Appendix 1 – Fire Test Procedures for Smoke Generation

Reference document: ISO 5659-2, Plastics – Smoke generation – Part 2: Determination of optical density by a single-chamber test

Avoidance of danger to test operators

So that suitable precautions to safeguard health are taken, the attention of all concerned in fire tests is drawn to the fact that harmful gases are evolved in combustion of test specimens. Care must also be taken during cleaning operations on the smoke chamber to avoid inhalation of fumes or skin contact with smoke deposits.

Attention is drawn to the hazards arising from the hot radiator cone, and the use of a mains voltage electricity supply. A safety blow-out panel, as specified in paragraph 7.2.1.1 of standard ISO 5659-2, is essential for the protection of operators from the risk of explosion from sudden pressure surges.

1 Scope

1.1 This appendix specifies a method of measuring smoke production from the exposed surface of specimens of essentially flat materials, composites or assemblies not exceeding 25 mm in thickness, when placed in a horizontal orientation and subjected to specified levels of thermal irradiance in a closed cabinet with or without the application of a pilot flame. This method of test is applicable to all plastics and may also be used for the evaluation of other materials (e.g., rubbers, textile coverings, painted surfaces, wood and other materials).

1.2 Values of optical density determined by this test are specific to the specimen or assembly material in the form and thickness tested, and are not to be considered inherent, fundamental properties.

1.3 The test is intended primarily for use in research and development and fire safety engineering in buildings, trains, ships, etc., and not as a basis for ratings for building codes or other purposes. No basis is provided for predicting the density of smoke that may be generated by the materials upon exposure to heat and flame under other exposure conditions, nor has correlation been generally established with measurements derived from other test methods. The fact that this test procedure excludes the effect of irritants on the eye shall also be taken into account when applying the test results.

1.4 It is emphasized that smoke production from a material varies according to the irradiance level to which the specimen is exposed. In making use of the results of this method, it shall be borne in mind that the results are based on exposure to the specific irradiance levels of 25 kW/m² and 50 kW/m².

2 Normative References

The following normative documents contain provisions which constitute provisions of this appendix:

.1 ISO 291, Plastics – Standard atmospheres for conditioning and testing;
.2 ISO 5659-2, Plastics – Smoke generation, Part 2: Determination of optical density by a single chamber test; and
.3 ISO 13943, Fire safety – Vocabulary.

3 Terms and Definitions

For the purposes of this appendix, the terms and definitions given in standard ISO 13943 and the following apply.

3.1 Assembly is fabrication of materials and/or composites, for example, sandwich panels. This may include an air gap.

3.2 Composite is a combination of materials which are generally recognized in building construction as discrete entities, for example, coated or laminated materials.

3.3 Essentially flat surface is a surface in which departure from a plane does not exceed ± 1 mm.

3.4 Exposed surface is that surface of the product subjected to the heating conditions of the test.

3.5 Intumescent material is a dimensionally unstable material, developing a carbonaceous expanded structure of thickness greater than 10 mm when exposed to a heat source during the test with the cone heater at 25 mm from the specimen.

3.6 Irradiance (at a point on a surface) is radiant flux incident on an infinitesimal element of the surface containing the point divided by the area of that element.

3.7 Material is a basic single substance or uniformly dispersed mixture, for example, metal, stone, timber, concrete, mineral fibre, polymers.

3.8 Mass optical density (MOD) is a measure of the degree of opacity of smoke in terms of the mass loss of the material under the conditions of the test.

3.9 Optical density of smoke (D) is a measure of the degree of opacity of smoke; the negative common logarithm of the relative transmission of light.

3.10 Product is a material, composite or assembly about which information is required.

3.11 Specific optical density (Ds) is optical density multiplied by a factor which is calculated by dividing the volume of the test chamber by the product of the exposed area of the specimen and the path length of the light beam (see paragraph 9.1.1).

3.12 Specimen is a representative piece of the product which is to be tested together with any substrate or treatment. This may include an air gap.

4 Specimen Construction and Preparation

4.1 Number of specimens

4.1.1 The test sample shall comprise a minimum of nine specimens if all three test conditions are to be tested: six specimens shall be tested at 25 kW/m²(three specimens with a pilot flame and three specimens without a pilot flame) and three specimens shall be tested at 50 kW/m² without a pilot flame.

4.1.2 An additional number of specimens as specified in paragraph 4.1.1 above shall be used for each face, in accordance with the requirements in paragraph 2.2 of part 2.

4.1.3 An additional nine specimens (i.e. three specimens per test mode) shall be held in reserve if required by the conditions specified in paragraph 8.8.2.

4.1.4 In case of intumescent materials, it is necessary to make a preliminary test with the cone heater at 50 mm from the specimen. Therefore, at least two additional specimens are required.

4.2 Size of specimens

4.2.1 The specimens shall be square, with sides measuring 75 ± 1 mm.

4.2.2 Materials of nominal thickness 25 mm or less shall be evaluated at their full thickness. For comparative testing, materials shall be evaluated at a thickness of 1 ± 0.1 mm. All materials consume oxygen when they burn in the chamber, and the smoke generation of some materials (especially rapid-burning or thick specimens) is influenced by the reduced oxygen concentration in the chamber. As far as possible, materials shall be tested in their end-use thickness.

4.2.3 Materials with a thickness greater than 25 mm shall be cut to give a specimen thickness between 24 mm and 25 mm, in such a way that the original (uncut) face can be evaluated.

4.2.4 Specimens of multi-layer materials with a thickness greater than 25 mm, consisting of core material(s) with facings of different materials, shall be prepared as specified in paragraph 4.2.3 (see also paragraph 4.3.2).

4.3 Specimen preparation

4.3.1 The specimen shall be representative of the material and shall be prepared in accordance with the procedures described in paragraphs 4.3.2 and 4.3.3. The specimens shall be cut, sawn, moulded or stamped from identical sample areas of the material, and records shall be kept of their thicknesses and, if required, their masses.

4.3.2 If flat sections of the same thickness and composition are tested in place of curved, moulded or speciality parts, this shall be stated in the test report. Any substrate or core materials for the specimens shall be the same as those used in practice.

4.3.3 When coating materials, including paint and adhesives are tested with the substrate or core as used in practice, specimens shall be prepared following normal practice, and in such cases the method of application of the coating, the number of coats and the type of substrate shall be included in the test report.

4.4 Wrapping of specimens

4.4.1 All specimens shall be covered across the back, along the edges and over the front surface periphery, leaving a central exposed specimen area of 65 mm x 65 mm, with a single sheet of aluminium foil (approximately 0.04 mm thick) with the dull side in contact with the specimen. Care shall be taken not to puncture the foil or to introduce unnecessary wrinkles during the wrapping operation. The foil shall be folded in such a way as to minimize losses of any melted material at the bottom of the specimen holder. After mounting the specimen in its holder, any excess foil along the front edges shall be trimmed off where appropriate.

4.4.2.1 Wrapped specimens of thickness up to 12.5 mm shall be backed with a sheet of non-combustible insulating board of oven-dry density 950 ± 100 kg/m³ and nominal thickness 12.5 mm and a layer of low density (nominal 65 kg/m³) refractory fibre blanket under the non-combustible board.

4.4.2.2 Wrapped specimens of thickness of more than 12.5 mm but less than 25 mm shall be backed with a layer of low-density (nominal 65 kg/m³) refractory fibre blanket.

4.4.2.3 Wrapped specimens of thickness of 25 mm shall be tested without any backing board or refractory fibre blanket.

4.4.3 With resilient materials, each specimen in its aluminium foil wrapper shall be installed in the holder in such a way that the exposed surface lies flush with the inside face of the opening of the specimen holder. Materials with uneven exposed surfaces shall not protrude beyond the plane of the opening of the specimen holder.

4.4.4 When thin impermeable specimens, such as thermoplastic films, become inflated during the test due to gases trapped between the film and backing, they shall be maintained essentially flat by making two cuts of 20 mm long in parallel by 20 mm spacing in the centre in the film to act as vents.

4.5 Conditioning

4.5.1 Before preparing the specimens for test, they shall be conditioned to constant mass at 23 ± 2°C and 50 ± 5% relative humidity. Constant mass shall be considered to have been reached when two successive weighing operations, carried out at an interval of 24 h, do not differ by more than 0.1% of the mass of the test specimen or 0.1 g, whichever is the greater.

4.5.2 While in the conditioning chamber, specimens shall be supported in racks so that air has access to all surfaces.

Note 1: Forced-air movement in the conditioning chamber may be used to assist in accelerating the conditioning process.
Note 2: The results obtained from this method are sensitive to small differences in specimen conditioning. It is important therefore to ensure that the requirements in paragraph 4.5 are followed carefully.

5 Apparatus and Ancillary Equipment

The apparatus and ancillary equipment shall be in accordance with standard ISO 5659-2, Plastics – Smoke generation – Part 2: Determination of optical density by a single-chamber test.

6 Test Environment

6.1 The test apparatus shall be protected from direct sunlight, or any strong light source, to avoid the possibility of spurious light readings.

6.2 Adequate provision shall be made for removing potentially hazardous and objectionable smoke and gases from the area of operation, and other suitable precautions shall be taken to prevent exposure of the operator to them, particularly during the removal of specimens from the chamber or when cleaning the apparatus.

7 Calibration Procedures

Calibration of the test apparatus shall be carried out in accordance with standard ISO 5659-2, Plastics – Smoke generation – Part 2: Determination of optical density by a single-chamber test.

8 Test Procedures

8.1 Preparation of test chamber

8.1.1 Prepare the test chamber in accordance with the requirements of clause 9 of standard ISO 5659-2 with the cone set at 25 kW/m² or 50 kW/m². For intumescent materials the distance between the cone heater and the specimen shall be 50 mm and the pilot burner shall be positioned 15 mm down from the bottom edge of the cone heater.

8.1.2 If a test has just been completed, flush the test chamber with air until it is completely clear of smoke with the test chamber door closed and both exhaust and inlet vents open. Inspect the inside of the cabinet and clean the walls and the supporting framework if necessary (see paragraph 9.9 of standard ISO 5659-2). Clean the faces of the optical windows inside the chamber before each test. Allow the apparatus to stabilize until the chamber wall temperature is within the range 40 ± 5°C for tests with the radiator cone at 25 kW/m² or within the range 55 ± 5°C for tests with the radiator cone at 50 kW/m². Close the inlet valve.

8.1.3 For intumescent materials testing, the chamber wall temperature shall be within 50 ± 10°C for tests with the radiator cone at 25 kW/m² or within 60 ± 10°C for tests with the radiator cone at 50 kW/m².

Note: If the temperature is too high, the exhaust fan may be used to draw in cooler air from the laboratory.

8.2 Tests with pilot flame

For tests with the pilot flame, with the burner in its correct position, turn on the gas and air supplies and ignite the burner, check the flow rates and, if necessary, adjust the flow rates to ensure that the flame is as specified in paragraph 7.3.6 of standard ISO 5659-2.

8.3 Preparation of photometric system

Set the zero and then open the shutter to set the full-scale 100% transmission reading. Close the shutters again and check and reset the zero if necessary, using the most sensitive (0.1%) range. Recheck the 100% setting. Repeat the sequence of operations until accurate zero and 100% readings are obtained on the amplifier and recorder when the shutters are opened and closed.

8.4 Loading the specimen

8.4.1 Place a wrapped specimen, prepared in accordance with paragraphs 4.3 and 4.4. Place the holder and specimen on the supporting framework below the radiator cone. Remove the radiation shield from below the cone and simultaneously start the data recording system and close the inlet vent. The test chamber door and the inlet vent shall be closed immediately after the start of the test.

8.4.2 If preliminary tests indicate that the pilot flame is extinguished before the shield is removed, immediately relight the pilot burner and release the shield at the same time.

8.5 Recording of light transmission

8.5.1 Record the percentage light transmission and time continuously from the start of the test (i.e. when the radiation shield was removed). Switch the range of the photodetector amplifier system to the next decade when required, so that readings less than 10% of full-scale deflection are avoided.

8.5.2 If the light transmission falls below 0.01%, cover the observation window in the chamber door and withdraw the range-extension filter from the light path.

8.6 Observations

8.6.1 Note any particular burning characteristics of the specimen, such as delamination, intumescence, shrinkage, melting and collapse, and note the time from the start of the test at which the particular behaviour occurs, including the time of ignition and the duration of flaming. Also note the smoke characteristics, such as the colour and nature of the settled particulate matter.

Note 1: The smoke generation from some materials differs significantly depending on whether combustion occurs in a non-flaming or flaming mode (see standard ISO 5659-2). It is important, therefore, to record as much information as possible about the mode of combustion during each test.
Note 2: Coated and faced materials, including sheet laminates, tiles, fabrics and other materials secured to a substrate with an adhesive, and composite materials not attached to a substrate, can be subject to delamination, cracking, peeling or other types of separation affecting their smoke generation.

8.6.2 If the pilot flame is extinguished by gaseous effluent during a test and fails to re-ignite within 10 s, the gas supply to the pilot burner shall be immediately switched off (see paragraph 7.3.6 of standard ISO 5659-2).

8.6.3 If inflation of a thin specimen that has not been cut (see paragraph 4.4.4 above) has occurred, the results from that specimen shall be ignored and an extra cut specimen tested.

8.7 Termination of test

8.7.1 The initial test at each test condition in paragraph 8.8.1 shall last for 20 min to verify the possible existence of a second minimum transmittance value. If the minimum transmittance value is shown by the initial test to occur within the first 10 min, then subsequent tests for that test condition may have an exposure of 10 min. Otherwise, the tests shall last 20 min.

8.7.2 Extinguish the burner if the pilot flame has been used.

Note: The burner is extinguished in order to obviate the possibility of air mixing with combustion products present and causing an explosion.

8.7.3 Move the radiation shield below the cone.

8.7.4 Switch on the exhaust fan and, when the water manometer indicates a small negative pressure, open the inlet vent and continue exhausting until a maximum value of light transmission is recorded, with the appropriate range selected, and noted as the "clear beam" reading Tc, for use in correcting for deposits on the optical windows.

8.8 Repeat tests

8.8.1 Three specimens shall be tested under each of the following conditions:

.1 irradiance of 25 kW/m² in the presence of pilot flame;
.2 irradiance of 25 kW/m² in the absence of pilot flame; and
.3 irradiance of 50 kW/m² in the absence of pilot flame.

8.8.2 For each individual specimen, determine the percentage value of light transmission and from this calculate the appropriate specific optical density as given in paragraph 9.1. If the value of Ds max for any individual specimen differs from the average value for the set of three specimens of which it is part by more than 50% of that average for no apparent reason, test an additional set of three specimens from the same sample in the same mode and record the average of all six results obtained.

Note: Even in the same test condition, a specimen may burn with flaming and the others may not burn with flaming. This would be an apparent reason.

9 Expression of Results

9.1 Specific optical density Ds

9.1.1 For each specimen, produce a graph of light transmission against time and determine the minimum transmission Tmin. Convert Tmin to the maximum specific optical density Ds max by calculation to two significant figures using the following equation:

Where:

132 is a factor derived from V/AL for the test chamber,
V is the volume of the chamber,
A is the exposed area of the specimen,
L is the length of the light path.
Note: The transmission used in this equation is the measured transmission. For the first four decades this is the value recorded by the system. For the final two decades (where the range-extension filter is removed from the light path) the transmission must be calculated relative to the actual measuring range of 0.01% or 0.001%. For example, if the measuring range is set to 1% with the range-extension filter removed, then the actual measuring range is 0.01%. If the displayed transmission value is 0.523 then the actual measured transmission is 0.00523%.

9.1.2 If required, add, to each value of Ds max determined in paragraph 9.1.1, the correction factor C_f , which depends upon the use of the range-extension filter. The value of C_f is:

.1 Zero:
- .1 if the filter is in the light path at the time the transmission was recorded (T ≥ 0.01%); or
- .2 if the photometric system is not equipped with a removable filter; or
- .3 if the ND-2 filter is found to be of the correct optical density of 2; and
.2 as determined by the procedure described in paragraph 9.5 of ISO 5659-2, if the filter is moved out of the light path at the time it is measured (T < 0.01%).

9.2 Clear-beam correction factor Dc

For each specimen, record the value of the "clear beam" reading Tc (see paragraph 8.7.4) to determine the correction factor Dc. Calculate Dc as for Ds max in paragraph 9.1.1. Dc shall not be subtracted from Ds max. Do not record the correction factor Dc if it is less than 5% of Ds max..

10 Other References

"Calibration of heat flux meter", "Variability in the specific optical density of smoke measured in the single-chamber test" and "Determination of mass optical density (MOD)" should be referred to annexes A, B and C of standard ISO 5659-2.