What flame spread rating applies to Class B interior wall and ceiling finishes?

The flame spread rating for Class B interior wall and ceiling finishes is indeed a range of 26-75. This classification is established by testing materials in accordance with specific standards, such as ASTM E84 (also known as the Steiner Tunnel Test).

Materials with a flame spread rating of 26-75 are considered to have a moderate potential for flame spread. This means that while they can ignite and burn, they are less likely to contribute significantly to the spread of flames compared to Class A materials, which have a rating of 0-25 and are deemed to have a lower flame spread potential.

The importance of understanding these classifications lies in their role in building safety, particularly in egress paths and occupancy types. Knowing the flame spread ratings helps inspectors ensure compliance with building codes and enhance fire safety for occupants.

In contrast, other ranges do not accurately define Class B materials; for instance, Class A, with a rating of 0-25, indicates very low flame spread potential, while Classes C, D, and higher ratings signify increasingly unacceptable flame characteristics in building applications.