1.1 This practice covers acoustical ceiling suspension systems and their additional requirements for application in areas subject to light to moderate seismic disturbance such as Uniform Building Code Seismic Zone 2, the BOCA Basic National Building Code where Av is less than 0.20 but greater than 0.10, and the Standard Building Code (SBC) where Av is less than 0.20 but greater than 0.05. This practice also covers areas subject to moderate to severe seismic disturbance such as Uniform Building Code Seismic Zones 3 and 4, the BOCA Basic National Building Code where Av is greater than 0.20, and the SBC where Av is greater than 0.20. The application of this practice is to be determined by local authorities. Current seismic maps published by recognized authorities such as those previously mentioned, should be consulted. Related material such as Open File 82-1033 and MS-812 Seismicity Map may also be consulted.

1.2 Specification C 635 and Practice C 636 cover suspension systems and their application without special regard to seismic restraint needs. They remain applicable and should be followed when this practice is specified.

1.3 This practice is not intended to stifle research and development of new products or methods which may simplify this specified application method. A variation, however, must be substantiated by verifiable engineering data.

1.4 A ceiling area of 144 ft² [13m ²] or less, surrounded by walls that connect directly to the structure above shall be exempt from this practice.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1.5 The values stated in either inch-pound or SI units are to be regarded as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the specification.