UL 94, the Standard for Safety of Flammability of Plastic Materials for Parts in Devices and Appliances testing, is a plastics flammability standard released by Underwriters Laboratories of the United States. The standard determines the material’s tendency to either extinguish or spread the flame once the specimen has been ignited. (From Wikipedia)
UL 94, the Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances includes small scale tests that evaluate the flammability of polymeric (plastic) materials, used for parts in devices and appliances, in response to a small, open flame or radiant heat source under controlled laboratory conditions. The scope of UL 94 clearly indicates that it does not cover polymeric materials used for building construction, finishing or contents such as wall and floor coverings, furnishings or decorative objects. The results of most UL 94 flammability tests are not applicable to materials whose thickness exceeds 13.0 mm, or whose surface area exceeds 1m2.
The UL 94 Standard provides a method for rating the ignition characteristics of plastic materials. Two UL 94 ratings that code officials commonly run across are HB and V (V-0, V-1, or V-2). These ratings are established using small-scale tests in which approximately 5 by ½ inch samples are subject to a ¾ inch, 50W Terrel burner flame ignition source. To achieve an HB rating, test samples, placed horizontally, burn slowly across the sample when the test flame is applied to the end of the sample. To achieve a V rating (e.g. V-2, V-1 or V-0) the test samples, placed vertically with the test flame impinging on the bottom of the sample, must extinguish within specified times, not burning to the top clamp or dripping molten material which ignites a cotton indicator.
Classification of UL-94
From lowest (Least flame-retardant) to highest (Most flame-retardant):
HB: slow-burning on a horizontal specimen; burning rate < 76 mm/min for thickness < 3 mm or burning stops before 100 mm
V-2: burning stops within 30 seconds on a vertical specimen; drips of flaming particles are allowed.
V-1: burning stops within 30 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
V-0: burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.
5VB: Burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may develop a hole.
5VA: Burning stops within 60 seconds on a vertical specimen; no drips allowed; plaque specimens may not develop a hole.
There are other classifications that apply to low-density foam materials (HF-1, HF-2, HBF) and thin films (VTM-0, VTM-1, VTM-2).
HF-2: burning stops within 3 seconds; afterglow less than the 30s; burning drips allowed.
HF-1: burning stops within 2 seconds; afterglow less than the 30s; no burning drips allowed. （Our foam can meet with this fire rating, click to the product)
Tests are generally conducted on a 5" x 1/2" (12.7 cm x 1.27 cm) specimen of the minimum approved thickness. For 5VA and 5VB ratings, tests are performed on both bar and plaque specimens, and the flame ignition source is approximately five times as severe as that used for testing the other materials.