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DUST MEASUREMENT - BASIC INFORMATION
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WE PROVIDE BASIC AIR SAMPLING PUMPS FOR DUST MEASUREMENT and can assist with filter weighing
This page starts with basic definitions for equipment and services click on the links above to subsequent page
DUST can contain a particles of a wide range of sizes. The effect of these particles when ingested into the body depends on the size shape and chemical nature of the particles. There are standard definitions used for dust based on the particle sizes as follows:
Total Inhalable Dust: This is the fraction of airborne particles which enters the nose and mouth during normal breathing. It is made up of particles of 100 microns diameter and less. This dust fraction is required to be measured in many European jurisdictions.
Thoracic Dust: This is the fraction approximately 10 microns diameter and less. This is also referred to as the PM10 in the USA. This fraction will pass through the nose and throat, and reach into the lungs.
Respirable Dust: This fraction is the particles approximately 5 microns and less. It certainly penetrates into the gas exchange region of the lungs, and is therefore the most hazardous particulate size. This fraction is required to be measured in many European jurisdictions.
DUST IN THE WORKPLACE: For many nuisance type dusts the occupational limits are around 10mg/m3 for total dusts and 5 mg/m3 for respirable or PM10 dusts. These are normally measured with small air sampling pumps running for a number of hours, or a quick measure of relative dust levels can be obtained by using a light scattering dust meter.
DUST IN THE ENVIRONMENT (or AMBIENT DUST): In outside areas the levels are usually much lower than in enclosed working areas, but the acceptable levels of dust before they become a nuisance are also set at lower levels than for workplace areas. Because ambient levels are lower they are more difficult to measure. If sampling pumps are used they need to be much larger and run for longer periods in order to collect a weighable amount of dust on the filter. Sometimes a measure of dust deposits on a surface is used to determine the amount of environmental dust.
PERMITTED DUST LEVELS vary in different jurisdictions, and will be lower for hazardous materials.
AIR SAMPLING PUMPS: These are simple vacuum pumps which draw air through a pre-weighed filter at a fixed flow rate for a known time. The pumps need for run for a number of hours to collect a weighable amount of dust. The filter is re-weighed to determine how much dust is present in a known volume of air. These filters will only collect a few milligrams or less of dust - a very sensitive and expensive balance is required. The filter holder needs to be specially selected to collect the particle size range required - e.g. PM10 or respirable. The filter holders are often only designed to operate at a pre-defined flow rate -if they are to collect the required particle size range. Personal pumps normally operate at about 2 litres/min. Ambient pumps operate at higher level - from 10 l/min - even up to 500 l/min. See links above for how we can help
DUST DEPOSIT GAUGES: These are used in the UK to monitor Dust Deposits. The Directional Dust Deposit Gaugeto BS.1747 does give some indication of monthly deposit levels in four compass directions. Very inexpensive. See link above for how to make one
RECORDING MICROBALANCE: Very sensitive device produced by Ruprecht & Pasternicht (USA). A vibrating rod with filter on top. Dust is collected on the filter. The change in the frequency of rod vibration is a measure of mass of dust on the filter. Instant recording. Expensive.
LIGHT SCATTERING DUST METERS: The trouble with Air Sampling Pumps is that the dust level they measure can only be a mean value for a measurement over several hours. Light Scattering Meters measure the light scattered by dust particles and can give an instant dust level measurement. Great care is required in using these. The number on the meter should be calibrated against measurements with an air sampling pump for your dust since they really measure scattered light - and the amount of light scattered by a particle depends on many factors, such as particle size distribution, density, reflectivity etc. NOT a true gravimetric method!
DUST LAMP: An inexpensive way to see dust. Shine a very intense parallel beam of light into an area. Look back towards the light and you can see the scattered light from any dust particles in the air.. (Just like in a cinema projector beam)!
© 2008 F.W.Parrett Limited