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

I'm going to do a "Ged" and say that's not what you said. :p Best of luck with the testing!

RL

Not sure what you meant by your last comment.
I was just trying to say that the QA-90 is more flexible than other older safety testers in that there is a separate earth connection, separate enclosure connection and a further ten separate applied parts connections on the tester itself.

It could be that on some devices you would have the enclosure lead connected to a part of the device where no patient contact would apply and applied parts leads to other parts of the device where the patient is likely to touch.

Mark

It was meant to be tounge-in-cheek Mark - no offence intended to you or Ged (who held me to my words in previous postings, hence my comment to you "doing a Ged"). Point taken about your tester.

Dear Mark, RL, Ged.

I don't mean to bore you by carrying on too much about this thread but the following just occured to me.

As I previously said I believe the bed frame to be an enclosure because its contact with the patient is incidental to the bed's function. However contact with the bed's hand set is necessary for the beds correct functioning.
So maybe I should be checking handsets as an AP.

PS: Sorry Ged, I meant "interpret the standard" in my previous posting, not "redefine" the standard.

Marc.

Yes Marcel - absolutely. Applying the rationale A.1.10 - It is reasonable to assume that the bed controller is applied parts because the contact is essential to the operation of the bed and because contact with the controller, by the patient, is deliberate; the controller will likely present a significant risk to the patient.

Marc –

I don’t really want to be drawn back into this debate, but just an observation below on your comments since you addressed them to me, amongst others. Then I really will shut up – honest.

My observation is not so much on your conclusion, but rather the reasoning which drew you to it.
We shouldn’t lose sight of the fact that the motivation for this consideration of distinction between Applied Part and Enclosure is for the purpose of electrical safety testing, not device functionality. When we consider how to electrically safety test a part of a device we should be asking not whether it is fundamental to device functionality, but rather what type of shock hazard it could pose to the patient or operator under normal and single-fault conditions. The level of hazard from Leakage Currents (Touch Currents) will depend upon the nature of contact between the person and the equipment.
For example, permitted Enclosure Leakage Currents from household items such as washing machines are typically higher than those allowed for hand-tools - because it is anticipated that the user will necessarily make much more intimate contact with the latter in normal use.
A similar principle extends to medical devices. If contact is casual and the operator or patient can easily withdraw in the event of a shock, then it ought to be considered Enclosure. If contact is prolonged/intimate, or if the patient would have difficulty withdrawing in the event of shock (due to illness, medication, anaesthesia, etc.), then the stiffer requirements for Applied Parts should apply – irrespective of whether contact with this part is essential to device functionality. This is the rationale underlying the definitions in the Standard. Whether the part is essential to the functioning of the device is only relevant insofar as if it is, then implicitly it will require deliberate connection to the patient so we can then automatically assume it is an Applied Part. If device functionality does not require the part to be purposely connected to the patient then the answer is less obvious – it is then that we must use professional experience/judgement to decide whether contact is possible during normal use, and if so what type of contact.

To stick with the bed example – patients often don’t lie still and tidy in the middle of the mattress. Look at the design of the particular bed – could the patient realistically make contact with any part of the electric bed’s frame whilst asleep/comatose? A dangling limb, for example?
When I was visiting a relative recently I observed the lady in the next bed had pulled her blankets back and subsequently rolled over in her sleep and was sleeping hard-up against the bed rail. An ill/comatose patient making intimate contact with part of the equipment; - applying the principle above that makes the bed rail an Applied Part which ought to be electrical safety tested as such (unless inspection reveals its material construction or manner of attachment to the bed are such as to preclude Leakage Current flow through the rail).

Remember that the Leakage Currents with which we are concerned here have no role in the functioning of the device – they are an unwanted by-product of the use of electricity which the designer would be quite happy to see eliminated to zero if realistically achievable. It is therefore illogical to use functionality as the criteria for distinguishing between Enclosure and Applied Part, which is a distinction regarding electrical safety, not functionality. However if we know that patient connection of a part is essential for device functionality then this informs our decision but indirectly - we know straight away that it must be an Applied Part because of the nature of contact it must therefore have with its patient. If connection is not essential then in deciding whether it is an Applied Part or not we must consider whether patient contact with it is likely, and if so what would the nature of that contact be. We should assess hazard potential, not level of functionality, in distinguishing between Enclosure and Applied Part. This is what A1.10 of the Standard is telling us to do, though it acknowledges that “… there can be difficulties ….” distinguishing between the two – this debate would certainly confirm that!

Ged, Mark,

After accessing the Part2 standards (Electrical Beds) I can only concur with your assessment of applied parts and associated safety aspects - this still raises more questions than answers when considering how to assess the various parts though; seeing as anything on a bed can be applied parts it seems. Unfortunately I was not aware of the availability of the part2 standard until I was browsing the BS website and downloaded it out of curiosity - my apologies for wasting of valuable time through my own misunderstanding and ignorance. Thankfully I am not involved in the maintenance of beds (yet).

Surely the distinction between an applied and non-applied part is defined by the manufacturer / function of the equipment ? If it has a "patient cable" that you stick electrodes to and connect to the patient, it's an applied part. If it's part of the case which the patient might come in contact with but this contact is not required to ensure the correct operation of the machine, then it's not an applied part and should be tested as part of the enclosure.

Roy

Think you should read BS EN 60601-1 for the correct Enclosure and Applied Part definition rather than defining it yourself.
See Appendix A1.10 of BS EN 60601-1:1990.

Mark

The part2 (electrical beds) standard does actually make the distinction between applied parts and enclosure (fig 111). Applied parts are generally located around the bed top and side rails and the bed frame is considered enclosure. 60601-1 is quite vague when you consider the definitions as applied to beds which is what caused my confusion. The part2 standard clarifies the definitions, somewhat, I think.