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The skull and crossbones, a common symbol for poison, and other sources of lethal danger.

Hazard symbols are 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.


Types of hazard symbols

Name Symbol Unicode Image
Toxic sign U+2620 Skull and crossbones
Caution sign U+2621 Caution sign used on roads pn.svg
Radiation sign U+2622 Radioactivity
Ionizing radiation sign ? ? Radioactivity
Non-ionizing radiation sign ? ? radiowave
Food irradiation symbol ? ? Radura
Biohazard sign U+2623 Biohazard
Warning sign U+26A0 Warning
High voltage sign U+26A1 High voltage
Magnetic field symbol ? ? DIN 4844-2 Warnung vor magnetischem Feld D-W013.svg
Chemical weapon symbol
? ? Chemical warfare
Laser hazard sign ? ? A typical laser warning symbol
Optical radiation ? ? Warning for optical radiation, symbol D-W009 according to German standard DIN 4844-2
More hazard signs can be found on the list of DIN 4844-2 warning signs

Radioactive sign

The early Radioactive trefoil. (1946)

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.[1] (See right.) The modern version is black against a yellow background, and 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°.[2]


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.[3] Experts have felt that the trefoil symbol had little intuitive value and was less likely to be recognized by those not educated in its significance. According to the IAEA, in a survey conducted at an international school, many children mistook the trefoil for a non-threatening propeller. Hence, the Agency, along with the International Organization for Standardization has devised this symbol for sealed radiation sources. It depicts, on a red background, a black colored trefoil radiating waves, a skull and crossbones, and a person running away from the scene. The radiating trefoil suggests the presence of radiation and the red background and skull and crossbones warn of the danger. More important, the person running away from the scene suggests the action of avoiding the labeled material. The symbol had been tested in countries with different population of varying groups, ages, and educational backgrounds to ensure that it clearly conveys the message “Danger - Stay away”. The new symbol is to be displayed prominently on the device that actually houses the radiation sources so that if, even by mistake, someone attempts to disassemble the device it provides an explicit warning not to proceed any further.[4]

Biohazard sign


Developed by the Dow Chemical company in 1966 for their containment products.[5]

According to Charles Baldwin[6], 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 straightedge. 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 is 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.[2]

Toxic sign

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 Skull and Bones, a secret society at Yale University, as well as the international male collegiate fraternity Phi Kappa Sigma. It is also part of the WHMIS home symbols placed on containers to confirm that the substance inside is dangerous in a way.

In the United States, 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


On warning signs, an exclamation mark is often used to draw attention to a warning of danger, hazards and the unexpected. It is normally supplied with a note, as it is a generic term.

Chemical hazard

NFPA 704 standard hazard sticker or placard. See NFPA 704 for details.
European hazard sign, saying highly inflammable (33) - gasoline (1203)

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 European Agreement concerning the International Carriage of Dangerous Goods by Road. 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 (harmful) and the Italian word nocivo (noxious).

Non-standarized warning signs

High voltage sign on fence around Beromünster Reserve Broadcasting Tower

Sometimes warning signs of non-standard designs are in use.

See also


  1. ^ "Origin of the Radiation Warning Symbol (Trefoil)". 
  2. ^ a b "Biohazard and radioactive symbol, design and proportions". 
  3. ^ 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 2007-02-15. 
  4. ^ "Deccan Herald - Drop it". 
  5. ^ "Biohazard Symbol History". 
  6. ^ "Biohazard Symbol History". 

External links


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