dlweber is right. When you do your risk assessment, e/stops should never factor into the risk reduction. They're like PPE - once you've made the machine as safe as possible using elimination, substitution, engineering and administration measures, then your PPE and the e/stops are a damage limitation device should all of your actual safety measures fail. The risk of the guy getting his arm mangled by a conveyor is the same with or without an e/stop, it's just the severity of the consequences that vary.
love that e-stop
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dcooper33
Lifetime Supporting Member + Moderator
We are saying the same thing here. As long as it stops quickly and under control, that's all I care about. And all the operators and owners should care about, IMO.
I put first out fault timestamp logging on all my machines. Many times this has proven (and therefore prevented) that an operator was using the estop instead of a line stop button. Sometimes the big brother effect is all you need
This has made my morning. Was it a maintained button operator, and did the machine stop again when you pulled it out?
brucechase
Member
You are talking a risk assessment vs a safety device. I would still say that it is a safety device and should be treated as such. It should be safety rated, utilized dual contacts and go back to a safety controller (or safety PLC) with pulse checking and properly integrated into the control system.
I choose to call my estop a safety device and treat it as such. That doesn't prevent me from mitigating the potential problems by engineering out all identified safety issues.
By the way, it would be pretty hard to track the belt if it isn't running. Not saying it would be impossible, but I think the majority of the time it is done with the belt running.
Midwest Maverick
Member
It was a parts wash machine. Momentary contact button. The light went out when the cycle was done. If you needed to stop in the middle of the cycle, you had to throw the disconnect.
I agree that it should be treated like a safety device in its quality, there are few that would argue that point. But its use is different.
From what you said there is safe places on that belt to put your hand and at least one really bad place... adding a fence, light curtain, railing, sensor, or anything that would prevent the hand from reaching that really bad place while the belt is running would be a safety device.
Estop cannot do this, it is just a switch...well unless you install the Estop and its enclosure in such a way that it blocks the really bad spot, that might make its enclosure part of the safety system...
It did its job mitigate the amount of damage when the safety system did not, not blaming anyone I understand some maintenance and set up needs to bypass the safety systems to be done
From what you said there is safe places on that belt to put your hand and at least one really bad place... adding a fence, light curtain, railing, sensor, or anything that would prevent the hand from reaching that really bad place while the belt is running would be a safety device.
Estop cannot do this, it is just a switch...well unless you install the Estop and its enclosure in such a way that it blocks the really bad spot, that might make its enclosure part of the safety system...
It did its job mitigate the amount of damage when the safety system did not, not blaming anyone I understand some maintenance and set up needs to bypass the safety systems to be done
I was hoping you were going to say the off button was blue or green...
Now you're being silly... It was yellow.
I came across a similar situation that I just couldn't believe..
If the E/Stop was pushed in, the motor (on a brick saw) would stop.... But if the isolator was turned off and then on, the motor would kick or jolt and then stop.
Further investigation revealed that a contactor with 4 normally closed contacts was wired to the motor. The E/Stop had normally open contacts... So if you Pressed the E/Stop in, the contactor would energise and stop the motor.
You would then pull the maintained E/Stop back out to get the motor running again. Kinda like an old-fashioned washing machine.
True Story.
saultgeorge
Lifetime Supporting Member
I was chief electrician for a seafood processor in Alaska when they called me to reset the hydraulics in a processing area. There was a belt system that had 45 e-stop stations. It took me a while (20 min. ) to find the station and reset it, much to the joy of the processors who had an unscheduled break. Next time, I walked through in 5 minutes and pulled on all of them very quickly.
20 years later I went back up there and they had installed contacts and inputs to a PLC and panel view. One simply had to get on the radio and call out which station is was. Processor break time foiled again!!
20 years later I went back up there and they had installed contacts and inputs to a PLC and panel view. One simply had to get on the radio and call out which station is was. Processor break time foiled again!!
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