The Reaction-to-Fire classification is designated by a letter from A to F. Four standardized tests are used to classify a material:
- EN ISO1182: Non-combustibility test. It measures mass loss, duration of sustained flaming, and increases in furnace temperature from the burning of the specimen. This test can in principle only be met by intrinsically non-flammable materials such as inorganic materials.
- EN ISO1716: Determination of the Calorific Value. Only materials with less than 1% organic substance can meet this in general.
- EN 13823: Single Burning Item (SBI) Test. A flame is directed directly onto the surface of the material. Measured is the FIGRA (Fire Growth Rate Index) which is related to the Heat Release Rate at the Cone Calorimetry Test, THR (Total Heat Release), and SMOGRA (Smoke Growth Rate Index).
- EN ISO11925-2: Ignitability Test. Similar to UL testing.
Table 1 gives a summary of the classes and tests:
| Class | Test Method | Comments |
| A1 | EN ISO1182 and EN ISO1716 | Metal, inorganics |
| A2 | EN ISO1182, EN ISO1716 and EN 13823 (SBI) | Inorganics with organic content below 1% |
| B | EN13823 and EN ISO11925-2 | |
| C | EN13823 and EN ISO11925-2 | |
| D | EN13823 and EN ISO11925-2 | |
| E | EN ISO11925-2 | |
| F | No performance determined | |
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