Mechanical Lockout/TestOut on an Interlocked System

[Girl Engineer]

If someone is going to lock out and work on a non-electrical portion of an interlocked system (eg. pump or a conveyor), what is a good method for testing out that system? A test start would be useless because of the interlock.
Electrically, we would test for lack of voltage, but that type of test would be exposing a mechanic to a greater hazard.

How can he/she safely test or verify that their lockout is correct?

 

[pfalcon]

There really is no definitive test. Electricians face the same problem when working within the throat of a mechanical machine. How does he know the platen won't close?

A knowledgeable person needs to create a lockout placard for the machine showing how to make it safe. Some of that can be tested. Some must be observed.

For example, when they lockout the electrical disconnect all the blinking lights should go out. That is typically enough to guarantee mechanical work is safe without putting a meter on the wires.

As you observed, pushing the start button is a rather pathetic test. But observing that the hydraulics, pneumatics, and operator screens died when pulling the disconnect pretty much guarantees the electrical Estop circuit tripped on a properly designed machine.

Since their electrical work should then be limited to quick disconnects and utilitization plugs they should be safe.

 

[don_resqcapt19]

I have seen installations where HOA switches are used for this purpose. The hand position is spring return to off and it bypasses all electrical interlocks except for the motor overload. The procedure is Try-Lock-Try. The first try is before you lock the stater out to prove that the HOA and motor are functional. The second try it to prove that you have the correct starter locked out.

 

[Girl Engineer]

These are both great suggestions. Thank you!

 

[WorkSafe]

Here's a worksheet we place on all our equipment here. The information on the form is filled in by the shop supervisors with help from our engineering.

 

[Electric Pete]

If someone is going to lock out and work on a non-electrical portion of an interlocked system (eg. pump or a conveyor), what is a good method for testing out that system? A test start would be useless because of the interlock.
Electrically, we would test for lack of voltage, but that type of test would be exposing a mechanic to a greater hazard.

How can he/she safely test or verify that their lockout is correct?

Is this for periodic maintenance or trouble shooting operational issues? Sometime a lock out tag out involves more than one craft group to verify a piece of equipment safe to enter or be worked on. You would not say some lights went out so the power must be off, and a test start after a lockout is not a pathetic test, it is one of many steps to prove the equipment is out of service. Your procedure would be; to perform an orderly shutdown of the machinery you would test for no power, test your meter first on a known live source, test equipment dead then test your meter on a known live source again, to make sure your test equipment is still operational. They do fail at the wrong time. Pull fuses, or remove conductors from an ACB for a visible break. Then you can operate your emergency stops that should be lockable in the emergency off position. When you get to the mechanical portion of you lockout you want to make sure to release all stored energy. In Example a liquid pump coupled to a motor would have the valves closed on both sides of the pump in order to prevent the motor from turning if you were working on it. In the case of hydraulics you would release any hydraulic pressure stored in the lines, if it were holding a piece of equipment in an up position a blade or press for example, you would have to use shoring to rest the apparatus on so workers could enter into an area were crushing or dismemberment could occur. You always try to operate the equipment after all these steps are used to insure the prints are not wrong or panels mislabeled. Some of these spaces inside machinery can also be classified as a confined space where retrieval equipment would be needed. Also using lockable devices and tags on all valves, disconnect switches, breakers, start buttons, emergency stops and whatever else needs to be done to insure that your workers and yourself climbing inside a piece of machinery go home at the end of the shift the way they came into work. What price do you put on yourself or others in the name of safety?

Electric Pete

 

[pfalcon]

Is this for periodic maintenance or trouble shooting operational issues? Sometime a lock out tag out involves more than one craft group to verify a piece of equipment safe to enter or be worked on.

I suspect she means for both. PM is usually but not always post-lockout. TS is usually but not always pre-lockout. So it would apply to both.

You would not say some lights went out so the power must be off, and a test start after a lockout is not a pathetic test, it is one of many steps to prove the equipment is out of service.

Just my opinion of a test start since virtually everything disables that. But not everything disables the manual functions which are just as important. Putting the mode in manual and trying to move an axis is better but still weak.
And yes, I would much rather observe that my processor power lights went out, my hydraulic pumps shut off, and my pneumatic feed solenoid popped for lockout than believe its down because the start button doesn't work.

Your procedure would be; to perform an orderly shutdown of the machinery you would test for no power, test your meter first on a known live source, test equipment dead then test your meter on a known live source again, to make sure your test equipment is still operational. They do fail at the wrong time. Pull fuses, or remove conductors from an ACB for a visible break.

Live-Dead-Live is great when you're an electrician planning to work on the wires. This question includes pipefitters planning to work on filtration as well. They don't get meters and we don't let them pull fuses. Hence back to the LOTO placard where someone has gone specifically through that machine to determine a way to verify the energy is locked out without resorting to trade specific tools.

Then you can operate your emergency stops that should be lockable in the emergency off position.

Why? Operating the Estops is for emergency use or for inspecting the Estop functions; not typically for locking out a machine. And yes I know they CAN be used for such but most systems have lockable disconnects and/or valves that are much more secure.

When you get to the mechanical portion ... In Example a liquid pump ... In the case of hydraulics ...

Which again is back to the "Knowledgeable person writing up the lockout placard" for the specific machine.

You always try to operate the equipment after all these steps are used to insure the prints are not wrong or panels mislabeled.

Always? Once you verify the energy is dead to the subsystem you are working on there is no need to try and operate the machine. If I lock out the coolant lines to my filters and verify, then I can safely change them. If I start the machine with the coolant locked out then I might damage the machine needlessly. Not everything has to be shut down for every service call.

Some of these spaces inside machinery can also be classified as a confined space where retrieval equipment would be needed.

Or vented, or tested for air quality.

Also using lockable devices and tags on all valves, disconnect switches, breakers, start buttons, emergency stops and whatever else needs to be done to insure that your workers and yourself climbing inside a piece of machinery go home at the end of the shift the way they came into work. What price do you put on yourself or others in the name of safety?

Electric Pete

Holy smoke! Lockables on ALL valves, devices, disconnects, breakers, starts, Estops, and more? No way! I'll do things for the sake of safety but not for its name. I don't need a lockout on every Estop since locking out one affects them all. Additional lock points for Estops would be a waste of money providing NO safety improvement. And if my lockout procedure calls for locking the main disconnect then I don't need any locks for Estops.

And as to that infamous price for safety: I won't pay to save one person on their death bed with the lives of several healthy people. So there is a price. We just haven't established it yet.

 

[pfalcon]

I have seen installations where HOA switches are used for this purpose. The hand position is spring return to off and it bypasses all electrical interlocks except for the motor overload. The procedure is Try-Lock-Try. The first try is before you lock the stater out to prove that the HOA and motor are functional. The second try it to prove that you have the correct starter locked out.

Yep, operator version of Live-Dead-Live.

We've removed all the spring returns and replaced them with positive engagement stab devices that have to be in place to operate. Pulling the stab physically separates the contacts through mechanical means. Then you put your lock on so it can't be reinserted until you're done.

 

[Electric Pete]

I hope no one gets hurt using your recomendation.

Electric Pete

 

[zbang]

I hope no one gets hurt using your recomendation.

"every valve" includes the drains and bypasses (ex: closing the pump isolation valves and the bypass valve probably doesn't make any sense).

You've got to use some measure of reason, especially on a big machine, to cover what makes sense and not make the task so difficult that it won't be performed at all.

 

[TxEngr]

Although it would seem that a voltage test is exposing the mechanic to a greater hazard, it is the only way to verify that electrical energy is removed as an energy source. As you stated, the bump test is useless in interlocked systems. It?s a pain to have to ?suit up? in all of the PPE to do the test, but it?s just part of the job these days. Performing the test is certainly a lot less hazardous than working on an improperly locked out piece of equipment.

 

[don_resqcapt19]

Yep, operator version of Live-Dead-Live.

We've removed all the spring returns and replaced them with positive engagement stab devices that have to be in place to operate. Pulling the stab physically separates the contacts through mechanical means. Then you put your lock on so it can't be reinserted until you're done.

I see no advantage to putting a lock on the control circuit. You have to lock out the energy source which is the power supply to the motor controller for a motor operated device. The ability to lock out the controls could lead to short cuts that could result in disaster.

 

[pfalcon]

Although it would seem that a voltage test is exposing the mechanic to a greater hazard, it is the only way to verify that electrical energy is removed as an energy source. As you stated, the bump test is useless in interlocked systems. It?s a pain to have to ?suit up? in all of the PPE to do the test, but it?s just part of the job these days. Performing the test is certainly a lot less hazardous than working on an improperly locked out piece of equipment.

The mechanic should not be working on conductors, therefore doesn't need to verify a total lack of electrical energy. For example, changing out an air regulator.

If conductors are involved then it should be an electrician, and he has a meter.

I see no advantage to putting a lock on the control circuit. You have to lock out the energy source which is the power supply to the motor controller for a motor operated device. The ability to lock out the controls could lead to short cuts that could result in disaster.

Agreed. Control power is often tapped from the line side to prevent controller memory loss. You could lock out the 24VDC control power and leave the 480VAC motor power online.

Again, best case is to get a knowledgeable person to create the specific lockout procedure for that specific machine. They will document which lockouts affect which sources of energy and how to test that it was done properly.

 

[TxEngr]

A mechanic could be working on a pump which is connected to a motor which has electrical wires connected to it. He would then need to lock out the electrical supply to that motor. If he were qualified, he could in fact lock the device out without being an electrician. An example is the multicraft mechanics found in many plants who are trained and qualified to perform proper lockouts.

Just because you aren't working on conductors doesn't mean you don't have to perform an electrical lockout.

Locking out the control power is NOT an acceptable lock out. OSHA requires the removal of all sources of energy that could cause inadverdent movement of the equipment that could injure an employee. By not removing the main power, you have not met that responsibility.

 

[pfalcon]

A mechanic could be working on a pump which is connected to a motor which has electrical wires connected to it. He would then need to lock out the electrical supply to that motor. If he were qualified, he could in fact lock the device out without being an electrician. An example is the multicraft mechanics found in many plants who are trained and qualified to perform proper lockouts.

Agreed

Just because you aren't working on conductors doesn't mean you don't have to perform an electrical lockout.

Agreed. Likewise, just because you perform an electrical lockout doesn't mean you have to meter the wires. Unplugging a portable gage table that has no electrical storage is considered LOTO. Unplugging the newly required disconnect when servicing store luminaires is considered LOTO. You don't need to meter the wires there.
Back once again to getting a knowledgeable person to determine the proper LOTO procedure instead of blanket expectations.

Locking out the control power is NOT an acceptable lock out. OSHA requires the removal of all sources of energy that could cause inadverdent movement of the equipment that could injure an employee. By not removing the main power, you have not met that responsibility.

I believe you misread me there. I agreed and gave an example of why locking out the control power was not enough. To better phrase it:
Agreed. Control power is often tapped from the line side to prevent controller memory loss. Locking out the 24VDC control power still leaves the 480VAC motor power online. That would be a bad thing. The control power doesn't typically cause motion and therefore may not be required on LOTO. The motor power can cause motion and therefore must be on LOTO.

 

[Girl Engineer]

I agree. You need to look at each area you are working on and identfy what the power sources are. Sometimes they are simple, like a starter where the contols are tapped off the main motor feed- just lock out the starter (mccs are a larger issue, because the line side terminals are not always guarded on these older installations). But then there are things like a conveyor motor. There are so many interlocks it would make your head spin. Then you have to have someone that intrinsically knows the system sit down and write out a procedure. We go to great extents to make sure these are reveiwed extensively and complete. But the question came from someone who is down there hanging his lock and eg. Changing rollers. How does HE know his lock is good?

I have to tell you, I love questions like this. That means he is thinking about his own safety and not taking for granted that someone else is. I do everything I can to make sure I plan a safe installation and the procedure review process is great, but there is only so much that can be done with procedures and design. A questioning attitude is what will really keep him safe.