Safety Interlock Bypass

[kckku]

Does your facility allow anyone to bypass door safety interlocks? I am against this but there's a discussion again at our plant about needing to do this. Sometimes this is needed during machine calibration, verification, and setup. This is only done as part of our maintenance activities (typically every 6 months). The maintenance guys say it's easier to do this type of work with the door interlock bypassed.

If your facility allows this, what is your procedure to allow this?

 

[alan_505]

I have seen sites where this is allowed but a strict procedure is required, machine has to run slow and area has to be barricaded and a permit obtained before this can be done.

 

[Jim3846]

Maybe modify the estop for captured key interlock? Not sure if these are aloud anymore? used them on ASRS to bypass gate and go inside to locally control an asrs machine. Looked it up on google, captured = trapped key.

Door has the captured key, take key out and stick onto the inside the fense where the machine is at. The machine runs in local with a pendant or local controls. The door is no longer an interlock. Push restart inside the fenced area where machine is located. Machined is run locally.

I would consult a safety consultant in your area to get his 2 cents, since these guys know the laws and what can be used and what cant be used. Maybe even do safety analysis with his fancy software for the relevant level of safety.

 

[kckku]

I have seen sites where this is allowed but a strict procedure is required, machine has to run slow and area has to be barricaded and a permit obtained before this can be done.

Our health and safety committee is coming up with a procedure on how this should be handled. This is why they are soliciting comments/questions from the engineering staff.

It's the right step I think because before it was a bit of a free for all.

 

[VAN]

Does your facility allow anyone to bypass door safety interlocks? I am against this but there's a discussion again at our plant about needing to do this. Sometimes this is needed during machine calibration, verification, and setup. This is only done as part of our maintenance activities (typically every 6 months). The maintenance guys say it's easier to do this type of work with the door interlock bypassed.

If your facility allows this, what is your procedure to allow this?

When you say bypassed do you mean messing with the sensor in a way to make the PLC think its operating correctly or like change to PLC code?

Generally any safety interlock I like hardwired and the PLC just gets to know the info. BUT long time ago, I use to install equipment that had hood sensors that people would just put metal caps on so they could lift the lids and watch the process. I'm not sure how dangerous it was but it was a factory's choice (after they paid for it).

I've never worked for a place that was OK with bypassing anything, and most people would get fired if caught. Several people died in that industry anyway, so bypassing safety systems in frowned upon.

 

[kckku]

Maybe modify the estop for captured key interlock? Not sure if these are aloud anymore? used them on ASRS to bypass gate and go inside to locally control an asrs machine. Looked it up on google, captured = trapped key.

Door has the captured key, take key out and stick onto the inside the fense where the machine is at. The machine runs in local with a pendant or local controls. The door is no longer an interlock. Push restart inside the fenced area where machine is located. Machined is run locally.

I would consult a safety consultant in your area to get his 2 cents, since these guys know the laws and what can be used and what cant be used. Maybe even do safety analysis with his fancy software for the relevant level of safety.

Our machines are actually really compact so there aren't really any large walk-in areas. We have enabling devices for manual actuation with the doors open. The enabling device already has an E-stop and a 3-position enabling switch. So usually this is enough.

For what they are asking now, they want to have the machine run at a full speed cycle to do the strain measurement. This is needed to qualify our equipment so we know the setup doesn't cause undue stress on the product. They want the door open because closing it will crush the wiring from the strain gauges to the measurement unit.

The other activity is basically calibrating a load cell to make sure it's reading correctly. To do this, you have to jog the press down slowly onto a fixture. You kind of have to see what you are doing so it's easier with the door open.

 

[Jim3846]

Sounds dangerous to have the machine run at full speed during a test?

The people that usually die in these situations is the maint guy who is so used to the machine that he forgets his common sense and will lean into the machine and now he has no head. Just warning what will happen!

So either put temporary light curtain set up around the area so you can interlock the machine or an area sweep sick device on flow. I think they sell these things so you teach it a certain wierd area. Paint a circle where that goes temporary

watch this youtube maybe this is what you need?
https://www.youtube.com/watch?v=i8mGGI5DSwU

 

[jstolaruk]

We provide a safety enabling device (formerly called a "dead man") that the technician must hold while in the cell and allows motion energy to be enabled (electric, air, etc) when activated. Risk assessment will identify the danger points. In the case of a robot, the enabling device is the teach pendant. Any personnel in the cell must have a enabling device.

 

[drbitboy]

... They want the door open because closing it will crush the wiring from the strain gauges to the measurement unit.

The other activity is basically calibrating a load cell to make sure it's reading correctly. To do this, you have to jog the press down slowly onto a fixture. You kind of have to see what you are doing so it's easier with the door open.

A cutout on the door or custom connector through a wall, and a remote camera (wifi, for Pete's sake), or maybe just a mini door in the door, are going to be far cheaper than the lawsuit and the guilt.

 

[cardosocea]

For what they are asking now, they want to have the machine run at a full speed cycle to do the strain measurement. This is needed to qualify our equipment so we know the setup doesn't cause undue stress on the product. They want the door open because closing it will crush the wiring from the strain gauges to the measurement unit.

Perhaps it's me being thick, but wouldn't a small cut out on the door for a cable to run (but not enough for a 5 year old wrist) is the safe answer here? How thick are these cables? You can even make the cut as a little door that can be put back after calibration.

Full speed and bypass is an accident waiting to happen, particularly if it's just because of a cable hanging.

 

[kckku]

Thank you all for your feedback and comments. This exercise turned out to be meaningless anyway. I showed up to work today and the 'new' policy was rolled out by management. I just got an email to acknowledge that I understand the new policy. So much for asking us for comments. It was a one day review and no response to my questions/comments from our safety coordinator. Unbelievable.