ASTM E662 Smoke Density

ASTM E662
Smoke Density Testing

ASTM E662 Smoke Density Testing

Specific Optical Density of Smoke Generated by Solid Materials

ASTM E662 (ASTM E-662) is a fire-test-response standard that covers determination of the specific optical density of smoke generated by solid materials and assemblies mounted in the vertical position in thicknesses up to and including 1 inch. Measurement is made of the attenuation of a light beam by smoke accumulating within a closed chamber due to non-flaming pyrolytic decomposition and flaming combustion. ASTM E662 results are expressed in terms of specific optical density which is derived from a geometrical factor and the measured optical density, a measurement characteristic of the concentration of smoke. For aerospace applications, smoke density testing is conducted in accordance with ASTM F814 or FAA Handbook Chapter 6. NFPA 258 is considered to be an equivalent standard to ASTM E662.

Which materials need to be tested in accordance with ASTM E662?

ASTM E662 testing is specified in transportation codes for trains and busses (NFPA 130 and 49 CFR Part 238). ASTM E662 is also specified in military specifications, such as MIL-STD-1623. ASTM E662 testing is often used in conjunction with other fire test methods that do not include a smoke measuring component (e.g. ASTM E162 and ASTM E648). The standard is intended for testing solid materials. Thermoplastic materials that overflow the sample holder trough will result in invalid test results.

Testing requirements should be verified with the Authority Having Jurisdiction (AHJ).

How is ASTM E662 testing performed?

Before the ASTM E662 testing begins, the specimens are placed into a preconditioning oven for 24 hours at 140 ± 5°F (60 ± 3°C) . After 24 hours, the specimens are moved to a conditioning environment that is held at 73 ± 5°F (23 ± 3 °C) and 50 ± 5% relative humidity until the specimens reach equilibrium moisture content as determined by weight.

The testing is conducted in an 18 ft³ chamber with a photometric system. The photometric system consists of a light source mounted at the bottom of the chamber and a photocell mounted at the top of the chamber. At the beginning of each testing day, the chamber is preheated and checked for airtightness.

An electrically heated radiant-energy source is positioned so as to produce an irradiance level of 2.5 W/cm² averaged over the central 1.5 inches (38.1 mm) diameter area of a vertically mounted specimen facing the radiant heater. The nominal 3 by 3 inch specimen is mounted within a holder which exposes an area measuring 2.56 by 2.56 inches (65.1 by 65.1 mm). This exposure provides the non-flaming condition of the test.

For the flaming condition, the radiant energy source is utilized, and a six-tube burner is added to apply a row of equidistant flamelets across the lower edge of the exposed specimen area and the trough on the specimen holder.

The test specimens are exposed to the flaming and non-flaming conditions within a closed chamber for 20 minutes or until 3 minutes after the minimum light transmittance value has been reached. The photometric system with a vertical light path is used to measure the varying light transmission as smoke accumulates. The light transmittance measurements are used to calculate specific optical density of the smoke generated during the time period to reach the maximum value.

What data will be included in an ASTM E662 report?

Specific Optical Density at 1.5 minutes - Ds (1.5)
Specific Optical Density at 4.0 minutes - Ds (4.0)
Maximum Specific Optical Density - Dm
Corrected Maximum Specific Optical Density - Dm (corr)

* Note: The average Ds (1.5), Ds (4.0), Dm or Dm (corr) or a combination of the averages may be used to demonstrate code compliance.

Interpreting ASTM E662 Results

ASTM E662 testing produces four values that are used to demonstrate code compliance: Ds (1.5), Ds (4.0), Dm, and Dm (corr). Regulations for the products intended application will specify which value has established limits.

Dm is the maximum specific optical density over the testing period. Dm (corr) is the corrected maximum specific optical density over the testing period. The Dm (corr) value corrects for soot accumulation on the glass between the photocell and light source. Prior to the adoption of this test method, it was customary to report the maximum smoke accumulated as Dm (corr), and for that reason it is included as a part of the test report. Subsequently, a statistical analysis of the round-robin data upon which the precision statement is based, showed that the Dm values were more uniform. Therefore, it is required that both Dm and Dm (corr) be reported.

Smoke density values determined by this test are speciﬁc to the specimen or assembly in the form and thickness tested and are not to be considered inherent fundamental properties of the material tested. Thus, it is likely that closely repeatable or reproducible experimental results are not to be expected from tests of a given material when specimen thickness, density, or other variables are involved.

The results of the test apply only to the thickness of the specimen as tested. There is no common mathematical formula to calculate the speciﬁc optical density of one thickness of a material when the speciﬁc optical density of another thickness of the same material is known.

ASTM E662 Test Specimen Preparation

Test specimens should be representative of the material or system which the test is intended to examine. The test specimens should be 3 by 3, +0, -0.03 inches (76.2 by 76.2, +0, -0.8 mm) by the intended installation thickness up to and including 1 inch (25.4 mm). At a minimum, six (6) specimens should be tested however Capital Testing recommends that Clients send in twelve (12) specimens to account for additional testing that may be necessary due to variable results and orientation screening.

The test method has proven sensitive to small variations in sample geometry, surface orientation, thickness (either overall or individual layer), weight, and composition. It is, therefore, critical that the replicate samples be cut, sawed, or blanked to identical sample areas. Specimens that include a pronounced grain pattern, process-induced orientation or other non-isotropic property, a minimum of three specimens shall be tested for each orientation in each test mode.

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Smoke Toxicity Testing (BSS 7239 and SMP 800C)

For some applications, smoke toxicity testing may be required. Capital Testing offers smoke toxicity testing in accordance with Boeing's BSS 7239 and Bombardier's SMP 800C. Smoke is generated and sampled while ASTM E662 or ASTM F814 testing is in progress. Additional specimens, beyond what are requested for ASTM 662 or ASTM F814 testing, are not needed to conduct smoke toxicity testing.

All gas toxicity testing is performed at Capital Testing using Dräger colorimetric pull tubes. The pull tubes change color when a specific gas reacts with the solid inside the tube. The length of the coloration or “stain” is proportional to the concentration of the gas when a fixed volume of sample gas is drawn through the tube. Dräger pull tubes are used as a semiquantitative indication of the presence of the particular gas.

Is Capital Testing an accredited ASTM E662 laboratory?

Capital Testing and Certification Services is ISO/IEC 17025 accredited to conduct ASTM E662 testing. ASTM F814 and 14 CFR Part 25, Appendix F, Part V are also covered under Capital Testing's scope of accreditation. Click Here for Capital Testing's full ISO 17025 scope.

Contact chrisp@capitaltesting.org for more information about ASTM E662, ASTM F814, or 14 CFR Part 25 smoke density testing.