UL94 is the globally recognized flammability standard formulated by Underwriters Laboratories. It evaluates the fire resistance performance of non-metallic plastic materials via standardized horizontal and vertical combustion tests. Widely applied in electrical, electronic, home appliance and automotive industries, UL94 rating serves as the core reference for material selection and product safety design.
1. What is UL94 Burning Test
UL94 simulates real fire scenarios to assess key combustion indicators including ignition speed, self-extinguishing time and burning drips. Materials are classified into different flame retardant grades to judge fire hazard risks. Two mainstream test methods are commonly used: horizontal burning HB grade and vertical burning V grades (V0, V1, V2).
2. Vertical Burning Test (V0 / V1 / V2)
Vertical combustion test is the most popular testing method, mainly applied for electronic enclosures and insulating components.
Specimen Size
127mm × 12.7mm, maximum thickness 12.7mm
Test Procedure
Suspend the test sample vertically. Place absorbent cotton 305mm below the sample. Apply 19mm standard blue flame to the bottom edge for 10 seconds for the first ignition, then record burning duration. Re-ignite another 10 seconds after flame extinction, and record afterflame time. Repeat tests on 5 separate samples.
V Grade Performance Criteria
| Rating | Single Burning Time | Total Burning Time | Drip Ignition Risk | Afterflame Time |
| V0 | ≤10s | ≤50s | No cotton ignition | ≤30s |
| V1 | ≤30s | ≤250s | No cotton ignition | ≤60s |
| V2 | ≤30s | ≤250s | Allowed cotton ignition | ≤60s |
V0 represents the highest flame retardant level. Materials can extinguish rapidly without flammable drips after leaving fire source.
3. Horizontal Burning Test (HB Grade)
HB grade fits thin materials with basic fire safety requirements, such as decorative parts and common housings.
Specimen Size
125mm × 13mm, thickness range: 1.59mm ~ 6.35mm
Test Procedure
Place sample at 45° inclined angle with steel wire net 10mm underneath. Ignite the free end with 19mm standard flame for 30 seconds. Measure flame spreading speed between 25mm and 100mm scale marks.
HB Judgment Standard
- Burning speed less than 76mm/min for thickness below 3mm
- Flame extinguishes before reaching 100mm marking line
4. Typical Application of Each UL94 Grade
- V0: Connector, relay shell, lithium battery separator, high voltage insulation parts
- V1 & V2: Home appliance casing, power adapter housing, common structural plastic parts
- HB: Monitor frame, interior decorative plastic components
5. Industry Value & Safety Significance
Reasonable UL94 grade matching effectively prevents fire accidents caused by short circuit and overheating. For manufacturers, designers and procurement teams, mastering UL94 flame retardant rules helps standardize material selection, meet international safety certification requirements and improve overall product safety performance.
