Understanding Flammable Liquid Classification (Class 3) for International Transport
1. Core Classification Criteria: Beyond Flash Point
According to the United Nations Model Regulations, a Flammable Liquid (Class 3) is primarily defined by its flash point: a closed-cup flash point (c.c.) not exceeding 60°C, or an open-cup flash point (o.c.) not exceeding 65.6°C. Liquids, mixtures, or suspensions meeting this definition fall under this category.
Crucially, classification also depends on transport conditions:
- Liquids offered for transport at temperatures at or above their flash point.
- Substances transported in a liquid state at elevated temperatures that release flammable vapors at or below the transport temperature.
2. The Critical Exception: Sustained Combustibility
A key provision in the regulations states that flash point alone is not the sole determinant for liquids with a flash point above 35°C but not exceeding 60°C.
Exemption Rule: Such a liquid is not classified as Class 3 if it does not sustain combustion.
Demonstrating Non-Sustained Combustion (meeting any one criterion):
- A "non-sustained" result in the UN Manual of Tests and Criteria, Part III, Section 32.5.2 (L.2 test).
- A fire point greater than 100°C (per ISO 2592:2000 or ASTM D92).
- A water-miscible solution containing more than 90% water by mass.
3. Practical Implications for International Logistics
This exception is why many common products like alcohol-based sanitizers (flash point 35-60°C) are often shipped as general cargo, not hazardous materials—they typically fail the sustained combustibility test.
Key Takeaway for Shippers:
Do not rely solely on the Safety Data Sheet (SDS) flash point data for classification. For liquids with flash points in the 35-60°C range, a full dangerous goods classification including the sustained combustibility test is essential to obtain a valid Transport Condition Assessment Report. This report is mandatory for compliant booking, documentation, and handling under IMDG Code (sea) and IATA DGR (air) regulations.
Critical Reminder for International Shippers
- Flash point ≤35°C: Always classified as Class 3 flammable liquid. No sustained combustibility test needed.
- Flash point 35-60°C: Requires sustained combustibility testing to determine if Class 3 applies. A "non-sustained" result means general cargo classification.
- Flash point 60°C: Not classified as Class 3 under normal conditions (unless transported at elevated temperatures).
- Always obtain a valid Transport Condition Assessment Report from an accredited laboratory before shipping.
Summary Table: Classification Decision Path
| Flash Point Range | Sustained Combustibility Test Required? | Classification Result | Typical Examples |
|---|---|---|---|
| ≤35°C | No | Class 3 Dangerous Goods | Gasoline, acetone, ethanol (pure) |
| 35°C - 60°C (sustained combustion) | Yes - Positive | Class 3 Dangerous Goods | Some fuels, certain solvents |
| 35°C - 60°C (non-sustained) | Yes - Negative | General Cargo | Alcohol-based sanitizers, some aqueous solutions |
| 60°C | No | General Cargo | Many vegetable oils, high-flash solvents |
Disclaimer: This guide provides general information for flammable liquid classification based on UN Model Regulations. Always consult certified dangerous goods personnel, your freight forwarder, and the latest IATA DGR/IMDG Code editions for specific cargo requirements. Final classifications must be based on a valid Transport Condition Assessment Report from a qualified laboratory.