What are the parameters used in UL 94 flammability tests?
Short answer
UL 94 is the standard used to classify the burning behaviour of plastics, and it comprises two tests: horizontal burning (HB) and vertical burning (V). In both, a sample less than 3 mm thick is held above a 50 W, 20 mm high open flame. For HB, the sample is horizontal and exposed for 30 seconds, and qualifies as HB if it burns at a maximum speed of 76 mm per minute. For V, the sample is vertical and hit by the flame twice for 10 seconds: V0 if the flame is extinguished within 10 seconds, V1 if within 30 seconds with no burning drips, V2 if drips are present. The 5V test uses a 500 W, 125 mm flame applied five times for 5 seconds, giving 5VA if the material self-extinguishes with no dripping or burn holes, and 5VB if holes are observed.
UL 94 is a standard defined by the US Underwriters Laboratories (UL) to evaluate and classify the burning behaviour of plastics. It comprises two different tests, horizontal burning (HB) and vertical burning (V), which determine the flammability and the ability to self-extinguish the flame respectively.
In both cases, a sample with a thickness below 3 mm is placed above a 50 W, 20 mm high open flame.
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HB: the material is placed horizontally and exposed to the fire for 30 seconds. The burning time is measured, and the polymer can be defined as HB if the sample burns at a maximum speed of 76 mm per minute.
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V: the material is positioned vertically and hit by a flame twice for 10 seconds. It can be classified V0 when the flame is extinguished within 10 seconds. If it takes up to 30 seconds, it can be categorised as V1 where there is no dripping of burning drops, or V2 where drops are present.
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5V: a 500 W flame with a height of 125 mm is placed underneath the sample five times for 5 seconds. If the material self-extinguishes the flame and shows no dripping or burn holes, 5VA standards are met. If holes are observed, the 5VB classification can be awarded.
Further detail on UL tests and their methods is published at https://www.spelsberg.co.uk/service/technical-information/technical-information/tests-and-test-methods-according-to-ul-underwriters-laboratories/
Our team uses UL 94 and many other UL standards on a regular basis. We operate an in-house test laboratory in Schalksmühle, Germany, to certify our products and ensure key capabilities such as robustness, safety and high performance, and both the laboratory and its devices are UL- and VDE-accredited. Thanks to our experience in material properties and advanced testing, we offer enclosures that provide maximum flammability rating and fire protection. In particular, we recommend using our WKE range (https://www.spelsberg.co.uk/fire-protection-cable-boxes/), which is made of durable thermoset plastic.
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