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Topic Title: Do Pull cord Estops need to be tension type to meet Cat3 PL-D?
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Created On: 25 September 2017 09:19 AM
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 25 September 2017 09:19 AM
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I have seen references to the below specific standards in datasheets for tension type safety (ESTOP) cables. Also sometimes I see that the same tension type safety cable systems say they meet CAT 3 PLD.

Formally - BS EN 418:1992
Now - BS EN ISO 13850:2015

I do not have access to fully read these standards through my company nor the personal money to buy them.

My main question revolves around the following example.

An old machine that is most likely built and operated pre Machinery Directive.
This machine is then not used for a few years and moved to another building on the same plant/premises.
This has an original design of Estop circuit that uses Safety Cable Estops that are not tension type but pull to break type i.e. if the estop cable went slack or was cut would not function correctly.
If the hazard on the machine can cause severe injury, the frequency of exposure (working close to the hazard) is high and there IS the ability to avoid the hazard under certain conditions (i.e. a trained worker can easily avoid the Hazard by Training but the Hazard is still possible then, from risk assessment, the system would now require a minimum of a Cat 3 Performance level d Circuit. Well that is my understanding. Feel free to correct me on that.

Q1) does an old machine as described require the safety circuit upgrading?
Q2) Can a "Cable Pull Switch without Broken Cable Detection" ever be used on machines which require Cat 3 Performance level D? i.e. if the machine is old and maintains original specifications.
Q3) Can a safety cable of any type ever meet Cat 4 Performance level E (I have never personally seen this)
Q4) I find it common to see safety cables used as inputs to an estop system that have both dual input redundancy and dual output redundancy in the reset loop, i.e. the safety relay is configured as CAT4, but if safety cables are only rated as CAT3 PL D, does that make the system in general as CAT 3 system and not a CAT 4, it is just a "more reliable" CAT 3 System?
 27 September 2017 07:36 AM
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Does anyone know of a safety contractor / machine manufacture that has a free up to date analysis of the requirements of BS EN ISO 13850:2015 so that I do not need to buy the standard to get a better understanding?
 27 September 2017 07:06 PM
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Yes I can assist you and, answer your questions.

Lets just take one at a time, else, it will get confusing.

Your Q1.
The view of HSE (seems to be) along with others in the machinery safety industry that if the machine has been decommissioned then re-located and re-commissioned, it must be subjected to a full assessment against the PUWER regulations.
There are several regulations under PUWER that would be relevant.
You need to inspect and check the machine for compliance with current standards, and if the machine does not comply then you are required to do a full risk assessment to justify your decision should you decide not to make changes.

It seems that you are suggesting that your preliminary analysis of the PLr is that you need to meet PLd.
I can't agree with that without seeing the machine, and the possibility of avoidance is often a very debated point, and if that is all that is giving you PLd, rather than PLe, then I would doubt that you can honestly risk assess away the decision not to re-engineer the safety systems.
The determination of the PLr is not really a risk assessment.

Moving forward, your description of the pull cord function is simply not acceptable for this application any longer.
 28 September 2017 10:25 AM
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Thank you for the reply paulskyrme.

Firstly I will not be performing the risk assessment directly myself.

But I fully understand the requirement for a full risk assessments of Hazards is required. And that the machine operates in a manner that would not foreseeably cause injury.

In this specific case the machine would fall under a Type C BS/DIN EN standard. In this accepted standard where there are exemptions to types of machines built before a certain year.

My understandings is that these machines can be used with the reasonable safety updates under these exemptions.
Where they fall out of this exemption is when they become an entirely new machine and must meet all of the new Type C requirements for a new machine (i.e. to evidence safe design, not as a specifically as a legal requirement). In a lot of cases this could make the bones of the machine scrap as its better to design a new machine from scratch.

My understanding is that the Type C standard recommends CAT3 Pld and an industry standard minimum for certain elements of the safety circuit.

From HSE

"Simple machinery refurbishment
Refurbishment of machinery amounting to disassembly and a rebuild to original specification albeit with replacement parts, which may be newer designs, will not usually attract the provisions of the Machinery Directive. Simply repainting a machine, undertaking servicing and routine maintenance, changing motors, replacing parts such as guards with essentially identical new ones, even the replacement of original safety critical parts with newer better ones (eg modern higher quality interlocks wired into the control system in the same way as before) does not amount to a substantial change. However, compliance with existing law (PUWER, etc on users of work equipment, section 6 duty on suppliers etc) is required.
My understanding you can upgrade the safety circuit as long as it does not significantly alter the safety function.
Can you tell me where it states that moving the machine 100 m from one building to the next specifically makes this a new machine?

My understanding was it uses the term relocation which is meaning coming from outside the EEA. Then it is automatically considered a new machine. If a machine was previously installed and ran in production inside of the EEA, and as long as it functionally stays the same meeting the minimum requirements for health and safety at work and the machinery directive and other relevant directives then it does not need to be considered a new machine.

I would be very interested in a PUWER citation that contradicts me though. Also knowing how this would relate to EU directives i.e. Directive 2009/104/EC - use of work equipment. As I am no longer working in the UK refference to the latter would probably be more useful but always interested in requirements of my home country should I move back there.


 28 September 2017 10:44 AM
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There are types of risk assessment structures where through hazard and hazard control methodologies effectively perform a PL_r assessment within the full risk assessment. Where the assessment includes the hazard magnitudes before and after controls are used e.g. guarding or area scanner interlocks etc.

Though I accept they are generally separate assessments.

1 Risk assessment.
2 Hazard prevention design/PL_r Assessment based on Hazard information from Risk assessment.
3 Implementation of design
4 Risk assessment re-evaluation (if failures go back to step 2)
5 Job Done

Obviously there are many other considerations but a good machine manufacturer should provide the customer with items 1- 4 in a singular risk control document along with maintenance manual/drawings/software and preventative maintenance schedule.
This makes the process of risk assessment of the installed machine by the health and safety department a little bit nicer. Obviously documenting any unforeseen hazards that arise from the installation and or unforeseen missuses of the machine.
 28 September 2017 12:57 PM
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For me the myth that a machine can remain the same if it is not moved or not slightly upgraded is a dangerous and a totally false one.

The above myth should never be used as a reason to not improve safety of a system.

Safe machine operation and safest current machine operational design standard practices are two totally different things.

I have never heard of a company winning a lawsuit where a man has been seriously hurt by an old existing unmodified designed machine. If the hazards by current standards are inadequately assessed by the company's EHS team's risk assessment or that the recommendations from a properly evaluated risk assessment were not carried out, then that is gross negligence on part of the company.

On the other hand if the machines that are old as originally designed and reasonable additional precautions are taken and minor upgrades (that do not constitute the machine being defined as brand new are made) so that all potential risks have been reduced to an adequate level without complete redesign then the machine. Then it is not a new machine and safely can be used.

My understanding is that there are dangerous old fashioned more manual machines that MAY have some form of grandfather rights (like for skilled carpentry work etc,) but and a big but that almost all of those type of exemptions have expired. If reasonably practicaple, adequate precautions and minor upgrades are not taken to improve the safety of machines then the company is negligent.

In my example we would plan to put in systems and minor modifications that would not warrant the complete redesign of the machine whilst maintain safety. If that cannot be "adequately done" then of course a costly redesign could be on the cards. I was never suggesting it wasn't.

Back to my original question
Upgrading a dual channel safety cable that is "pull to break type without slack detection" to a dual channel safety cable of a better "tension type with slack and cable break detection" type does not constitute a significant change to design and function but it does improve reliability and safety. Potentially taking a system from PL-c to PL-d.

Do safety cables definitely have to be "tension type" in all circumstances to meet PL-d. If so which standard does this come from?
 28 September 2017 05:32 PM
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This is just too much to cover in this medium like this, we need to deal with smaller issues one thing at a time.
I also can really only comment on the UK implementation of the Directives, even though this is based on the directives and my CMSE is TUV Nord.

Which bits do you want me to address first?

Which C-Type standard covers the machine?

EN 13850 requires that a cable type actuator operates on both increasing and decreasing tension..
 29 September 2017 03:38 PM
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New techno-speak terms to learn. Wot fun.


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