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grams per cubic meter (µg/m 3 ) of air, can be as variable as the silica content in the dust. Obviously, then, by the time the results of the traditional method are back from the laboratory, dust and silica levels in the mine might be completely different, and because of the variability in silica content, even the PDM can provide only very limited infor- mation on silica levels. How the New Solution is Going to Work The new monitoring solution being devel- oped by OMSHR combines the current prac- tice of collecting respirable dust samples for silica analysis with the use of a portable instrument for the immediate determina- tion of silica collected in each sample. Since coal mines already have personal sampling pumps and dust samplers, this initiative builds on the availability of these devices and their already established use for sampling silica in the mine. Even the sampling cassette currently used in coal mines will be the same. In the future, an optimized cassette or a new sampler might be useful for the in-field determination of silica in the dust sample (in fact, efforts are already in progress to investigate possible options), but the immediate goal is to min- imize any change in current practices for mine operators. What will be different? At the end of the shift, the person in charge of the dust sam- pling will simply open the plastic portion of the sampling cassette and insert the filter cartridge in the compartment of a portable instrument (see sequence in Figure 3). Within one minute, the instrument will pro- vide an estimation of the amount of silica collected and an average silica concentra- tion in the section where the sample was collected. OMSHR is currently testing several com- mercially available instruments for their use with this new monitoring solution, and they are all lightweight enough to be transported in a Pelican case, while still being robust enough to be used in the field. The portable instrumentation will be an infrared analyzer that uses what is commonly known as a direct-on-filter technique, which means that the dust sample does not need to be removed from the filter to be analyzed (such as is done in lab-based methods). An infrared beam simply passes through the dust-laden filter and is analyzed by a sensi- tive detector on the other side. A mathemat- ical protocol optimized by OMSHR will be used to quantify the silica based on the detector response. The first and foremost benefit is the quickness of the overall process. In a short period of time and with little effort, it will be possible to measure silica level for multiple samples, which translates to increased pow- er of the results. When a section foreman knows the level of silica dust within a few hours of the end of the shift, an intervention to address high levels can be implemented right away, and the effect of the interven- tion could be assessed within a few shifts. Development of the New Monitoring Solution OMSHR has thoroughly investigated the use of a portable infrared instrument for the direct-on-filter analysis of silica in coal dust samples, and our positive test results have generated increasing confidence in the suc- cess of this new approach. A calibration for the new method using samples prepared from standard silica materials was devel- oped. Performance of the method was fur- ther verified using coal dust samples collected in a dust chamber at the OMSHR laboratory in Pittsburgh. That evaluation included dust samples from different coal sources, all containing silica. Once the method was verified with dust samples generated in a controlled dust chamber environment, they decided to challenge the methodology with samples collected in active mines. So far the method has been tested with more than 150 sam- ples collected in several coal mines, includ- ing surface mines. The in-field study is providing data to adjust the calibration of the method, to study the sensitivity of the analysis, and to verify that the method can work for samples collected in mines with different geologies. While this effort is still in progress, the technique has shown suffi- cient sensitivity to provide accurate estima- tion of silica in the dust samples, down to less than 20 µg of silica. This amount corre- sponds to an average silica concentration of 20 µg/m 3 for a full 8-hour shift — well below any action limit enforced by MSHA in coal mines. In our tests, the accuracy of the estimation for each sample is always verified with the MSHA P7 method for silica quantification, which is possible because the OMSHR in-field technique does not destroy or disturb the sample. The samples collected for the data in Figure 1 were analyzed using both methods, and the results generated with our direct- on-filter technique compared well with the P7 method results (see Figure 4), with a coef- ficient of 0.97 — very close to the ideal 1 for a perfect correlation. This very strong correla- tion is also true for "lightly loaded" samples (i.e., containing less than 50 µg of silica). Implementing the Solution OMSHR researchers are continuing to develop the direct-on-filter method with the intent of encouraging mine companies to adapt it as part of their strategy to help reduce exposure to silica. Future research includes: 1. Verification of the technique with dust samples collected in more coal mines, both underground and in surface operations. The goal is to optimize the calibration pro- cess to cover any possible variability in geol- ogy. For this reason, any collaboration with active coal mines is welcomed. 2. Creating a step-by-step process or standard operating procedure to guide mine operators and health and safety man- agers through the use of this new technique. When the technique is deployed, these indi- viduals will ultimately be in charge of the analysis. The process will include the peri- odic verification of the technique with stan- dards, the interpretation of the results, and basic data analysis. 3. Creating a user-friendly software that will contain the step-by-step process described above. This software will be most likely a NIOSH product, freely distributed to the coal mine industry. 4. Beta testing the new solution in coal mines so that we can get feedback and com- ments are received on how the analytical process and software interface can be opti- mized for usability. For this purpose, again, OMSHR is very interested in collaboration with active coal mines. This new monitoring solution has the potential to help reduce worker exposure to silica, and thereby reduce the number of future cases of silicosis in coal miners. It will also empower mine workers and health and safety managers to help them achieve one of their shared goals — to protect the health of coal miners in the present and the future. Emanuele Cauda is a senior service fel- low at the OMSHR at NIOSH and can be reached at ecauda@cdc.gov. Lauren Chubb is a physical science student trainee at the OMSHR at NIOSH and Art Miller is a senior scientist at the OMSHR at NIOSH. Disclaimer The findings and conclusions in this manuscript are those of the authors and do not necessarily represent the views of NIOSH. Mention of company names or products does not constitute endorsement by the Centers for Disease Control and Prevention. January 2016 www.coalage.com 33 r e s p i r a b l e d u s t c o n t i n u e d