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Hazard symbol


Hazard symbols are easily recognizable symbols designed to warn about hazardous materials or locations. The use of hazard symbols is often regulated by law and directed by standards organizations. Hazard symbols may appear with different colors, backgrounds, borders and supplemental information in order to signify the type of hazard.


Common hazard symbols

Because of technical limitations, some web browsers may not display some special characters in this article.
Name Symbol Unicode Image
Toxic signU+2620Error creating thumbnail:
Caution signU+2621
Radiation signU+2622Error creating thumbnail:
Ionizing radiation sign??Error creating thumbnail:
Non-ionizing radiation sign??radiowave
Biohazard signU+2623Error creating thumbnail:
Warning signU+26A0Error creating thumbnail:
High voltage signU+26A1High voltage
Chemical weapon symbol
(U.S. Army)[1]
Laser hazard sign??

Radioactive sign


The international radiation symbol (also known as trefoil) first appeared in 1946, at the University of California, Berkeley Radiation Laboratory. At the time, it was rendered as magenta, and was set on a blue background.[2] It is drawn with a central circle of radius R, an internal radius of 1.5R and an external radius of 5R for the blades, which are separated from each other by 60°.[3]


On February 15, 2007, the IAEA and the ISO announced this new ionizing radiation symbol to supplement the traditional trefoil symbol. The new symbol is aimed at alerting anyone, anywhere to the potential dangers of being close to a large source of ionizing radiation. [4]

Biohazard sign


Developed by Dow Chemical company in the 1960s for their containment products.[5]

According to Charles Dullin, an environmental-health engineer who contributed to its development:

We wanted something that was memorable but meaningless, so we could educate people as to what it means.


All parts of the Biohazard sign can be drawn with a compass and/or ruler. The basic outline of the symbol is a plain trefoil, which is three circles overlapping each other equally like in a triple venn diagram with the overlapping parts erased. The diameter of the overlapping part is equal to half the radius of the three circles. Then three inner circles are drawn in with 2/3 radius of the original circles so that it's little tangent to the outside three overlapping circles. A tiny circle in center has a diameter 1/2 of the radius of the three inner circle, and arcs are erased at 90°, 210°, 330°. The arcs of the inner circles and the tiny circle are connected by a line. Finally, the ring under is drawn from the distance to the perimeter of the equilateral triangle that forms between the centers of the three intersecting circles. An outer circle of the ring under is drawn and finally enclosed with the arcs from the center of the inner circles with a shorter radius from the inner circles.[7]

Toxic sign

Main article: Skull and crossbones
Skull and crossbones

The skull and crossbones symbol, consisting of a human skull and two bones crossed together under the skull, is today generally used as a warning of danger, particularly in regard to poisonous substances.

The symbol, or some variation thereof, was also featured on the Jolly Roger, the traditional flag of European and American pirates. It is also used by the Skull and Bones, a secret society at Yale University, and is part of the WHMIS home symbols placed on containers to confirm that the substance inside is dangerous in a way.

In the USA, due to concerns that the skull and bones symbol's association with pirates encourages children to play with toxic materials, the Mr. Yuk symbol is also used to denote poison.

Warning sign

Main article: Exclamation mark

On warning signs, an exclamation mark is often used to draw attention to a warning of danger, hazards and the unexpected.

Chemical hazard

   A chemical hazard label is a pictogram applied to containers of dangerous chemical compounds to indicate the specific risk, and thus the required precautions. There are several systems of labels.

The U.S.-based National Fire Protection Association (NFPA) has a standard NFPA 704 using a diamond with four colored sections each with a number indicating severity 0-4 (0 for no hazard, 4 indicates a severe hazard). The red section denotes flammability. The blue section denotes health risks. Yellow represents reactivity (tendency to explode). The white section denotes special hazard information. This label is used primarily in the USA.

In Europe, another standard is used, as fixed in the ADR-Agreement. Vehicles carrying dangerous goods have to be fitted with orange signs, where the lower number identifies the substance, while the upper number is a key for the threat it may pose.

European hazard symbols

These hazard symbols for chemicals are defined in Annex II of Directive 67/548/EEC. A consolidated list with translations into other EU languages can be found in Directive 2001/59/EC (See the links section).

The 'n' in Harmful (Xn) stands for the French word nocif and the Italian word nocivo (noxious).

See also

  • International Standard ISO 3864: Graphical symbols — Safety colours and safety signs.
  • NFPA 704 Fire Diamond
  • Pictogram
  • British Standard BS 5378: Safety signs and colours.
  • Warning sign


  1. ^
  2. ^ Origin of the Radiation Warning Symbol (Trefoil).
  3. ^ Biohazard and radioactive Symbol, design and proportions.
  4. ^ This symbol is included in ISO 21482:2007. ISO International Standards are protected by copyright and may be purchased from ISO or its members (please visit for more information). ISO has not reviewed the accuracy or veracity of this information. New Symbol Launched to Warn Public About Radiation Dangers. Retrieved on 2007-02-15.
  5. ^ Biohazard Symbol History.
  6. ^ Biohazard Symbol History.
  7. ^ Biohazard and radioactive Symbol, design and proportions.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hazard_symbol". A list of authors is available in Wikipedia.
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