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MCDM AG.COM | M A RCH /A PR IL 2017 | Medical Construction & Design 37 BY PAUL A. HOUGH A suspended acoustical ceiling repre- sents a signifi cant percentage of a room's surfaces. As such, it is critical to control- ling the noise level in a room and between rooms. It is also critical to controlling the growth of a fi re in a room by providing a separation between the room and the space above the ceiling. Because of this separation, a suspended ceiling can delay a fi re that starts in an occupied space from reaching potentially combustible materials in other areas of the building. Most codes rely on two fi re ratings to evaluate suspended ceilings: the Material Flame Spread/Smoke Developed Index Rating and the Fire-Resistance Assembly Rating. The ratings are the result of testing based on ASTM standards. Compliance is determined by independent testing ser- vices such as Underwriters Laboratories Incorporated. It is important to note that Flame Spread/Smoke Developed and Fire Resistance ratings are separate issues and must be addressed independently. Flame Spread/Smoke Developed ratings The Flame Spread Index is the relative rate at which a fl ame spreads over the sur- face of the material and not an indication of its fi re resistance. It is compared against an index of 0 for inorganic cement board and 100 for red oak. The Smoke Developed Index is a mea- sure of the amount of smoke a material emits as it burns. Like FSI, it is based on an arbitrary scale in which cement board has a value of 0 and red oak has 100. To be rated Class A for plenums, acous- tical ceiling panels require a FSI of 25 or less and a SDI of 50 or less — which is also the required standard for most healthcare applications. Class A-rated panels are designed to limit the spread of fl ames and production of smoke, and not to contain or compartmentalize a fi re. Fire-Resistance Assembly ratings The Fire-Resistance Assembly rating indicates the degree, measured in hours, to which an entire ceiling assembly, not individual components, withstands exposure to fi re and high temperatures. It essentially defi nes an assembly's abil- ity to prevent the spread of fi re between spaces and provide additional protection to the structure. Two types of fi re-resistance-rated construction assemblies have acoustical ceiling systems as a component: > Roof/Ceiling Assemblies – Includes the ceiling system, lighting, heating, ven- tilating and air conditioning outlets and other penetrants through the ceiling, the plenum, roof support structure and roof Acoustical Ceilings & Fire Safety Suspended ceiling systems play important role in controlling growth of fi re in facilities Panels with a tegular or reveal edge fi t tighter into the grid system than square lay-in panels, reducing the possibility of air leakage that may allow smoke transfer between spaces.