Dangerous novices programming plc's

[iraiam]

Machines controlled by plc’s can injure and kill people if something is not programmed right!

I saw an incident the other day that heightened my concern - a man and all his tools was thrown off a conveyor and injured because someone else actuated a sensor.
This sensor should not have done this until several other conditions had been met but due to terrible programming and no ‘event’ control - the conveyor started up although the conveyor system was off (not e stop - just the red stop button)
I am all for helping people to learn programming and I always give advice where I deem it proper and know what or where the poster is struggling.
But the plain truth is - some posters here should not be allowed within 50 ft of a plc controlled machine until they have fully understood the machine/plc and all the possible consequences of their actions.

For starters, The mechanic in question failed to properly LOCK OUT the power to the conveyor, An accident like that (failing to lock out a piece of equipment before walking on it) would get you fired where I work!

LOTO is there for EXACTLY this reason, with automation today an "engineer" can access a PLC ladder remotely from half a world away, so locking out equipment is even more important than ever.

The accident you describe was a direct result of failing to follow proper LOCK OUT TAG OUT procedure! Bottom line: There is no safety device to account for a man walking on a conveyor without the energy source locked out.

 

[Lancie1]

No, Iraiam, you have completely missed Goody's concern. All you said is true - the mechanic should have done LOTO, but even if he did not, the conveyor should not start UNLESS IT RECEIVES A START COMMMAND.

...the conveyor started up although the conveyor system was OFF.

That is a programming error, no matter what else went wrong, and any good trial lawyer would love to take a case like this. It will not matter to the court that the mechanic was at fault. They will also look at WHO ELSE was to blame. How would you ever convince a jury that the PLC program was not faulty! If I was on that jury (and I have been on a few) I would have to vote with the deceased mechanic's widow.

Actually, I blame this on the people who are teaching programmers that this type of programming is okay. I think in many cases the instructors that think like this are the ones who have never actually worked in a plant environment. Theroretical knowledge is good, but it needs tempering with some hands-on real-life nitty-gritty experiences, like watching someone get hurt because a machine started even though no one gave it a start signal.

Eventually, due to legal liability, all this poor and irresponsible PLC programming will inevitiably lead to a "Legally Controlled Start", where a dangerous machine can only be started when some legally responsible person is there to push the special locked-and-sealed Legal Start button.

The bottom line is: Programmers must accept some responsibility for machine saftey. The program logic is the last chance to prevent a machine start when all other methods have failed, been ignored, or been bypassed.

 

[iant]

I have a small issue with the "legally Controlled start"
it is a good idea, but, if a machine line has totally enclosed guarding.
and the process is designed as a JIT (Just in time) system.
when the next process is clear it automatically calls for the part to be processed.
In Goodies incident - the unfortunate man has isolated the conveyor - OK
But the next process is for the binding - Probably does not require the conveyor running.
Unfortunately he had triggered the next process.
I Agree with you Lancie1, But in this case the "line start" signal had been given, And I bet the isolatior is not tied in to that sequence - (that is not a cat 4 safety interlock anyway)
The automatic line guarding must be foolproof - As hinted -
The output area need preventative measures in place -
There are both Physical and Non contact Guarding posibilities.
All Hinge on COST
What cost do you place on a life.

I have seen an automatic machine guard system modified - do not know why.
the guards were 6' (6 feet) tall.
for some reason they lowered them to 3' - so you can jump over them.
This allows 100% access to a fully automatic 500 ton 'B' class mechanical Press.
I wasn't working there but I did inform the manager.
(this machine has been removed since - luckly no accidents)
Some 'Engineer' had allowed an unsafe condition to exist.
That person was glad that an old safety stickler (who designed the guarding) like me - no longer worked there - so they could take away the safety systems. - he no longer works there either.

A machine start button is pressent But only to start the process.
Not to start each cycle.

the fibre glass insulation mfg system - is very suspect
they won't (Can't) stop the line there, so they pull material away from the line with out stopping it - that looks scary.

 

[Lancie1]

but, if a machine line has totally enclosed guarding.
and the process is designed as a JIT (Just in time) system.
when the next process is clear it automatically calls for the part to be processed.

I understand. What you are saying is the owner-producer-manufacturer-insurers standard touted line to employees: follow our safety rules, wear the safety equipment, use the safety interlocks, lock out and tag out, and then we have done OUR job so if you get hurt, it is your problem and not our responsibility.

Except they all know that it is not true, that if you get hurt, they are still held legally liable in court. It is that last part that will eventually sink this leaking ship. If all the above is not enough to avoid liability, then the next step will be someone to be responsible (and liable) for each equipment start.

In the meantime, many companies have moved their dangerous operations (metal forging, mining, chemical plants) to other countries where the burreaucrats are more bribable.

 

[milldrone]

the fibre glass insulation mfg system - is very suspect
they won't (Can't) stop the line there, so they pull material away from the line with out stopping it - that looks scary.

Ian,

I'm not sure what you have seen in regards to fiberglass mfg. I work for in fiberglass mfg. The procedure in place at the facility I work at is approximately the same hazard as what a front end bucket loader is exposed to when he takes sand away from a pile that is being continuously filled by a conveyor belt. In the case of fiberglass there is a gap between the hot end conveyors and the cold end. The hot end continues to produce and cold end stops, the clamp truck (specialized forklift) clamps the pile of product that accumulates between the two conveyor systems and pushes it aside (later to be shredded for blow wool).

If the entire process were to stop the employees on the hot end would be exposed to hot liquid glass. This exposure would also happen when the line was started again.

Concerning safety, some things are safe by equipment design, some things are safe by procedure. When I analyze safety situations I see many more processes that are safe by procedure than those that are safe by equipment design.

 

[Lancie1]

But when they [PLCs] are not connected to Dangerous machines then they can be toys.

PLC as a toy, now that is a thought that makes me want to not ever go into a plant again. This recent post is still another example of the lack of training and the dangerous attitudes that are apparently becoming the normal instead of the exception.

 

[iant]

i agree with you lancie1 - there is a slight difference in the 'Legal'
code here - an employer must provide a safe workplace.
if the Risk analisys is correct - there is a fine line between over design and under design - so over design it has to be.

I know from experiance that there are engineers who continually question guarding requirements - hopefully they will not cause someones death.
One of these guys is now a company manager in china.

our industrial umpire 'Workcover' can be called to look at any machinery at any time either by the employee's or the employers.
No one can protect someone who deliberately and knowingly crawls through a guard space. if the machine was relay controlled instead of PLC the result would be the same.
Access via a part exit is the hardest area to guard - if there are different sizes and shapes to come out.
Non-contact guarding (light curtain etc.)- maybe - but not always possible

 

[yam785]

Sounds like three of us, have spent time between the oven, and the slitter blades.

I'm not sure what you have seen in regards to fiberglass mfg. I work for in fiberglass mfg. The procedure in place at the facility I work at is approximately the same hazard as what a front end bucket loader is exposed to when he takes sand away from a pile that is being continuously filled by a conveyor belt. In the case of fiberglass there is a gap between the hot end conveyors and the cold end. The hot end continues to produce and cold end stops, the clamp truck (specialized forklift) clamps the pile of product that accumulates between the two conveyor systems and pushes it aside (later to be shredded for blow wool).

If the entire process were to stop the employees on the hot end would be exposed to hot liquid glass. This exposure would also happen when the line was started again.

Concerning safety, some things are safe by equipment design, some things are safe by procedure. When I analyze safety situations I see many more processes that are safe by procedure than those that are safe by equipment design. the fibre glass insulation mfg system - is very suspect
they won't (Can't) stop the line there, so they pull material away from the line with out stopping it - that looks scary.

Ugh at very itchy. Between the oven and the cooling box / slitter blades, nasty place, espcially if they are running duct board on that line.

 

[iant]

you are right - I was only programming a contracted water filter/cooling system.
So I don't need to work there any more .

 

[kirso]

"But when they [PLCs] are not connected to Dangerous machines then they can be toys. "
As Lancie1 knows I said the above quote.
As per usual it has been taken out of context. It was in regard to someone wanting to learn by "having a play" using a plc.
There seems to be an elitest group who have some major issues with newbies on this site.
These people need to get out of their "emperors new clothes syndrome" and realise that things have changed in the world.People are not having to do 5yr apprentice courses and having to work as hard as you maybe did to get a qualification.But such is life.
The great thing about PLC,s is you can have a "play" and not be tied to the outside world. I can now try out lots of options and not have to wire a single contactor or relay to see the results. All I need is a piece of software.
There are lots of "toys" out there that are as powerful as the early PLC,s. Look at the Lego systems. But look on Utube and you will see lots of examples of people doing plc progs for FUN. Also no one can tell me there is not a bit of fun when using Logixpro as a learner.
In my apprenticeship years I was told to have "a play" on many occasions when this would not put me or anyone else in danger.I learnt alot from those times.
It may be just a case of a US/UK interpretation, but over here "having a play" is a common phrase.
But some of the elite cant seen to grasp this and feel it is an insult to their hard earned knowledge and experience to "belittle" their work by infering some one may have fun doing it.

 

[Lancie1]

Having fun is fine.

Playing is good.

Children play, adults don't.

 

[kirso]

Having fun is fine.

Playing is good.

Children play, adults don't.

I think you must be a very sad adult if you dont play Lancie1
Maybe thats what is missing in your life that makes you so pedantic and bitter.

 

[silva.foxx]

Having fun is fine.

Playing is good.

Children play, adults don't.

Can'o'worms

Of course adults play. Fathers love to play. Grandfathers love to play.

Children do play and they also know/learn when play can be harmful. Adults, being big kids at heart, also know when play has the potential to be harmful then this is when they choose whether or not to be responsible!

Adults play responsibly... well most do!

 

[PeterW]

Having fun is fine.

Playing is good.

Children play, adults don't.

Speak for yourself

 

[leitmotif]

Having fun is fine.

Playing is good.

Children play, adults don't.

Lancy

Where did you get the notion adults do not play?
Golf? Tennis? Checkers? Chess? Cards?
Yeah let us go and work a round of golf.

Dan Bentler