Calibration-free benzene sensor for fire environments based on interband cascade laser absorption spectroscopy near 5 μm

The toxicity of effluents from fires that occur at the wildland-urban interface is a growing concern among first responders, health professionals, and local populations. Benzene ( C₆H₆ ) is a key fire emission of particular concern because of its high carcinogenicity. To better understand C₆H₆ production in harsh fire environments, this paper presents a calibration-free scanned-wavelength interband cascade laser absorption spectrometer for C₆H₆ that is demonstrated to be robust, portable, and accurate. The spectrometer targets a narrow-band absorption feature located near 2006 cm −1 ( λ ₀ = 5~μ m). This wavelength selection is shown to be advantageous for measurements at near-ambient pressure conditions and to be well-suited for robust spectrally-resolved measurements with the limited scanning range of modern interband cascade lasers. The sensor employs a multi-pass Herriott cell to achieve an increased optical pathlength in a volume small enough to make the sensor portable for field measurements. The sensor is demonstrated to measure C₆H₆ over a wide dynamic range (sub-ppm to thousands of ppm) relevant to first-responder exposures. The method is also shown to remain stable over long durations of continuous logging and to effectively measure C₆H₆ content in structural fire effluents with varying ventilation conditions, accounting for potential interferers.