Division 4.2 must be separated from which classes?

• A. Class 1, Class 5.1
• B. Class 2, Class 3
• C. Class 6.1, Class 8
• D. Class 7, Class 9

Answer: (A)

Safety separation rules for dangerous goods transport focus on keeping incompatible materials apart to prevent ignition or explosion. Division 4.2 comprises substances that are liable to spontaneous heating, so they must be kept away from materials that could trigger a dangerous reaction. They are separated from explosives because any shock, heat, or friction could push a self-heating substance over the edge into an explosion. They are also separated from oxidizers because contact with oxidizing agents can supply the oxygen and energy needed to start or accelerate fires, turning a gradual self-heating problem into a rapid, violent event. The other classes don’t pose the same immediate combination of shock sensitivity or strong oxidizing environment with Division 4.2, so the specific separation is from Explosives and Oxidizing Substances.