• Defined hazards include simple asphyxiants and combustible dust.

OSHA has also added two “defined hazards” into the HazCom standard to address known hazards that have no corresponding Globally Harmonized System (GHS) classification. These OSHA defined hazards are:

• Simple asphyxiant: A substance or mixture that displaces oxygen in the ambient atmosphere, and can thus cause oxygen deprivation in those who are exposed, leading to unconsciousness and death.
• Combustible dust: Finely divided solid particulates of a substance or mixture that pose a flash-fire hazard or explosion hazard when dispersed in air or other oxidizing media.

Hazards not otherwise classified (HNOC)

A “hazard not otherwise classified” is an adverse physical or health effect identified through evaluation of scientific evidence during the classification process that does not meet the specified criteria for the physical and health hazard classes addressed in 1910.1200. This does not extend coverage to adverse physical and health effects for which there is a hazard class addressed in 1910.1200, but the effect either falls below the cut-off value/concentration limit of the hazard class or is under a GHS hazard category that has not been adopted by OSHA (e.g., acute toxicity Category 5).