Skull and Crossbones
Universal symbol for poison, toxic substances, and mortal danger.
International · c. 1400 CE – present
Radiation Warning Symbol (Trefoil)
International symbol warning of ionizing radiation hazards.
Description
The radiation warning symbol (trefoil) was developed at the University of California Radiation Laboratory (now Lawrence Berkeley National Laboratory) in 1946. The symbol consists of a central circle surrounded by three blades arranged at 120° intervals. The original colors were magenta on yellow. ISO 361 and ISO 7010 (W003) standardize its use internationally. The symbol warns of the presence of ionizing radiation from radioactive materials or radiation-generating equipment. A newer supplementary symbol (ISO 21482) was developed in 2007 to convey the danger more intuitively.
Origin & Cultural Context
Developed at the University of California Radiation Laboratory in 1946. Standardized internationally by ISO 361.