Smoke gas analysis by Fourier transform infrared spectroscopy: The SAFIR project

The determination of toxic components from fire gases is difficult because the environment is hot, reactions are often temperature dependent, and a lot of soot may be produced. Due to the different properties of the gas components, a different time-consuming procedure for each species has traditionally been used. The use of FTIR (Fourier Transform InfraRed) spectrometers as a continuous monitoring technique overcomes many of the problems in smoke gas analyses. FTIR offers an opportunity to set up a calibration and prediction method for each gas showing a characteristic spectral band in the infra-red region of the spectrum. The objective of this project was to further develop the FTIR gas analysis of smoke gases to be an applicable and reliable method for the determination of toxic components in combustion gases related to fire test conditions. The project included the following tasks: small scale and large scale sampling; analysis, calibration and software techniques; the verification of the method; and an interlaboratory trial. The optimum probe design, filter parameters and the most suitable sampling lines in terms of flow rate, diameter, construction material and operating temperature have been specified. The gas adsorption onto the filter and the soot have been measured. In the large scale, special concern was given to the probe design and the effects of the probe location in relation to the fire source as well as practical considerations of the sampling line length. Quantitative calibration and prediction methods have been constructed for different components present in smoke gases. Recommendations on how to deal with interferents, non-linearities and outliers have been provided and a verification method for the spectrometer for unexpected variations and for the different models have been described. FTIR measurement procedures in different fire test scenarios have been studied using the recommendations of this project for measurement techniques and analysis, and real precision values for specific test scenarios have been estimated. Also a proposal for draft standard of the FTIR method for smoke gas analysis has been prepared. An interlaboratory trial of the FTIR technique in smoke gas analysis was carried out to define the repeatability and reproducibility of the method in connection with a small scale fire test method, the cone calorimeter.