NFPA Article 13.2.1 indicates that "Emergency stop pushbuttons shall be located at each operator control station." Does this mean that every box any where in the system that has at least (1) button, must also have an E-STOP?? Thanks

 

Hi Mohan,

Whether it's a REQUIREMENT or not may be questionable, but if the box with (1) button is considered a control station (which it probably IS), then the answer is yes. I usually wind up with more E-Stop pushbuttons than control stations. They should be located throughout a machine to provide a readily accessible way to stop the machine in an emergency. Since you've already got an enclosure for that (1) button, why not just put an E-Stop there? It can't hurt to have it, but it MAY hurt (someone) if it's NOT there!

- Eric Nelson
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Controls/Software
Packaging Associates Automation Inc. [email protected]
Rockaway, NJ, USA

 

I don't think that a "box" with a pushbutton necessarily means it's an operator control station, but it's a pretty good indication. I have seen small pushbutton stations that are used to control no moving machinery without E-stop buttons, for example, a device that only selects product type. Emergency stop buttons should be placed with accessibility in mind anywhere
there are likely to be personnel in proximity to moving machinery. Personnel could mean operators, maintenance types, spectators, visitors, etc. When placing emergency stop push buttons you need consider safety rather than just
"one E-stop button per operator control station". For example, it is a good idea to place several emergency-stop pushbuttons along side a very long conveyor, even if you have an operator station at on end with an E-stop button.
This is so an individual has access to an E-stop button without having to run a thousand feet. Finally, I don't know if it is possible to have too many emergency-stop pushbuttons and that "common sense" goes an awful long way.
Also, you may want to take a look at NFPA 79 - Electrical Standard for Industrial Machinery:
"http://www.nfpa.org/Codes/NFPA_Codes_and_Standards/List_of_NFPA_documents/NFPA_79.asp":http://www.nfpa.org/Codes/NFPA_Codes_and_Standards/List_of_NFPA_documents/NFPA_79.asp

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An operator control station can be defined as any station where the process/machine is controlled from or where an operator has access to a hazardous area of the machine. The emergency stop must be within the operator's reach especially if the operator is reaching within the hazardous area and is trapped.
Do not confuse e-stops with cycle stops. They are two very different actions. A very good source of information on this is NFPA79.
Another issue that must be addressed is CONTROL RELIABILITY (essentially 2 channel with monitoring) of the estop control system. ANSI
specifications cover specific types of machinery and if that specification calls for control reliability it needs to be employed. Keep this
in mind because if there is an accident and the system doesn't conform to industry accepted standards ....