Chemical detectors are crucial tools for first responders during emergency-response scenarios and for continuous monitoring of public spaces for general safety. For those who depend upon chemical detectors for safety and security, ensuring that detectors alarm at specified levels is critical. During detector performance evaluation, the accurate delivery of known concentrations of the chemical target to the detector is a key aspect of the test. Referee methods enable the analyte test concentration and associated uncertainties in the analyte test concentration to be validated by independent analysis, which is especially important for reactive analytes. This work demonstrates a method to use Fourier transform infrared (FT-IR) absorption spectroscopy for quantitatively evaluating the composition of vapor streams containing hazardous materials at acute exposure guideline levels (AEGL) under test conditions defined in recently published standard specifications for chemical vapor detectors. The described method covers the use of primary reference spectra to establish analyte concentrations, the generation of secondary reference spectra suitable for measuring analyte concentrations under specified testing environments, and the use of referee feedback to compensate for depletion of the test analyte. Important benefits of this approach included verification of the test analyte concentration with characterized uncertainties by in situ measurements co-located with the detector under test, near-real-time feedback, and broad applicability to toxic industrial chemicals.