More information on listing services for fire ratings is provided in NCMA FAQ 21-14, What is the difference between fire resistance ratings for masonry assemblies obtained through IBC versus a listing service such as UL or FM? (ref. The system also is somewhat inflexible in that little variation from the original tested wall assembly is allowed, including unit size, shape, mix design, constituent materials, and even the plant of manufacture. The listing service also monitors materials and production to verify that the concrete masonry units are and remain in compliance with appropriate standards, which usually necessitates a premium for units of this type. Private commercial listing services allow the designer to select a fire rated assembly that has been previously tested, classified and listed in a published directory of fire rated assemblies. The calculation method is fully described in ACI/TMS 216.1 and IBC Section 722, and determines fire resistance ratings based on the equivalent thickness of concrete masonry units and the aggregate types used to manufacture the units. The calculations are based on extensive research, which established relationships between the physical properties of materials and the fire resistance rating. Of these, the calculation method is an economical and commonly used method of determining concrete masonry fire resistance ratings.
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