3.10.1.: Definitions and general considerations These criteria provide a means of classifying substances or mixtures that may pose an aspiration toxicity hazard to humans. ‘Aspiration’ means the entry of a liquid or solid substance or mixture directly through the oral or nasal cavity, or indirectly from vomiting, into the trachea and lower respiratory system. Aspiration toxicity includes severe acute effects such as chemical pneumonia, varying degrees of pulmonary injury or death following aspiration. Aspiration is initiated at the moment of inspiration, in the time required to take one breath, as the causative material lodges at the crossroad of the upper respiratory and digestive tracts in the laryngopharyngeal region. Aspiration of a substance or mixture can occur as it is vomited following ingestion. This has consequences for labelling, particularly where, due to acute toxicity, a recommendation may be considered to induce vomiting after ingestion. However, if the substance/mixture also presents an aspiration toxicity hazard, the recommendation to induce vomiting shall be modified. Specific considerations A review of the medical literature on chemical aspiration revealed that some hydrocarbons (petroleum distillates) and certain chlorinated hydrocarbons have been shown to pose an aspiration hazard in humans. The classification criteria refer to kinematic viscosity. The following provides the conversion between dynamic and kinematic viscosity:

image Although the definition of aspiration in section includes the entry of solids into the respiratory system, classification according to point (b) in Table 3.10.1 for Category 1 is intended to apply to liquid substances and mixtures only. Classification of aerosol/mist products
Aerosol and mist forms of a substance or a mixture (product) are usually dispensed in containers such as self-pressurised containers, trigger and pump sprayers. The key to classifying these products is whether a pool of product is formed in the mouth, which then may be aspirated. If the mist or aerosol from a pressurised container is fine, a pool may not be formed. On the other hand, if a pressurised container dispenses product in a stream, a pool may be formed that may then be aspirated. Usually, the mist produced by trigger and pump sprayers is coarse and therefore, a pool may be formed that then may be aspirated. When the pump mechanism may be removed, and the contents are available to be swallowed then the classification of the substance or mixture shall be considered.