- Author
-
Blevins, L. G.
- Title
- Exploring New Measurement Techniques for Real-Scale Fires: The Potential of Fiber-Coupled Communication Lasers for Probing Gas Composition. BFRL Fire Research Seminar. VHS Video.
- Coporate
- National Institute of Standards and Technology, Gaithersburg, MD
- Report
-
Video,
September 28, 1999,
- Keywords
-
probes
|
lasers
|
gas composition
- Abstract
- Due to technical difficulties the first 5 minutes of the seminar is missing. Measuring species concentrations in and around fires is important for understanding toxic gas formation, discerning local ventilation conditions, determining the rate of heat release, and validating fire models. As we move toward performance-based fire codes, there is a pressing need to quantify the temporal and spatial resolution and uncertainty of the species concentration data used to develop and validate fire models. Presently-used extractive probe sampling methods make this difficult because (1) temporal and spatial resolution are poor and hard to quantify, and (2) several sources of uncertainty exist, such as chemical reactions in the probe, sampling system soot deposition, and sample alteration in the water and soot traps. The limitations of extractive probe sampling provide motivation to explore new techniques such as tunable diode laser absorption (TDLAS) for measuring species concentrations in real-scale fires. TDLAS is a promising type of spectroscopy to use for new fire instruments, in part because market forces in the communications industry have recently made room-temperature, near-infrared semiconductor lasers, detectors, and fiber optics readily available. The low-cost, compact tunable diode lasers feature single-mode performance, long-term wavelength stability, fiber-optic compatibility, low power consumption, and suitability for implementation of rapid, sensitive detection schemes. Diode lasers can potentially be used to measure CO, O2, CO2, C2H2, CH4, and H2O concentrations, soot volume fraction, and temperature in and around flames. As part of its Improvement and Development of Fire Diagnostics project, BFRL is studying the feasibility of developing a near-infrared, fiber-coupled TDLAS probe for use in and around fires. This seminar will describe BFRL efforts to develop a CO concentration sensor for use in fire gases which have temperatures between 300 K and 1200 K and are partially obscured by soot. To date, the effort has involved optimizing detection methods, developing and using calibration facilities, formulating and applying computer models of sensor signals, operating the sensor in a laboratory flame, and building a first-generation prototype of a cooled and purged fiber-optic probe. This seminar will provide an overview of recent progress on these topics as well as a big-picture view of this technology as a large-scale fire diagnostic.