It indicates a flammable or explosive gas.
A hazard class 2 would be compressed gases.
Red is used for flammable, yellow for oxygen, green for non-flammable gases, and white for inhalation hazards.
explosives
symbol, UN hazard class number, color, UN identification number
COLOR
The Dangerous When Wet placard is a square on point (or diamond) placard with white markings on a blue background. The words "Dangerous When Wet are printed across the middle, with a drawing of a flame centered in the upper corner, and the numeral four (4) in the bottom corner to indicate the Hazard Class.
The hazard class of the substance being carried
A placard identifying hazard class 6 describes the presence of a poisonous gas. For an image, see the related link, below.
Poisonous or infectious materials are in Hazard Class 6. The several labels and placards for Class 6 are white in color, with black printing.
Bottom
The placard on a tanker carrying hazardous materials will tell you the class of the hazard (flammable, explosive, corrosive, etc). If you have access to the North American Guide or a similar reference, the placard will also tell you something a bit more specific about the identity of the hazardous material - its category, or sometimes its chemical name.
Hazard Class 3
Class 1 materials are explosives.Materials that have an explosive hazard are in Hazard Class 1.
The second number given with a hazard class is referred to as?