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].