Which symbol is used to indicate radioactive material?

• A. Skull and crossbones
• B. Diamond hazard
• C. Flame symbol
• D. Trefoil symbol

Answer: (D)

The symbol used to indicate radioactive material is the trefoil. This international warning sign features three blade-like arms radiating from a central circle, usually in black on a bright yellow background, chosen for high visibility and quick recognition from a distance or in poor lighting. It signals that radioactive sources or materials are present, so appropriate safety measures—such as shielding, controlled access, and limited exposure—must be used. You’ll see it on containers, storage areas, and transport packaging handling radioactive substances.

Skull and crossbones marks poison or toxic hazards, not radioactivity. The diamond hazard panel (the NFPA/GHS-style diamond) communicates multiple general hazard ratings, not the specific presence of radioactive material. The flame symbol denotes flammable materials.