yourself costs more, and you'll almost never win anyway. Juries like giving money to injured people, even if the person is an idiot who bypassed 4 different safety measures and ignored standard protocols.

From what I've been told, anywhere the European Machine Directive is in effect, as long as the original machine builder follows the official standards, they have no liability. I don't know where integrators fit into that picture.

WillM said:

I've heard mixed opinions on this matter but if a machine is to go through a control system upgrade to what extent are you liable for reviewing the safety and design aspects?

Common sense and all the studying I've been doing over the last few days say it should be reviewed and upgraded to the latest standards however what if the upgrade is purely control hardware based?

I'll give an example... A customer has a PLC which is now redundant and spares are becoming hard to find. They don't want a full machine retrofit. They just want a new PLC running the same code as before.

What are your thoughts on this?

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The legislation is the HSW act - so if you have any concerns you need to raise them and make sure they are documented. If not and something happened no doubt as an experienced, professional in the field the authorities will have expected you to have spotted it and mentioned it.

The law is about what is "reasonably practical". No one can expect a contractor hired in to do a PLC replacement to have carried out a full HAZOP and SIL review themselves although it would probably be worth asking the customer if they have done this and noting it down if they haven't.

As soon as you change out from the original specification you could be seen as upgrading the equipment so would have to apply the latest standards, saying that, The only way I've been able to get around it is going down the replacing like for like route where the original equipment is no longer available due to obsolescence and has been replaced with an alternative which does the exact same thing. for instance replacing a S5 plc to S7 would not require re evaluation unless the converted code significantly changed from the original in one way or another.

Thanks for the replies all.

Mrslipmat said:

As soon as you change out from the original specification you could be seen as upgrading the equipment so would have to apply the latest standards, saying that, The only way I've been able to get around it is going down the replacing like for like route where the original equipment is no longer available due to obsolescence and has been replaced with an alternative which does the exact same thing. for instance replacing a S5 plc to S7 would not require re evaluation unless the converted code significantly changed from the original in one way or another.

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That's pretty much what I've been told by an integrator who's got an awful lot more experience than myself.

I have a potential project in the pipeline where this is the situation and I'd only want to undertake it if it was all above board and done acceptably.
The said project is caged, well interlocked, and has had hardwired safety upgrades within the last 10 years.