Optimization of FTIR Spectroscopy
for Measuring Toxic Gas Concentrations
Inclusive Dates: 02/13/06 06/13/06
Background - The SwRI Fire Technology Department obtained a Fourier Transform Infrared (FTIR) spectrometer in 1998 to conduct a research program on fire smoke toxicity funded by the United States Coast Guard. Because of the program results, SwRI gained Coast Guard recognition for testing according to the International Code for Application of Fire Test Procedures (FTP Code) of the International Maritime Organization (IMO). The U.S. Navy has recently adopted a similar fire smoke toxicity test procedure, but the limits are much lower. These lower limits required a recalibration of the SwRI system to accurately provide required data to the Navy's clients.
Also, the International Organization for Standardization, Technical Committee 92, Subcommittee 1, Working Group 12 (ISO/TC92/SC1/WG12) recognized the need for a standard international test method using FTIR spectroscopy for measuring toxic gas concentrations in effluents from fire tests and initiated the development of one. The SwRI fire testing and research laboratory is the only facility in the United States to use FTIR spectroscopy for this purpose. Therefore, it was important to validate our procedures and present the results at the ISO WG12 meeting in May 2006.
Approach - The three major objectives of this project where to: a) improve the method used to quantify toxic gas concentrations by utilizing improved chemometric techniques, b) calibrate and find the optimum operating parameters of the Fire Technology Department's FTIR 10-meter gas cell, and c) demonstrate that when the proper sampling system is used, the smoke densities inside a closed-system smoke chamber are not affected when gas samples are drawn for FTIR analysis.
The first two objectives were accomplished by purchasing standard reference gases and running standard spectral collections until the signal output was optimized and then complete calibration data were collected. The improved analysis method was developed using updated software and utilized Classical Least Squares (CLS) as the mathematical principle for quantification. The third objective was addressed by selecting a material with reproducible smoke density results and testing it at a heat flux of 50 kW/m2 in an unpiloted exposure in the apparatus described in ISO 5659 Standard, PlasticsSmoke GenerationPart 2: Determination of optical density by a single chamber test (1994). Ten runs were conducted on the material under three sets of conditions: no toxicity samples pulled from chamber environment, toxicity samples pulled for three minutes around the time of peak smoke, and toxicity samples collected for the entire 20-minute test run. The data from all three runs were analyzed and compared.
Accomplishments - The two major accomplishments of this project were the development of an ASTM Practice detailing the FTIR gas sampling and analysis, and the results from the smoke density and fire smoke toxicity testing, which demonstrated that our sampling and collection does not affect smoke density results. The ASTM Practice was written and submitted for comments to ASTM International and was presented at the ISO/TC92/SC1/WG12 meeting held on May 2, 2006, in Italy. The results from the smoke density test were also presented at this meeting. One of the major outcomes of this presentation was making the ISO WG aware of the fact that the FTIR standard currently under development by ISO does not address calibration of the FTIR apparatus or quantitative method development. This information will be included in the next revision of this document or might become a separate document. SwRI's participation and presentation at these meetings have confirmed SwRI as a world leader in fire smoke gas analysis. SwRI's participation in the upcoming round-robin testing is highly anticipated, along with continued participation in the standard method development.