The hazard potential of airborne dust, solid particles, or droplets is dependent on the mass concentration as well as the particle size.

Particle size determines the deposition site within the respiratory tract and the subsequent health effect. Therefore, the American Conference of Governmental Industrial Hygienists (ACGIH), has recommended that particle-size selective Threshold Limit Values (TLVs) be developed for inhalation hazards in the workplace. Particle-size selective TLVs consider two points: The size-fraction most closely associated with the specific health effect. The mass concentration within that size fraction which should represent the TLV.

Since inhalable particulate mass is defined as those materials that are hazardous when deposited anywhere in the respiratory tract, including the nose and mouth, a sampler designed for the collection of inhalable dust should have a median cut-point of 100 µm.