Which type of material ignites when they contact each other?

Which type of material ignites when they contact each other?

• A. Pyrophoric
• B. Hypergolic
• C. Autoignition
• D. Combustible

Answer: (B)

Hypergolic materials ignite when two reactive components meet—the fuel and the oxidizer ignite instantly on contact, without any external heat or flame. This is what makes hypergolic pairs particularly hazardous in storage and handling, since just mixing or coming together of the components can start a fire. Pyrophoric substances, by contrast, ignite upon exposure to air, not simply because they touch another chemical. Autoignition refers to materials that ignite after being heated to their ignition temperature, not because they contact a second chemical. Combustible materials can burn, but they require an external ignition source or sufficient heat, not spontaneous ignition from direct contact with another substance.

Hypergolic materials ignite when two reactive components meet—the fuel and the oxidizer ignite instantly on contact, without any external heat or flame. This is what makes hypergolic pairs particularly hazardous in storage and handling, since just mixing or coming together of the components can start a fire. Pyrophoric substances, by contrast, ignite upon exposure to air, not simply because they touch another chemical. Autoignition refers to materials that ignite after being heated to their ignition temperature, not because they contact a second chemical. Combustible materials can burn, but they require an external ignition source or sufficient heat, not spontaneous ignition from direct contact with another substance.