Chemical Hazard Classification (GHS)

Legal Requirements

The Hazard Communication Standard (29CFR 1910.1200) requires all manufacturers or distributors of any products containing chemicals to evaluate the chemical hazards of the product. The evaluation is performed by classifying each chemical based on published toxicological or other data to determine its physical and health hazards.

The identified hazards have to be communicated on the container label and in documents called Safety Data Sheets (SDS). Manufacturers and distributors are required to provide safety data sheets to their clients that describe the results of the classification and all known hazards of a chemical.

Globally Harmonized System (GHS)

The Globally Harmonized System (GHS) was developed by the United Nations for international standardization of hazard classification and communication. OSHA has adopted GHS, and beginning June 2015, all manufacturers are required to prepare labels and SDS according to GHS. Some manufacturers already comply with this regulation. 

GHS Label Elements

The main health and physical hazards have to be indicated on the product label by using pictograms, signal words, and standardized hazard statements. The pictograms are explained in the next paragraph. The signal word "Danger" is used for severe hazards and "Warning" is used for less severe hazards. Based on the classification of the product, the hazards are described in standardized phrases called "hazard statements". For example, a highly toxic chemical requires a statement "Fatal if inhaled or swallowed".

GHS Hazard Classes

The GHS classification further divides health and physical hazards into separate classes such as toxicity, irritation, sensitization, flammability, etc. The severity of the hazard within each class is described by the category. Some classes have five categories; other classes have only one category. Category 1 or A always represents the highest hazard within that class. The higher the category number, the lower the hazard. The classes, their categories and pictograms are as follows:

Health Hazards

Acute Toxicity (Category 1 through 5)

Compounds in Category 1 through 3 are identified by the Skull and Cross Bone pictogram. They are highly toxic in small amounts and can cause serious health effects or death. Compounds in Category 4 are labeled with the Exclamation Mark symbol (!). They are still harmful but cause lethal effects only after exposure to large amounts. Compounds in Category 5 may pose a hazard for vulnerable populations. As the toxicity depends on the route of exposure, chemicals may have different categories for oral, dermal, or inhalation toxicity.

Skin Corrosion / Irritation (Category 1 through 3)

Compounds in Category 1 can cause severe skin damage. They are marked with the Corrosion symbol. Compounds in Category 2 and 3 can cause reversible damage and are labeled with the Exclamation Mark symbol.

Eye Effects

Compounds that can cause irreversible, serious eye damage are classified as Category 1 and are marked with the Corrosion symbol. Eye irritants are classified as Category 2a and 2b. They can cause reversible adverse effects and are labeled with the Exclamation Mark.


Respiratory sensitizers that can induce hypersensitivity of the airways after inhalation are marked with the Health Hazard symbol. A skin sensitizer that can induce an allergic response following skin contact is labeled with the Exclamation Mark.

Compounds with the following health classifications are labeled with the Health Hazard symbol

Mutagenicity (Category 1a, 1b and 2) A Category 1 compound is known to produce heritable mutations in human germ cells. Compounds in Category 2 are suspected to cause mutations.

Carcinogenicity (Category 1a, 1b and 2) A Category 1a compound is known to cause malignant tumors in humans. Compounds in Category 1b are presumed to cause cancer in humans based on animal carcinogenicity. For compounds in Category 2, there is limited evidence of human or animal carcinogenicity.

Reproductive Toxicity (Category 1a, 1b and 2) A Category 1a compound is known to cause effects on human reproduction or development. Compounds in Category 1b are presumed to cause such effects, based on the results of animal experiments. Compounds in Category 2 are suspected to cause reproductive effects. An additional category describes effects through lactation.

Target Organ Toxicity (Category 1 through 3) Chemicals in this category have significant health effects upon single or repeated exposure that can impair the function of one or more organs. Category 1 refers to chemicals that are known to cause such effects. Compounds in Category 2 are presumed to cause adverse effects. Category 3 chemicals cause only transient narcotic effects or respiratory tract irritations and are labeled with the exclamation mark symbol.

Aspiration Hazard (Category 1 and 2) Compounds in Category 1 are known to pose adverse effects such as pulmonary injury when aspirated. Compounds in Category 2 are presumed to cause such effects, based on the results of animal studies and physical properties.

Environmental Hazards

Acute and chronic aquatic toxicity

A substance that can cause injury or other adverse effects to aquatic organisms with either a short-term or long-term exposure. This class is divided into four categories. Acute aquatic toxicity Category 1 and chronic aquatic toxicity Category 1 and 2 are labeled with the Environment symbol.

Physical Hazards

Corrosive to metals

A substance that will react with and damage metals. This class is marked with the Corrosion symbol (the same symbol as used for skin and eye corrosives).


Explosives: A chemical that is by itself capable of producing gas at a temperature, pressure, and speed that it can cause serious damage to the surroundings. Explosives are divided into groups 1.1 through 1.6 depending on sensitivity. Divisions 1.1 through 1.4 are labeled with the Exploding Bomb symbol.


All flammables are identified by the Flame symbol and include:

  • Gases: A gas having a flammable range in air under standard conditions (20°C, 101.3 kPa).
  • Aerosols: Compressed, liquefied, dissolved gas, or gas mixture in a non-refillable container containing flammable components.
  • Liquids: A liquid having a flash point of not more than 93°C / 200⁰F. Based on their flash points, flammable liquids are assigned to Category 1 through 4.
  • Solids: Solids that are readily combustible or may cause or contribute to fire through friction. Depending on the burning rate flammable solids are assigned to category 1 or 2.

Gases under pressure

Gases that are contained in a receptacle at a pressure not less than 280 Pa at 20°C or as a refrigerated liquid. They are identified by the Gas Cylinder symbol.

Organic peroxides

Organic liquid or solid that contains the bivalent O-O structure. Such substances may explode, burn rapidly, be sensitive to impact or friction, or react dangerously with other chemicals. Substances are assigned to types A through G with A being the most dangerous. Compounds are either marked with the Exploding Bomb (categories A and B) or the Flame symbol (categories C through F).

Oxidizing gases, liquids or solids

A chemical that in itself may not be combustible but causes or contributes to the combustion of other materials. This class is marked with a Flame Over a Circle symbol.

Pyrophoric liquid or solid

A chemical that ignites within five minutes after coming into contact with air. This class is identified by the Flame symbol.

Self-heating substances

A substance that self-heats by reacting with air. Unlike pyrophorics, it ignites only when in large amounts (kilograms) and after long periods of time (hours or days). Compounds are marked with the Flame symbol.

Self-reactive substance

A thermally unstable liquid or solid that can undergo an exothermic decomposition without the participation of oxygen. This class is divided into categories A through G. Compounds in categories A and B possess explosive properties and are marked with the Exploding Bomb symbol. Categories C through G are less hazardous and are marked with the Flame symbol.

Substances, which in contact with water emit flammable gases

Solids or liquids that give off flammable gases in dangerous quantities when brought in contact with water. This class is divided into categories 1 through 3 depending on the speed of gas evolution. All are labeled with the Flame symbol. 

Summary Pictograms

The image below shows the pictograms used for labeling. Underneath each pictogram is a list with classes the pictogram is used for.

Safety Data Sheets

Safety Data Sheets (SDS), formerly called Material Safety Data Sheets (MSDS), communicate the hazards associated with using chemicals. They are an important source of information for workers, lab personnel, emergency responders, and emergency medical personnel. As they often provide very limited information on safe handling procedures, they should be used in conjunction with safety guides provided by DRS and other knowledgeable sources (Prudent Practices, eEROS, textbooks, etc.) and standard operating procedures written for your group.

Managing SDS in a Laboratory

SDS can be available as electronic version or as hardcopies. A computer with internet connection is particularly useful to quickly access the latest SDS. Webpages like Sigma-Aldrich or Fisher Scientific are convenient and reliable sources for finding SDS. If no internet access is available, SDS of the most hazardous, largest volume, and most frequently used materials should either be stored on a computer accessible to everybody working in the lab, or as hardcopies in a binder.

Besides electronic access it is highly recommended to have hardcopies of highly toxic and corrosive chemicals available in the laboratory so they can be taken to the hospital if an exposure occurs.

Content of a Safety Data Sheet

In compliance with the new Hazard Communication Standard, SDS are divided into 16 sections and are required to provide the following information:

  1. Identification: Product identifier used on the label; manufacturer or distributor name, address, phone number, emergency phone number; recommended use; and restrictions on use.
  2. Hazard Identification: This section lists the GHS classification and hazard statements. Every hazard statement has a corresponding precautionary statement recommending measures to minimize or prevent adverse effects such as “Do not breathe dust.” This section may also show the label pictograms and give any other information related to known hazards of the product. Classifications by other entities such as OSHA, HMIS, or NFPA may also be given.
  3. Composition/Information on Ingredients provides a list of all hazardous ingredients, their CAS numbers, and their concentrations or concentration ranges in the product. For each ingredient, the hazard classification is given. Depending on the concentration, the classification for each individual compound may be different than the classification of the mixture found under section 2.
  4. First-Aid Measures describes potential symptoms and acute or delayed effects resulting from exposure. It gives information on how to respond to exposure and on appropriate medical treatment.
  5. Fire-Fighting Measures lists suitable extinguishing techniques and equipment as well as potential hazards arising from a fire, such as toxic fumes.
  6. Accidental Release Measures lists emergency procedures for responding to a spill, required protective equipment, and basic methods of containment and cleanup.
  7. Handling and Storage lists brief precautions for safe handling and storage. It should contain information about incompatibilities with other chemicals, but it is often not exhaustive. Refer to the DRS chemical storage guide for more detailed information.
  8. Exposure Controls/Personal Protection lists OSHA's Permissible Exposure Limits (PELs) and Threshold Limit Values (TLVs) for each ingredient. This section should also give information on personal protective equipment (PPE); e.g., appropriate respirators and gloves, and engineering controls.
  9. Physical and Chemical Properties lists the characteristics of the product such as color, boiling point, pH, and density etc.
  10. Stability and Reactivity lists chemical stability, possibility of hazardous reactions, conditions to avoid, incompatible materials, and hazardous decomposition products.
  11. Toxicological Information describes possible routes of exposure; symptoms related to physical, chemical and toxicological characteristics; acute and chronic effects; and numerical measures of toxicity such as LD50 values if available.
  12. Ecological information includes available information on ecotoxicity, degradability, bioaccumulation, and other adverse effects on the environment.
  13. Disposal considerations is relevant for professional waste disposal services. Refer to the DRS chemical waste guide for disposal practices.
  14. Transport information lists DOT UN number, proper shipping name, and class.
  15. Regulatory information includes other applicable local regulations on safety, health, and environment.
  16. Other information includes the date of preparation of the SDS or its last revision.


A Guide to The Globally Harmonized System of Classification and Labeling of Chemicals (GHS):

OSHA 1910.1200 Hazard Communication Standard:

OSHA Brief: Hazard and Communication Standard: labels and Pictograms

Last Update: 9/19/2016