OK, Take two...
Lancie1, my statement is to the point, but it bears no evidence of criticism towards Bungouk. It states a fact. Nothing more.
If you had posted it complete, its context is much clearer in that it's a helpful statement, followed by helpful info.
All that preceded it to analyse why the references are incorrect info. I didn't go to all that trouble, just to put him down at the end!
I'm here to try educate those I feel are way off the mark with this topic.
I might seem very serious about it all, but it is a very serious subject. It's life or death! I'll stress it again.
Health and Safety is paramount. Its sole purpose is the prevention of harm, injury or death to persons.
Health and safety is indiscriminate. It does whatever is deemed necessary to safeguard human life.
It is a selfish discipline. It does not care who or what it inconveniences in the pursuit of its goal.
As long as the methods used to achieve it's goal, of protecting persons, are safe and suitable.
Health and safety dictates whether or not a PLC, or part of it, should stay on or not, not anyone else.
I love a debate, as much as the next, but there is none when it comes to health and safety, all else is secondary to it.
I'm not picking on you here Lancie1, but you are still missing the point. This is directed at anyone who thinks different.
Once the topic contains health and safety in it, it's all about personnel safety, not the PLC or anything else.
Anything you discuss in this topic that does not relate to health and safety with regard to protecting human life, does not belong here.
There are valid ideas and points being made about good PLC practices when dealing with safety triggered events and maintaining PLC power for fault indication. But these discussions belong elsewhere. If health and safety has deemed it safe to leave a PLC powered on during a hazard assessment, this is merely a convenience. Health and safety protocol does not consider if someone wants it on to show faults or message remotely.
It could say ....health and safety when driving a car, discuss.
You have to assess the risks and hazards that exist to persons involved.
Can you remove, reduce, or control the hazards?
If a risk assessment deemed it necessary to remove the engine management system to perform a task, so be it.
The mechanics can whine all they like about having no diagnostics, human life comes first, always!
You don't then start discussing all sorts of controls you would alter to get the faults some other way!
You discuss the risks and possible hazards to persons and measures to protect them, period.
Of course common sense has to play a part, Health and safety cannot be implemented to a level that inhibits a process to run efficiently.
Most posts here are just directed at the PLC, and parts of it.
No mention of people, persons, operators, risks/hazards to them and control of them.
Please remove yourself from the PLC world for a minute.
I'm going to demonstrate a couple of examples.
in some faults - as soon as you cut the power you loose the fault.
What have process faults got to do with H&S? Different topic.
Exactly right. If the machine is controlled by a PLC, and you kill power to the "whole machine"
(desirable for a mechanical tech or someone else working on it) then the electrical and controls guys
will lose some valuable information in the PLC that could save days of hair pulling. Kill all power EXCEPT the PLC,
check out the PLC for faults, test the inputs and outputs, and then maybe kill the PLC if needed.
If the power to the "whole machine" was switched off intentionally as a H&S requirement, in order for a "mechanical tech" or "someone else" to carry out a risky or hazardous task, then the needs of the "electrical and controls guys" are irrelevant.
If they were turned off as a result of something other than a H&S requirement, it's a different topic.
If steps are required by tech dept to retrieve valuable info before the manual switchout, then they need to setup an SOP(standard operating procedure) to be carried out in parallel with the H&S switchout. This SOP is not the H&S Dept's responsibility , but it would be included in the documentation of the H&S switchout procedure.
Leaving the PLC on for any period is not your call. Again if H&S requires it off, off it goes. You cannot override H&S and leave it on for a period to suit your needs, "then maybe kill the PLC". How about "then maybe kill" someone?
I'm not saying H&S doesn't allow PLCs to remain on. But that the decision lies within H&S, no one else.
If your talking about keeping PLCs on after faults, then its a different topic.
I've chosen this as it's from a PLC trainer.
I am surprised with all these great replies
Some replies are good, not great. Only a couple mentioned the human aspect of the question, no one actually defined health and safety.
Why mention forces? What have they to do with personnel safety?
You should not have a Force installed longer than 24 hours
Why? What risk?
Everything to do with forces is dangerous and should be treated with normal safety procedures. (Installing, activating, removing, forcing on, forcing off, etc. should be approached cautiously)
Dangerous? why?...treated with normal safety procedures...why?...approached cautiously? Why?
In our training, we focus on many other safety issues in addition to the ones mentioned above
Name them and their relevance to personnel safety?
Many people in our training can't explain how "verify file" and "verify project" are safety risk
What's the risk?
I'm not saying your contributions are not valid, just you need to provide more detail as to their relevance.
Understand the human aspect of health and safety first, then look at the environment your assessing in detail.
If assessing health and safety with a running machine where a PLC faults, I/O fails, outputs latch on, forces exist, file or project is verified, gremlins, fairy dust, whatever. Stop discussing whether they are possible, or to be used with caution.
They can(risk) or will(hazard) happen. Now it's up to you to decide if they are a risk or hazard to personnel safety.
If some or all are, then how can you remove/reduce or control the risk/hazard. If none are a risk or hazard to personnel safety, then they are also irrelevant.
Remember, just because something can happen because of an involuntary action or inaction, does not necessarily make it a risk or hazard to personnel safety. It may just damage raw material or plant machinery. This is not relevant here!
I'm really getting worried now that professionals are operating in these potentially dangerous environments without the necessary awareness to ensure their own safety and the safety of others.
PLCs , and their code, are an unpredictable, lethal weapon, even in the hands of people who know what they are doing. That's why H&S does not accept it as even a remote possibilty of a safety intervention method.
Please think about this.
G.