UL 94 Flammability Tests

Hello all!

I'm having some trouble interpreting the meaning of some UL 94 ratings.

The data sheet for our preferred product, which is Makrolon 2658, shows the following ratings for the UL vertical and horizontal tests:

Thickness 0.81 mm UL 94 Class V-2 Thickness 1.5 mm UL 94 Class V-2 Thickness 3.0 mm UL 94 Class HB Thickness 6.0 mm UL 94 Class HB

Although the four lines of data in the table are arranged in ascending order of thickness, they refer to the test conditions that were used on two *different* procedures.

The more stringent test is the vertical one, and a V-2 rating indicates less flammability than V-0. Performance of the material on this test may vary by thickness of the sample, since burn rate and combustibility will be higher for thinner cross-sections. So thicker is better. And other products (eg Makrolon 2667) show a rating that rises with increased thickness.

My challenge is to justify that a 2mm thick instrument housing, fabricated from Makrolon 2658, meets V-2 standards. However, if thicker is *always* better, why would the vendor even publish the numbers for the HB test on this particular polymer? Horizontal tests are typically done with thicker samples than vertical ones anyway, and it would seem to me that the vertical test takes precedence in this case.

Any thoughts on this would be much appreciated.

Thanks!

--------------------------------------------------------------------- John Murray PhD CEng Pemstar Pacific Consultants

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