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How to manage silica dust

Preventing exposure to respirable crystalline silica is the only reliable method to protect workers’ health.

Because of its effects on workers’ health, many countries have set legal exposure limits for silica. These are the maximum allowable concentrations in workplace air, averaged over a period of time (usually eight hours). Example in this table are from Industrial Safety and Hygiene News.

Country Silica exposure level (mg/m3)
Australia 0.1
Austria 0.15
Belgium 0.1
British Columbia 0.025
Bulgaria 0.07
Czech Republic 0.1
Denmark 0.1
Estonia 0.1
Finland 0.05
France 0.1
Greece 0.1
Hungary 0.15
Ireland 0.1
Italy 0.05
Lithuania 0.1
Luxembourg 0.15
Mexico 0.025
Netherlands 0.075
Norway 0.1
Poland 0.3
Portugal 0.025
Romania 0.1
Slovakia 0.1
Slovenia 0.1
South Africa 0.1
Spain 0.1
Sweden 0.1
Switzerland 0.15
United Kingdom 0.1
United States 0.05

Measuring silica

A qualitative way of assessing the amount of airborne dust is to use a dust lamp, sometimes called a Tyndall bean. It illuminates very fine dust that would otherwise be invisible to the naked eye.

A bright beam of light is shone through an area where it is predicted a particle dust cloud may be present. A flat panel is used to shield the observer’s eyes from the main beam. For example, this could be a piece of card, or by using the worker’s body or a piece of machinery as a shield.

The particle dust cloud is observed behind the shield by looking up the beam towards the source of illumination. The beam should be observed at a slight angle (5-15°) off the centre of the beam. A dark background should be used to help with the observation.

The dust cloud will then be made visible as the particles are suspended in the air. Normal lighting conditions can be used, but better results are obtained by suppressing the ambient lighting. It may be surprising just how much particle dust occupies the air.

Read the Health and Safety Executive’s guide on the use of a dust lamp, which includes helpful images.

The quantitative measurement of exposure to silica requires occupational hygiene support.

An occupational hygienist uses equipment, including a battery-operated sampling pump, polythene tubing, cyclone sampling head, pre-weighed PVC filters, a flowmeter (to measure the amount of air flowing through the sampler), clips and belts.

The equipment is worn by a worker throughout a shift, with the sampling head close to the operative’s nose/mouth area. After the shift, the filter is sent to a specialist laboratory for analysis for crystalline silica.

The result is expressed as a concentration – milligrams of crystalline silica per cubic metre of air sampled (mg/m3). You can also ask the laboratory to reweigh the filter to give the respirable dust concentration and the percentage of silica on the sample.

The data can then be compared with your country’s legal exposure limit.