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ABS plastic : which IEC 60601-1 tests to redo?

#1
The ABS plastic we are using for our class IIB medical device is soon obsolete.
The supplier is proposing us an alternative ABS plastic.
I need your help to find a deterministic method to determine which IEC 60601-1 tests to redo.

Thanks in advance

Best regards
 

Benjamin Weber

Involved In Discussions
#2
This depends strongly on the way you are using the material in your device.

You should evaluate at least if the following are applicable for your material:
- Dielectric strength (if used as solid insulation)
- Resistance to heat / Ball pressure test (if used as solid insulation)
- Flammability classification (depends on your way to prevent fire)
- Mechanical strength
- Resistance to agressive substances (consider cleaning, disinfection, sterilization procedures)

But this is only a very general list. If you provide more information in the use in your device, there might be more tests.
 

Benjamin Weber

Involved In Discussions
#4
You should apply your risk management process.

Consider all relevant aspects of the existing RM that relate to the material and re-evaluate those. And consider the differences between the old and the new material.

Example: You use the material for the enclosure and requirements regardig dieelctric strength, ball pressure test and mechanical strength apply.

If you have proof that the new material has a ball pressure temperature of at least that of the old material, than the ball pressure test might be excempted (though the test is not very complex and testing in a competet test house should not be very expessive).
The same is true for the dielectric strength.
Regarding mechanical strength, I would be very careful, since the test results depend on the way the material is processed. But again, if you have proof, that the mechanical characteristics of the old and new material are equal or better and that influences of the processing charactersitics (e.g. injection molding temperature...) for the old and new material are equal or better, retesting might not be necessary.
 

Tidge

Involved In Discussions
#5
Thanks for your reply.

How should I justify the tests I won't redo?
You should apply your risk management process.

Consider all relevant aspects of the existing RM that relate to the material and re-evaluate those. And consider the differences between the old and the new material.
Benjamin Weber is correct. It is possible that you have structured your risk file in such a way that it explicitly identifies the ABS material as the implementation of one or more specific risk controls. If you have done that, you should be able to see which tests (the objective evidence of the effectiveness of the risk control) are necessary to be repeated.

As he concluded, it is possible that retesting will be unnecessary. You should consult your 60601-1 report to see if your notified body needs to be informed of the change to material. If they need to be informed, they will certainly tell you which tests (if any) are necessary.
 
#6
There's a common mistake about how to write up changes, if it is done properly then the process and decision making is a little clearer.

Consider you have Model XYZ configuration 1.7 (hardware, software, mechanical).

The material supplier phases out the ABS plastic, and you need to change to a new type. This then creates Model XYZ configuration 1.8 (C1.8), which is identical to C1.7 except for the plastic case.

Let's say we do some background analysis and decide to do just "ball impact" and "push"(250N) test , while skipping dielectric and ball pressure, stress relief, drop test, leakage current etc are all OK without test. We then do those two tests and write up a report saying it passed just those tests. Put the test report in the design file. End of story.

Well, not really ...

According to the law, you need at least a document (report) that clearly states configuration 1.8 complies with all the applicable standards (as were used for C1.7).

Compliance with each individual requirement may be based on:
  • new tests on C1.8
  • assessment that the tests on C1.7 are representative of C1.8 (changes don't impact compliance)
  • spot checks on C1.8 on the assumption that C1.7 is representative
  • other rationale (e.g. material specifications indicate new design is OK without tests)

Regardless, the document needs to state that C1.8 complies with all the requirements, including ball pressure test, dielectric strength, drop test, leakage current etc even if the tests were not done for whatever reason.

Going back to the original request:
"[please tell me] a deterministic method to determine which IEC 60601-1 tests to redo"

The concern is that this kind of approach overlooks the records related to the tests not done. If for example you engaged an expert but give them two options:

1) analyse the difference between C1.7 and C1.8, make a list of tests to redo on C1.8, and make a report just for those differences​
2) same as (1) but make a report that says C1.8 complies with all requirements (using data from tests on C1.7 as appropriate)​
then you would get two different lists of tests.

By the way, RM isn't the format for this. It's too vague and the requirements in standards are too specific to be handled in an oversimplified RM table. Plus most of the decisions are simple engineering judgement (e.g. old material is ball pressure test rating of 80°C, new material is rated 85°C so obviously OK, no test required). Just make a checklist of all requirements (compressed as appropriate, but still covering all requirements), go though and record the decision and justification. Make sure it's prepared by a qualified engineer that signs the report and takes responsibility for the decisions.
 

Ronen E

Problem Solver
Staff member
Super Moderator
#7
Slightly off topic -
Intended role of the ABS part?...
IEC 60601 is no doubt important, but it's a standard focused on electrical aspects. The way it handles mechanical aspects is quite crude.
"ABS plastic" is super-generic terminology. Two ABS grades may seem similar / interchangeable, but may have a subtle difference that makes the change over very tricky / risky.
Depending on the role of the part(s), I would have managed this as a full-scale design change project. Maintaining IEC 60601 compliance would then be one aspect of that project.

May the force be with you.
 
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