​Ceiling Performance FAQs

1. What is NRC?
   NRC means Noise Reduction Coefficient. It is the average sound absorption coefficient measured at four frequencies: 250, 500, 1,000, and 2,000 Hz expressed to the nearest integral multiple of 0.05. It is measured in accordance with ASTM C423 and rates the ability of a ceiling, wall panel, or other material to absorb sound. The NRC is averaged over all angles and sound frequencies, and represents the average absorption per unit area. The NRC ranges from 0.00 (concrete floor) to 1.00 (high performance acoustical products like OPTIMA).
2. What is CAC?
   CAC means Ceiling Attenuation Class. It is a single-number rating that represents a ceiling system’s efficiency as a barrier to airborne sound transmission between adjacent closed spaces that share a common air plenum. This is a 2-pass test – sound will radiate through the source room’s ceiling as well as the receiving room’s ceiling as defined by ASTM E1414.
3. What is NIC?
   NIC means Noise Isolation Class. It is a single-number rating calculated in accordance with ASTM E413 using measured values of noise reduction. Whereas STC, CAC, and NRC are laboratory measurements of material performance, NIC provides an estimate of the total sound isolation between two enclosed spaces that are acoustically connected by many paths.
4. What is AC?
   AC means Articulation Class. It is a single-number rating for the performance of a ceiling in an open office with a partial-height divider. Defined by ASTM 1111, the attenuation of sound that travels over a divider and reflects off of the ceiling is measured at human speech frequencies. Ceilings best suited for use in the open office have AC values of 170 or greater. A standard acoustical ceiling (NRC 0.55) will normally have an AC of 150. Non-absorptive materials, such as gypsum board, will have an AC of 120. The highest AC that can be achieved by a ceiling is 230.
5. What is Sabin?
   Sabin is the unit of measure for total sound absorption of an acoustical object. For items like baffles, clouds, and canopies the entire object is tested and the acoustical absorption of each object is measured. For continuous ceiling material the total absorption is measured but it is divided by a known surface area producing absorption coefficients.
6. What is the difference between STC and CAC?
   STC means Sound Transmission Class. It is a single number rating corresponding to the sound reduction from one side of a barrier to the other. The STC is used to rate the performance of walls, partitions, windows, etc. For this test sound is passing through the material once – from one side to the other. In a CAC test sound passes from a source room, through the ceiling plane, across a shared air space and then through the ceiling plane of the receiving room.

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1. What is flame spread and smoke developed? How does this relate to fireguard and class A?
   Surface Burning Characteristics Rating (Formerly Flame Spread Rating)
   The Surface Burning Characteristics Rating of a material is a number, calculated from the results of a test, which indicates the relative rate at which flame will spread over the surface of the material as compared with flame spread on asbestos-cement board, which is rated 0, and on red oak, which is rated 100. Note that this rating is not the rate at which the flame actually spreads along the surface and is not at all an indication of the fire resistance of the material.
   

   Test Method 
   The test used to obtain results from which a rating is calculated is called "Method of Test of Surface Burning Characteristics of Building Materials" (NFPA No. 255, ASTM E84, UL No. 723). It is commonly known as the Tunnel Test; the test equipment is referred to as the 25' tunnel. Although several small-scale tests have been developed to predict flame spread ratings based on the tunnel test, these are primarily bench tests for product development. The National Fire Protection Association (NFPA) has not accepted any alternate methods for determining the flame spread characteristics of materials to be used in buildings; for this purpose, NFPA recommends only the Tunnel Test.

   The sample of material to be tested (minimum 18" wide, 25' long) is installed beneath the removable top panel. A gas flame is applied at one end and a regulated constant draft is directed through the tunnel from the flame end. The progress of the flame front along the sample is observed through side windows. A flame spread rating is a relative number. It has no direct relationship to a fire resistance rating, which is a rating in hours determined by an entirely different test, known as "Standard Methods of Fire Tests of Building Construction and Materials" NFPA No. 251, ASTM E119, UL No. 263). The exposed surface (ceiling) of an assembly with a high (good) fire resistance rating; and, conversely, the exposed surface of an assembly possessing very little fire resistance could both have a very low flame spread. There is not necessarily any correlation between the two ratings. There are numerous laboratories with 25 foot tunnels that do commercial testing.

   Applying the Ratings
   Relative figures on how fast fire will spread over the surface of the material allow fire protection engineers to deal with problems involving possibilities of (1) people being trapped within a building before orderly evacuation can be accomplished, and (2) rapid spread of fire through an entire building or area of a building before the usual fire protection measures can be put into effect to control or extinguish the fire.

   Building codes generally group flame spread ratings into classifications as follows:

   • Class 25 or Class I or Class A = Flame Spread Ratings 0-25
   • Class 75 or Class II or Class B - Flame Spread Rating 26-75
   • Class 200 or Class III or Class C - Flame Spread Rating 76-200
   • Class IV or Class D = Flame Spread Rating 201. 

   ASTM E119 and FIRE GUARD Products ASTM E119 is an assembly test, not a product test. This is the test method (UL) used for fire resistance rated assemblies. UL does make note of this in the UL Fire Resistance Directory under INTRODUCTION. Therefore, any of our FIRE GUARD products have been tested according to this method.

2. Will ceilings alone provide me with a one-hour rating?
   

   No, Fire resistance ratings apply to a floor/ceiling or roof/ceiling assembly in its entirety. Individual components, such as ceiling panels or suspended grid systems, are not assigned fire resistance ratings. If your architect has not yet determined which UL design should be followed for your specific project, you may have to select a UL Design for code official approval. If so, here is how to select the correct UL fire-rated assembly: 

   • Establish the hourly rating needed to meet code requirements.
   • Determine the existing or planned building elements, including structural, mechanical, electrical and finish materials, in the fire-rated assembly. 
   • Refer to the Fire Resistive Rating Summary in the back of the Armstrong ceilings catalog to determine which UL design numbers resemble your building. The summary is divided into categories based on construction type and components. 
   • Submit the chosen UL design to the code official for approval.
3. Which Armstrong ceilings and grid can I use if a fire-rated assembly is required?
   Only Armstrong "FireGuard" ceilings and grid can be used in fire-rated assemblies. These products are identified by our FIRE GUARD icon.
4. How do types BF, P and PC in UL designs relate to actual products?
   

   PC=FINE FISSURED CERAMAGUARD #605, #607 and #608
   P=All other products designated FIREGUARD

5. How do I obtain an hourly rating for a corridor?
   

   Below is a list of construction practices used in the industry to obtain an hourly rating for a corridor:

   • If the corridor walls do not go to the deck, find the appropriate UL Design and install the specified fire-resistive ceiling and fire-resistive grid in corridor ceiling and adjacent areas. 
   • If the walls in the corridor run to the deck above, find the appropriate UL Design and install the specified fire-resistive ceiling and fire-resistive grid in the corridor ceiling; fire-damp where walls are penetrated