Basic testing program
The basic testing program to achieve UL Recognition involves three identification tests: infrared spectroscopy (IR), thermogravimetry (TGA) and differential scanning calorimetry (DSC). In addition, since most end users benefit from plastics being flame-rated, most UL Recognized plastics products include flame classification.
Once the identification and/or flame tests are successfully completed, a unique grade designation is published. Thereafter, UL field representatives conduct quarterly Follow-Up Services visits to each manufacturing location. In addition, the plastic is picked up annually and sent to UL for comparison to the IR, TGA and DSC reference graphs on file. Flame testing is required if the plastic material is vertically rated.
Successful comparison to the archived reference IR, TGA and DSC is an indication that no polymeric change(s) have occurred and is evidence that mechanical and electrical properties of the material remain unchanged. Successful correlation of flame class between Follow-Up Services and the published rating are also required to maintain UL Recognition for the product. Should any of the above tests not comply, action is taken to remove Recognition or downgrade the plastic. This usually includes a mandatory name change as an indication of a degraded characteristic variation.
Plastics with "flame only" Recognition are selected (for use in end-products) for their flame characteristics only. Electrical and mechanical properties are more than likely evaluated on the end product or possibly not required based upon their application. Despite the fact that the mechanical and electrical characteristics of the material were not evaluated, UL's liability rests in the evidence that the untested properties remain unchanged (via IR, TGA and DSC comparison to reference).
The continued publication of a specific material (with a specific designation or name) enables the continued use of that plastic material in end-use products, so long as the original characteristics are maintained. Besides the obvious safety aspects of using a Recognized plastic material, end-product users (of the Recognized plastic) are subject to a reduced test program of the product, and similar advances apply to the use of UL Recognized switches, appliance wire, terminal blocks, etc.
