Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R01-OH-007680, 2008 Feb; :1-64
The primary goal of this research under NIOSH sponsorship is to develop an in situ, real-time, low-cost, and high-performing continuous monitor of particulate matter and specific gas-phase chemical hazards present in mine atmospheres. This novel instrument employs three complimentary spectroscopic techniques - elastic (Mie) visible light scattering, laser-induced fluorescence (LIF), and non-dispersive infrared absorption (NDIR) - to probe an adjacent air column or sample from said column for aerosols and gases that represent an occupational hazard to miners. Ultimately, optical signals from the sensor modules will be interpreted automatically to yield bulk chemical, size (for aerosols), and concentration information on these toxic materials. The project may be divided into four key areas: 1. An extensive, model-based analysis of elastic scattering measurements as applied to complex aerosol samples such as are typically found in mine atmospheres, 2. Development of a compact, high-performance microlaser platform to be used in scattering and LIF measurements and that is suitable for use in a field instrument, 3. Design and construction of instrument modules for aerosol measurement: elastic scattering and LIF, 4. Design and construction of instrument modules for gas-phase measurement: NDIR. The initial project approach of a single open-path instrument to obtain size, chemical, and concentration information for both particles and gases by combining multivariate data collection with automated model and database interpretation was revised following the modeling analysis of elastic scattering. Based on the complexity of the modeled results and on the availability of new technology, a shift to a module-based approach for obtaining three key data types (scattering intensity and asymmetry, fluorescence, and infrared absorption) was made. This constitutes a significant enhancement from the original project plan. Key to the implementation of our approach was the development of a suitable microlaser platform for field use. Such a platform is an enabling technology required for the successful transfer of laboratory-based spectroscopic techniques to field-based in situ monitoring applications. Although micro laser development, other than adding harmonic generation to the commercially available Northrop-Grumman microlaser, was not part of the original research plan, the proposed microchip laser was no longer commercially available when the project started, forcing us to develop our own. This unexpected addition to the research forced the addition of significant resources to the project, both in time and money, leading in inevitable delays in obtaining a field-ready instrument. We have successfully developed a microchip laser platform that combines low-cost (approximately $2500) with high performance and flexibility superior to those commercially available today. This in itself is a very significant achievement. Lasers with both continuous wave (CW) and pulsed UV and visible output were assembled based on well-established Ng:YAG and Nd:YV04 solid state laser technology. The laser platform is designed to use off-the-shelf optics and parts, and maintains the versatility to readily incorporate new and improved optics and parts as they become available in the rapidly developing optics industry. Three instrument modules were designed, constructed, and evaluated in the laboratory. For gas-phase hazards, a NDIR sensor for methane, carbon monoxide, and hydrocarbons (measured as propane equivalents) was built and tested in the laboratory and is ready for field deployment. This module is based on a flexible platform that allows for rapidly customized sampling systems and instrument layout to be developed for a particular field site. Additionally, the gases measured may be changed through a simple substitution of optical filters and re-calibration. Other gases that can be measured include CO2, H2O, N2O, NO, and HCl. For the elastic scattering and LIF modules, instruments have been designed and assembled in the laboratory. Initial laboratory testing of aerosol-monitoring modules has been completed, and the modules are ready to be evaluated using laboratory generated aerosol samples.
Marc M. Baum, Oak Crest Institute of Science, 2275 E. Foothill Blvd., Pasadena, CA 91107