What Does Poison, Class A or B Mean?
The United States Department of Transport uses a classification system for poisons which divides them into either Class A or Class B poisons. Class A poisons are highly toxic and can be lethal even in very small dosages. Class B poisons are less toxic, but still considered to be dangerous for humans.
Safeopedia Explains Poison, Class A or B
Some Class A poisons can be lethal if people breathe in their gas or vapor from the atmosphere. Examples of Class A poisons include nitrogen peroxide, cyanogen and phosgene. Potions may be liquid, solid, paste or semi-solid. The Department of Transportation deems all Class A and B poisons to be hazardous to health during transportation.