Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
Flammability of Polymeric Interior Materials: Guide to SAE J369 Horizontal Test Method
SAE J369-2019 defines a standardized, laboratory-scale horizontal test method for evaluating the burning behavior of polymeric materials used in the interiors of automotive vehicles and off-road machinery. The standard is technically equivalent to FMVSS 302, ISO 3795, and ASTM D5132, making it a cornerstone reference for material qualification and regulatory compliance. This guide walks through the procedure, classification system, and practical engineering considerations for implementing the test.
1. Understanding the SAE J369 Horizontal Burning Test
The test measures the rate and extent of flame propagation along a horizontally mounted specimen inside a draft-protected cabinet. A controlled flame from a Bunsen or Tirrill burner is applied to one end of the specimen for 15 seconds. The key apparatus specifications include a burner tube with 9.5 mm ± 0.3 mm inside diameter and a metal cabinet with dimensions approximately 380 by 355 by 200 mm. The burner is positioned so its top is 19 mm below the surface of the lower specimen frame.
Specimen Preparation and Conditioning
Accurate and repeatable results depend on careful specimen preparation. Standard specimen dimensions are 102 mm x 356 mm, with a minimum acceptable size of 95 mm x 300 mm. The maximum specimen thickness is 13 mm; thicker materials must be mechanically reduced from the side not facing the occupant compartment. For composite or layered materials, any layers that do not adhere at every point of contact must be tested separately. Fully adhering layers are tested as a composite assembly. Specimens must be conditioned for 24 hours at 23 °C ± 2 °C and 50% ± 10% relative humidity before testing. A minimum of five specimens is required for a valid test.
🛠️ Engineering Design Insight: To improve compliance, design interior materials with controlled flame propagation characteristics from the start. If the material has a grain pattern or specific construction direction, it must be tested in both the transverse and longitudinal directions. Testing the occupant-facing side down is mandatory. For materials that soften severely or have a width of 51 mm or less, a support frame with heat-resistant wires spanning at 25 mm intervals must be used to ensure the specimen remains in place during the burn.
2. Material Classification Categories
SAE J369 provides a clear, hierarchical classification system based on how the material behaves after the 15-second ignition period. Understanding these categories is essential for correct reporting and material selection.
| Classification | Burn Behavior Description | Report As |
|---|---|---|
| DNI | Does not ignite or support combustion. Flame front does not reach the first scribed line (38 mm). | DNI |
| SE/0 | Ignites but self-extinguishes before reaching the first scribed line (38 mm). | SE/0 |
| SE/NBR | Self-extinguishes before burning for 60 seconds and before the charred distance exceeds 51 mm from the timing start point. | SE/NBR |
| SE/B | Flame front passes the first scribed line but self-extinguishes before the second (254 mm). Burn rate is calculated if distance exceeds 51 mm or burn time is 60 s or greater. | SE/B |
| B | Burns the full 254 mm distance between the scribed lines. Burn rate is calculated (254 mm divided by burn time, converted to mm/min). | B |
| RB | Rapidly Burning. Flame front travels more than 51 mm beyond the first scribed line at a rate too fast to measure. Common for thin films or flash-igniting nap surfaces. | RB |
⚠️ Common Pitfall: A frequent testing mistake is misapplying the SE/0 and SE/NBR classifications. SE/0 requires the flame to extinguish strictly before the first scribed line (38 mm). If the flame passes the first line but stops within 51 mm and before 60 seconds, it is correctly classified as SE/NBR, not SE/0. Carefully monitor the flame front relative to the holder’s engraving marks.
3. Frequently Asked Questions
How does SAE J369 relate to FMVSS 302 and ISO 3795?
SAE J369 is technically equivalent to FMVSS 302 (49 CFR 571.302), ISO 3795, and ASTM D5132. While the regulatory requirement for passenger vehicles in the U.S. is FMVSS 302, many engineering specifications call out SAE J369 directly because it provides more detailed instructions on apparatus dimensions and sample preparation that are essential for reproducible laboratory work.
How should composite specimens with adhering layers be prepared?
If layers adhere at every point of contact, they are tested as a single composite specimen. The composite thickness must not exceed 13 mm. If non-adhering layers are present within 13 mm of the occupant surface, they must be tested individually. In all cases, the side of the material that faces the occupant compartment must be oriented downward during the test.
What is the difference between SE/NBR and SE/B?
SE/NBR (Self-Extinguishing / No Burn Rate) applies when the material extinguishes quickly—before 60 seconds and before the burn distance exceeds 51 mm from the timing start. SE/B (Self-Extinguishing / Burn Rate) applies when the material extinguishes after the first scribed line but before the second, and the burn distance or time exceeds the threshold, requiring a burn rate calculation. If the material burns the full 254 mm, it is classified simply as B.
What are the primary causes of test variability?
Common causes of variable results include insufficient specimen conditioning, incorrect burner fuel heating value (must be 37 MJ/m³ ± 1 MJ/m³), improper burner tube internal diameter (9.5 mm ± 0.3 mm), and using a non-standard cabinet setup. Additionally, the presence of a drip tray can alter burn characteristics; it must be removed if any difference is observed due to its presence. Always test the minimum of five specimens to establish a reliable average burn rate.
