What is the most severe rating in the GHS classification system?

In the Globally Harmonized System (GHS) of Classification and Labeling of Chemicals, the severity of hazards is rated on a scale that categorizes them from one to four, with one indicating the highest level of risk. A classification of one signifies that the substance poses a significant hazard, such as being highly toxic, corrosive, or flammable, making it the most serious rating among the options provided. This classification system is designed to ensure that hazards associated with chemical substances are communicated clearly and effectively to those who may be exposed, safeguarding health and safety in the workplace.