Dangerous novices programming plc's

Right on, Plcs programs are not recognized by a government burreacy as promoting their goals. Many of the OSHA goals are first orginated by a company selling safety devices.

As for protecting the guy in the plant floor, if you depend solely on a government-dictated program, you are never going to be safe, just legal.


Based on 20 years experience in safety and health work:
1. there were myriad rules and regulations and guidelines before OSHA came into effect in 1970. Some included ANSI, SAE, ACGIH, ASSE, etc etc etc.
2. MAny employers did not even know what they were much less follow them
3. OSHA was not pushed in by safety companies but was pushed in by labor.
4. New OSHA rules are not pushed by the safety equipment companies. As examples Mine Safety Appliance and Scott (maker of SCBA) were in business long before OSHA and still do not need OSHA to stay in business. A fair amount of their business is the fire departments who switched to SCBA in 1955 to 1960 era.
5. New OSHA rules are heavily fought by industry. Example the ergonomic standard - I gave up on keeping track of that.
6. Most OSHA inspectors know very little about electricity - same for state program inspectors. That was teh way it was in 1980 - I did most of the electrical fatalities in Portland OR and yes I checked recently here in Washington.
7. I completely agree with Lancie that compliance with OSHA results in mostly a paper tiger. the empahsis is on record keeping which is easy to inspect and easy to verify compliance. Besides the inspectors dont have to go out there in teh heat dust and dirt.
8. Employers squak about penalties. Here at a marina a guy got a leg burned off when contact 13,000. Penalty was 1000 for that and 9 thou for completely unrelated items. 10 thou for a leg?? I agree with my Dad they should have the doors nailed shut for 30 days and top management continues payroll out of their pockets. You would see safer work places if a few more Cxx's and Prez did some jail time for killing and maiming employees.
9. Yes employees do stupid things even when they know better. Lady I know chopped off a hand in a saw and still does not know why she did it after 5 years on those machines.
Yes I went to clear the exhaust chute on a running lawn mower - only felt the wind of the blade. Decided to shut it down and continue drinking my beer.
10. Having people come to work on crutches is in many ways a good thing - keeps insurance cost down, some really do want to work, and does keep them active and reduces depression. With good competent physicians writing good work releases overall it is a good thing but for sure can be abused by both employer and employee.
11. We had a safety awards program at Boeing but found after a year or so employees were not declaring injuries because crew would lose their safety prizes. So they stopped it only because the criteria of an injury when you get down to it was just a piece of paper and basically a worthless one at that.
I let a nurse write up one when I went to see a Boeing doc to get a fiberglass sliver from my boat pulled out of a finger - non work related I thought - there was hell to pay when the form hit our outfit probably because they could not figure out how to classify it oh Lawzy the consternation and confusion I caused.
12. E stops should be designed to protect the machine and to shut it down to reduce injury. Machine should slow and shut down as quick as possible and IF POSSIBLE AND SAFEST place all moving parts in zero energy state (bleed compressed air, put rams on bottom of stroke etc etc). E stops should dump all main power and interrupt outputs on PLCs where they can. Lock out tagout TESTOUT will prevent many injuries but not all. 13. Navy electrician school 1968 taught us to NEVER trust controls - tag it out ALWAYS.

Dan Bentler
 
This place is the exception to the norm. We just gave away a 2010 Dodge Challenger for going 1,000,000 man hours without a lost time accident. That kind of incentive along with the one mentioned above tends to keep the safety culture here as close to perfect as I have ever seen. People will rat each other out over a $40000 prize! And everyone knows it...

Paul

Hey... don't mean to be negative... but how many cover-ups and near misses got away from an LTA, especially when a fantastic record is on the horizon?

Maybe you work in cotton wool packing industry, I don't know.
.
 
Maybe its a low risk environment...









I'm naive... maybe cotton wool, as soft and lush and fluffy and unoffensive as it is, takes lots of safety risks due to high speed high danger moving parts to put it into fragile soft plastic sleeves with delicate string ties.
 
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I thought about this (and looked at a wiring diagram with a NC E-Stop) and I see why it should be wired NC. If a wire breaks it would be the same as pushing the E-Stop button and open the circuit -- the machine or process would stop. However, if it were wired NO and a wire breaks then nothing would happen. The circuit would be open, the E-Stop would be disabled and the machine or process would continue to run.

Sound good?
Exactly. But in the PLC case, it could be programmed either way, if someone uses the PLC as an MCR control (not good idea).
Think contact block coming loose from switch frame. In the PLC example, think blown control fuse and N/O stop contact( seen this one, machine keeps chugging along!).

No power (on control cct) = No stop signal.

On newer machines (in Canada, anyway), E-stops are supposed to be twist-to-reset now. How many have seen these switches, loose in their mounts because they weren't tightened correctly upon installation. Open them up and the wires are twisted into a knot, or the contact blocks are loose.

Jlfrady's example isn't as bad as it sounds, though I doubt it would pass safety inspection. At least it used a hard wired control of the PLC's output power. I think his point is that releasing the E-stop is not allowed to re-start the machine i.e. you should have 2 button control.
 
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Going back to the original, there's no problem in a stopped line being automatically re-started as long as there are signs to state this and a warning sound before restart.

Anyone who decides to work on 'live' equipment in a gung ho way deserves what they get. Its the Darwin effect.
 
In Europe, after e-stop event, e-stop circuit needs to be reset from second button. It is not allowed to self reset when e-stop button itself is reset.
 
In Europe, after e-stop event, e-stop circuit needs to be reset from second button. It is not allowed to self reset when e-stop button itself is reset.


I was shocked when I first come over here and found the operators pressing an e-stop to walk on a conveyor (20 feet up) to clear a jam, then walk back, get off, pull the e-stop back out and the line restart. :unsure:


After any fault, the fault should have to be reset and the system restarted.

In normal operation though conveying systems can go into 'energy save' and restart without warning.

The systems are automatic after all.
 
QUOTE I think his point is that releasing the E-stop is not allowed to re-start the machine i.e. you should have 2 button control. UNQUOTE

I believe every machine I have worked on was wired such that resetting E stop restarted machine. I have never liked that and believe it is indicitive of cheap short sighted management who really do not care about employee safety.

Dan Bentler
 
Here the regulations state that re-setting an E Stop is not allowed to restart the machine. There shall be one reset button that should if possible be placed in a location where all the affected machines are visible. The E Stop needs to be reset then the operator needs to press the master reset button.
Regards Alan Case
 
I believe every machine I have worked on was wired such that resetting E stop restarted machine.

It must be industry specific. I have worked everywhere north to south and east to west, and have never seen that. Nearly every installation I've seen uses something like a Pilz safety relay to make sure the machine's control power has to be explicitly reenabled and the machine restarted.
 
Lancie1 said:
. . .Your plant is heading for a catastrophe, and everybody thinks the ship ain't got no holes....

I have no idea what I said that would cause you to make a statement like that.

silva.foxx said:
Hey... don't mean to be negative... but how many cover-ups and near misses got away from an LTA, especially when a fantastic record is on the horizon?

Maybe you work in cotton wool packing industry, I don't know.

It's a meat packing plant. We make about 900,000 lbs of burger and sausage patties per day.

There could be some near misses that don't get reported. I am not naive enough to think that never happens. Our biggest issues are slips and falls and repetitive trauma, but the production folks and safety dept. do all they can to minimize those. We also have cameras monitoring nearly all parts of the plant, so when there is an accident, they always can go back and review the footage to corroborate the reports. Everyone knows they're being recorded too, so that helps keep people honest and following procedure.

The point I was trying to make was that if you follow lock out tag out properly, then no matter how poorly the PLC program (or even the safety circuit) is designed, you can still safely work on it.

Okay, sorry for getting off topic.

Paul
 
One thing that always worries me is the safety contactors.
Our regulations say that safety contactors have to be as far as practicable not easily defeatable. I have seen many contactors that claim to be safety rated that can be manually energised by pushing the contact block via the front panel. The AB ones can't do this but you can manually energise them by on the side .

Scenario:
Machine uses a Pilz system that drops out the 2 in series safety contactors.
This is done via a lockable isolation point at the machine.
Guy locks out machine and starts to work on it.
Electrician working in switchboard decides to power up a separate machine for testing by holding in the safety contacors. He makes a mistake and pushes in the wrong set of contactors therefore inadvertantly livening up the machine that is tagged out.

Where I work a lot of people call me anal but I always glue blanking plates over the side actuation points of AB safety contactors and will not use a so-called safety contactor that can be energised by a screwdriver from the front.

Regards Alan Case
 
One thing that always worries me is the safety contactors.
Our regulations say that safety contactors have to be as far as practicable not easily defeatable. I have seen many contactors that claim to be safety rated that can be manually energised by pushing the contact block via the front panel. The AB ones can't do this but you can manually energise them by on the side .

Scenario:
Machine uses a Pilz system that drops out the 2 in series safety contactors.
This is done via a lockable isolation point at the machine.
Guy locks out machine and starts to work on it.
Electrician working in switchboard decides to power up a separate machine for testing by holding in the safety contacors. He makes a mistake and pushes in the wrong set of contactors therefore inadvertantly livening up the machine that is tagged out.

Where I work a lot of people call me anal but I always glue blanking plates over the side actuation points of AB safety contactors and will not use a so-called safety contactor that can be energised by a screwdriver from the front.

Regards Alan Case

If pushing a contactor manually will result in movement of a machine while someone else is working on it then lockout tagout was not properly done
OR
the disconnect does not disconnect all power. If so then machine should be labeled for how to completely put it in zero energy state including multiple disconnects for electrical, pneumatics, hydraulics, recirc water etc etc etc

Dan Bentler
 
Hi Dan.
If you study a cat 3 or cat 4 safety circuit you will see that the disconnect from the power is 2 safety contactors in series controlled by a safety relay. Now with the isolator attached to the safety relay tagged out we would assume there is no way for power to get to the machine. Normally this is the case until someone with nothing more than 2 pens manually energises some so called safety contactors. The machine should not start but it will be energised ready to start if the start circuit is activated.
Regards Alan Case
 

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