The method described by this Test Guideline provides information that allows hazard assessment for short-term exposure to a test article by inhalation, and allows the substance to be classified according to the Globally Harmonized System of Classification and Labelling of Chemicals (GHS). The test method is based on a stepwise procedure, each step using 3 animals of each sex (the preferred species is rat). Animals are exposed in  inhalation chambers to a pre-defined concentration for 4 hours. Absence or presence of compound-related mortality of the animals at one step will determine the next step. Animals in severe pain or distress should be humanely killed. The starting concentration is selected from one of four fixed levels corresponding to GHS categories 1-4 for gases, vapours or aerosols. Animals are observed daily for clinical signs of toxicity for a total of at least 14 days. Animals' body weights should be determined at least weekly. All the animals should be subjected to gross necropsy.