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Posted By John Merrell
Can anyone tell me the criteria for emergency stops, we have a situation whereby we move large volumes of items that have been "sorted" from various chutes and move them to pallets etc, due to this movement and the various sizes of items being moved the "e" stops are always getting hit accidentally
I know that "e" stops have to be in "range" of the operatives hands and accesible, we have tried moving the "e" stops, we have tried raising them to a more remote area (but still accesible)and to be frank about it both staff and management are on a short fuse about them, what I am looking for is a solution to this problem that you may have come across before,like is there a cover somewhere that can be purchased that will allow easy access but at the same time will stop the accidental operation of the "e" stop
I still have a full head of hair at present but slowly it is getting pulled out one by one over this
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Posted By Martin Taylor
have you thought of using a pull cord system - there are several proprietary ones on the market. They would give better coverage and less prone to the damage that you describe
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Posted By Jeffrey Watt
John
Good answer from Martin. We had a plating line that ran a pull cord system along it's length.
also had false alarms from trollies of parts hitting call points and e-stops. We mounted little stainless steel "deflectors" either side of the call points resembling wedges/ramps that stopped the line of the trolly making contact. In either case these deflectors did not affect the ease or operation of the e-stop or the call pont.
Kind regards
Jeff
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Posted By Merv Newman
And if you have the type which require a key to be turned back on - please don't leave the keys in the locks. I have known of a cut palm with severe bruising because the employee banged hard on the es. As they tend to do in haste.
Merv
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Posted By Roger Caldwell
The fitting of stainless steel deflectors has been the solution to this problem when I have experienced it. If this is the chosen resolution regular checks will need to be made to ensure that they do not get bent in and cause the ES to be permanently pressed.
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Posted By John Merrell
Thanks for all the replys, couldn't reply earlier myself as for some reason I couldn't sign in at home
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Posted By Frank Tomei
In terms of determining when an es is required I would use ISO 14121 Risk Assessment and specifically the element of risk called Avoidance or Limiting the Harm.
The question that ought to be raised is if an es would avoid or limit the harm?
If the presence of the es would not achieve avoid or limiting the harm then the es would not play a usefull role from a safety perspective. The question then becomes - why even have it?
We must remember that the es is not a safeguarding device since in theory it would only and because all safeguarding has failed.
We can call the safeguarding the preventive action.
An es on the other hand is a device that one would hope to never need to use but when it is needed it is very important.
The es in this case would be the corrective action whereby given that an event has occurred how do we minimize the damage.
Feedback on this approach would be appreciated.
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Posted By Martin Taylor
I am resurrecting this post as the points made by Frank at the ned are very good.
In my mind designers often through em stops onto equipment 'because they have to' and the location of them often leaves much to be desired.
How do other practitioners regard em stops and what arguments are there for removing manufacturers stops that provide no additional protection
martin
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Posted By Frank Tomei
I must apologize but there was a clerical error in my earlier submission.
In terms of determining when an es is required I would use ISO 14121 Risk Assessment and specifically the element of risk called Avoidance or Limiting the Harm.
The question that ought to be raised is if an es would avoid or limit the harm?
If the presence of the es would not achieve avoid or limiting the harm then the es would not play a useful role from a safety perspective. The question then becomes - why even have it?
We must remember that the es is not a safeguarding device since in theory it would only be used and because all safeguarding has failed.
We can call the safeguarding the preventive action.
An es on the other hand is a device that one would hope to never need to use but when it is needed it is very important.
The es in this case would be the corrective action whereby given that an event has occurred how do we minimize the damage.
Feedback on this approach would be appreciated.
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Posted By Tony Brunskill
Frank,
Possibly in some cases you are correct. But situations do occur where E Stops prevent the operator being injured. Examples include Lund Bars on two roll mills.
Often E Stops provide a third party with the ability to stop a M/C before entering a point of danger or even before the danger occurs. Consider schools where the EStops are placed around the classroom to allow the teacher or other to stop dangerous situations occuring.
Regards
Tony
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Posted By Frank Tomei
Thank you very much John for your comments.
I believe that you have emphasized exactly what I have proposed. In the type of machines you have identified total safeguarding is not practical. Therefor we must accept the fact that a hazardous event may occur and we must look at some control measure that if the event does occur we could avoid or limit the harm. As such the use of an estop function would do just that. It can be demonstrated using the elements of risk identified in ISO14121 and assigning scales to each of the elements.
WITHOUT THE ESTOP
Probability of the occurrence of the hazardous event (scale 0-10) = 3 (Based on established scale I use)
Frequency/ duration of exposure (scale 0-10) = 4 (Based on established scale I use)
Severity (scale 0-100)= 12 ((Based on established scale I use)
Possibility to avoid or limit the harm (%scale) = 10%
Risk = 3x4x12x.9=130
Risk is deemed to high and an estop is introduced
RISK ASSESSMENT with ESTOP
Probability of the occurrence of the hazardous event (scale 0-10) = 3 (Based on established scale I use)
Frequency/ duration of exposure (scale 0-10) = 4 (Based on established scale I use)
Severity (scale 0-100)= 12 ((Based on established scale I use)
Possibility to avoid or limit the harm (%scale) = 50%
Risk = 3x4x12x.9=72
Conclusion: the risk assessment process has helped us to identify that and some control beyond safeguarding is required (in the form of an stop) and that the estop can reduce the risk significantly enough to warrant it's use.
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Posted By John B. Salmon
I would like to offer some feed back on emergency stops. How much does an E-stop contribute to preventing a loss? E-Stop buttons E-Stop cable pull lanyard stops are excellent devices when properly applied. If E-Stop cable pull lanyard stops are used they need to meet tension monitoring requirements and distance restrictions.
Frank is correct it is important not to use an E stop as a substitute for a guard. Peppering process lines with E-stops is usually not a good approach. We need to discriminate between an interlocked device signalling a machine to stop and an E-stop primarily used to protect property.
Devices such as light curtains, knee bars, safety mats, laser scanners, bump strips, etc. are safety devices. These devices may stop equipment in an emergency.
All too often by the time an E-stop is deployed it is too late. It might make sense to put a process stop in and not call it an E-stop, if we are trying to protect upset conditions on a line that is entirely different that trying to protect the worker.
Also safeguarding of any kind should never be implemented without a Risk Assessment and proper planning.
E-stops can be less than effective if the equipment that is being shut down does not stop in a short enough time to prevent access.
This could be a false sense of security for the uneducated. It is important to also design the system such that a single component failure would not lead to loss of safety function i.e. a welded contactor or stuck valve. Imagine if the E-stop was pressed and the contact block was not monitored or the contactor stuck and the equipment did not stop and a loss occurred, very often a control reliable design is required to achieve a satisfactory solution. If a loss occurred we would then modify the process in a reactive manner.
NFPA 79 offers good application data on E-stop categories 0 1 and 2 with respect to functionality and energy isolation. This is not to be confused with type and category ratings as described in EN 954.
E-stops are quite often mandatory and have their place. Each safety situation is unique and should be analyzed by experts just like the brakes on your car. I have a report I have prepared on application of E-stops which is rather technical but informative.
The question is is when are we safe?
SAFE is a situation or state where the risks are quantified, controlled acceptable.
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Posted By Frank Tomei
Hi John:
Thanks for the analysis. It is the type of analysis I believe is badly needed in order to get rid of the idea that an estop is a "big red button". I was particularly interested and in full agreement with the concept of "operational estop" vs. Estops required to avert physical harm to a worker.
You mention a technical report you have with respect to estops. I am very interested in such a report and would ask if it possible to get a copy.
Thank you.
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Posted By John B. Salmon
Frank
Thank you for your reply. This is my first visit to this site. Tom Doyle pointed this site out to me. I look forward to further discussions on this and other topics.
Is there a Canadian forum like this?
I will forward the technical report to your email soon.
Thanks Frank
John B. Salmon
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Posted By John B. Salmon
I forgot to mention that very often guarding solutions are possible but sometimes with some creativity the potential for loss can be reduced through some simple measures.
John B. Salmon
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Posted By Darren J Fraser
ES come in several styles, including as already mentioned the pull cord system, and recessed casings.
Hope you are able to solve your problems.
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