Emergency Stop Button

Hello all. I hope to get some general safety knowledge help. I am being asked to put a shield/guard around a RED illuminated emergency stop button. I am worried that this is not kosher.

Everyone at the plant replies that "Well we have them like that on other machines", but I don't believe two wrongs,(if it is wrong), make it right.

The problem is that operators inadvertently push in the E-Stop with there leg when they are working around the machinery. I would rather put a larger leg guard up higher or something, but if it is okay for a shield than that would be the most economical thing to do.

Any advice on where to find this in the OSHA standards?

Thanks,

Glenn

Don't know if it's legal, but at my facility we have numerous shielded E-stops. IMO as long as access is not reduced, it shouldn't be an issue.

Ken

As a matter of fact, most electrical OEMs make a circular guard for just that purpose!

Bitmore

Thanks everybody, I found the shield but I felt it was more for protecting a start button than a Emergency Stop. I felt the shield will prevent someone from being able to "slam" the button in an emergency. It sounds like I am barking when I don't need to be, so I guess we will be adding the shields.

Thanks again,

Glenn

E-stop button

Hi Glenn,

Your concerns are well founded. I would also hesitate to shield an E-stop button.

Can you have the location of the E-stop changed so that it will not be prone to accidental activation?

Otherwise, Klockner-Moeller makes a really neat bubble guard for mushroom pb's that requires a little more effort to activate and is not prone to nuisance tripping. This guard is approved for E-stop buttons. Ask for P/N M22-PL-PV.

In regard to start buttons; the button should be flush or recessed in the shroud. Stop buttons should be extended.

I hope you can use some of this information.

Norbert

Hey Guys,
At our facility this was a big problem as it took a few hours to get back on line whenever a e-stop was activated. Our solution was to mount a u-bolt on each side of the button to prevent this from happening. It blocks the button unless something the approximate size of a hand engages it. It also prevents snagging.
Hope it's useful.

I took a quick look at NFPA 79 to see if that says anything, and as usual, there are interpretations and possible conflicts to read into the text.

The following is meant for educational purposes only and not meant to convey any authority or conclusions regarding the application of e-stop devices.

From 10.1.2.2 Hand operated Control devices. The actuators of hand-operated control devices shall be selected and installed as follows:
(1) ....
(2) ...
(3) The possibility of inadvertent operation is minimized.

From 10.7.1.1 Stop and emergency stop pushbuttons shall be continuously operable and readily accessable.

From 10.7.2.2 Pushbutton-type devices for emergency stop shall be of the self-latching type and shall have positive (direct) opening operation.

From 10.7.2.3 Emergency switches shall not be flat switches or graphic representations based on software applicaitons.

From 10.7.4 Emergency Stop Acuators. Actuators of emergency stop devices shall be colored RED. The background immediately around pushbuttons and disconnect switch acuators used as emergency stop devices shall be colored YELLOW. The actuator of a pushbutton-operated device shall be of the palm or mushroom-head type. The RED/YELLOW color combination shall be reserved exclusively for emergency stop applications.

Note, please do NOT ask me to cite other SPEC text. I don't have time for that. You can get your copies of the NEC and NFPA documents at The NFPA Online Catalog

Pushbutton manufacturers won't make what they can't sell, and this being the case, look in almost any catalog and you can find a Ramp or Shield type guard specifically for the unintentional operation of a switch. An example for 30mm PB is ABs PN 800T-N310J or 800T-N339. There are those that don't like to use shields but that doesn't make them "illegal". Personally I don't like them but I know they are sometimes necessary.
The answer to your question glenn, as you noted, is that it's okay to use shields as long as they don't impede the operation of the switch.

You have been given some good information and guidelines. Like so many things electrical, there is common sense. practical applications, and sometimes a judgement call. Basically, a lot of grey area.

Is the machine dangerous to the operator or those in its vicinity?

Is it imparative that the machine stop instantly?

Is the e-stop just to stop the machine if there is a jam or problem with the materials/product?

If the purpose is actually for safety, then the "accessable" part comes into play. The button must then be able to be pushed, smacked, kicked, or hit with a thrown object.

If safety is not a concern, then just to stop the machine doesn't matter all that much.

Always Remember - "Safety First!". Operators can only be as safe as they want to be.

Safety can be a nuisance, specially when it is not a concern. I had problems with a machine I was modifying once. It came with a leg bar e-stop that would stop the machine, and the reset process was lengthy. I would inadvertantly lean into it about half the time. The machine was for checking golf cart tires for being out of round. Everything was well guarded. The tire spun at about 3 rpm. Drive motor had a clutch set to very weak. No danger at all. I heard my replacement disconnected it.

Anyway, my $0.02 USD, tax not deducted.

regards......casey