Not all inhaled materials are deposited in the same location (within the respiratory tract) and the location in the respiratory tract where disease is experienced may vary. Several factors influence this such as the physical characteristics of the inhaled material (e.g., is it too large to infiltrate the lungs?), the chemical properties of the material (and/or its toxins), as well as the dose of inhaled material, or the amount of exposure (e.g., is it something one is regularly exposed to at work or is it a one-time event). For example, contradistinctions may be made between soluble and less soluble gases. While soluble gases tend to affect the upper region of the respiratory tract (as well as moist tissue around the eyes; ammonia being an example), less soluble gases tend to affect the middle or deep regions of the respiratory tract (e.g., phosgene gas). 

When an Indoor Environmental Quality (IEQ) assessor responds to the concerns of an occupant, these considerations are important in ensuring the assessment process will be specific to the concerns of the occupant. They must be accounted for. For example, when sampling for an airborne particle, the assessor must prepare by performing a size-selection sampling strategy (SSS). The American Conference of Governmental Industrial Hygienists (ACGIH) has defined three particle size fractions that are used during the SSS: inhalable, thoracic, and respirable.