This is generally considered the easiest test to pass and materials that pass any of the V or VTM tests will usually be accepted by UL for applications that require 94HB. To be sure, check with the UL representative assigned to the device in which the film will be used. The 94HB rating would typically be acceptable for portable, attended, intermittent-duty, household-use appliance enclosures (i.e., hair dryers) or for decorative parts.
The test uses a ½" x 5" specimen held at one end in a horizontal position with marks at 1" and 5" from the free end. A flame is applied to the free end for 30 seconds or until the flame front reaches the 1" mark (see Fig. 2.1). If combustion continues the duration is timed between the 1" mark and the 5" mark. If combustion stops before the 5" mark, the time of combustion and the damaged length between the two marks are recorded. A set of three specimens are tested.
A material that is less than 0.118" in thickness will be classified 94HB if it has a burning rate of less than 3" per minute or stops burning before the 5" mark. If one specimen from the set of three fails to comply, then a second set of three are tested. All three of this second set must comply.
