According to the World Health Organisation (WHO),
“Dusts are solid particles, ranging in size from below 1 µm (micrometre) up to at least 100 µm, which may be or become airborne, depending on the origin, physical characteristics and ambient conditions.”
Dust can be created by manual processes, such as cutting, crushing and grinding and particles can be so small that they are invisible to the naked eye. Different types of dust also carry different risks to human health and can be classified into three types: L Class (Low Risk), M Class (Medium Risk) and H Class (High Risk). Each class has a maximum allowable concentration, which is essential for employers to understand.
L Class Dust (Low Risk)
L Class dust is of lower toxicity and includes simple house dust, soil, general construction dust/waste, soft woods and solid surface material. The workplace exposure limit/maximum allowable concentration (MAC) for L Class dust is >1 mg/m3. This means that you need a dust extractor that catches 99% of the dust. For L Class dust, there should be a Filter Leakage no greater than 1% of the collected dust.
M Class Dust (Medium Risk)
Dusts in the M classification include hard woods (e.g. oak and beech), board material/man-made woods (MDF), repair compound, filler and clear coats, cement, tile cement, brick, mortars (silica), concrete dust, quartziferous materials (e.g. sand) and paints, such as oil paints and latex. They present a medium degree of risk to human health and the workplace exposure limit/maximum allowable concentration (MAC) for M Class dust is ≥ 0.1 mg/m³. Thismeans you need a dust extractor that catches 99.9% of the dust. For M Class dust, there should be a Filter Leakage no greater than 0.1% of the collected dust.
H Class Dust (High Risk)
H Class is high toxicity dusts containing pathogenic or carcinogenic particles, as well as asbestos, mould spores, bitumen, mineral fibres and artificial mineral fibres, like glass wool. They present a high degree of risk to human health and the workplace exposure limit/maximum allowable concentration (MAC) for H Class dust is < 0.1 mg/m³. This means you need a dust extractor that catches 99.995% of the dust. For H Class dust, there should be a Filter Leakage no greater than 0.005% of the collected dust.
Another category of dust, as highlighted by Health & Safety Executive (HSE) is combustible dusts. A combustible substance, mixed with air and with the addition of a source of ignition will cause an explosion. Workplaces that typically produce potentially explosive atmospheres include those handling fine organic dusts, such as wood or flour dust and those where processes release flammable gases or vapours, such as vehicle paint spraying. The Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR) make employers responsible for eliminating or controlling the risks from explosive atmospheres in the workplace. According to HSE,
“In DSEAR, an explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions*, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.”
*Atmospheric conditions are commonly referred to as ambient temperatures (–20°C to 40°C) and pressures (0.8 to 1.1 bar).
There are two European Directives for controlling explosive atmospheres: Directive 99/92/EC (also known as ‘ATEX 137’ or the ‘ATEX Workplace Directive’) and Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’).
Dust Control Considerations
It is important to use the right dust extraction equipment. In fact, HSE are giving out substantial fines where the wrong/no dust extraction equipment is being used.
When choosing dust extraction equipment the following should be taken into account:
- Type of dust you need to control (L, M or H Class, explosive dust)*
- Volume of dust to be extracted to match the extraction rate
- Storage capacity of the extractor
- Disposal of dust – with secure disposal required for H Class waste
* most L and M Class dust extractors will have similar suction rates and filtration levels
Different types of dust present different risks. At HVDS, we help you choose the right dust control solution for your particular workplace. For more information contact us here. To find out more about our dust, fume, mist, spray and oil extraction service, click here.