Not all dusts have assigned exposure standards. However, it should not be assumed that this indicates that these unlisted particulates do not represent a hazard to health.

In addition to any specific physiological effect related to the unique properties of an individual particulate, high concentrations of particulates in the workplace may cause unpleasant deposition of dust in the ears, eyes and upper respiratory tract, and reduce visibility in the workplace. in addition, the mechanical action of these dusts, or the cleaning procedures necessary for their removal, may cause injury to the skin or mucous membranes.

Where no specific exposure standard has been assigned and the substance is both of inherently low toxicity and free from toxic impurities, the recommended exposure standard for PNOC in general should be 10mg/m3 for inhalable particulates and 3mg/m3 for respirable particulates. However, this general exposure standard should not be applied where the particulate material contains other substances, which may in themselves be toxic or cause physiological impairment at lower concentrations. In such circumstances, the exposure standard for the more toxic components should be applied. For example, where a dust contains asbestos or more than one per cent crystalline silica, such as quartz, cristobalite or tridymite, the exposure to these materials should not exceed the appropriate value for these substances.

Providing the airborne particulate does not contain other hazardous components, compliance with the exposure standard for dusts in general should prevent impairment of respiratory function even over many years of exposure.