Flame retardancy of a material refers to its ability to burn with a flame under specified test conditions. It encompasses properties such as ease of ignition and ability to sustain combustion. After years of development, flame retardancy testing has evolved into various standards, becoming a key testing item in the relevant industry.
What national standards are used for flame retardancy ratings?
Currently, different standards have been developed based on the flame retardancy testing of different materials. For plastics, the UL94 rating is the most widely used standard for the flammability of plastic materials. It evaluates the material's ability to extinguish after ignition. Various evaluation methods are used based on burning rate, burning time, drip resistance, and whether the dripping beads burn. Each material tested can receive multiple values depending on color or thickness. When selecting a material for a product, its UL rating should meet the thickness requirements of the plastic part wall.
What are the UL ratings and characteristics?
UL94 has 12 fire ratings:
HB, V-0, V-1, V-2, 5VA, 5VB, VTM-0, VTM-1, VTM-2, HBF, HF1, and HF2.
VTM-0, VTM-1, and VTM-2 apply to plastic films,
HBF, HF1, and HF2 apply to foam materials.
Plastic flame retardancy levels increase progressively from HB, V-2, V-1, V-0, and 5VB to 5VA:
1. HB: The lowest flame retardancy rating in the UL94 standard. Requirements: For samples 3 to 13 mm thick, the burning rate must be less than 40 mm/minute; for samples less than 3 mm thick, the burning rate must be less than 70 mm/minute; or the sample must be extinguished at the 100 mm mark.
2. V-2: After two 10-second burning tests, the flame must be extinguished within 60 seconds. Burning material may fall off.
3. V-1: After two 10-second combustion tests, the sample flame extinguishes within 60 seconds. No burning material may fall.
4. V-0: After two 10-second combustion tests, the sample flame extinguishes within 30 seconds. No burning material may fall.
Each level is further divided into five grades: A, B, C, D, and E.
Taking 94V-0 as an example:
A: No sample continues to burn with a flame for more than 10 seconds after the test flame is removed (flaming burning time).
B: For each set of 5 samples, after 10 ignitions, the total burning time with a flame does not exceed 50 seconds.
C: No sample burns all the way to the fixture (including both flaming and glowing).
D: No sample has molten droplets ignite cotton in more than 12 locations.
E: No sample continues to burn with a glowing flame for more than 30 seconds after the second removal of the test flame (flameless burning time).
The above is an introduction to the national standards for flame-retardant cables and UL ratings. UL ratings should be reported along with thickness values; reporting only the UL rating without the thickness is insufficient. You can choose the standard of flame-retardant cable you want based on your specific needs.
