EBME Forums Forums Maintenance Technical Assistance Class III equipment

Hi,

I'm writing up and revising some teaching notes for our Kyambogo University project, Uganda and I would be grateful if I could get some clarification on Class III equipment.

I know what IEC doesn't recognize Class III equipment (as noted in the article here on EBME), but I'm mentioning it in the course material as there's still a chance our students and graduates will meet them.

Unfortunately, the only reference I can find that shows a symbol is http://en.wikipedia.org/wiki/Appliance_classes#Class_III

Knowing the issues that wiki can sometimes have in relation to being accurate, any advice on the subject would be very welcome.

Regards,

Steven

Seems reasonable to me.

In other words, if the complete equipment (ie, together with any power supply or charger) includes a mains power plug, then it (the whole thing) should be tested for electrical safety.

In practice, I doubt that your students will ever encounter Class III equipment in any hospital or clinical environment. But if they do, then my advice to them would be to remove it!

Geoff,
I think they will encounter class III equipment that is purely battery powered, for example pacemakers, TENS machine, small portable pulse-oximeters, AED defibs such the FR2.
However two of these actually produce voltages higher than SELV.
Now there is a conundrum. I think that is why it went from being class III to Internally Powered as the classification.
Robert

Would any of those devices be marked as Class III?

But it's an interesting area this, so let's discuss it further. I would split stuff like that mentioned into three types straight away:-

1) The AED defibs (what are they marked as? Class II, I suspect)
2) Small battery powered devices (such as TENS) ... that have no mains chargers or "adaptors"
3) Pacemakers (external, presumably) ... a special case, IMHO

What does "electrical safety" say about each type? For a start the defib is meant to deliver an "electrical shock", is it not (but hopefully only to the patient)?

And ... how can a TENS unit, nerve stimulator et al powered by 9 VDC PP-3 battery muster up enough Joules to really hurt anybody? "Startle", perhaps!

In my experience, "minor" devices like this often crop up. In fact they are everywhere, and many are privately owned (eg, TENS). So this is an issue worthy of discussion ... please discuss.

Other than that, I stand by the simple rule that everything with a mains plug gets "Tested and Tagged" (tested for electrical safety, that is), whilst (small) battery powered devices don't (getting just a functional test instead). Or, put another way, how can you Rigel* a TENS unit?

* Other manufacturers of fine medical electrical safety testers are available.

I think you have to get away from "Rigelling" equipment and get back to basics for this type of equipment. Obviously you are not going to get mains related leakage currents etc but you can get auxillary currents between two patient applied parts. Even on a simple TENS unit if it is faulty and with external pacemakers this could be very significant were it not to be picked up. The FR2 typre defib is purely battery powered so cannot be class I or II but again there is the possibility of significant auxillary currents if something is faulty. Could you also get inductivly or capacitivly coupled enclosure leakage currents when it is charging and faulty?
What I am saying is that just because something is purely battery powered does not mean it cannot cause harm hence some form of safety testing is necessary. This goes back to the original question should people be taught about it? Yes andn ot as happens in a lot of UK institutions (in my experience) it is battery powered so we do not safety test it. I also know of one place where "custom" said they did not need to test class II equipment as you were very unlikely to get a shock from a plastic case.
Robert

Yes, "back to basics" is good. But to be honest, I'm not sure what Steven is asking in particular ... I guess we need to hear more from him, but I'm assuming that his course is aimed at techs who will be "testing the kit", as it were.

But we need to be careful about what it is we're talking about here:-

1) Kit marked as Class III? In theory, such should not exist in clinical environments.
2) Small battery powered devices such as TENS units and nerve stimulators? As I say, a functional test should show up any faulty and/or potentially hazardous conditions, I would have thought.
3) AED defibs ... how are they marked? Then test accordingly and as best you can. In my experience, there's not a lot you can do with them.

Yes, Robert ... I too have come across many biomed shops where basic knowledge (not to mention attitudes) was ... er, somewhat lacking. That's why we have to keep on "spreading the word", Old Buddy!

The True Biomed never stops learning, and there's always something new to "master". Each time we encountered (what to us was) a new piece of kit, old 'uns like myself always used to ask the question:- "how am I going to test that?" ... and I suspect that is what Steven is driving at. And if not, Steven, why not?

Hello Rojo, in your post"custom" dictated that they did not routinely test Class II equipment, this is not necessarily incorrect, if you follow the general guidance on electrical testing from the IEE, I can see how such a decision has been arrived at using a logical process.

Regards
Sean

Extract from The IEE Code of Practice (3rd Edition)
In-service Inspection and Testing of Electrical Equipment

7.1 Inspection

In-service inspection and testing of equipment are essential to ensure to ensure safety, and a regime of time and risk assessment based inspections and tests should be implemented.

In-service inspections can be carried out by the user of the equipment, and in some circumstances this may be all that is necessary.

An example of circumstances where user inspections may be the only inspection required is in a low risk environment where Class II equipment is used.
Inspection should always precede testing.

A properly carried out inspection can identify many faults that will not necessarily be apparent from electrical tests, such as a cracked case, a loose connection, a damaged flex and evidence of overheating.

7.2 Categories of inspection and testing

Three categories of in-service inspection and testing are referred to in this Code of Practice.

User checks: faults are to be reported and logged and faulty equipment should be removed from service. No record is required if no fault is found.

Formal visual inspections: inspections without tests, the results of which, satisfactory or unsatisfactory are recorded.

Combined inspections and tests: the results of which are recorded.

7.3 Frequency of inspection and testing

The relevant requirement of the Electricity at Work Regulations 1989 is that equipment shall be maintained so as to prevent danger. Inspection and testing are means of determining when maintenance i.e. required.

The frequency of inspection and testing will depend upon the likelihood of maintenance being required and the consequence of lack of maintenance. No rigid guidelines can be laid down, but factors influencing the decision include the following.

The environment: equipment installed in a benign environment, such as an office, will suffer less damage than equipment installed in an arduous environment, such as a construction site.

The users: if the users of the equipment report damage as and when it becomes evident, hazards will be avoided. Conversely, if equipment is likely to receive unreported abuse, more frequent inspection and testing are required.

The equipment construction: the safety of a Class I appliance is dependant upon a connection with the earth of the fixed electrical installation. If the flexible cable is damaged the connection with earth can be lost.

The safety of Class II equipment is not dependant upon the integrity of the electrical installation.
If equipment is known to be Class II and is used in a low risk environment, such as an office, recorded testing (but not inspection) may be omitted.

The equipment type: An appliance that is hand-held is more likely to be damaged than a fixed appliance. If such an appliance is also Class I the risk of danger is increased, as safety is dependant upon the continuity of the protective conductor from the plug to the appliance.

The most important check that can be carried out on a piece of equipment is the visual inspection. The visual inspection can identify many defects, particularly in the case of portable appliances or hand held tools where defects in the plug, the cable or casing occur.

If the user cannot routinely disconnect the equipment to facilitate a user inspection, this should be taken into account when determining the frequency of inspection.

7.4 Review of frequency of inspection and testing

The intervals between checks, formal inspections and tests should be kept under review, particularly until patterns of failure, or damage, if any, are determined.

Particularly close attention should be paid to initial checks, formal inspections and tests to see if there is a need to reduce the intervals or change the equipment or its use.

I seem to recall that DB-9801 Supplement 1 was a bit "limp-wristed" in regards to Class II, as well.

But how about Class III?

Interesting that they say "... a regime of time and risk assessment based inspections and tests should be implemented", though (my italics).

"DB9801 Supplement 1 emphasised that new equipment under test should not be subjected to currents or voltages exceeding those experienced under normal operating conditions. Hence none of the recommended tests involved shorting applied parts together or applying high voltages to electrodes. It was also suggested that medical electrical equipment not having applied parts could be safety tested satisfactorily using non-specialist portable appliance testers."

So if we consider Class III Battery powered devices, not connected to a charger, with no patient applied parts, visual inspection and output checks should suffice.

Class III BF/CF? such as in the case of wall mounted external AED Defib such as FR2? output checks, but applied parts (Apex/Sternum) patient auxilliary leakage current checks required, I would hazard a guess?

But if the complete equipment can be used whilst plugged into a charger, then it gets tested as Class I/II (depending upon what Class the charger appears to be)?


But ... how is the FR2 marked? And/or what Class does the manufacturer's documentation declare it to be?