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UL 94 Flammability classification test for plastic materials

UL94 is the standard applied by the American Underwriters Laboratories for the testing of the flammability and fire safety of plastic materials used in devices and appliances. In the UL94HB (Horizontal Burning) test the burning of a horizontal plastic specimen is tested and in the most demanding UL94V (Vertical Burning) tests the burning of a vertical test specimen. Precise details of the equipment, conditions and test systems to be used can be found in the UL94 standard.

Horizontal Burning test for flammability classification UL94HB

The length of the test specimen is 127mm (5”) and width 12.7mm (0.5”). The test sheet cannot be more than 12.7mm (0.5”) thick. Lines are marked on the sheet at the 25.4mm (1”) and 101.6mm (4”) locations. The sheet is fixed horizontally at one end and tilted 45 degrees in the direction of the width, as shown in the diagram. The burner used is adjusted so that it forms a 25.4mm (1”) long blue flame. The flame is directed at an angle of 45 degrees to the front edge of the plastic sheet so that about quarter of the test specimen’s front edge is in the flame. The flame is applied for 30 seconds, after which it is removed. If the test specimen burns to the 25.4mm (1”) line before 30 seconds have passed the flame is removed immediately. The test is carried out on three test sheets.

The material under investigation is classified as UL94HB if, after the removal of the flame:

  • A) The speed of burning does not exceed 38.1mm (1.5”) per minute when the test specimen thickness is 3.05 – 12.7mm (0.120” – 0.500”)
  • B) The speed of burning does not exceed 76.2mm per minute when the thickness of the specimen is less than 3.05mm (0.120”)
  • C) Burning finished before the flame reaches the 101.6mm (4”) line

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