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:
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.
There is an ISO/IEC symbol for an emergency stop that could also be used .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!
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.
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.
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.
 “IEC 60417 – 5638, Emergency Stop”, Iso.org, 2017. [Online]. Available: https://www.iso.org/obp/ui/#iec:grs:60417:5638. [Accessed: 27- Jun- 2017].