The highest flammability rating typically used for materials is "Class A" or "Class 1." This rating represents the lowest level of flammability and indicates that the material has excellent fire resistance. Class A or Class 1 materials have a low tendency to ignite, burn slowly, and contribute minimal heat release during a fire. They are considered highly flame-resistant.
Flammability ratings can vary depending on the standard or testing method used. For example, in the United States, materials tested according to ASTM E84 may receive a rating of Class A, B, or C, with Class A being the highest rating. In the European Union, materials tested according to EN 13501-1 are classified as A1, A2, B, C, D, E, or F, with A1 being the highest level of non-combustibility.
UL 94-5VA Surface Burn; Burning stops within 60 seconds, test specimens MAY NOT have a burn-through (no hole). This is the highest (most flame retardant) UL94 rating.
It's important to note that the specific flammability rating systems and classifications may differ depending on the industry, country, and standards being applied. It's essential to consult the appropriate standards and regulations for the specific context in which the flammability rating is being considered.