The “ ISO 4589 Plastics - Determination of combustion behavior by oxygen index” standard, developed by the International Organization for Standardization (ISO) , consists of the following sub-sections published under the same title:
In the ISO 4589-2 standard, the material can be tested either as a rigid specimen or as a flexible specimen in a specific holder mounted in a transparent chimney through which a mixture of oxygen and nitrogen flows upwards in a laminar flow pattern. Once the specimen has been conditioned, the test is carried out at room temperature. This is the simplest form of the test. In the top surface ignition procedure, the applied flame is allowed to impinge on the top surface of the specimen for a maximum of 30 seconds and the flame is periodically removed every 5 seconds to check that the specimen is burning. This also ensures that the temperature of the specimen does not rise excessively, as this would normally reduce the oxygen index (OI) value. In the spread ignition procedure, the flame is allowed to impinge on the vertical edges of the specimen to a depth of approximately 6 mm. In the thin film procedure, the film is wrapped in a 45 degree spiral around a rod and taped, the rod is then pulled and the top end of the specimen is cut off at a distance of 20 mm from the top.
In ISO 4589-3, the material is tested in the same way, but the test is performed in a heated column where both the incoming gas and the gas passing through the column are heated. At the beginning of the test, the sample and the sample holder are preheated in the gas flow for 240 s plus/minus 10 s to ensure that they reach temperature equilibrium before the test. The flame is applied for the same duration as in ISO 4589-2.
This standard provides a procedure for determining, for comparative purposes, whether the oxygen index (OI) values of a material are above a specified minimum value. It may not be possible to apply these methods satisfactorily to materials that exhibit a high degree of shrinkage when heated, for example highly oriented thin film.
A small test sample is supported vertically in a mixture of oxygen and nitrogen flowing upward through a transparent chimney. The upper end of the sample is ignited and the subsequent burning behaviour of the sample is observed to compare the time during which combustion continues or the length of time the sample burns with the limits specified for that type of combustion. By testing a series of samples with oxygen at different volume fractions, the oxygen index (OI) is estimated. Alternatively, for comparison with a specified oxygen index, three test samples are tested using the relevant oxygen volume fraction. At least two of these must give an “oxygen” response to meet the specified oxygen index.
The methods are provided for testing materials in the form of vertical bars or sheets up to 10,5 mm thick, self-supporting at the test temperature. However, they are not applicable to the V-shape, which requires a supporting frame as defined in ISO 4589-2. These methods are suitable for solid, laminated or cellular materials characterized by an apparent density of 100 kg/m3 or greater. The methods are also applicable to some cellular materials having an apparent density of less than 100 kg/m3. A method is provided for testing flexible sheet or film materials while vertically supported.
This standard also includes a method for determining the temperature at which the oxygen index of small vertical test specimens in air is 20,9 percent under specified test conditions. The temperature at which this occurs is defined as the flammability temperature, and the method is limited to determining temperatures less than 400 degrees. The method is not applicable to materials having an oxygen index greater than 20,9 percent.
These methods may not be able to be applied satisfactorily to materials that exhibit high levels of shrinkage when heated, such as highly oriented thin films.
The method described in the ISO 100 standard is valid for the evaluation of flame spread properties of cellular materials with a density of up to 3 kg/m3582.
The high gas velocity oxygen index expresses the minimum volume fraction of oxygen in a mixture of oxygen and nitrogen at a specified gas velocity that will support flame combustion of a material under specified test conditions.
A small test sample is supported vertically in a mixture of oxygen and nitrogen flowing upwards through a transparent chimney. The volume fraction of oxygen in the gas mixture is predetermined, controlled and measured. The vertical velocity of the gas mixture gas is predetermined, controlled and measured. The upper end of the sample is ignited and the subsequent combustion behaviour is observed to compare the burnt length of the sample with the specified limits. The high gas velocity oxygen index (HOI) is determined from a series of tests using different oxygen volume fractions.
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