Mining Contract: Development of a Silica Dust Direct Reading Sampler with Sensitivity for Dust Components and Size

Contract # 75D30120C08386
Start Date 9/1/2020
Research Concept

The contract research employs a novel approach to develop a small, wearable, personal exposure monitor that provides real-time indications to mine workers when their exposure to respirable coal and silica dust potentially exceeds safe levels. In the future, this device may be useful for compliance purposes. This proof-of-concept development project will yield a stand-alone exposure-monitoring device capable of selectively measuring respirable and submicron mine particles and differentiating between silica (crystalline) and coal dust.

Contract Status & Impact

This contract is ongoing. For more information on this contract, send a request to mining@cdc.gov.

The objective is to develop a device and construct a sensor for dust differentiation. A 25-mm personal sampler containing a capacitive sensor, which collects/measures respirable particles, has been designed and it has been used to collect dust during drilling activities at the Edgar mine; numerous nano- to micrometer-sized particles were collected. The collected particle agglomerates on the filter primarily measured a few micrometers to submicrometers in size, as analyzed by scanning electron microscopy (SEM). This device will use capacitive sensors to monitor the volume of deposited particles and convert the detection results to a real-time exposure level; and use coordinated optical and capacitive sensor responses to determine the total quantity of silica.

The designed sampler will be 37 mm in size. The optical sensor will measure the optical reflectance or transmittance on the deposited particle film, and in conjunction with the capacitive sensor (for mass detection) will provide information regarding the proportions of silica and carbon (coal) in the dust to aid estimation of their concentrations. When operated during a full work shift, the proposed device will provide real-time mass measurements of respirable dust. When operated for short-term samplings, the collected particles will be analyzed off-line using a microscope to obtain information regarding particle composition, morphology, size distribution, and number. In the proposed project, the contractors will perform the proof-of-concept development.

The proposed exposure-monitoring device provides novel features:

1) An optical sensor to differentiate between silica and other types of dust.

2) A capacitive sensor for real-time reading of dust mass/volume.

3) Direct collection of particles in the sampler housing and deposition on a filter without particle loss during passage through the sampling tube or cyclone. The cut-off size (D50, particle size at 50% cumulative probability or overall particle distribution) is determined by the sampler design.

4) Smaller pore-size filters (polycarbonate 0.2 µm) and a lower flowrate (0.3 L/min) than other samplers, to collect more small-sized dust (e.g., measuring a few micrometers or less).

The proposed approach will integrate capacitance- and optical-based methods to quantitate the total particle deposition as well as the relative composition of coal vs. silica dust. Measuring the relative quantity of coal vs. silica dust may be relatively straightforward, given the large differences in reflectance, particularly in the visible region. The proposed technique identifies silica and coal dust present as individual particles when the majority of the content is silica or carbon. Regarding the anticipated accuracy of coal or silica dust measurements. Two aspects of accuracy will be addressed. The first is the stability (drift) of the sensor due to changes in environmental conditions and the presence of condensation or water droplets. The second aspect of accuracy is the relative calibration (i.e., determining the relative response to the deposition of various minerals). The relative calibration will be investigated in the present study by quantitating the response to various materials of interest.


Page last reviewed: 3/23/2021 Page last updated: 3/23/2021