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Respirable Dust Sampling and Measurement 193

Figure 12.2 Mining research establishment gravimetric dust sampler.
Source: By Hartmann, John Wiley, 1982.

12.2.2 The US Personal Gravimetric Sampler
A 10 mm cyclone is used for size selection in this instrument. Fig. 12.3 shows the
details.
The dusty air is drawn at 1.7 L/min through a cylindrical chamber tangentially and
follows an inward spiral path with increasing velocity as it approaches the axis before
escaping through a smaller diameter axial outlet tube. Because of the centrifugal force,
large particles are removed from the airstream and collected in a receptacle at the bot-
tom of the lower conical section of the cyclone chamber. Respirable dust penetrating
the cyclone is collected on a filter. The preweighed filter is weighed again to determine
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the respirable mass per unit volume of air in mg/m for an 8-h duration.
The personal gravimetric sampler consists of two basic components: (1) a recharge-
able, battery-powered, diaphragm-type pump with calibrated flow rates and (2) the
cyclone assembly with preweighed cassette or filter holder to collect the dust sample.
The pump is worn on the miner’s safety belt, and the cyclone assembly containing the
filter is clipped onto the shirt lapel. The pump and cyclone are connected by a synthetic
tubing.
In spite of the design differences, there is very good linear relationship between the
two instruments’ readings. In general, the mass concentration as measured by MRE
instrument at 2 L/min flow is equal to 1.38 mass concentration measured by the
US personal sampler at 1.7 L/min. The personal sampler has an accuracy of 20%,
and several measurements on consecutive shifts are necessary to derive an average reli-
able respirable dust concentration. The law requires five samples, each taken over a
consecutive 8-h shift, for averaging.