Hazard Class 6 materials are poisons that are solids and liquids. Some of the liquids are volatile and produce vapors, which are an inhalation hazard. Volatile poisons that are an inhalation hazard require the transport vehicle to be placarded regardless of the quantity. Class 6 is divided into two subclasses: 6.1 and 6.2. The DOT defines a Class 6.1 poison as a material, other than a gas, known to be so toxic to humans as to afford a health hazard during transportation or which, in the absence of adequate data, is presumed to be toxic to humans because it falls within any one of the following categories when tested on laboratory animals.