The Laboratory Standard defines a hazardous chemical as any element, chemical compound, or mixture of elements and/or compounds that are a physical or health hazard.
A chemical is a physical hazard if there is scientifically valid evidence that it is a flammable, a combustible liquid, a compressed gas, an explosive, an organic peroxide, an oxidizer, pyrophoric, unstable material (reactive), or water-reactive.
A chemical is a health hazard if there is statistically significant evidence based on at least one study conducted in accordance with established scientific principles that acute or chronic health effects may occur in exposed employees.
In most cases, the label will indicate if the chemical is hazardous. Look for key words like caution, hazardous, toxic, dangerous, corrosive, irritant, carcinogen, etc. Old containers of hazardous chemicals (before 1985) may not contain hazard warnings.