Plastic is potentially flammable. Flammability is a trait tested in commercial plastic products by Underwriters Laboratories, the industry standard in plastic flammability ratings. Underwriters Laboratories testing assigns a horizontal or vertical burn rating to plastic products, certifying those that meet its standards.
To obtain UL certification, a plastic product must pass the horizontal or vertical burn level test based on its thickness. A plastic less than 3 millimeters thick is tested horizontally and must burn at a rate less than 76 millimeters per minute. Thicker plastic components are tested vertically, and burning must self-extinguish within 10 to 30 seconds to obtain certification.