GHS hazard categories make up the fundamental hierarchal elements of the GHS building black approach. The GHS has 3 main hazard groups: physical, health, and environmental. Each group acts as an umbrella for a set of distinct hazard classes. A hazard is classified into a particular group based on how it elicits its dangerous effects.
GHS hazard categories define the next level of organization within the building block model, acting as a means to compare the severity of a hazard within a specific hazard class. The GHS hazard categories are carefully chosen based on classification criteria and analysis of scientific/experimental data; both of which are harmonized to align with globally approved scientific standards. An example which illustrates use of the categorical, building-block approach would be how a manufacturer classifies a particular chemical substance:
1. Hazard Group = Health – Grouped into health hazards because intrinsic properties of this substance may result in adverse health effects.
2. Hazard Class = Acute Toxicity – Put into the acute toxicity class if adverse effects occur via oral or dermal administration of this substance either as a single dose or multiple doses within 24 hours; if adverse effects occur upon inhalation exposure over 4 hours or less.
3. Hazard Category = Oral, Category 2 – Administration via the oral route fulfills the cut-off LD50 criteria for an Acute Toxicity Estimate (ATE) of 50mg/kg, putting it into category 2; one of five categories for this class.
GHS hazard categories are arranged such that ascension into higher numerical values typically corresponds to a decreasing degree of hazard severity, e.g. category 2 is less severe than category 1. At minimum, Each hazard class contains at least 1 hazard category, which may sometimes be further divided by letter into sub-categories, e.g. 1A & 1B are sub-categories with B indicating a hazard of lesser severity. Some countries may adopt all categories of a particular hazard class, while others may only adopt the first 2. It is recommended to always incorporate at least the category of highest hazard severity. Each hazard category is also associated with some combination of specific hazard symbols, signal words, and statements, all of which are prescribed according to the nature of the hazard.