PM10 Sampling

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 16 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 16 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 3 mg/m3 of air sampled. An action level of 1.5 mg/m3 is set and a significant risk level of 0.3 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 16 micron that are collected with regard to PM10 Sampling.

Below is an extract from the Federal Register Part IV, EPA, 40 CF Parts 53 and 58, Revised Requirements for Designation of Reference and Equivalent Methods for PM2.5 and Ambient Air Quality Surveillance for Particulate Matter; Final Rule.

“EPA also retained the current annual PM10 standard at the level of 50µg/m3, which would be met when the 3 – year average of the annual arithmetic PM10 concentrations at each monitor within an area is less than or equal to 50 µg/m3.

Further, EPA retained the current 24-hour PM10 standard at the level of 150 µg/m3, but revised the form such that the standard would be met when the 3-year average of the 99th percentile of the monitored concentrations at the highest monitor in an area is less than or equal to 150 µg/m3.”