EBME Forums Forums Management Medical Equipment Management Electric Beds - PAT or Medical Safety Testing

The jist of Marks' query was should the Touch Currents (whether you call them Enclosure or Applied Part Leakage) from hospital beds be measured to medical device safety requirements? - If you use an ordinary PAT Tester, as many Estates Departments do, the tests it performs and the limits it tests to, will be programmed for non-medical devices.

When I responded to Mark's posting I also queried, in passing, your description of Type categorisation. I still question it - please read the definitions in Section 2 of 60601-1 (Mark has already quoted some); they clearly are not consistent with your original description of them. I also think your subsequent use of the word 'Enclosure' has been inconsistent in the postings above. Also your reading of the Rationale in A1.10 has been selective - A1.10 specifies 2 criteria for distinguishing Enclosures from Applied Parts, but you apply only the first of these.


Much as I'd like to respond to some of the other points in your last mailing, I think we're beginning to go round in circles here.
I’ll make 2 last points -
- If I perform Touch Current tests the on bed frame as an Applied Part and you test it as an Enclosure, what will be the difference? Well one obvious difference is that you won’t have measured DC leakage whereas I will have. Small DC currents are only potentially hazardous if the patient is in prolonged contact with the source of them – which is why there are no limits specified for Enclosures. Is a sick/drugged patient likely to make prolonged contact with the frame of the bed on which she is lying?
- And no, I wouldn't advocate dismantling the equipment - we'd seek confirmation from the manufacturer before completing the Acceptance Test

Ged,

All I'm asking is how you make the distinction between enclosure and applied parts, irrespective of the absolute word-perfect textbook definitions - the practical aspects of safety testing that Mark's going to be interested in - absoulutely imperative that you can make the distinction if you are to use the medical tester appropriately i.e. there are seperate tests and connections for each test and different limits depending upon the classification and type of equipment.

Ok, if I were to accept your views then how do you achieve the measurements according to your interpretation - how do you determine what's enclosure and what're the applied parts? All applied parts or a combination of enclosure and applied parts? Perhaps you could you give me an example of a test on a piece of equipment you've done recently perhaps?

Regarding electrical safety; all I can say is that applied parts usually means the patient circuit or patient connection needed for the correct function of the device. B, BF and CF being the degree of isolation of the patient connection from mains. All that is left to decide is which bits are enclosure and which are applied parts.

Yes I'm going around in circles asking a question that you're not inclined to answer. I have never had a discussion with any of the many colleagues I have worked with regarding this interpretation of applied parts - very strange.

The answer as I’ve already said, is in A.1.10 – which you selectively quoted.
I haven’t the time or energy to type it all out – but to paraphrase –
There are 2 criteria to distinguish between Enclosure & Applied Part –
1: Is patient contact essential in normal use ?
YES = Applied Part
NO = Go to 2 below –
2: Is contact only incidental/ requiring deliberate action from patient ?
YES = Enclosure
NO = (by inference) Applied Part
(ie: if contact with the patient is likely to be intimate/prolonged then it is an Applied Part, whether or not the answer to 1 was YES)

eg: I’ve already quoted this example from the Standard – “A table top supporting a patient is an Applied Part …. the conductive parts of the table would be classified as Patient Connections”

I gave a practical example in the last posting – the bed we started with. A patient conceivably could make prolonged contact with such equipment. I illustrated treating the bed as Enclosure or Applied Part would make a practical difference for testing to ensure electrical safety of patient (ie: measurement of DC-leakage currents). If no “Enclosure” test is needed then so be it – test the bed for insulation resistance, earth bonding, earth leakage, and patient AC & DC leakage under applicable normal & single-fault conditions. (Though if other devices are plugged into the bed then it could become more complicated of course – as Mark pointed out)

Yes A1.10 was selectively quoted because it gives a sensible rationale to make a decision as to whether a piece of equipment should be considered to have applied parts or not. Hence the appropriate level of routine electrical safety testing required on something like a bed can be justified, in my view. Simple tests that are sensible and appropriate, taking into account the really significant risks to the patient.

Of course you're interpretation is just different to mine and I must respect your views, since I am by no means an authority but now we have justification for testing applied parts tests because of the risk of DC leakage - risk of electrolysis is it? Don't your beds have mattresses (the real applied part)?

We would decide an appropriate level of acceptance inspection/testing and subsequent routine inspection/testing (which wouldn’t necessarily be the same) upon consideration of the particular device – as I’m sure you do. I’ve explained why I think a bed frame is potentially an Applied Part - if using a pre-programmed automated safety tester, as I think most of us now do, the time saved testing it as an Enclosure rather than an Applied Part would be negligible anyway.
Can I suggest we close this topic now? – have a final posting if you wish.
Whilst I don’t claim to be an authority either, I’d be more than interested to continue this discussion directly with you – I think we’ve hogged this forum for long enough. I’m contactable on 0115-962-7646 should you wish.

No that's ok - thanks for your valuable time and your generous offer to discuss this matter over the telephone. I am a bit old and set in my ways to be "re-educated" so perhaps your time would be better spent explaining your unconventional interpretation to Mark.

That's the important thing - that he and others like him get the right end of the stick by reading and thinking about what's in this thread - not whether you or I appear ridiculous or come out on top in a discussion

Great debate chaps,
I will use this as part of our module 1 course ' intro to clinical technology' which includes electrical safety testing. Your discussion points out a number of important key issues on electrical safety testing of medical devices. www.cap-medical.co.uk.

Thanks for the discussion on this subject.

I tend to agree with Ged on this one, as my interpretation of the standard is the same and can’t be swayed any other way at the moment.
Unfortunately with such comprehensive documents as BS EN 60601-1 there is often a conflicting opinion as to what statements or a combination of statements actually mean. However, my view has always been to go with the safer approach.

On the basis that only a few people have discussed this subject, it makes me wonder if I have raised an issue that some have never thought about. It could be that EBME staff are worried as they may end up carrying out more safety testing to BS EN 60601-1 on equipment that traditional didn’t come under their responsibilities? I wonder how many Estates Electrical dept’s have a medical safety tester?

As regards the actual test, what time does it take to connect an applied part lead from the safety tester to say the side rail of a bed and then run the automated test sequence, “not a lot of time”. Therefore in my view it is best to go for the safer option and carryout a full medical safety test (edge on the side of caution – belt and braces) after all that is what a safety test is all about.

If in doubt, edge on the side of caution, I’m sure most would agree?

Mark

Mark - a (well known) problem associated with automated tests is that by locating a single test point - you don't "scope" for various test points (as you would when actually "looking" for sources of leakage) irrespective of whether you test applied parts or enclosure whatever (on enclosure leakage, earth bond, etc). Using your method you can potentially miss something accessible that presents a significant risk (i.e non-earthed conductive parts neither connected to the enclosure or the "applied part" whatever your definition).

I and many of my colleagues prefer manual or manually controlled semi-automated tests (scoping for test points) rather than "push and go" automated (after the connections have been made).

Thinking-on perhaps selecting a single test point defeats the object of testing - hence not the safest option despite using the single, "safer" applied part? Again practicalities come into it. Enough said.

RL

The Metron QA-90 that we use has the ability to connect an earth lead, enclosure lead and ten applied parts, therefore we can cover all angles by assessing what lead/s we need to connect.

Mark