The personal dust monitor (PDM) [NIOSH 2006] is another real-time sampler, which has been
developed and tested by NIOSH, has been approved for use in underground mines by MSHA,
and has reached commercial production. The PDM uses tapered element oscillating
microbalance (TEOM) technology to obtain a real-time, gravimetric-based measure of respirable
dust concentrations. The TEOM is a hollow tube that vibrates at a known frequency and has a
filter mounted on the end. As respirable dust is deposited onto this filter, the TEOM frequency
changes and this change can be related to a dust concentration. The PDM provides the wearer
with a readout of the cumulative dust concentration to that point in the shift and the percent of
the permissible exposure limit (PEL) that has been reached. This information can be used by the
wearer to reduce their dust exposure prior to becoming overexposed. The sampler is incorporated
into a standard cap lamp housing and has the sampling inlet located at the cap lamp (see Figure
2-3).