The UL 94 flame rating (Figure 1) classifies materials based on their flammability characteristics. Plastics are tested in accordance with the UL-defined procedures under lab conditions. The results are used to help select the appropriate material for a specific application.
It should be noted that UL 94 is intended to determine the flammability of plastics employed in appliances and devices. Standards like the ASTM E84 apply to polymeric materials used in construction and building applications. Although UL 94 is a single standard, it includes multiple ratings for solid plastic materials:
UL 94 HB
UL 94 V (V-0, V-1, and V-2)
UL 94 5V (5VA, 5VB)
HB is the rating for the horizontal burning of solid plastic materials and V represents the vertical burning (Figure 2). UL 94 has multiple vertical-burn testing standards, each with their own requirements. The UL Prospector website contains information on how each test for solid plastics is performed.
UL 94 Flammability
The flame resistance of solid plastics with a UL 94 HB rating is inferior compared to materials that comply with UL 94’s vertical burning standards. In general, achieving UL’s horizontal burn rating is believed to be easier than achieving all other UL 94 flame ratings.
For some applications, UL 94 HB plastics could be ideal. These materials are generally employed in portable, attended enclosures for appliances or devices with intermittent, light-duty use, such as calculators and hair dryers.
The UL 94 V rating is more challenging compared to UL 94 HB, but is also applied to consumer goods, like coffee makers. UL 94’s V-0, V-1, and V-2 ratings each have a different total combustion time for five samples under total flaming conditions. Plastic materials that are compliant with V-0 and V1 ratings do not cause flaming drips to ignite surgical cotton, which is used in medical, hygienic and sanitary applications.
The UL 94 5V vertical burn rating is the highest UL 94 flame rating for solid plastics, testing the flammability of materials used in fixed enclosures for electrical equipment. The UL 94 5V is for plastic materials that have already a UL 94 V-0 rating. The UL 94 5VA rating is more strict than the UL 94 5VB as the 5VA rating dos not permit plaque specimens to exhibit burn-through. Plaque is deposits from the plastic material that have dripped onto the surgical cotton.
Conclusion
For more than two decades, Elasto Proxy have supplied custom-fabricated rubber and plastic components for a myriad of industries, including construction, automotive, mobile specialty vehicles, medical equipment, mass transit, green power, food equipment, electronics, and defense. Collaborating with a custom fabricator with a strong understanding of UL94 flame ratings for solid plastic components can help industries to strengthen their supply chain.