Class 2
Class 2 — gases
Class 2 covers gases: flammable, non-flammable, and toxic. The division is the real label.
Class 2 is gases. The division tells you which kind. 2.1 is a flammable gas. 2.2 is a non-flammable, non-toxic gas. 2.3 is a gas poisonous by inhalation. Those three should never be collapsed into the single word "gas" if you can see the division.
Liquefied petroleum gas is the class 2 load railfans meet most often, commonly under identification number 1075 and a 2.1 placard. Chlorine and anhydrous ammonia are different gases, with their own numbers and a 2.3 placard. The tank looks similar from a distance. The placard is how you tell them apart.
A green, red, or white diamond is only a hint. Faded paint and odd light will lie to you. Read the division and the four-digit number.
Identification only. If a car is leaking or in a wreck, move away and call your local emergency number. Responders use the Emergency Response Guidebook. This page is not that book.