The extensive use of chemical products world-wide commands the need for countries to utilize a more systematic approach in regulating their use and trade. Implementation of the Globally Harmonized System of Chemical Classification and Labelling (GHS) does exactly that; the United Nations created GHS in hopes that different countries would adopt a more globally recognized hazard communication program. Countries choosing to adopt GHS enforce the standardized system of labelling chemical products to include GHS signal words, symbols, hazard statements, and precautionary statements on labels for hazardous products.
GHS’s 7th revised edition of The Purple Book defines signal word as “a word used to indicate the relative level of severity of hazard and alert the reader to a potential hazard on the label.” “Danger” indicates hazards of greater severity, often referring to chemicals that can be further subdivided into categories. e.g., for the ‘flammable liquids’ class, category 1 hazards are more severe than category 2, but both are represented by the signal word ‘Danger’ (this may vary depending on the number of categories in a specific hazard class). “Warning” indicates hazards of lesser severity and is typically assigned to chemicals that have lower category rankings. e.g., the flammable liquids class is divided into 4 categories with “Warning” being used for chemicals assigned to categories 3 and 4.
The standardized format of chemical labels requires GHS signal words, pictograms, and hazard statements to be grouped together and placed in a prominent location on the label. A rule of thumb when using GHS signal words is to ensure only one signal word is placed on any one chemical label; always use the signal word pertaining to the most severe hazard classification! For an in-depth summary of which informational elements are to be used for each specific hazard class, take a look at Annex 1: Classification and Labelling Summary Tables of GHS’S most current edition of The Purple Book.