10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Determination of the Effect of Lens Fouling of the CAS-POL for the Measurement of Airborne Float Coal Dust
CLARA E. SEAMAN, Michael R. Shahan, National Institute for Occupational Safety and Health
Abstract Number: 1210 Working Group: Instrumentation
Abstract Float coal dust (FCD) is defined as coal dust particles smaller than 75μm that are generated by various mining operations and transported by ventilating air until settling in the mine entries. FCD has been identified as an explosion hazard in coal mines, contributing to 18% of U.S coal mining related fatalities between 2001 and 2010. The main mitigation of this hazard is the application of rock dust. Water sprays may be used as an additional method for controlling FCD by preventing it from leaving the mining face. Traditionally, gravimetric techniques are used for evaluating the effectiveness of water spray controls. However, gravimetric measurements are only able to provide a shift average efficiency measurement and are unable to provide insight into the size distribution of FCD. The Cloud Aerosol Spectrometer with Polarization (CAS-POL) has been successfully used in NIOSH pilot studies to determine the efficiency of a single spray in open space. During this testing, a reduction in the dust concentration as measured by the CAS-POL was observed over the course of a day even though the dust source was held constant. It is believed that this shift in the dust concentrations measurements may be linked to the buildup of dust on the CAS-POL lenses. This study was designed to determine the impact of lens fouling on the CAS-POL data and to establish guidelines for cleaning the lenses in order to minimize measurement errors due to fouling.
For this investigation, the CAS-POL was centered in the Pittsburgh Mining Research Division longwall gallery and subjected to different types of dust loading. During each loading test, the dust was cycled on for 30 minutes and off for 3 minutes to establish baseline values for the CAS-POL as the lenses were loaded with dust. Tests were varied by length and type of dust used. It was observed that during a test the total number of particles detected in a cycle did not change significantly over time, but total weight significantly decreased. When particles were segregated by size fractions, the number of small particles (D ≤ 4 µm) increased while the number of larger particles (4 µm < D ≤ 20 µm and D>20 µm) decreased significantly. Using the sizing data to estimate mass, all three size fractions decreased significantly over time following a linear decease for small particles and a power relationship for larger particles. The change in particle count and mass for both size fractions is correlated to the sizer high baseline value, one of the CAS-POL housekeeping variables, which increases linearly in response to length of dust exposure. Together these results suggest that lens fouling leads to an increase in sizing errors which can be monitored using the sizer high baseline value. Further analysis will focus on determining an acceptable threshold for the sizer high baseline value which will be used to indicate the need to clean the CAS-POL lenses.