Benzene and carbon monoxide sensing in urban fire environments via tunable interband cascade laser absorption spectroscopy

An increase in synthetic construction materials has dramatically changed the toxicant profiles that are encountered by first responders in urban fire environments. Benzene (C₆H₆) production is of particular concern because it is a known carcinogen that is hazardous at relatively low concentrations. There is a need for robust, accurate, and fast benzene measurement systems that can withstand the harsh conditions faced by first responders. An optical sensing approach is presented that uses a tunable interband cascade laser at around 5 µm to measure C₆H₆ production in urban fires. The sensor utilizes scanned-wavelength laser absorption spectroscopy and a multi-pass optical cell to measure C₆H₆ with a lower detection limit below 1 ppm. The sensor is demonstrated to be robust in the presence of combustion species based on a multi-spectral fitting method to account for nearby water and ethylene transitions. The sensor is used to measure the C₆H₆ concentrations in controlled burns of common construction materials. These controlled burns are also used to demonstrate the same laser absorption sensor’s ability to measure carbon monoxide (CO), which is a highly toxic gas that is produced in large quantities in structural fires. Fire experiments demonstrate the functionality of the sensor and help provide insight into which materials pose more significant threats to first responders. The optical sensing method is expected to help inform safety precautions at urban fire sites and enable timely awareness of risk of C₆H₆ and/or CO exposure.