Comparison of coarse coal dust sampling techniques in a laboratory-simulated longwall section

Abstract

Airborne coal dust generated during mining can deposit and accumulate on mine surfaces, presenting a dust explosion hazard. When assessing dust hazard mitigation strategies for airborne dust reduction, sampling is done in high-velocity ventilation air, which is used to purge the mining face and gallery tunnel. In this environment, the sampler inlet velocity should be matched to the air stream velocity (isokinetic sampling) to prevent oversampling of coarse dust at low sampler-to-air velocity ratios. Low velocity ratios are often encountered when using low flow rate, personal sampling pumps commonly used in underground mines. In this study, with a goal of employing mine-ready equipment, a personal sampler was adapted for area sampling of coarse coal dust in high-velocity ventilation air. This was done by adapting an isokinetic nozzle to the inlet of an Institute of Occupational Medicine (Edinburgh, Scotland) sampling cassette (IOM). Collected dust masses were compared for the modified IOM isokinetic sampler (IOM-MOD), the IOM without the isokinetic nozzle, and a conventional dust sampling cassette without the cyclone on the inlet. All samplers were operated at a flow rate typical of personal sampling pumps: 2 L/min. To ensure differences between collected masses that could be attributed to sampler design and were not influenced by artifacts from dust concentration gradients, relatively uniform and repeatable dust concentrations were demonstrated in the sampling zone of the National Institute for Occupational Safety and Health experimental mine gallery. Consistent with isokinetic theory, greater differences between isokinetic and non-isokinetic sampled masses were found for larger dust volume-size distributions and higher ventilation air velocities. Since isokinetic sampling is conventionally used to determine total dust concentration, and isokinetic sampling made a difference in collected masses, the results suggest when sampling for coarse coal dust the IOM-MOD may improve airborne coarse dust assessments over “off-the-shelf” sampling cassettes.

Comparison of the CAS-POL and IOM samplers for determining the knockdown efficiencies of water sprays on float coal dust

“…These relatively large CV values were not unexpected; a previous study conducted in the same NIOSH test gallery found that static IOM samplers distributed across the gallery cross section could experience a CV of 24% due to position of the sampler alone. [49] Variation can also be attributed to the lack of uniformity of the dust within the test space. Higher air-speeds and coarser dust can contribute to high concentration gradients.…”

“…A previous laboratory investigation by NIOSH found that the IOM has an average CV of 4.6% for varying test conditions. [49] The current study was the first conducted by NIOSH using the CAS-POL and was not optimized for establishing an instrument CV, although this is expected to be done in future work. The CAS-POL was mounted so that the inlet extended into the free-stream air while the IOMs were mounted behind and above the top of the CAS-POL wing.…”

Review of Published Laboratory-Based Aerosol Sampler Efficiency, Performance and Comparison Studies (1994–2021)

“…The IOM inhalable sampler, a modified IOM sampler with an interchangeable isokinetic nozzle (IOM-MOD), a Zefon Coal Dust Sampling Cassette (directly in line and facing the wind tunnel) and a Zefon Coal Dust Sampling Cassette at 90 • to the flow and facing the tunnel floor, have been compared for sampling coarse coal dust [43]. The authors used a long wall gallery (38 m length, 6 m width and height of 3 m) with two types of coal dust used (Keystone Mineral Black (Fine) 325BA and custom-ground coal dust with a 53 µm volume mean diameter).…”

“…This difference does not allow a direct comparison between articles to be undertaken. Twelve articles performed their experiments in a wind tunnel, six articles performed the experimental work in an aerosol chamber, five articles were performed in a test chamber or an air chamber, one article was performed in a long wall gallery [43] and one article used an outdoor environmental chamber [33].…”

Best practices for dust control in coal mining, second edition.

“…Although the standard IOM sampler is an open-face design, NIOSH designed and fabricated an inlet adapter, as a replacement for the front plate, that would allow for isokinetic sampling as shown in Figure 6.2, right [Patts and Barone 2017]. Isokinetic sampling matches the sampler inlet velocity to the velocity of the airstream being sampled, thus minimizing errors resulting from particle inertia in uneven airstreams [Wilcox 1956].…”