Before the Globally Harmonized System (GHS), the same chemical could have different hazard classifications, different label formats, and different Safety Data Sheets in different countries — creating confusion and genuine safety risks for workers and emergency responders. GHS was developed under the auspices of the United Nations to bring consistency to chemical hazard communication globally.
In the US, OSHA's Hazard Communication Standard (HazCom 2012) adopted GHS, replacing the previous MSDS system with 16-section Safety Data Sheets and standardized labels. Understanding these requirements is essential for anyone who works with hazardous chemicals.
GHS Hazard Classification
GHS classifies chemicals across two main hazard categories, each with specific sub-classes:
Physical Hazards
- Flammable liquids (Categories 1–4 based on flash point and boiling point)
- Flammable gases, aerosols, and solids
- Oxidizing liquids and solids
- Explosives and self-reactive substances
- Compressed gases
- Organic peroxides
- Corrosive to metals
Health Hazards
- Acute toxicity (Categories 1–5 by oral, dermal, and inhalation routes)
- Skin corrosion/irritation
- Serious eye damage/irritation
- Respiratory or skin sensitization
- Germ cell mutagenicity
- Carcinogenicity
- Reproductive toxicity
- STOT — specific target organ toxicity (single and repeated exposure)
- Aspiration hazard
The most important thing to understand about GHS hazard categories is the numbering: Category 1 is always the MOST hazardous, and higher numbers represent decreasing hazard. A flammable liquid Category 1 (flash point <23°C, boiling point <35°C) is more hazardous than Category 4 (flash point 60–93°C).
The 16-Section SDS Structure
GHS SDS have a standardized 16-section structure. The sections you'll use most frequently in emergency situations:
- Section 1: Chemical identity and supplier contact (including emergency phone number)
- Section 2: Hazard identification — GHS classification, signal word, hazard and precautionary statements
- Section 4: First-aid measures — what to do if someone is exposed
- Section 5: Firefighting measures — suitable extinguishing media, special hazards
- Section 6: Accidental release measures — spill containment procedures
- Section 8: Exposure controls/PPE — OELs and required protection
- Section 14: Transport information — UN number and shipping classification
GHS Label Elements
GHS labels on hazardous chemical containers must include six elements:
- Product identifier: Chemical name or trade name
- Signal word: Either "Danger" (more severe hazards) or "Warning" (less severe)
- Hazard statements: Standardized phrases describing the hazards (e.g., "H225 Highly flammable liquid and vapor")
- Precautionary statements: Standardized phrases describing protective measures (P codes)
- Pictograms: The nine GHS pictograms (flame, skull and crossbones, exclamation mark, etc.) in a red-bordered diamond
- Supplier information: Name, address, and emergency phone number
HazCom 2012 Employer Obligations
Under OSHA HazCom 2012, employers who use hazardous chemicals must:
- Maintain a written hazard communication program
- Maintain a chemical inventory and SDS for all hazardous chemicals in the workplace
- Ensure SDS are accessible to employees at all times during their shift
- Ensure all containers are properly labeled
- Train employees on GHS and the hazards of the specific chemicals they work with
The training requirement is the most commonly cited deficiency in OSHA chemical standard inspections. Generic "GHS awareness" training is not sufficient — employees must understand the specific hazards of the chemicals they use and the protective measures required for their specific tasks.