The process of transporting chemicals and hazardous materials requires clear, standardized communication to ensure safety throughout the logistics chain. This standardization is achieved through a globally agreed-upon framework that dictates how manufacturers and shippers must classify and label products. Labeling systems provide immediate, actionable information to handlers, emergency responders, and end-users regarding the specific dangers posed by a substance.
What Are Signal Words?
Signal words function as a standardized component within the Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. Their purpose is to immediately convey the relative severity of a hazardous material to any person handling or encountering the product. The GHS framework recognizes only two designated signal words for this function: DANGER and WARNING. These words are always accompanied by specific hazard statements and pictograms that provide detailed information about the nature of the risk.
The Rule of Exclusivity
On any compliant shipping label governed by the GHS, only one signal word will be present. This singular requirement is based on a regulatory principle designed to prevent the dilution of the most serious hazard warning. When a chemical product or mixture presents multiple hazards, the signal word used must reflect the highest level of severity present in the product’s classification. For example, a substance may be classified as both a moderate skin irritant and highly flammable, which would separately warrant both signal words, but the rule dictates that the word corresponding to the more severe hazard must take precedence.
Differentiating DANGER and WARNING
The distinction between the two signal words is based entirely on the hazard category assigned to the chemical, reflecting the potential for harm. The signal word DANGER is reserved exclusively for the most severe hazard categories across physical, health, and environmental risk classifications. This includes highly toxic materials, Category 1 flammable liquids, and substances that are corrosive enough to cause severe skin burns and eye damage. WARNING is used for hazards that are less severe but still require careful handling and specific precautions, such as mild skin irritants, certain Category 2 flammable gases, and materials that pose a moderate hazard if swallowed or inhaled.
Placement on Shipping Documentation and Labels
The placement of the signal word distinguishes between different regulatory requirements for transport and product communication. The signal word is a mandatory element of the GHS container label, which is required by the Occupational Safety and Health Administration (OSHA) Hazard Communication Standard (HCS) for the primary container. Transport regulations, such as those from the Department of Transportation (DOT) or the International Air Transport Association (IATA), typically govern the outer shipping package or overpack using hazard class numbers and placards. The signal word is found on the GHS-compliant label affixed to the immediate container that accompanies the shipment, not necessarily on the large, exterior transport placard.
Regulatory Requirements for Signal Words
The mandate for using signal words stems from the adoption of the Globally Harmonized System, which is implemented in the United States through OSHA’s Hazard Communication Standard (29 CFR 1910.1200). This regulatory framework requires that every container of a hazardous chemical shipped within or imported into the U.S. must bear a label that includes the appropriate signal word. Adherence to these specific labeling requirements is mandatory for any entity involved in manufacturing, distributing, or importing hazardous chemicals, ensuring all employees and downstream users receive standardized information.