Specifications Questions & Answers

What does UL V0 mean?

UL V0 is a standard for measuring the burning behaviour of a plastic material.

UL (Underwriters Laboratory) are an independent test house who test plastic materials. One of the tests they undertake is the burning behaviour of different plastic materials which are then classified.

The classifications fall into 2 main types which are determined by the test method. One is the Horizontal burn test, the other the vertical burn test. Both tests involve lighting a specimen sample of plastic and seeing if it continues to burn or goes out (self-extinguishes)

To be classified as meeting the horizontal burn test, a sample, when held horizontally and set alight, needs to burn more slowly than a defined rate. Plastics which meet the requirement are classified with a designation of UL-HB.

A more severe test is the vertical test. In this test the sample is held vertically, the base set alight and the time taken for the sample to self-extinguish is measured and any plastic drips which occur as a result of burning are recorded.

Depending on how quickly the sample has self-extinguished and how many drips come from it in that time a classification is given. These range from UL V0 to UL V2.

Materials rated UL-V0 self-extinguish within 10 seconds and do not drip.

Materials rated UL V1 self-extinguish within 30 seconds and do not drip.

Materials rated V2 self-extinguish within 30 seconds but do drip.

These tests are done on varying thicknesses of sample 0.4mm, 0.8mm, 1.6mm etc. The thinner the sample the more likely it is to continue to burn and hence the test is more severe.

Very flame-retardant materials are UL V0 rated at thin sections (0.4mm or 0.8mm).

Lesser flame-retardant materials rated at UL V1 or UL V2 or UL HB.


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