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/obp/ui/#iec:grs:60417:5638. [Accessed: 27- Jun- 2017].

Series Nav­i­ga­tionSTO)”>Safe Dri­ve Con­trol includ­ing Safe Torque Off (STO)

Author: Doug Nix

Doug Nix is Managing Director and Principal Consultant at Compliance InSight Consulting, Inc. (http://www.complianceinsight.ca) in Kitchener, Ontario, and is Lead Author and Senior 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. For more see Doug's LinkedIn profile.