Hi all, so before I start my query, I have read Reg 19 of L22, and I didn't clearly understand why the use of an interlocked guard or ES controls are not suitable means of isolation (so just want to get that out in the open before people start quoting that at me :)); the only thing I could think why (because unless I missed something, it didn't seem to expand upon why it wasn't) was the chance for machinery to be restarted (if guards are closed or if the ES button is taken out; hopefully someone can confirm this). Onto my main query.

So, as I'm no engineer and I'm sort of 'picking things up' as I go, what I'm trying to understand is whether or not it is acceptable to use emergency stops to carry out planned maintenance under certain conditions or service work (if say, there are 2 or more people working on a machine and ensure it remains in that positon) versus the use of an isolator? Again, I know what Reg 19 says about it not being suitable, but why? If the machine has an ES pulled out/used etc so the machine cannot run, and as long as one person is standing guard (to ensure it does not get restarted in error), is this an acceptable way of 'isolating' (I know it's not really considered isolating) the machine to work on it? I get this a lot where there seems to be much resistance to simply turning the power off at the isolator and using a lock-off device and what I want to understand is, where - and if - the use of an emergency stop can be considered a viable, safe alternative to the former or whether this is a complete no-no all the time. I'm assured by my maintenance team - and many contractors doing different types of work - that using an ES kills the power and as long as the ES is being prevented from being pushed back in again, then it is perfectly safe. However, I am sure there will most likely be limitations with - even if considered safe - where it won't be acceptable to use. Please advise? I would appreciate if you could keep it as least technical as possible (or if you are going to be technical, trying and explain it in layman's terms) as again, it's not the background I'm from, so if it's too technical, I most likely won't understand it. Thanks.

An emergency stop is functional safety and it is secondary protection.

There is some conflict as certain EU documents call this function isolation, but it does not necessarily meet the requirements of EAWR89 for isolation.

Then you have the potential for failure, any safety funciton can fail, and, in the absence of a specification requiring a higher level then an e-stop function only needs to meet PLc.  For whole body access &/or potential ftaility we would be looking for PLe a much higher level of reliability from the safety function.

An e-stop is only really suitable for routine tasks which do not involve the dismantling of parts of the machine.

It certainly does not isolate the machin electrically, it is only required to remove power/energy from actuators, not the rest of the machine.

Just a start for you, got to dash off, sorry.

Thank you for the replies.

So, if the work is general maintenance and servicing (i.e. lubricating, greasing, visual checks of machinery etc) and doesn't involve any changing of parts/dismantling or doing any electrical work, would this then be an acceptable method? Would it be more acceptable to use multiple ES, if say, one were to fail, the other could act as a backup?

Again, thanks.

E-Stop activated whilst an employee worked inside a machine.

Supervisor walked past, released the E-stop and started the machine - one employee less.

Corporate response was everyone sent Lock Out Tag Out procedue to immediately implement.

Well designed machinery would have remote lubrication points otherwise isolate.

I agree with all of the people who have posted.  The primary aim of isolating a machine is to prevent restart when it is under maintainance.  I have however found that a lot of people do not understand the difference between switching off, relying on an interlock and isolating.  The most extreme case I have come across was a few years ago when I was doing a liability survey for an insurance company.  The company used injection presses to make plastic boxes.  They had an issue where on occasion the the boxes would not eject from the mould.  The standard practice was for the operator to open the access gate which stopped the machine as the interlock had been activated.  The operator then enter the guarded area and reached between the mould heads and pulled the box out.  On talking to the operator I asked why he did this.  Firstly he hadn't considered that someone could come along ang just close the gate and that there was the possibility that the press could start and trap his arm and probably remove it. Secondly he said that to use the isolation process meant that he would not be able to make as many boxes during his shift and he wouldn't be able to beat his target and he would lose his bonus.  The subsequent discussion with the MD was to say enlightening.  As was the one with the underwriter.  I see that the factory has now closed and has been replaced with a carpark  To me it reinforced that need for isolation to carry out any work inside a machine and not to rely on a interlock or off switch.  So for me its always isolation regadless of the machine downtime or a failure to reach a target or the loss of a bonus. 

Originally Posted by: AcornsConsult

ES May simply break the live supply rather than isolate the whole supply. For the sake of turning off and isolating versus the issues of it going wrong, why not isolate?

I ask this question myself, and from what I recall, it's primarily because some of the machines are so old, that trying to restart them (even after corretly shutting them down) can be a real problem. It's also an issue because some of the isolators are so old, that they can't have a lock-off device fitted. Lastly, because of time factors; complaints by production teams that if they constantly have to be isolated and locked-off, it can take lots of time to restart the machine to get back to running production (whereas with an ES, its just take it out and away you go; not saying that's right, but that's the issue).

I think we've agreed that where electrical work is done, absolutely has to be isolated and locked-off; same for work on anything hydraulic or pnuematic (and stored energy is dissipated as Hilary mentioned). Judgement call depending on other things depending on what work they are doing and the likelihood of something moving that could give way to an injury, how that machine has to run (not just like hitting a button, but a number of sequences involved by the operator), visibility in terms of the operative and worker respectively etc.

Just to add an example in to this very interesting discussion. I'm not an electrician.

Came across this a few years back. A particular machine had a low voltage brake system on the main motor drive. In effect activating the e-stop removed the main drive circuit, but a lower voltage was still applied to the drive to act as a type of brake. 

The example was an inclined conveyor system. If "isolated" the weight of any product on the inclined conveyor, plus gravity, could in effect mean that the conveyor would move backwards. 

So, e-stop did not remove all power, it left the machine in a "static" and "safe" condition for the operator. Isolation left the machine in a "safe" condition for the maintenance team to get their spanners out. Maintenance team working on the machine with the e-stop activated, but not isolated, would be exposed to live electicals.

Hope this is one example of the difference.

regards

James