Risks for the respiratory system

Fumes, dust, and exhalations can be very harmful if they reach the respiratory system of the human being which can be divided into three parts: the upper airways, the tracheobronchial tree, and the alveolar region.

Based on this subdivision, three particle fractions have been defined according to their size: the inhalable, thoracic and alveolar fractions (according to AFNOR EN 481) which provide guidance on the penetration and deposition of particles into the respiratory system and their potential health effects.

• Inhalable fraction: mass fraction of airborne particles that can enter the body from the mouth and nose, and then settle in the respiratory tract; they include particles whose aerodynamic diameters can reach 100 μm.

• Thoracic fraction: a mass fraction of particles that, when inhaled, can penetrate beyond the larynx; they include particles whose aerodynamic diameter can reach 30 μm.
• Alveolar fraction: a mass fraction of particles which, when inhaled, can penetrate to the alveoli of the lungs; they include particles whose aerodynamic diameter can reach 10 μm. In relation to particles emitted outside welding and cutting activities having an aerodynamic diameter of less than 1 μm, the alveolar fraction plays a central role with regard to health effects. Inhalable dust data lead to an overestimation rather than an underestimation of exposure.

Source: INRS ED 6132 Guide on welding fumes risks