What is Flammability Rating (UL 94 HB / V-2)?
One-Sentence Definition
Flammability Rating (UL 94 HB / V-2) is a safety classification that measures how plastic materials, such as acrylic, resist burning under specific test conditions, with HB indicating horizontal burn resistance and V-2 indicating vertical burn resistance with limited self-extinguishing capability.
Detailed Explanation
UL 94 is a globally recognized standard developed by Underwriters Laboratories to evaluate the flammability of plastic materials. The HB (Horizontal Burn) and V-2 (Vertical Burn) ratings are two of its most common classifications:
- HB (Horizontal Burn): The material is tested in a horizontal position. To achieve HB, the burning rate must not exceed 75 mm/min for samples under 3 mm thick, or 40 mm/min for samples 3–13 mm thick. If the flame self-extinguishes before reaching a set distance, the material also qualifies as HB (UL Solutions).
- V-2 (Vertical Burn): The material is tested vertically. After two 10-second flame applications, the sample must stop burning within 30 seconds. Flaming drips are allowed and may ignite a cotton indicator below (SpecialChem).
UL 94 ratings are thickness-dependent and can vary with changes in material formulation or colorants. Always verify the rating for the specific thickness and composition you intend to use.
Key Components
- Test Orientation: HB (horizontal), V-2 (vertical)
- Burning Time: HB—burn rate limits; V-2—must self-extinguish within 30 seconds
- Dripping Behavior: V-2 allows flaming drips that may ignite cotton below
- Thickness Dependency: Ratings apply only to tested thicknesses
- Certification: Verified by UL Yellow Card for each material and thickness
| Rating | Test Position | Max Burn Time | Dripping Allowed | Typical Use Cases |
|---|---|---|---|---|
| HB | Horizontal | ≤75 mm/min (<3mm) or ≤40 mm/min (3–13mm) | Yes | General plastics, display stands |
| V-2 | Vertical | ≤30 sec | Yes (may ignite cotton) | Enclosures, covers, storage boxes |
Real-World Applications
For manufacturers like Toyin Acrylic Products Co., Ltd. (TOYIN), UL 94 HB and V-2 ratings are crucial for ensuring that acrylic products—such as display racks, storage boxes, and protective covers—meet fire safety regulations in home, office, and retail environments. For example, an acrylic display stand used in a retail store may require a V-2 rating to comply with US or EU safety standards, especially if installed near electrical equipment.
Why does this matter?
- Compliance: Many markets require UL 94 certification for plastic components.
- Safety: Reduces fire risk in public and private spaces.
- Market Access: Products with proper ratings are more likely to pass regulatory checks and be accepted by global brands.
Related Concepts
- UL 94: The overarching standard for plastic flammability testing.
- ASTM E84 / EN 13501: Standards for building materials; focus on surface burning, not small parts.
- Flame Retardant: Additives or material properties that slow ignition and flame spread.
- UL Yellow Card: Official certification document for material flammability ratings.
For a deeper dive into UL 94 and its importance for acrylic products, visit UL Solutions or SpecialChem’s UL 94 Guide.
Looking for custom acrylic products that meet global safety standards? Explore TOYIN’s certified solutions for home, office, and retail: www.toyinltd.com