Airborne particulate matter, or dust, occurs everywhere - indoors and outdoors. It is caused by natural processes (shedding of pollen grains or mould spores) and also by human activities such as driving cars, manufacturing things, and even just walking around. Since dust can be inhaled, it enters the body and is known to cause a number of health issues, including asthma, heart disease and cancer. Where exposure to particulate matter occurs in the workplace setting, employers need to take steps to clean the air and protect the health of employees.
Particulate matter (PM) consists of airborne particles whose size is 60 microns or less. Particles larger than this tend to settle, rather than remain airborne. PM is sometimes also known as dust. One way of classifying PM is by size. The three categories are:
- PM10 – particles of 10 microns or less
- PM2.5 – particles of 2.5 microns or less
- Ultrafine particles (also known as nanoparticles) – particles of 0.1 microns (100 nanometres) or less.
The composition of PM varies widely, depending upon its source. Examples include soot, flour dust, wood dust, metal dust, asbestos.
Cutting, grinding, mixing, crushing - all these processes produce PM. So it is hardly surprising that many different industries, from traditional (farming) to high tech (electronics) produce dust in the workplace. Nanotechnology - a growing industrial sector, which includes electronics, cosmetics, pharmaceuticals and paints/coatings - is a relatively new source of dust in the nanoparticle range.
The smaller the particle, the deeper it will penetrate into the body. The following particulate size ranges are significant:
- 25 – 0.4 microns - trapped in the nose and throat
- 5 – 0.05 microns – deposits in the windpipe and the upper part of the lungs
- 1 – 0.002 microns – penetrates as far as the lower part and the gas exchange region of the lungs (and therefore the bloodstream)
Therefore, the health impact of PM pollution tends to come from inhalation, rather than by ingestion or absorption through the skin, which may be significant routes into the body for other types of pollution. It is already known from the United States Six Cities study that PM pollution in the atmosphere is linked to excess mortality and other research shows a connection between environmental PM pollution and heart disease. However, less is known about the specific impact of occupational PM exposures on the heart. A recent study of over 176,000 male construction workers in Sweden showed that occupational exposure to a range of dust, especially from diesel exhaust, increased the risk of heart disease.
Occupational asthma can be a significant problem arising from workplace exposure to PM pollution. The condition should be suspected in any adult developing asthma symptoms such as wheezing which clears up on absence from the workplace - on sick leave or on holiday. Occupational asthma may develop on exposure to allergens in:
- Grain dust (farming)
- Pollen, mould (horticulture)
- Flour dust (baking, flour mills)
- Wood dust (sawmills, joining)
Hardwood dust has been linked to cancer while mesothelioma, a very rare cancer, affects people who have been exposed to asbestos dust. Asbestos also causes lung scarring is known as asbestosis, and lung cancer. Meanwhile, quartz dust is an important industrial pollutant linked to a condition called silicosis which affects miners and sandblasters and leads to heart failure. Quartz dust is maybe also linked to stomach, lymphatic and skin cancer, kidney disease and autoimmune disorders.
Potter's lung is a lung condition caused by exposure to feldspar, a mineral used in pottery glazes.
Iron dust exposure among welders can lead to siderosis, a form of lung fibrosis. Byssinosis is a lung condition characterised by a chronic cough, wheezing and shortness of breath, caused by exposure to fibres in flax, cotton and hemp mills. Finally, exposure to wood dust among furniture makers, carpenters and sawmill workers can cause asthma and cancer of the nose and throat.
There are a number of air sampling devices that can be used to measure both size range and number of particles in the air. These include:
- The condensation particle counter
- The optical particle counter
- The laser particle counter
The Control of Substances Hazardous to Health (COSHH) regulations set a workplace exposure limit ( WEL, measured in mg/m3) for dust. Dust of any kind (whether or not its components have a WEL) also has a WEL. The inhalable fraction must not exceed 10 mg/m3 and the respirable fraction must not exceed 4 mg/m3. Inhalable means dust particles getting into the nose and mouth which can, therefore, get into the lungs. Respirable means the smaller particles, namely the fraction of this that actually gets into the gas exchange section of the lungs. A number of industrial dust have WELs, including:
- Cotton 2.5 (8 h)
- Flour 10 (8 h), 30 (15 min)
- Hardwood 5 (8 h) – also classed as a carcinogen
- Softwood 5 (8 h)
- Portland cement 10 (inhalable, 8 h); 4 (respirable, 8 h)
- Rubber 6 (8 h)
- Silicon 10 (inhalable, 8 h); 4 (respirable, 8 h)
There are a number of approaches to controlling PM pollution. The dust-generating process itself should be carried out in such a way as to prevent dust escaping into the surrounding air. This can involve:
- Enclosure/fume hood
- Local exhaust ventilation
- General workplace ventilation
In some situations, personal protective equipment (PPE) such as respirators (which filter incoming workplace air) or breathing apparatus (with an external air supply) may be appropriate. Dust masks are sometimes used but these should have a CE mark if they are to be effective.
Filtration plays an important role in controlling workplace PM pollution. An industrial grade high-efficiency particulate air (HEPA) filter like the IQAir HyperHEPA series can remove particles down to 0.003 microns with a guaranteed minimum efficiency of 99.5 per cent.
Employees can protect themselves from workplace PM pollution by making sure they receive proper training and that they always follow the correct safety procedures. Problems such as occupational asthma symptoms or lack of protective equipment should be reported to occupational health and/or the local health and safety executive.