Plastics are widely used in daily life and industry, but their flammability poses safety risks. Flame retardant (FR) ratings measure plastics’ fire resistance and determine their application scope. The globally recognized standard is UL94 (equivalent to China’s GB/T 2408), which classifies FR performance via standardized burn tests. Below is a simplified breakdown:

1. Core Evaluation Logic

FR ratings are determined by standard burn tests + quantitative metrics:

Test types: Vertical burn (for rigid plastics) / Horizontal burn (for flexible plastics/films).

Key metrics: Burn duration, self-extinguishing ability, drip ignition risk, burn rate.

Supplementary metric: Oxygen Index (OI) – the minimum oxygen concentration needed to sustain combustion (OI < 21%: Flammable; 21% ≤ OI < 27%: Combustible; 27% ≤ OI < 32%: Flame-retardant; OI ≥ 32%: Highly flame-retardant).

Note: Plastic thickness affects ratings; labels include thickness (e.g., “UL94 V-0 @ 1.5mm”).

2. UL94 FR Ratings

UL94 categorizes ratings into two systems:

(1) Vertical Burn Ratings (for rigid plastics)

Test: Vertically mount samples, ignite the top twice (10s each) with 50W/500W flame:

V-0 (High FR): Single burn ≤10s; total burn ≤50s; no ignitable drips; no burn to fixture. Use: Circuit breaker housings.

V-1 (Mid-High FR): Single burn ≤30s; total burn ≤250s; no ignitable drips. Use: Motor enclosures.

V-2 (Standard FR): Same as V-1, but drips may ignite. Use: Appliance casings.

5VA/5VB (Extreme FR): 500W flame test; 5VA: No flame/drips/burn-through; 5VB: Limited drips/burn-through allowed. Use: Rail transit interiors.

(2) Horizontal Burn Rating (for flexible plastics/films)

Test: Horizontally mount samples, ignite one end; only HB (Basic FR):

HB40: ≤3mm thick; burn rate ≤40mm/min.

HB75: ≥3mm thick; burn rate ≤75mm/min or self-extinguish at 50mm. Use: Packaging materials.

3. Typical FR Ratings for Common Plastics

PC: V-0/5VA (OI ≥32%).

ABS: V-0 (OI 28-30%).

PP: V-2 (OI ~17% unmodified; V-1 with advanced FR).

PVC: HB (unmodified); V-0 (with FR, OI ≥30%).

PA (Nylon): V-0 (OI 29-31%).

Conclusion

Choose FR ratings based on application: V-0+ for critical components; HB for daily items. Halogen-free FR materials are preferred for environmental compliance. UL94 is the universal benchmark for safe, compliant plastic selection.