Hazard symbol

Type of hazard	Unicode glyph	Unicode	Image
Generic caution	⚠	U+26A0
Poison	☠	U+2620
Ionizing radiation	☢	U+2622
Ionizing radiation – high-level source
Non-ionizing radiation
Biological hazard	☣	U+2623
Carcinogen
High voltage	⚡︎	U+26A1
Laser hazard
Accident	⛌	U+26CC
Disabled car	⛍	U+26CD
Icy road	⛐	U+26D0
More hazard symbols can be found on the list of GHS hazard pictograms and the list of ISO 7010 warning pictograms

Tape with yellow and black diagonal stripes is commonly used as a generic hazard warning. This can be in the form of barricade tape, or as a self-adhesive tape for marking floor areas and the like. In some regions (for instance the UK)[1] yellow tape is buried a certain distance above buried electrical cables to warn future groundworkers of the hazard.

Generic warning symbol
(Background colour varies)

On roadside warning signs, an exclamation mark is often used to draw attention to a generic warning of danger, hazards, and the unexpected. In Europe and elsewhere in the world (except North America and Australia), this type of sign is used if there are no more-specific signs to denote a particular hazard.[2] When used for traffic signs, it is accompanied by a supplementary sign describing the hazard, usually mounted under the exclamation mark.

This symbol has also been more widely adopted for generic use in many other contexts not associated with road traffic. It often appears on hazardous equipment, in instruction manuals to draw attention to a precaution, on tram and train blind spot warning stickers or on natural disaster (earthquake, tsunami, hurricane, volcanic eruption) preparedness posters, as an alternative when a more-specific warning symbol is not available.

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

The symbol, or some variation thereof, specifically with the bones (or swords) below the skull, was also featured on the Jolly Roger, the traditional flag of European and American seagoing pirates. It is also part of the Canadian WHMIS home symbols placed on containers to warn that the contents are poisonous.

In the United States, due to concerns that the skull-and-crossbones symbol's association with pirates might encourage children to play with toxic materials, the Mr. Yuk symbol is also used to denote poison.

The international radiation symbol is a trefoil around a small central circle representing radiation from an atom. It first appeared in 1946 at the University of California, Berkeley Radiation Laboratory.[3] At the time, it was rendered as magenta, and was set on a blue background. The shade of magenta used (Martin Senour Roman Violet No. 2225) was chosen because it was expensive and less likely to be used on other signs.[4] However, a blue background for other signs started to be used extensively. Blue was typically used on information signs and the color tended to fade with weathering. This resulted in the background being changed on the radiation hazard sign.[5] The original version used in the United States is magenta 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°. The trefoil is black in the international version, which is also used in the United States.[6]

The symbol was adopted as a standard in the US by ANSI in 1969.[5][7] It was first documented as an international symbol in 1963 in International Organization for Standardization (ISO) recommendation R.361.[8] In 1974, after approval by national standards bodies, the symbol became an international standard as ISO 361 Basic ionizing radiation symbol.[9] The standard specifies the shape, proportions, application and restrictions on the use of the symbol. It may be used to signify the actual or potential presence of ionizing radiation. It is not used for non-ionizing electromagnetic waves or sound waves. The standard does not specify the radiation levels at which it is to be used.[9]

The sign is commonly referred to as a radioactivity warning sign, but it is actually a warning sign of ionizing radiation. Ionizing radiation is a much broader category than radioactivity alone, as many non-radioactive sources also emit potentially dangerous levels of ionizing radiation. This includes x-ray apparatus, radiotherapy linear accelerators, and particle accelerators. Non-ionizing radiation can also reach potentially dangerous levels, but this warning sign is different from the trefoil ionizing radiation warning symbol.[10] The sign is not to be confused with the fallout shelter identification sign introduced by the Office of Civil Defense in 1961. This was originally intended to be the same of the radiation hazard symbol but was changed to a slightly different symbol because shelters are a place of safety, not of hazard.[5][11]

On February 15, 2007, two groups—the International Atomic Energy Agency (IAEA) and the International Organization for Standardization (ISO)—jointly announced the adoption of a new ionizing radiation warning symbol to supplement the traditional trefoil symbol. The new symbol, to be used on sealed radiation sources, is aimed at alerting anyone, anywhere to the danger of being close to a strong source of ionizing radiation.[12] It depicts, on a red background, a black trefoil with waves of radiation streaming from it, along with a black skull and crossbones, and a running figure with an arrow pointing away from the scene. The radiating trefoil suggests the presence of radiation, while the red background and the skull and crossbones warn of danger. The figure running away from the scene is meant to suggest taking action to avoid the labeled material. The new symbol is not intended to be generally visible, but rather to appear on internal components of devices that house radiation sources so that if anybody attempts to disassemble such devices they will see an explicit warning not to proceed any further.[13][14]

• 
  ISO 361 International ionizing radiation trefoil symbol
• 
  Yellow and magenta ionizing radiation trefoil used in the US
• 
  Early ionizing radiation symbol (1946)
• 
  ISO 21482 high-level sealed-source ionizing radiation symbol

The biohazard symbol is used in the labeling of biological materials that carry a significant health risk, including viral and bacteriological samples, including infected dressings and used hypodermic needles (see sharps waste).[15]

Geometry

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 circles, and arcs are erased at 90°, 210°, and 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.[6]

A chemical hazard symbol is a pictogram applied to containers of dangerous chemical compounds to indicate the specific hazard, and thus the required precautions. There are several systems of labels, depending on the purpose, such as on the container for end-use, or on a vehicle during transportation.

Canada

Main article: Workplace Hazardous Materials Information System

Example WHMIS symbol

The Workplace Hazardous Materials Information System, or WHMIS, is Canada's national workplace hazard communication standard.

United States

Main article: NFPA 704

See also: Toxic Substances Control Act

NFPA 704 standard hazard sticker or placard

The US-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. One example of a special hazard would be the capital letter W crossed out (pictured left), indicating it is water reactant.

Sign on a fence around the Beromünster Reserve Broadcasting Tower in Switzerland, warning of high voltage and danger of death

A large number of warning symbols with non-standard designs are in use around the world.

Some warning symbols have been redesigned to be more comprehensible to children, such as the Mr. Ouch (depicting an electricity danger as a snarling, spiky creature) and Mr. Yuk (a green frowny face sticking its tongue out, to represent poison) designs in the United States.

• Bouba/kiki effect – Non-arbitrary attachment of sounds to object shapes
• Pictogram
• ISO 7010 – ISO standard for safety symbols
• ISO 7001 – ISO standard for public information symbols.
• GHS hazard pictograms – Symbols used by the Globally Harmonized System of Classification and Labelling of Chemicals
• Safety sign

Wikimedia Commons has media related to Hazard signs.

Wikimedia Commons has media related to DIN 4844-2 warning signs.

• Hazchem Guide from The National Chemical Emergency Centre
• European Chemicals Bureau
• Directive 2001/59/EC
• Hazchem panel information