Explanation of UL94 Flame Retardant Testing for Plastics

The UL94 flammability rating is the most widely used standard for assessing the flammability performance of Ultra-High Molecular Weight Polyethylene (UHMWPE) materials. It evaluates the material's ability to extinguish after being ignited. Various methods are used to judge based on burning speed, burning time, drip resistance, and whether drips ignite. Each material tested can receive multiple values depending on its color or thickness. When selecting a material for a specific product, its UL rating should meet the thickness requirements of the plastic part's wall. The UL rating should be reported together with the thickness value; reporting only the UL rating without the thickness is insufficient.

Summary of UL 94 Ratings: Plastic flammability ratings increase from HB, V-2, V-1 to V-0.

• HB: Horizontal specimens less than 3mm in thickness burn slowly with a burning rate of less than 76mm/min.

  • Can burn, but must meet burning speed requirements.

• V-2: Vertical specimens stop burning within 30 seconds; burning drips are allowed.

  • Extinguishes within 30 seconds, dripping is allowed.

• V-1: Vertical specimens stop burning within 30 seconds; no drips allowed.

  • Extinguishes within 30 seconds, no dripping allowed.

• V-0: Vertical specimens stop burning within 10 seconds; no drips allowed.

  • Extinguishes within 10 seconds, no dripping allowed.

• 5V: Test rods are burned 5 times, each flame being larger than the V-test flames, with each burn lasting 5 seconds. Burning stops within 60 seconds.

  • 5VB: Specimen boards are burned through (producing a hole).

    • Must meet V0 materials, burning through is allowed.

  • 5VA: Specimen boards are not burned through (no hole produced) - the highest UL rating.

    • Must meet V0 materials, burning through is not allowed.

1. UL 94 HB* Horizontal Testing Procedure Materials with safety requirements for flammability are not allowed to use HB-rated materials. Generally, HB-rated materials are not used in electrical appliances but may be used in mechanical or decorative items. Sometimes, there is a misconception that non-FR materials (or materials not intended for FR use) automatically meet HB requirements. Although it is the least stringent, UL 94 HB is still a flammability classification that requires testing.

2. UL 94V0, V1, and V2* Vertical Testing Procedure Vertical testing uses the same specimens as the HB test. The burning time, glowing time, when dripping starts, and whether the cotton underneath is ignited should all be noted. Burning drips are considered a primary cause of flame spread and are the distinguishing factor between V1 and V2 ratings.

3. UL 94-5V* Vertical Testing Procedure UL 94-5V is the most stringent of all UL tests.