The standard "ISO 19021 Test method for the determination of gas concentrations in ISO 5659-2 using Fourier transform infrared spectroscopy" developed by the International Organization for Standardization (ISO) describes a test method suitable for analyzing wastes produced during pyrolysis and combustion of samples and products tested in accordance with the standard "ISO 5659-2 Plastics - Smoke formation - Part 2: Determination of optical density by a single-chamber test". This test method is based on Fourier transform infrared (FTIR) spectroscopy described in the standard "ISO 19702 Toxicity testing of fire wastes - Guide to the analysis of gases and vapors in fire wastes using FTIR gas analysis" and includes additional information on appropriate test apparatus and analyzer calibration for its application to this physical fire model.
This standard is intended for use in conjunction with ISO 5659-2 and ISO 19702. The test method provides gas concentrations over time during the entirety of an ISO 5659-2 test. This standard does not address the accuracy of this fire model for any product application, nor does it address the accuracy of gas concentrations relative to real-scale fire tests or fire scenarios.
For the future transformation of this standard into an international standard, it is intended to conduct an interlaboratory trial to amend Annex B. This standard does not include any toxicity assessment or provide input data for fire safety engineering.
Since combustion conditions vary depending on the rate of oxygen consumption in the enclosure during the ISO 5659-2 test, this physical fire model is not considered representative of any specific fire scenario. Therefore, it is difficult to compare test results with real-scale fire conditions. Consequently, if this test method is used to make comparisons between materials or products, it is intended to be done in conjunction with other fire tests.
For the purposes of this standard, the terms and definitions given in ISO 13943, ISO 5659-2 and ISO 19702 standards apply.
The studies forming the technical background to this standard are described in detail in this standard. Fire effluents are sampled continuously from a cumulative smoke chamber (ISO 5659-2). The gas sampling flow should be such that it is representative of the composition of the atmosphere in the chamber, and any effects of gas sampling systems (such as filters, probes, pipes, tubes and pumps) should be minimised. A filtration system prevents smoke particles from entering the chamber of the gas analyser. The concentrations of the specified gases in the sampled effluent flow are determined using FTIR spectroscopy in accordance with ISO 19702. The amount of atmosphere withdrawn from the chamber and used for FTIR analysis (approximately 20 L/min for 1,5 min) should be kept within limits that allow the sampling to be compensated for by the thermal effects of the radiant cone and the expansion of air due to combustion of the test sample. In this way, the chamber pressure is kept relatively constant throughout the sampling period. The time and distance the fire effluent travels through the gas sampling system should be minimised.
In these tests, the test apparatus specified in the ISO 5659-2 standard is used.
The general arrangement of the gas sampling system is specified below in addition to the requirements of the ISO 19702 standard. The gas sampling system shall consist of a sampling probe, a primary filter, a gas sampling line, a secondary filter, a gas cell, a pressure transducer, an optional cooler, a pump and a flow meter. The primary filter shall be placed directly after the probe. The gas analyzer shall be placed after the end of the sampling line and upstream of the pump. An example of a suitable sampling system is shown in the figure.
Other arrangements are possible if they respect the basic points of this standard: flow rate conditions, a main heated filter immediately after the sampling probe and a heated zone from the outlet of the smoke density chamber to the outlet of the FTIR gas cell. The smoke density chamber should be equipped with a pressure transducer that allows the internal chamber pressure P to be recorded as a function of time. A system using a higher extraction rate and recirculating the extracted gases back to the test device has been successfully tested by some laboratories when the pressure inside the box is kept relatively constant. For such systems, the user should estimate the deviation from the general arrangement described in this standard. The ISO 12828 series of standards can be used for such an assessment.
The sampling probe shall be made of a 5 mm internal diameter stainless steel tube with a closed end. It shall be fixed at the midpoint of the chamber ceiling and shall project 80 mm inward from the chamber ceiling. The probe shall have 40 55 mm diameter sampling holes, positioned at 70 mm, 2 mm and 3 mm measured from the chamber interior ceiling, facing the rear of the chamber. Some acid gases may react with the inner surface of the probe, causing loss of these gases. This is particularly important at low concentrations. A shielded thermocouple shall be placed near the mid-hole of the internal probe, 8 mm plus/minus 2 mm from the hole, to measure the temperature of the sampled gas. The temperature shall be recorded when sampling is performed to calculate the mass concentration of the gas species.
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