E-stop buttons

[dougjl]

There has been some discussion at my office concerning e-stop push buttons and shrouds. One of the mills we do work for has a number of stations that have the e-stop button shrouded by a sleeve around the red mushroom head button. This sleeve is there to stop somebody from falling on the button and actuating it. There is no cover over the button. The argument becomes is this button "accessible" as defined in NFPA-79 10.7.1.1 and/or would you then define this as a flat button? Although the sides of the guard are open and the switch is a maintained tpye, the sleeve makes you have to push the button with your fingers and not the palm of your hand. Opinions / codes please.

Thanks,
Doug

 

[fangas]

Hi Doug,

This is just an opinion.

As soon as you limit access to this "e-stop" it ceases to be an e-stop and becomes just a stop. I can't say that I've even seen a run-of-the-mill stop button shrouded, let alone an e-stop.

Consider:
If the machine was eating itself or you were caught up in it, would you rather fumble around with a stop button enclosed in a shroud or slap anyway you can it that big red e-stop button?

Ed

 

[dpc]

I have used shrouded pushbuttons for "emergency trip" pushbuttons in control rooms - things like boiler trip.

I don't think it is a good idea to use a shrouded pushbutton for local Emergency Stop near a piece of equipment. Especially if workers will have gloves on.

We generally use mushroom head pushbuttons for field E-Stop applications.

 

[ScottI2R]

Hi,
I do not recommend that any E-stop button be shrouded. The company I work for generally uses those types of switches on a cycle start ciruit. This insures against accidentally starting an operation or sequence. A system we built was transferred to France a few years ago, and the French installed a "key-locking" E-stop. This was obviously so the supervisor would have to come and release the machine from an E-stop situation. That is all fine, until we, as humans, get lazy and leave the keys in that big red stop right NOW button. I still have a scar on the palm of my hand from that incident! Never obsure an E-stop or otherwise limit its access! Rules to live by and keep all your digits. ( See FANGAS's post)
Scott

In a hundred years, it isn't going to matter anyway.

 

[jraef]

Are you sure they are actually Emergency Stop buttons? Often times there will be just regular Stop buttons that are mushroom head just so that it is a big surface that can be pressed by a gloved hand, and the guard serves to protect against accidental contact. If only becaomes an "Emergency Stop" push button when specifically labeled as such. If it has a big label that saye "Emergency Stop", OSHA would not allow it to have a guard.

"Venditori de oleum-vipera non vigere excordis populi"

 

[jraef]

fat fingers typing...

 

[dougjl]

jraef,
yes they are e-stops and labeled as such. I could find nothing in OSHA that prohibits the use of the guards. I did however contact NFPA yesterday and they sent me the following:

"Thank you for your email. Section 10.7.1.1 requires that all stop pushbuttons be readily accessible.

The term readily accessible is defined as "capable of being reached quickly for operation...". Accordingly, anything placed on top of or surrounding the button that inhibits its quick operation would not be permitted. And, since the button is required to be a mushroom head operating device in accordance with 10.7.4, it could be interpreted that concealing or sleeving the mushroom head would be prohibited also. Even though the NFPA 79 text does not specifically prohibit the use of an open front protective sleeves that do not cover the operating button head, the committee and I strongly urge users not to use them, since sleeves could effectively defeat the safety features afforded by a mushroom head operator and thereby inhibit quick operation of the emergency stop

I hope this satisfies your concerns. Please understand that this has not been processed as a Formal Interpretation, it must be considered as my personal opinion. Please see the statement below.

Very truly yours,

Joseph V. Sheehan, P.E.

Principal Electrical Engineer
Important Notice:

This correspondence is not a formal interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author, and does not necessarily represent the official position of the NFPA or its Technical Committees. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.



NFPA's mission is to reduce the worldwide burden of fire and other hazards on the quality of life by providing and advocating scientifically-based codes and standards, research, training, and education."

 

[jsummerfield]

Guarded shutdown pushbuttons are very common. I recommend them.

Some facilities consider CCTV cameras for video to monitor pushbutton stations.


John