This trefoil is the international warning symbol for radioactive substances and ionising radiation. This symbol can be found on the packaging of radioactive substances, on equipment containing a radioactive source and in rooms where radioactivity is used.
This international hazard symbol is used to indicate a biological risk. Biological substances that present a danger to human, plant or animal health are marked with this symbol.
Substances in an extremely cold condition (cryogenic substances) are marked with this symbol. Most cryogenic substances are gases condensed to liquid such as liquid nitrogen (-196 ºC), helium (-269 ºC) and oxygen (-183 ºC). Carbonated snow, solid carbon dioxide or dry ice (-78 ºC) is also a cryogenic substance.
An explosive atmosphere may arise if flammable gases, vapour, mist or dust are mixed with ambient air (oxygen). An explosion hazard area is marked with this symbol (ATEX 137 directive). Equipment in this area must be explosion-proof (ATEX 95 directive).
In addition to their normal chemical or physical properties, nanoparticles also have special properties or risks associated with their size and shape. In rooms where nanoparticles are used, which may pose a health risk, this symbol is sometimes used. However, this pictogram is not prescribed by law.
Asphyxiation hazard due to insufficient oxygen is possible in rooms where liquid nitrogen, helium or dry ice is used. These substances can displace oxygen in the room through rapid evaporation. These rooms are therefore sometimes marked with this symbol. However, this pictogram is not prescribed by law.