Emergency Stop Failures

This entry is part 13 of 13 in the series Emergency Stop

I am always look­ing for inter­est­ing examples of machinery safety prob­lems to share on MS101. Recently I was scrolling Reddit/​r/​OSHA and found these three real-​world examples.

Broken Emergency Stop Buttons

The first and most obvi­ous kinds of fail­ures are those res­ult­ing from either wear out or dam­age to emer­gency stop devices like e-​stop but­tons or pull cords. Here’s a great example:

Won’t be stop­ping this elev­at­or any­time soon. from OSHA

The oper­at­or device in this pic­ture has two prob­lems:

1) the but­ton oper­at­or has failed and

2) the e-​stop is incor­rectly marked.

The cor­rect mark­ing would be a yel­low back­ground in place of the red/​silver legend plate, like the example below. The yel­low back­ground could have the words “emer­gency stop” on it, but this is not neces­sary as the col­our com­bin­a­tion is enough.

Yellow circular legend plate with the words "emergency stop" in black letters. Fits A-B 800T pushbutton operators.
Allen-​Bradley 800T Emergency Stop legend plate

There is an ISO/​IEC sym­bol for an emer­gency stop that could also be used [1].

Emergency stop symbol. A circle containing an equalateral triangle pointing downward, containing an exclamation mark.
Emergency Stop Symbol IEC 60417 – 5638 [1]
I won­der how the con­tact block(s) inside the enclos­ure are doing? Contact blocks have been known to fall off the back of emer­gency stop oper­at­or but­tons, leav­ing you with a but­ton that does noth­ing when pressed. Contact blocks secured with screws are most vul­ner­able to this kind of fail­ure. Losing a con­tact block like this hap­pens most often in high-​vibration con­di­tions. I have run across this in real life while doing inspec­tions on cli­ent sites.

There are con­tact blocks made to detect this kind of fail­ure, like Allen Bradley’s self-​monitoring con­tact block, 800TC-​XD4S, or the sim­il­ar Siemens product,3SB34. Most con­trols com­pon­ent man­u­fac­tur­ers will be likely to have sim­il­ar com­pon­ents.

Here’s anoth­er example from a machine inspec­tion I did a while ago. Note the wire “keep­er” that pre­vents the but­ton from get­ting lost!


Installation Failures

Here is an example of poor plan­ning when installing new bar­ri­er guards. The emer­gency stop but­ton is now out of reach. The ori­gin­al poster does not indic­ate a reas­on why the emer­gency stop for the machine he was oper­at­ing was moun­ted on a dif­fer­ent machine.

sure hope i nev­er need to hit that emer­gency stop but­ton. its for the machine on my side of the new fence. from OSHA

No Emergency Stop at all

Finally, and pos­sibly the worst example of all. Here is an impro­vised emer­gency stop using a set of wire cut­ters. No fur­ther com­ment required.

Emergency stop but­ton. from OSHA

If you have any examples you would like to share, feel free to add them in com­ments below. References to par­tic­u­lar employ­ers or man­u­fac­tur­ers will be deleted before posts are approved.

References

[1]     “IEC 60417 – 5638, Emergency Stop”, Iso​.org, 2017. [Online]. Available: https://​www​.iso​.org/​o​b​p​/​u​i​/​#​i​e​c​:​g​r​s​:​6​0​4​1​7​:​5​638. [Accessed: 27- Jun- 2017].

Series NavigationSafe Drive Control includ­ing Safe Torque Off (STO)

Author: Doug Nix

+DougNix is Managing Director and Principal Consultant at Compliance InSight Consulting, Inc. (http://www.complianceinsight.ca) in Kitchener, Ontario, and is Lead Author and Managing Editor of the Machinery Safety 101 blog.

Doug's work includes teaching machinery risk assessment techniques privately and through Conestoga College Institute of Technology and Advanced Learning in Kitchener, Ontario, as well as providing technical services and training programs to clients related to risk assessment, industrial machinery safety, safety-related control system integration and reliability, laser safety and regulatory conformity.

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