EBME Forums Forums Maintenance Technical Assistance Class I electrical safety test on Class II equipment

More detail about the case.

The piece of audiometer passed the auton ClassI (Company said it was ClassII machine after) auto EST the first time, though the charger is visually burned during the test. And the audiometer did not pass the protective earth resistance test after that. However, the charger still supplied power to audiometer and everything working all right after, with the burning smell from the charger.

Thanks, Ling and Ian, for your suggestion.

I would like to rise another question here. Does any one test the patient lead that enclosed totally by rubber or plastic? Such as cuff, SpO2 finger sensor, and earphone. The engineer suggestted that NO patient lead need to be tested as the earphone from audiometer has no patient-connected metal wire back to machine.

How is every one test the patient leakage on Vital sign monitor? NO patient lead tested? I am always connecting the SpO2 finger sensor and even cuff to patient lead test. Although, it does seem unnecessary at all in theory.

Please do give your suggestion and what is your test on this? Many thanks.

Yes, Jerry, I have even seen guys attaching the probe to IV giving sets! I’ve also seen people insisting on testing Class II equipment resting on a metal plate with the tester earth lead clipped to it (the plate, that is). Time well spent? Personally, I doubt it. A modicum of common sense is called for when carrying out electrical safety tests, I would have thought.

For class 2 I think 200cm^2 of aluminium foil is is what's usually attached to the (non-conductive) case or underneath it if it's a small device. Foil is also specified for wrapping around SpO2 probes and suchlike, in particular standards, as far as I'm aware.

If there's ultrasound probes or invasive BP applied parts then transducers can be immersed in saline or PM sets can be flushed with it before the applied parts connections from the safety analyser are immersed in the fluid.

Since there's 500Vdc insulation-resistance test voltages and the possibility of mains on applied parts then this sort of thing shouldn't be done in clinical areas and care must be excercised in the workshop setting.

Of course we're not doing type testing but for CF and BF parts then it's usual to test to conductive applied parts directly and perform SFC (AP-earth and AP-mains) if it's considered appropriate, i.e. not if applied parts are type B and earthed, perhaps.

Personally speaking if there's a risk of injury, no applied parts accessories available, or they're obviously non-conductive and in good condition then I prefer not to test rather than risk damage or injury - unless, perhaps, if fluid ingress into AP (probe) is likely be picked up by testing.

It's down to personal preference and assessing the risks at the moment. Probably only really valid initially at acceptance or evaluation to ensure a device is safe from new. However I tend to test APs routinely wherever possible.

Incidentally (Bao) my name's Richard or Mr Ling - I was always told that using someones surname on it's own is impolite.

... impolite to our British sensitivities, perhaps, Richard. But common practice in some far-away cultures, I’m afraid Old Chap (not to mention British "Public" Schools, the Armed Forces, etc. etc.).

Yes Hannis, also with our much loved football/rugby teams...

Davies (not Simon or Jonathan by the way)

I know it's going off the main issue but I used to have an "old school" boss when I worked for the PHLS many years ago who always insisted in calling me by my surname without the Mr when I always had to prefix his surname by "Dr" (he was a phD)I hated this and have alway preferred being called by my first name. I believe that it's more polite than insisting that I'm called Mr. Anyway, I've been called much worse than this as Geoff will know!
Getting back to the question of "applied parts". My understanding is that this is any electrical connection to the patient for the purpose of measurement or therapy e.g. ECG connections or defib. paddles etc. There are "grey" areas such as metal temperature probes which I would treat as an applied part and connect to the applied part terminal on the safety tester. In the case of insulated devices such as SpO2 probes I did make up a metal "finger" for our safety tester so that it could be connected to the applied parts terminals. However, I doubt the value of doing this. I also, doubt the value of connecting an IV set by some means to the applied part terminals of your tester. Whilst, the liquid in the set may be conducting (e.g. saline solution) it is totally enclosed in a insulated tube that passes through the IV pump and has no normasl electrical connection to the pump what-so-ever. Although, I suppose some would say that if the pump or tube is faulty there is a possibity of this due to leakage of the conducting liquid into the pump. However, this would be picked up during the visual check before testing.
I agree that we need to be sensible about this and weigh up the risks and the possibility of these sort of problems when carring out electrical safety tests on medical equipment, especially when the equipment is Class I BF or CF, or for that matter Class II.

HI, Mr Ling,
Very sorry about this, I am always confused with the surname and first name. I will remember your name now.

I received a letter from the audiometer company regarding the classification and electrical safety testing, saying that "although technically classified as Class I Type B devices, the electronic control unit should be treated as a Class II device for testing purposes".

Bit disappointed that this letter did not come with the returned audiometer. And there is not sign for Classification on audiometer or charger.

Dear Mr Ling, you said that we can report this to MHRA, could you please tell me an email address to report?

Many thanks,

Thanks for every one giving their opinions here.

Theoretically, there are no point to test the isolated applied part.
Practically, I normally safety test the SpO2 applied part (with wire inside). Can pick up some leakage current sometime, with few greasy finger sensor.

Could any one give me any authoritative reference on this?

... enough greasy leakage current to constitute a risk? I doubt it, somehow. Time on your hands, then, Jerry?

Jerry
I use a cut off piece of copper pipe for SpO2 sensor tests and a metal can that I wrap the cuff around for NBP testing.
I also take an electrical connection to the end of a fluid filled syringe or infusion set fitted to a pump for pump electrical test.
I can't give you any reference for the above practices. My peculiarities are referenced to my own head !
However I think the type tests in the IEC standard are where people get the idea of putting foil onto equipment enclosures or standing Class 2 items on a metal plate.
With a modern automated safety tester the additional time per unit taken for these precautions is minimal. The point of a safety test is in fact to show something is safe. Having no failures isn't a waste of time, it shows the equipment is safe! In the unlikely event of someone suffering imagined "burning" or genuine shock it can be shown that up to the point of the last test the unit was safe and it's history is consistently good.

Geoff
I don't think you should be spending your valuable time suggesting technicians who are zealous have "spare time". Risk assessment takes time in itself and places a far higher burden of liability upon a technician than does covering all the bases in a simple and practical manner.

Marc