ISO 19702 pdf download – ISO 19702 pdf Toxicity testing of fire effluents —Guidance for analysis of gases and vapours in fire effluents using FTIR gas analysis.
7.1 Unlvarlate
These methods .,clude peak height and peak areaS.
Specific regions of the spectra of the specific gas are selected to be as tree as possible of interference froni other gases. It may be necessary to select more than one region. The fre gas spectra are then compared to that of the specified gas and, where necessary, the spectrum of interfering gases can be subtracted from that of the fire gas spectrum. The specified fe gas is then quantified using either the height or area of a selected peak or peaks and corrected for any non-linearity of the absorptIon/concentration characteristics of the gas.
These methods are simple and can be applied only for smiple cases, I.e. cases with minimal Interference between different fe gases. This is often not the case for fire effluents where there are numerous gases present ii the fire effluents. For complex mixture of gases, the univanate methods can provide erroneous results. To identity errors from urwvarlate methods. Ills important to manually inspect selected spectra to Identify possible intertenng gases and erroneous concentration calculations.
7.2 Multivariate analysis
These methods include the following;
— multilinear rewession (MIR):
— dasalcal least squares (CIS);
— ridged regression (RR);
– partial least squares (PLS):
riplicit non-linear latent regression;
— target factor analysis (TFA).
It is not proposed to discuss these techniques, as they are extremely complex. In essence, they use a number of mathematical models and processes to combine the spectra of known or suspected interferences to match the fire gas spectrum. The spectrum of the specified gas is then identified and the gas quantified using correction curves to allow for any non-linearity in the response of the FTIR.
These methods require the Interferences to be Identified within the analysis method or selected from a large database of spectra by the analytical method.
7.2.1 General observations
It is possible to develop FTIR analysis methods to provide good levels of accuracy, especially for a single gas or for a simple mixture of known gases; but it must be acknowledged that as the complexity of the gas mixture Increases and the number of known and unknown interferences are increased, then the accacy of the FTIR analysis can decrease In practice, it may be desirable to use a combination of both univanale and multivariate methods to analyse fire gas samples which inherently contain a large number of gases, many of which may be unknown or even unexpected
It Is increasingly common for most spectroscopéc software packages to Include most of the methods listed above. The calibration procedure will therefore depend on the reqi,srements of the method selected and the software package being used.
8 Test start-up
Before a test, the sampling system and gas sampling cell are heated 10 their chosen wvrking temperatures Ample time should be alowed for temperature equilibration of the whole sampling system. A new or clean filter should be used when determining acid gases The throughput of the lR beam shall be checked to ensure correct performance of the spectrometer and suitable wave number reproducibility. A background reference spectrum is obtained.
An optimized sampling device has been proposed in the SAFIR project.The Figure A.1 gives a schematic ofthe optimized sampling device.
The point for gas collection in the exhaust duct shall be placed at a distance where the gaseous mixtureis homogeneous and the gas flow is not disturbed.
The distance between the combustion area and the probe should be as short as possible to avoidcondensation.
The filter shall be placed between the probe and the transfer line. Another filter may be used between thelline and the gas cell to protect the cell from fine soot particles.
The flow meter shall be placed after the pump and it is recommended to trap the water between the pumpand the flow meter.
– The temperatures of the filter, sampling line and gas cell should be as similar as possible.
ISO 19702 pdf download – ISO 19702 pdf Toxicity testing of fire effluents —Guidance for analysis of gases and vapours in fire effluents using FTIR gas analysis
