Aerosols and fibers

Aerosol is a suspension of tiny particles or droplets in the air, such as dusts, fumes, smoke or mists. The aerosol can be generated during various industrial processes, and could consist of a range of materials such as wood dust, welding fumes, flour dust, etc. Fibers are fine, thread-like structures that may also be present in the air due to certain types of work, such as textile manufacturing (cotton, wool) or insulation installation (mineral fibers, asbestos). Aerosol and fibers may be inhaled and can sometimes cause adverse health effects for workers.

Two key factors which are important when assessing exposure from aerosols; The chemical composition of the material (toxic effect) and particle size (where it deposits in the respiratory system). These properties of aerosols determine the sampling method to be used for exposure measurements. The air concentration of aerosols is normally expressed in mg/m3, while the particle size is expressed in µm. The size of the particles, the Aerodynamic Diameter (AD), can vary from less than 0.01 to more than 100 µm The International Standards Organisation (ISO) has classified aerosols according to particle size;

• Inhalable fraction: The particles are less than or equal to 100μm, and are inhaled through the nose and mouth.

• Thoracic fraction: The particles have a size of less than 10μm, and penetrate to below the larynx.

• Respirable fraction: The particles penetrate to the alveolar part of the lungs. The particle size is below 4μm.

Classification of aerosol fractions according to particle size and where it deposits in the respiratory system.
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Measurement of aerosols/dust

Measurements of the airborne concentration of aerosol and fibres should be taken in the breathing zone of the worker. The most common approach in workplace exposure assessment is the use of filtration samplers where the sampling head is preloaded with a filter and attached in the breathing zone of the worker. The sampling head is connected to a pump that pulls air through the sampling head/filter at a predefined flow rate. In order to compare exposure concentrations with Occupational Exposure Limits, the sampling time should be 8 hours. The weight gain of the filter, the sampling time and the flow rate are used to calculate the average exposure concentration for the worker. Dust sampling at a workplace. The dust sampler is placed in the breathing zone of the worker, while the pump is attached to the belt.