Superpressure

's NBS* (NIST)** Smoke Density Chamber is the first commercial instrument that measures smoke properties (

photometrically

self-integrating vertical optical system

With the vertical optical system, a completely integrated determination of specific optical density is obtained as the layers of smoke accumulate and light transmittance is reduced. These results are precisely plotted in terms of specific density. The specific optical density value expresses the smoking properties of any quantity of material, contained within any volume or space, when viewed at any distance. The relationship under this method is expressed by the following formula:

Ds = V / AL log 100 / T

The specific optical density (Ds) is a dimensionless attenuation coefficient of a specimen of given thickness. It represents the optical density measured over unit path (L) within a chamber of unit volume (V) produced from a specimen of unit surface (A) . . . where (T) is the percent of light transmittance.

The above formula is derived from

Bouguer's law of extinction

This method of measuring smoke assumes the applicability of Bouguer's law to the attenuation of light by smoke, and smoke quantity is therefore reported in terms of optical density rather than light absorption or transmittance. Optical density is the single measurement most characteristic of a "quantity of smoke" with regard to visual obscuration.

Superpressure

*National Bureau of Standards "National Institute of Standards and Technology (NIST)

OPERATION

In operation, a 3" x 3" specimen in a special holder with a fixed orientation and fixed area of exposure is exposed to a precisely adjusted and regulated radiant source for radiant non-flaming tests. For radiant-flaming exposure, the specimen is also subjected to multi-jet impingement by a special flaming jet with precise setting of both gas and air supply. As smoking occurs, the collimated light is attenuated and read-out to an optical density of 6 is obtained by means of the solid state photomultiplier photometer.

The spectral response of the system does not deviate excessively from the standard ICI luminosity curve representing the human eyes' sensitivity (i.e., not more than that corresponding to a type S4 response with a tungsten source at 2200°K.). The light source operating through a voltage-regulated power supply is maintained at 4 volts (±0.2) to provide reproducible light source characteristics.

By photometer sensitivity attenuation in conjunction with the movable neutral density filter, it is possible to obtain optical density determinations corresponding to a transmittance of only 0.0001 percent of the original incident light.

ESTABLISHED AS STANDARD PROCEDURE

The Gross et. al. test procedure was established under specification E662 Fire Test Methods, American Society for Testing and Materials, after round-robin testing to prove the test procedure's statistical accuracy and reproducibility (NBS Tech Notes No. 708). The list of products or materials requiring smoke testing since the establishment of ASTM Specification E662 is increasing. This list includes items from office furniture to materials used in aerospace applications. Additional information pertaining to products or materials requiring smoke testing is listed under the section entitled descriptive literature.

FURNACE AND BURNER

The furnace for non-flaming radiant and flaming-radiant smoke production provides highly concentrated, uniform irradiance of 2.5 watts/cm2 over a 3" diameter opening, so that heat is concentrated on the sample with a minimal heating effect on the balance of the system.

The furnace temperature is adjusted by means of a calibrated

Gardon Radiometer

PHOTOMETER

The photometer system includes a voltage regulated light source, a dual lens, collimated 36" light beam passing vertically through the test space, a neutral density filter to provide two decades of attenuation and range, a light source compensating filter to adjust for variations in photomultiplier luminous sensitivity, a heated lower chamber window to minimize corrections for condensation, and a multi-range solid?state photomultiplier photometer. The multiplicity of controls enables system adjustment through a wide range of variables. The increase of optical density which occurs with the generation of smoke is indicated on the photometer and may be recorded on a recorder or computer.

The photometer features four fixed steps of readout for transmittance (100%, 10%, 1 % and 0.1 %), automatic zero, and dark current and sensitivity adjusts. The movable neutral density-2 filter extends the range of sensitivity of the system to 0.01 to 0.001 % of transmittance. The photomultiplier housing permits installation of attenuator discs or slits or special filters. It is provided with a two blade shutter assembly which permits easy movement of the neutral density filter in or out of the light path, without disturbing text conditions.

EXHAUST AND GAS SAMPLING

The chamber is provided with a centrifugal fan for venting the products through an exterior exhaust system after completion of the test. In normal testing, the effluents are retained, providing cumulative data throughout the test period. The effluent may be sampled or withdrawn through the sealed tube fitting in the roof during the test or after the test is completed. Effluents are exhausted from the chamber by opening the front wall and floor dampers which automatically starts the blower providing rapid evacuation.

SAMPLE HOLDERS

Stainless steel sample holders for both melting and non?melting samples are provided to accommodate sample thicknesses ranging from films to 1" panels. Sample holders are designed to expose exactly the same surface area in the same furnace orientation while protecting the edges and rear of the test sample from direct irradiance. A sample mover rod passing through the rear wall, and operated from the front, permits movement of the sample holder or Radiometer along two support rods to an exact position in front of the furnace without the need to open the chamber.

RADIOMETER

The furnace is adjusted at regular intervals to assure reproducible irradiance of the sample under both the non-flaming and flaming modes of exposure by means of the Radiometer, calibrated in accordance with National Bureau of Standards procedures and Standard Reference. A water cooled heat flux gauge is supplied for FAA testing.

DESCRIPTIVE LITERATURE

Department of Transportation, Advance Notice,

Smoke Emission Testing of Materials

Specifications Governing the

Flammability and Smoke Developed Ratings of Carpets.

Interlaboratory Evaluation of Smoke Density Chamber. National Bureau of Standards TECHNICAL NOTE 708 (CONDENSED)

U. S. Department of Housing and Urban Development, Operation Breakthrough,

Smoke Testing Criteria 8.4.3.1, C.4.3.1, D.4.3.1, E4.3.1, F.4.5.1, L.4.2.1.

ASTMINBS Round Robin Test Data Report on Smoke Density Chamber?National Bureau of Standards TECHNICAL NOTE 708A

The Smoke Density Chamber Method for Evaluating the Potential Smoke Generation of Building Materials. National Bureau of Standards TECHNICAL NOTE 757

Standard Test Method for Specific

Optical Density of Smoke Generated By Solid Materials

Smoke Generated By Solid Materials, NFPA STD 258, National Fire Protection Association, 470 Atlantic Ave., Boston, MA 02210

MODIFICATIONS

• Smoke chambers modified to conform to

  Airbus Industries specification ATS 1000.01

  are available.
• Special flame burners conforming to

  British Navy specification NES 711

  are available.
• Special sample holders for testing insulated wire are available.

ABOUT US

Based on over 60 years of expertise in the

high pressure