The Compound Specific Analyzer - Combustion Products is used on the International Space Station as a warning monitor of smoldering or combustion events and, after any fire event, to indicate that toxic gas levels have subsided for safe re-entry of the crew to the affected area. This monitor is being phased out of service. Southwest Sciences Inc. proposes to develop a replacement laser-based sensor using wavelength modulation spectroscopic absorption. This device would be capable of real-time measurements of the four most important gases of interest at concentration levels relevant to pre-combustion events and with a one second response time. This battery-operated device would be hand-held, use very little electrical power, and have a multi-year lifetime without the need for consumables, re-calibration, or maintenance, in contrast to the currently-used sensor. The Phase I research would perform a trade study and then test the most promising opto-mechanical designs for making simultaneous measurements of the four gases in a single optical cell with a minimal number of lasers. It would also demonstrate the ability to make multiple gas measurements over a wide range of concentrations using a single spectral scan. This work will allow us to design, test and build a prototype sensor in Phase II.