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A versatile portable tunable diode laser based measurement system for measuring elevated concentrations of hydrogen cyanide (HCN) in a time-resolved manner is developed for application in the fire environment. The direct absorption tunable diode laser spectroscopy (DA-TDLAS) technique is employed using the R11 absorption line centered at 3345.3 cm−1 (2989.27 nm) in the fundamental C–H stretching band (ν1) of the HCN absorption spectrum. The measurement system is validated using calibration gas of known HCN concentration and the relative uncertainty in measurement of HCN concentration is 4.1% at 1500 ppm. HCN concentration is measured with a sampling frequency of 1 Hz, in gas sampled from 1.5 m, 0.9 m, and 0.3 m heights in the Fireground Exposure Simulator (FES) prop at the University of Illinois Fire Service Institute, Champaign, Illinois. The immediately dangerous to life and health (IDLH) concentration of 50 parts per million (ppm) is exceeded at all the three sampling heights. A maximum concentration of 295 ppm is measured at the 1.5 m height. The HCN measurement system, expanded to measure HCN simultaneously from two sampling locations, is then deployed in two full-scale experiments designed to simulate a realistic residential fire environment at the Delaware County Emergency Services Training Center, Sharon Hill, Pennsylvania.

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