mdshunk
Senior Member
- Location
- Right here.
George's incident makes me like cable pull e-stops and light curtains even more.
Emergency Stop Safety Circuit
- Thread starter bobhudon
- Start date
- Status
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
These cases sound like a combination of bad machine design and poor operator training/supervision.
In most cases, the estop should be thought of as a way to protect the machine or the product from mechanical damage rather than to protect the operator from the machine.
In most cases, the estop should be thought of as a way to protect the machine or the product from mechanical damage rather than to protect the operator from the machine.
deadshorts
Member
- Location
- nebraska
yes. Please explain this.
megloff11x
Senior Member
Emergency Stops are discussed in NFPA79 STandard on Machinery chapter 9 control circuits. All machines must have a category 0 stop, which jerks all power from machine actuators when engaged. You can provide a controlled stop (category 1) to supplement this and make this your emergency stop, and a stop need not be immediate if this would create a greater hazard - an example would be a chemical process.
Section 9.2.7.3.1 states "operator control stations shall include a separate and clearly identifiable means to initiate the stop function of the machine OR OF ALL THE MOTIONS THAT CAUSES A HAZARDOUS CONDITION..."
Can someone be eaten by the conveyer belt too? I would say yes.
Having once followed a conduit run to find the main disconnect on an older CNC milling machine bent on drilling itself to death after slapping the stop and e-stop buttons, and having watched other machines break themselves with up to $10000 in self inflicted damage while screaming at the man next to the button to hit the e-stop, and have him reply "where is it?" and have to bowl over people standing in rapt fascination to get to said button myself, and having seen folks get trapped by or worse, chewed up by machinery, I tend to take this issue seriously.
If you have a conveyer running stuff to several machines I would suggest a safety review of the system. When someone gets chewed up that manager who whined to have the conveyer kept alive will deny everything and point the finger at you, and absent a paper trail, he may succeed. Get it in writing and keep a copy and make sure OSHA had a look too.
Each machine on the line should have its own clearly identified stop and the conveyer should likewise have one within reach at any point on the line. Each push button station costs about 15 minutes of lawyer time. I've had machines with battery backed up brake releases to allow you to free someone after killing the power too.
Lastly, whoever works there needs to be trained. The first thing is, where is the stop button and what does it look like. They're all supposed to be red with a yellow background, or at least red. After every incident I had to ask "what (expletives deleted) are you doing operating this machine if you don't know how to stop it?" and received the usual deer in headlights look in response.
Matt
Section 9.2.7.3.1 states "operator control stations shall include a separate and clearly identifiable means to initiate the stop function of the machine OR OF ALL THE MOTIONS THAT CAUSES A HAZARDOUS CONDITION..."
Can someone be eaten by the conveyer belt too? I would say yes.
Having once followed a conduit run to find the main disconnect on an older CNC milling machine bent on drilling itself to death after slapping the stop and e-stop buttons, and having watched other machines break themselves with up to $10000 in self inflicted damage while screaming at the man next to the button to hit the e-stop, and have him reply "where is it?" and have to bowl over people standing in rapt fascination to get to said button myself, and having seen folks get trapped by or worse, chewed up by machinery, I tend to take this issue seriously.
If you have a conveyer running stuff to several machines I would suggest a safety review of the system. When someone gets chewed up that manager who whined to have the conveyer kept alive will deny everything and point the finger at you, and absent a paper trail, he may succeed. Get it in writing and keep a copy and make sure OSHA had a look too.
Each machine on the line should have its own clearly identified stop and the conveyer should likewise have one within reach at any point on the line. Each push button station costs about 15 minutes of lawyer time. I've had machines with battery backed up brake releases to allow you to free someone after killing the power too.
Lastly, whoever works there needs to be trained. The first thing is, where is the stop button and what does it look like. They're all supposed to be red with a yellow background, or at least red. After every incident I had to ask "what (expletives deleted) are you doing operating this machine if you don't know how to stop it?" and received the usual deer in headlights look in response.
Matt
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
edamico11 said:
I will try.
The basic idea behind making a machine safe(er) is to reduce or eliminate the possibility of an injury to a human being. An estop can be used to prevent an injury, such as using it to stop motion before taking some action that might be hazardous if there was motion, but is not if the motion ceases. It is not an acceptable practice to install an estop for the purposes of reducing the level of injury, and think you have done yourself a favor. If you know there is a risk of injury, the correct answer is to deal with that risk head on and get rid of it.
Bottom line, you need to design the machinery to reduce the risks, rather than rely on an estop to reduce the injury after the fact.
This is a lot like working hot. No matter what you do, there is a risk if you work on live wires, that is much greater than if there are no live wires present.
patersonra said:
I'm sorry I just do not agree. There is no such thing in design (IMO) as ridding oneself of risk. You can attempt to build the safest situation, but risk will always be there. It is not possible to calculate all the different situations one will fall into once the system, you designed, is in use. So in my systems if there are moving parts, an estop is there, not because I did not design a safe situation, because I know emergencies happens everywhere.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
edamico11 said:
You cannot eliminate all hazards - that is true.
It is also true that it is a requirement to have an estop to stop all motion.
The main thing is that you cannot rely on the estop to deal with known hazards. Known hazards have to be dealt with by eliminating them if possible, or by reducing the level of likely injury. Just slapping an estop on a machine does neither.
- Status