Page 216 - Advanced Mine Ventilation

196 Advanced Mine Ventilation

12.3.2 The US GCA RAM-1 (and RAM-1-2G)

GCA Corporation of the United States developed an instrument similar to SIMSLIN,
but it used a 10 mm nylon cyclone for size separation. The instrument was intrinsically
safe and could be used on mining machines at the working place. It could give instan-
taneous as well as cumulative dust concentration over the 8-h shift. The scattered light
of 0.9 mm wavelength is collected over a forward angle of 45e95 degrees. It had three
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ranges for dust concentration, 0e2, 0e20, and 0e200 mg/m .

12.3.3 The German Tyndallometer
It was a modification of their old Tyndall beam reflector instrument and performed
similar to SIMSLIN and GCA RAM-1 instruments. The laser light beam had a wave-
length of 0.9 mm. The instrument could only give instantaneous readings, but it did not
use any size-selective devices. The monitor had two dust concentration ranges: 0-2 and
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0-99 mg/m . The instrument is calibrated using a light-scattering standard provided by
the manufacturer.

12.3.4 Performance Evaluation of Light-Scattering Instruments

Thakur, Reister, and Hatch [6] carried out extensive field evaluation on all three light-
scattering instruments, namely, SIMSLIN, GCA RAM-1, and the Tyndallometer.
Main defects that disqualified them as a dust monitoring device for compliance with
the law were as follows:
1. These instruments could not distinguish between dust particles and water particles used for
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dust suppression. They read a dust concentration of 4e5 mg/m when no coal cutting was
being done and only water sprays were turned on. This was the biggest shortcoming of these
instruments. The GCA RAM-1 was least impacted by water and humidity.
2. Size distribution of coal dust particles impacted the readings. The instruments would give
reliable readings only for the size distribution of the dust cloud that it is calibrated for. As
discussed before, different ranks of coal and minerals in coal, such as silica, have different
characteristic size distributions. Particle size, shape, and its refractive index also impacted
the readings.
3. Light-scattering instruments failed to yield reliable readings when compared with personal
gravimetric samplers. Under controlled laboratory conditions, the variation in calibration
was 20%e30%, but under in-mine conditions the readings differed by a factor of 2.23.

12.4 The Tapered Element Oscillating Microbalance
Instrument (A Personal Dust Monitor)

After the failure of the light-scattering instruments for continuous dust monitoring, the
US government funded research to develop a more reliable instrument for personal
dust monitoring. The TEOM is a promising development in this area, but it still lacks
approval for compliance measurements. It is, however, a good tool for the engineering
control of dust and related research.