We have
just begun to look at the technology of
PM 10 sampling, so we do
not claim to be experts.
Our first question is:
Question:
What is the purpose of determining less
than 10 micron dust quantities?
Less
than 10 microns falls just above the
respirable dust range. The
respirable dust is normally determined
with a little pump and a little cyclone
that separates the respirable and non
respirable particulate.
The
respirable particulate is collected on a
filter and the rest is collected in a
little container that is cleaned out
afterwards.
The PM10
sampling method uses a stationery
sampling point at the perimeter
of the mine and continuously pulls in
sub 10 micron particles (ideally).
This differs
from the gravimetric sampling in that
personnel are not monitored.
This puts
PM10 sampling in the general
environmental health category of a mine,
in contrast to the gravimetric sampling
that pertains the health and safety of
people working in specific areas in
the mine.
Logically
the only value of knowing the dust
quantities below 10 micron will be to
somehow quantify the risk for people to
inhale the dust and as a result develop respirable diseases and other
related health problems.
The
Department of Minerals and Energy of
South Africa limits (OEL) all respirable
dust to 5 mg/m3 of air sampled. An
action level of 2 mg/m3 is set and a
significant risk level of 0.5 mg/m3 is
set.
As
different people, depending on age and
fitness, have a different upper limit
for respirable dust, the idea of PM10
sampling could be to cover this variable
upper limit of respirable dust.
Although
numerous studies have indicated that the
upper limit is around 7 micron, and that
normally it is around 5 micron, because
a certain percentage of the 7 micron
particles are collected in the nasal
pathways.
There
is one error that is common to both PM10
and gravimetric sampling, and that is
the density of the dust. Both
systems make use of the inertia of the
particle and relate this to the size of
particle collected.
A
higher density particle will have more
inertia and will thus have only smaller
particles collected. While a less
dense material will have particles sizes
of over 10 micron that are collected.
