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ISO 22324:2022,Security and resilience — Emergency management — Guidelines for colour-coded alerts, is an international standard developed byISO/TC 292 Security and resilience. This document provide guidelines forcolor codes to indicate severity of hazards in public warnings.

There are many different systems are already in use, such ascolour state of meteorological condition or formerHomeland Security Advisory System, and the standard is intended to be an approach to eliminate confusion due to such differences.^[1]

ISO 22324 includes the following main clauses:^[2]

1 Scope
2 Normative references
3 Terms and definitions
4 Guidance for use of colour codes
     4.1 General
     4.2 Colour codes to express the status of hazard
     4.3 Colour codes to give supplementary information
     4.4 Consideration for human factors and colour blindness
Annex A Examples on the use of colour codes in practice
Annex B Recommendations for colour selection

Three basic color codes for severity levels are defined with meaning and proposed action, as in following table.^[3]

Basic color codes

Color	Text color	Meaning	Proposed action
Red	White	Danger	Take appropriate safety action immediately
Yellow	Black	Caution	Prepare to take appropriate safety action
Green	White	Safe	No action required

If more than three levels of hazards are needed, the standard recommends use of colors on the spectrum between the red and green. The number of levels should be minimized to avoid confusion, not to exceed seven colors.

Diversity of human limitation of ability to recognize color, includingcolor blindness, should be paid attention when a color code system is brought into operation.The standard recommends to pay special care to provide supporting information, such as:

• text (recommended color is shown in the table), numbers, shape, symbol or size
• audible color name, such as audible "red alert" voice
• positional cues i.e. colors should always be placed in a certain defined order in increasing levels of severity, such as left to right or bottom to top

The standard gives additional color codes for supplementary information, defined with meaning and usage limitation, as in following table.^[4]

Color	Text color	Meaning	Usage
Black	White	Fatal danger	Can be used with red; can be replaced by black-and-white checkerboard pattern
Purple	White	Fatal danger	Can be used with red
Blue	White	Informational purposes	Should not be used to indicate level of severity
Grey		No information available	To indicate no information is available

Black and purple can be used to indicate special cases of danger, i.e. red color code, thus supporting information such as text (recommended color shown in table above) is also recommended.

An example is the sequence black–red–yellow–green, used intriage tag in most part of the world.

The Annex B (informational) of the standard gives recommended selection of color for above-defined color codes.Each color code has saturated and unsaturated cases, both defined inMunsell,CMYK, andRGB systems.

ISO 22324 is part of a series ofISO standards andTechnical Reports onEmergency management, including^[5]

• ISO 22320:2018 Security and resilience – Emergency management – Guidelines for incident management^[6]
• ISO 22322:2022 Security and resilience – Emergency management – Guidelines for public warning^[7]
• ISO 22325:2016 Security and resilience – Emergency management – Guidelines for capability assessment^[8]
• ISO 22326:2018 Security and resilience – Emergency management – Guidelines for monitoring facilities with identified hazards^[9]
• ISO 22327:2018 Security and resilience – Emergency management – Guidelines for implementation of a community-based landslide early warning system^[10]
• ISO/TR 22351:2015 Societal security – Emergency management – Message structure for exchange of information^[11]

This standard was published for the first time in 2015.

• Catalogue entry for ISO 22324:2015 (contains link to preview for partial text)

• ISO standards

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