Hi Kaz:
Answering the question, "what's the safety concern,"
is a reverse-engineering process with respect to the
various requirements contained in the standard.
Applying the requirements of the standard to the
specific construction may involve or even require
interpretetation of the standard.
These are two, separate activities.
My point is, while a certification house engineer
(and you) may enjoy a reverse-engineering discussion,
he cannot judge a construction based on what he
learns from reverse engineering.
However, he can judge a construction based on his
interpretion of the requirements.
Since "small part" is not defined in the standard,
application of the "small part" rule is an
interpretation of the standard, and is not an
application of "what is the safety concern."
Likewise, whether the V-1 PWB can serve as a barrier
is an interpretation.
The exemption of certain small parts from the V-2
requirement may or may not have a valid rationale.
Reverse engineering suggests that the qualities of
"small-ness," "function," "distance" or a "barrier,"
(with respect to an electrical part which, under
fault conditions, is likely to exceed the ignition
temperature of the small part) will prevent ignition
of the small part. Or, that if ignited, will not
contribute sufficient fuel to spread the fire within
the equipment.
Unfortunately, the reverse engineering that I have
stated above, is also an interpretation. And, it
is quite wrong from a thermodynamics point of view.
Anyone who has lit a campfire knows that it is much
easier to ignite small units of fuel than large
units of fuel, and that the burning small units of
fuel ignite the large units of fuel.
Many of the requirements in our safety standards
are the result of inverting a bad experience. That
inversion of a specific bad experience is then
generalized. The generalization makes reverse-
engineering to the specific bad experience almost
impossible.
Those of us who are manufacturers always object to
anything found by a certifier that causes us to
change the product. In this case, the certification
house has taken a position that the stand-off must
be V-2. Establishing traceability of flame-rating
of a stand-off may be quite difficult or impossible.
So, we seek a way out. Most often, we either attack
the certification house or we seek a favorable
re-intepretation. Attacking the certification house
never works (and THAT is the voice of experience).
Discussion can be very effective at arriving at a
favorable re-interpretation. But, while the
discussion may involve some degree of "what's the
safety concern," the decision must be one of
interpretation.
Where the interpretation remains unfavorable to the
manufacturer, testing always proves (or disproves)
the hypothesis.
Best regards,
Rich
> Rich,
>
> As always, you've succinctly provided the full story on an approach that in
> this case, will work to get Terry's product approved. I think your
> interpretation of my suggestion of asking "what's the safety concern" is a
> bit off however.
>
> Personally, I'd rather have a 5 minute conversation first before taking the
> time to run the tests right away. It's possible the agency rep. may not be
> all that familiar with the product and so is simply going by the book on
> default (or what he/she's advised to from more senior staff), thereby
> eliminating the application of engineering judgment in those areas open to
> interpretation...a discretionary thing.
>
> By asking the question, both parties will bring to light the exact concerns
> raised in the course of this particular product approval. While it's true
> that a safety certification agency certifies a product to a given standard,
> it's the interpretation of that standard's requirements by the parties
> involved that have raised many an interesting discussion I'd wager. In my
> own view, engineering judgment is not only to be used by a safety agency
> rep. when applying the requirements. How else does one raise questions
> which might result in an interpretive dispute but also deal with such
> disputes?
>
> By the way, the exemption also applies to materials separated by a solid
> barrier of V-1 or better (60950 ed.2), which might also be the case
> here....depends on whether the stand-off falls into a "small part" criteria
> as agreed upon by the agency.
>
> My opinion and not that of my employer.
>
> Regards,
> Kaz Gawrzyjal
> kazimier_gawrzy...@dell.com
>
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