Ring Guards on Emergency Stop Pushbuttons?

Looking through the NEC2002 I see no Articles pertaining to your question. Safety systems are usually designed by the maker of the equipment or spec'd by the Customer. You'd have to call your local electrical inspector to see if they have any issues with the purposeful guarding of Safety Stops on a piece of equipment. If you need a tool or key or something to operate the E-stop in case of emergency--and you are in danger because of it--I'd call it a violation worthy of a phone call to OSHA.

Emergency Stop Button Cover

Precedents for a method of preventing accidental operation occur with fire alarm systems.

Many manual fire alarm boxes have what is called dual opertion. Example:

LIFT COVER AND PULL DOWN HANDLE

BREAK GLASS, OPEN DOOR AND PULL DOWN HANDLE.

Some street fire alarm boxes in San Francisco have what is called a "stopper," a plastic cover to be pulled out of the way before breaking a glass and pulling down a lever.

I am not sure what a ring guard would be, but a friend had trouble with accidentally setting off the alarm on his car door remote. He glued a thick washer at the alarm button, and hasn't had a problem since. If this concept were used on the emergency stop buttons, and the depth to which one had to reach were appropriate, this might solve the problem.

As to locking out the system once the button is pushed, this can easily be done electrically, within the system.

This Site Might Help You.

RE:

Ring Guards on Emergency Stop Pushbuttons?

Can ring guards (shrouds) that prevent accidental operation legally be installed on emergency stop pushbuttons on industrial machinery in the United States? ANSI/RIA 15.06 clearly prohibits this, but this particular application (let's call it a conveyor system) does not have a robot. ANSI...

When I have talked with OSHA officers they always look for ring guards as a citable offense. They cite readily accessible and explain it to me, that from any angle I can flatten the button with my hand. If you have a shroud, partial shroud, ring, or flip cover on the E-Stop, you can't flatten it with your hand. You could push it with your finger but we are talking about an emergency here.

Many companies have adopted ANSI/RIA 15.06-1999 as their standard to "how do I figure out its safe".

NFPA 79-2012 9.2.5.4* Emergency Operations (Emergency Stop, Emergency Switching Off). Emergency operation requirements are as follows:

(1) This section specifies the requirements for the emergency stop and the emergency switching-off functions of the emergency operations, both of which are initiated by a single human action.

"Single human action" being the key phrase.

and:

10.7 Devices for Stop and Emergency Stop. 10.7.1 Location and Operation.

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

I would say, for the sake of safety, on a machine (not a fire alarm, where you have more time to think and do) make sure you have an Emergency Stop that is very accessible and not guarded by a ring.

If the machine was built in the EU, they are governed by the "Machinery Directive" and this topic is not covered. If your machine is in the US, OSHA will cite NFPA79 as the consensus standard for electrical devices.

So, do you need an Emergency Stop? Yes and No. You need one where the Operator stands, At the Operator control station and where it is needed. OSHA does not allow the E-Stop to be a safety device. Its a shut down for some reason. OSHA wants Lockout tag out for safety but they also allow "other" types of safety devices instead of LOTO.

The LOTO code 1910.147, we are interested in (a)(2)(ii)(B) from the OSHA website osha.gov

"An employee is required to place any part of his or her body into an area on a machine or piece of equipment where work is actually performed upon the material being processed (point of operation) or where an associated danger zone exists during a machine operating cycle.

Note: Exception to paragraph (a)(2)(ii): Minor tool changes and adjustments, and other minor servicing activities, which take place during normal production operations, are not covered by this standard if they are routine, repetitive, and integral to the use of the equipment for production, provided that the work is performed using alternative measures which provide effective protection (See Subpart O of this Part). "

This takes you to "How to protect the worker with special safety rated circuits and devices"

A longer discussion but I think you would have your answer if you don't head on over to

http://discover.rockwellautomation.com/_Safety_Sol...

for a lot more safety information.

Or reply to this note and I will do my best to answer.

Isn't a emergency stop switch required to lock and you have to manual reset it.

How can you "manually"reset a guarded push-button? Are there more then one emergency stop push buttons? If so i know that would be illegal for sure. Because you can't override someone else's e-stop.

This sounds more like a question for a lawyer :P Because anyone doing this is just asking for it.