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In situ determination of molecular oxygen concentrations in full-scale fire-suppression tests using tunable diode laser absorption spectroscopy
The fast and accurate determination of oxygen in air is important for fire research. Available O2 sensors (paramagnetic, electrochemical, ZrO2) are only of limited use because of significant errors caused by the specific sampling or measurement process, so that a purely optical, in situ detection is of great interest. Optical methods can account for the dilution of O2 by water (both vapor and drops) and are thus valuable tools for studying the effectiveness of water for replacing halogenated fire suppressants. To fulfill this need, a tunable diode laser based absorption spectrometer (TDLAS) has been developed for the in situ detection of molecular oxygen at 760 nm (A band, b1 Sigma+g implied by X3 Sigma- g). The device was successfully tested during full-scale fire-suppression tests carried out at the Naval Research Laboratory Chesapeake Bay Detachment facility in a 28-m3 test compartment. A specially protected open-path Herriott multipass setup with an absorption length of 1.8 m was developed to restrict the probe volume to a base length of 30 cm. Various scenarios including water mist only, unsuppressed fires, and water-suppressed fires (methanol and n-heptane, both pool and cascading fires up to 400 kW) were investigated. O2 concentrations were measured at a 2.5 Hz repetition rate with a resolution of 0.01 to 1 vol % O2 depending on the transmission conditions. This demonstrated for the first time the capability for in situ oxygen measurements under fire-suppression conditions with large and rapid obscuration changes (transmission of as little as 0.8% of the emitted laser power). It also showed that the TDLAS results account for dilution of O2 by water vapor without any interference of other species.
In situ determination of molecular oxygen concentrations in full-scale fire-suppression tests using tunable diode laser absorption spectroscopy
The fast and accurate determination of oxygen in air is important for fire research. Available O2 sensors (paramagnetic, electrochemical, ZrO2) are only of limited use because of significant errors caused by the specific sampling or measurement process, so that a purely optical, in situ detection is of great interest. Optical methods can account for the dilution of O2 by water (both vapor and drops) and are thus valuable tools for studying the effectiveness of water for replacing halogenated fire suppressants. To fulfill this need, a tunable diode laser based absorption spectrometer (TDLAS) has been developed for the in situ detection of molecular oxygen at 760 nm (A band, b1 Sigma+g implied by X3 Sigma- g). The device was successfully tested during full-scale fire-suppression tests carried out at the Naval Research Laboratory Chesapeake Bay Detachment facility in a 28-m3 test compartment. A specially protected open-path Herriott multipass setup with an absorption length of 1.8 m was developed to restrict the probe volume to a base length of 30 cm. Various scenarios including water mist only, unsuppressed fires, and water-suppressed fires (methanol and n-heptane, both pool and cascading fires up to 400 kW) were investigated. O2 concentrations were measured at a 2.5 Hz repetition rate with a resolution of 0.01 to 1 vol % O2 depending on the transmission conditions. This demonstrated for the first time the capability for in situ oxygen measurements under fire-suppression conditions with large and rapid obscuration changes (transmission of as little as 0.8% of the emitted laser power). It also showed that the TDLAS results account for dilution of O2 by water vapor without any interference of other species.
In situ determination of molecular oxygen concentrations in full-scale fire-suppression tests using tunable diode laser absorption spectroscopy
Schlosser, H.E. (author) / Wolfrum, J. (author) / Ebert, V. (author) / Williams, B.A. (author) / Sheinson, R.S. (author) / Fleming, J.W. (author)
2002
8 Seiten, 18 Quellen
Conference paper
English
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