As per UL94 standard, a material shall be classified HB as described as below:
A. Not have a burning rate exceeding 40mm per minute over a 75mm span for specimens having a thickness of 3.0 to 13 mm, or
B. Not have a burning rate exceeding 75mm per minute over a 75mm span for specimens having a thickness less than 3.0mm, or
C. Cease to burn before the 100mm reference mark
Our company has UL94 Burning Tester, which meets with UL94 standard and apply to HB, V-0,V-1, V2 testing.