Division 4.2 hazards are best described as which of the following?

• A. They ignite within 5 minutes of contact with air.
• B. They spontaneously combust without heat input.
• C. They are self-reactive substances that do not detonate.
• D. They are substances liable to spontaneous heating under normal conditions of transport or that can heat up with contact to air to catch fire.

Answer: (D)

Division 4.2 hazards are materials that can generate heat on their own or heat up when exposed to air, during normal transport, to the point of catching fire without an external ignition source. The emphasis is on spontaneous heating or air-induced heating that can lead to ignition while in transit. This captures both ways such substances pose a fire risk without needing a flame or external heat. It’s not about ignition after a fixed short time, nor about self-reactive materials with different behavior, which is why this description best fits Division 4.2.