Flammability Classifications

The Underwriter Laboratory specification UL94 is commonly accepted as a way of classifying the flammability of materials, especially plastics and composites such as those found in circuit boards, electronic components and enclosures.

The tests carried out by the laboratory are either vertical or horizontal burn tests depending on the viscosity of the material.

The vertical burn tests are used to determine the time taken for the material to cease burning once ignited and also to determine if any burning droplets (or flame drips) can ignite gauze placed below the test sample.

The horizontal burn tests are use to determine the rate of burning of the material. i.e. the speed of the flame front.

Classification Self Extinguishing Time Ignition from Flame Drips
UL94-V0 Within 10 seconds No
UL94-V1 Within 30 seconds No
UL94-V2 Within 30 seconds Yes
UL94-HB Reduced burn rate when horizontal


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