Machine Safety: e-stop devices versus safety devices

Safety devices and e-stop machine safety requirements consistently raise questions and merit review. The universal (and global) emergency stop device is not so universally understood. An e-stop is NOT a safeguarding device and certainly an e-stop is NOT a reset button. Review these e-stop device requirements according to machine safety standards.

05/27/2014


Jokab Safety, part of ABB, showed this giant e-stop at a Pack Expo show.Use of e-stops in machine design is one of those things that frequently suggests a refresher understanding might be helpful. The universal (and global) emergency stop device is not so universally understood. An e-stop is NOT a re-set button. So far I have not encountered anyone in industry who ever have considered an emergency stop device as a re-set button. [Some days, I wonder.]

An emergency stop device is well defined as a red button on a yellow background. The time has come again to touch on e-stop device classification according to industry machine safety standards.

In the United States there are two primary machine safety standards that call out requirements for emergency stop devices and their stopping functions. They are ANSI B11.19; 2010 and NFPA 79; 2012. ANSI B11.19, Performance Criteria for Safeguarding in clause 12.9, page 73 reads as follows:

12.9 Emergency stop devices

"Emergency stop devices are not safeguarding devices. They are complementary to the guards, safeguarding devices, awareness barriers, signals and signs, safeguarding methods and safeguarding procedures...."

Types of devices usually covered by the safety standards and used for the emergency stop function can include, but are not limited to, the following:

• Pushbutton-operated devices

• Rope pull (cable pull) operated devices

• Foot-operated device without a mechanical guard

• Disconnect switch actuator

• Rod-operated device

• Push-bar-operated device 

Furthermore, the actuators of emergency stop devices are required to be colored RED, and the background immediately around the actuators are required to be colored YELLOW. This distinctive color combination is globally reserved for emergency stopping devices. NFPA 79, Electrical Standard for Industrial Machinery, also covers the information and requirements listed above along with several international IEC and ISO machine safety standards.

As I’ve discussed this question with other industry experts, in my opinion, the consensus is that safeguarding devices are always exclusively used to achieve a dedicated safety related function. Emergency stopping devices are not considered safeguarding devices because they are complementary devices and because they are not exclusively used to achieve a safety related function.

Please add your comments to this narrative either supporting or dissenting. Add your comments, thoughts, ideas, experiences, and challenges in the comments section below.

Related articles linked at the bottom of this post:

E-Stops aren’t safety devices

Machine Safety: Thinking of bypassing an e-stop? Have you talked to an attorney?

Machine Safety: My main disconnect e-stop isn’t red with a yellow background

Not again – E-Stops do not equal machine safety

Contact: http://www.jbtitus.com for “Solutions for Machine Safety”.



Anonymous , 06/18/14 05:40 PM:

I tend to think of E-stops as devices that are used after an accident has occured. One purpose would be to rescue an injured worker. I don't think of them as pro-active safety devices like machine guards and safety interlock switches. Yes, I do think they are necessary, but rarely used unlokc other safety equipment.
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