Safety System design, Crazy Customer request

I am working on a very large machine at the present time. This machine has several safety zones and up to 8 light curtain guarded areas. It is divided by these safety zones to allow operators to enter certain areas during certain times. It has muting circuits where an operator can press "Mute" enter a zone and if he leaves the zone and presses "Reset Button" the machine doesn't have to completely stop. However if he is still in that zone when operations begin in that area then we stop that section of machinery,. This is done quite regularly throughout the industry.
NOW MY ISSUE:
This customer has requested I design a safety system that works like this:
As operator(s) enter a zone they must step on a sensing mat. The safety system counts the number of people who enter that zone. Now when they leave the safety system counts how many people left that zone. And when (By Counting) everyone has left the zone the machine can continue with operations in that area.The Ingress or Egress is determined by the operator(s) hitting a button.
My concern is there is nothing to prevent an operator just stomping the mat several times and thus allowing someone to remain behind.
I am fighting this every way possible. But I Need AMMUNITION to fight it with. I realize the customer / end user is responsible for safety, However when an injury occurs as we all know The lawyers sue everybody involved.

Count isn't reliable. If you allow bypass of safety curtains, then you need mats covering every foot of space in the protected zone, or secondary safety curtains.

You need a safety assessment that every one involved has signed off on. Then you can design your circuit.

Could you use a safety area laser scanner in this area? It would be better then counting for the exact reasons you pointed out.

If we are having this conversation, you already know it's wrong.

Your ammunition is your reputation and your livelihood. If, in good conscience, you cannot conceive this being a good idea (completely safe and completely infallible), tell the customer and stand your ground.

Even if the safety team polls the operators, and they all buy off and buy in, it takes one person in a moment of distraction to cause injury or death because of an ingress procedural error.

Super high ups have to sign off.

John Morris said:

If we are having this conversation, you already know it's wrong.

Your ammunition is your reputation and your livelihood. If, in good conscience, you cannot conceive this being a good idea (completely safe and completely infallible), tell the customer and stand your ground.

Even if the safety team polls the operators, and they all buy off and buy in, it takes one person in a moment of distraction to cause injury or death because of an ingress procedural error.

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The CEO and Plant manager are the ones who have to sign off on a safety issue. I will bet neither one of those would do it. Lower level managers may, but plant managers and CEO go to jail.

I have went through this before with people that worked for me in a plant. I would tell them to get the manager to sign this paper saying they approve a unsafe act, then we will take it to the plant manager. Never had one sign there was always a proper way found.

Last year I went round and round trying to find ways to keep track of who enters and exits a safety guarded zone.

In the end, it boiled down to using laser scanners. Seems everyone makes them these days, and they are all relatively the same. And when properly used, they ensure that no one and no thing is inside the guarded area before the zone is reset and allowed to operate again.

It really simplified the safety circuit and operation. So now there's just a standard fence system with locking safety device, and any number of scanners inside (exact number depends on size and layout) to identify when people or objects are inside of the caged area.

You've already done the analysis in your head. Write up a hazard analysis that shows mayhem, dismemberment, and death is the logical conclusion.

Essentially all you have is the PLC taking a guess that they followed procedure.

Not only is it a safety hazard it is a reliability issue as well. What if the PLC counts two going in, but only one going out because the two walk out together. The machine is safe, but you wouldn't be able to restart it. How many times will Bubba have to call maintenance to figure that one out?

You need cameras, or scanners, and/or full coverage safety mats.

just the cowboy said:

The CEO and Plant manager are the ones who have to sign off on a safety issue. I will bet neither one of those would do it. Lower level managers may, but plant managers and CEO go to jail.

I have went through this before with people that worked for me in a plant. I would tell them to get the manager to sign this paper saying they approve a unsafe act, then we will take it to the plant manager. Never had one sign there was always a proper way found.

Click to expand...

This is the way to handle this issue. What the "creative" plant people came up with is NOT safe.

Bio-metric Thumb Print scanners may be a decent solution.
This way you can handle access permissions as well as it being almost impossible to circumvent.

GTUnit said:

Bio-metric Thumb Print scanners may be a decent solution.
This way you can handle access permissions as well as it being almost impossible to circumvent.

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The problem for me always came down to "forcing them to do it". Cause once the gate was unlocked and opened, any number of people could enter the area without being forced to do anything. Person A unlocks the gate, but Person B, C, and D enter the area without being required by the system to do anything, because the gate is already unlocked and opened.

Sounds like this customer has a similar concern. And is attempting the automatically count who goes in and out. (Which is not reliable in pretty much any way).

What about turnstiles?

https://www.perco.com/products/turnstiles-gates-railings/full-height-solutions/

Maybe not as quick as counting on a mat, but much more reliable. I would recommend trapped key interlocking in this situation:

http://www.fortressinterlocks.com/Range/3/tgard-customisable-safety-system

Somebody has jurisdiction over the safe operation of automation systems (L&I ?). I would find out who and see what regulations they have the covers this sort of thing.

tarik1978 said:

What about turnstiles?

https://www.perco.com/products/turnstiles-gates-railings/full-height-solutions/

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Essentially the same problem. Wouldn't take an operator long to figure out all they need to do was turn an empty turnstile. So, that their buddy, Bubba, could stand in the danger zone.

If operators spent as much time trying to figure out how to stay safe rather than how to defeat interlocks workplace accidents would all but disappear.

Timbert said:

If operators spent as much time trying to figure out how to stay safe rather than how to defeat interlocks workplace accidents would all but disappear.

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I almost saw a pig fly the other day.

To quote someone I never knew " Ya git what ya pay fer"

I'm not sure 580 Mb is enough to outwit an incessant twit

Darwin once said "life is inherently dangerous and only the strongest and smartest would live to procreate.

I blame the democrats, Dr. Spock, and soccer moms who believe "everyone should have a trophy"

There's your operators.

Sorry for the rant...................30 years of operators will do that to you.

My apologies to everyone that doesn't apply to.