UL94 HB Flammability Standard

Specimen

  • Length 125 mm (5 in) x Width 13 mm (0.5 in) x Thickness [typically 1.5 mm (1/16 in) or 3.0 mm (1/8 in) or 6.0 mm (1/4 in)].

Procedure

  1. Three specimens of each thickness are tested after conditioning for 48 hours at 23 degrees C and 50% RH.
  2. Each specimen is mounted with its long axis horizontal and its short axis at a 45 degree angle.
  3. Each specimen is marked with two lines, 25 mm and 100 mm from one end of the specimen.
  4. Each specimen is supported at one end such that its lower edge is 10 mm above a piece of wire gauze.
  5. A 20 mm high blue Bunsen burner flame is applied to the free end of the specimen for 30 second and then removed. If the specimen continues to burn after the removal of the test flame, the time for the flame front to travel between the two gauge marks is measured and the burning rate calculated in millimeters per minute.

Requirements for HB

  1. The specimens may not have a burn rate exceeding 40 mm per minute over a 75 mm span for specimens having a thickness of 3.0 mm to 13 mm, or
  2. The specimens may not have a burn rate exceeding 75 mm per minute over a 75 mm span for specimens having a thickness less than 3.0 mm, or
  3. The specimens cease to burn before the flame reaches the 100 mm mark.