Materials can be tested for the degree of flammability and combustibility in accordance with the German [http://www.din.de/ DIN] 4102. DIN 4102, as well as its British cousin [http://www.bsi-global.com/ BS] 476 include for testing of passive fire protection systems, as well as some of its constituent materials.
The following are the categories in order of degree of combustibility and flammability:
A more recent industrial standard is the European EN 13501-1 - Fire classification of construction products and building elements—which roughly replaces A2 with A2/B, B1 with C, B2 with D/E and B3 with F.
B3 or F rated materials may not be used in building unless combined with another material that reduces the flammability of those materials.