Reviewer:

Affiliation: S ensidyne

Comment:



### Dear Colleague:

Sensidyne, LP is the manufacturer of the CDEM

- 1000, the commercial version of the CDEM prototype that was tested in the NIOSH Draft Information Circular, NIOSH Docket 255, Coal Dust Explosibility Meter Evaluation and Recommendations for Application. We have reviewed the draft document and have found the document to be complete, accurate and very well presented. We do have some comments that are collectively assembled by our engineering group that developed the commercial version. The main focus of the comments is to recognize the improvements that were made in the instrument between the prototype and commercial versions. A list of the major improvements is given below.

o The s oftware was updated to improve the calibration procedure and to incorporate various safety features and checks in the software logic and user interface.

o The red/yellow/green format was simplified to a red/green format.

o A methane enhancement mode was added to allow the user to input the ambient methane level as measured from another instrument, which shifts the required RD level accordingly.

o An extended red mode allows the user to see the RD level after a red indication. This is presented as a range (e.g., 7 5% to 78% RD), and provides the user with a reference to indicate the remaining level of RD required to reach an 80% RD level.



### While this information is presented in the course of the document, it should be conveyed earlier that the testing was conducted with prototypes that were available in 2009, and the commercial version released in 2011 has improvements that address perceived shortcomings of the prototype model. Indeed, the comments from the MSHA inspectors in this study were considered in the

commer cial unit development. Some specific comments are listed below.

1. We encourage the addition of a footnote or text to the Executive Summary section with the suggested verbiage as follows. The testing was conducted with the prototype version of the CDEM that w as available in 2009, and the commercial version CDEM

- 1000 released in 2011 has improvements in both software and hardware over the prototype model. These improvements are listed under the “Commercial CDEM Development” section starting on page 20. Many of the comments from the MSHA inspectors listed in Appendix E were considered in the development of the commercial unit

.

Response: Thank you for this comment. F ootnote 5 has been added and states “ The testing was conducted with a prototype version of the C DEM that was available in 2009. The commercial version, CDEM

- 1000, was released in 2011 and includes improvements in bothsoftware and hardware. These improvements are listed in the “Commercial CDEM Development” section and consider many of the MSHA comme nts listed in Appendix E.”

2. Page 7 footnote 10: Recommendation for calibrating with 83% RD and telling the instrument it is 80% RD. In the commercial version CDEM

- 1000 this would distort the % Methane correction as well as the Extended Red reporting, esse ntially rendering the unit good for only red/green reporting. The magnitude of the distortions would need to be established to evaluate this recommendation. Previous verbal discussions with NIOSH on this matter had determined that the 80% value was conse rvative since it does not account for inherent coal IC as well as moisture content. If there is a concern about the instrument accuracy, it should be addressed by the instrument red/green acceptance criteria instead of intentional mis

- calibration. Accordi ngly, it should be noted that Sensidyne does not endorse the calibration of the CDEM

- 1000 with 83% RD and telling the unit it is 80% due to the errors such a process can introduce to the methane compensation built into the commercial version of the softwar e logic.

Response: Thank you for the correction. The footnote has been removed.

3. Page 21 “Calibration and Programming of the Commercial CDEM”, paragraph 3: This paragraph distorts the Extended Red Reporting. We actually report the measured value, rounde d up or down to the nearest integer % minus 3% RD, as a safety factor. Their paragraph implies we give a +/

- reading based on the 2% error alone. The paragraph should state what we actually report.

Response: Thank you for the correction. The document n ow states “ If a sample is indicated as RED, i.e., explosible, the display will indicate a range of % rock dust measured which is based on the measured value rounded up or down to the nearest integer percentage and the rounded value minus 3%.”

4. Page 22 “NIO SH Recommendations” bullet # 2: Using the CDEM as an enforcement tool if reporting and acceptance criteria were changed

– would the CDEM need to be re

validated as an analytical instrument and method? If so, who’s validation protocols would apply, NIOSH, MSHA, other? The commercial version CDEM

- 1000 as currently released is not designed to be and should not be used as an analytical tool.

Response: The authors' original intent was for the mine operators and the regulatory inspectors to use the CDEM as a screening tool to provide an immediate assessment of the explosibility of the mine dust sample. The use of the CDEM as an enforcement tool would
req uire a rule change by MSHA from requiring % total incombustible to % rock dust, along with the development of a validation protocol for the use of colorimetric methods as acceptable enforcement. Then Sensidyne would re

- validate the CDEM as an analytical

co lorimetric method for assessing explosibility of coal and rock dust mixtures. However, until this rule and validation protocol are established by MSHA, the CDEM could still be used to screen samples to determine which samples re sent to their laboratory f or additional testing. As a screening tool, the CDEM would allow the mine operators and inspectors to provide immediate remediation to rock dust deficient areas.5. Creation of calibration standards: NIOSH does not mention that the RD and CD need to be drie d before they are weighed out for a calibration standard, this is a requirement that needs to be mentioned. In addition, in the MSHA response to questions section, response 2.f. mentions weighing out calibration standards using the sample cup as a materia ls container. Using the sample cup (not the sample vials) would mean measuring out a 1 to 2 gram sample ; the chances for error on this are substantial. There needs to be a minimum standard measurement weight that would reduce the chances of weighing erro r (e.g. a 0.1g error on weighing a 1 gram sample is 10%, yet the same 0.1 gram error is only 0.5% of a 20g sample.

Response: The authors have made the drying of samples more explicit by stating “ For proper calibration, both the PPC and mine rock dust (RD) should be dried prior to making the boundary calibration samples” in the Preparation of Calibration Sample section of Appendix C. The following statement has also been added as a footnote (1 8 )

t o the response to section 2 f in Appendix E to address the error in weight issue: “ Also, the commercial CDEM is supplied with large containers for meter calibration. These 4

- oz containers provide enough volume to create 30 g or 50 g samples. The small sa mple cups should not be used for the preparation of a calibration sample .”

6. The light source in the commercial unit is a red LED, which may be described as a red/near infrared source, but probably should not be described as infrared as it is under “CDEM Ope ration”.

Response: Thank you for the correction. Those references to infrared radiation in the paper have been changed to near

- infrared.

7. Regarding footnote 16 on page 50, there are also no established criteria for sample averaging. Repeated measurements of the same sample on the same unit or different units can readily produce different readings, as the sample mix and orientation changes.

Response: We understand that there are variations in multiple readings of the sample on the same unit or different u nits. The p ressing and releasing action may cause particle re

orientation against the lens as the larger coal and rock dust particles tend to rise to the top of the sample and favor a larger part of the field of view. In the study, we had actually taken three separate measurements of the collected dust sample (three separate full cup s ) . If the output was two GREEN and one RED, we called it GREEN. This way we could better define the measurements if the sample happened to be on the boundary of the GREEN/R ED.