Common Alerting Protocol (CAP)

What is Common Alerting Protocol (CAP)?

The Common Alerting Protocol (CAP) is an XML-based data format standard for exchanging alert data among many different technologies and systems. CAP allows a warning message to be sent simultaneously over many CAP-compliant warning systems to many different outlets (such as radio, television, cell phones, Internet).CAP is a well established international technical specification developed by the Organization for the Advancement of Structured Information Standards (OASIS). The concept grew out of an earlier effort of the Partnership for Public Warning. 

"Mapping" between CAP and CMAS/WEA

The primary purpose of a CMAS/WEA message is to briefly alert the recipient that a hazardous event is occurring (or will occur) in the geographic area in which the recipient is located. The CMAS/WEA specification limits the message to not more than 90 characters. As noted in the previous section, CMAS/WEA does not use any values from the CAP description, instruction, or area description elements for “imminent threat” alerts. Instead, IPAWS generates text derived from other CAP elements to compose the message using a specific format. 


CAP Data Elements

Alert Category: 

Geo: Geophysical (including landslides)
Met: Meteorological (including floods)
Safety: General emergency and public safety
Security: Law enforcement, military, homeland and local/private security
Rescue: Rescue and recovery
Fire: Fire suppression and rescue
Health: Medical and public health
Env: Pollution and other environmental
Transport: Public and private transportation
Infra: Utility, telecommunication, other non-transport infrastructure
CBRNE: Chemical, Biological, Radiological, Nuclear or High-Yield Explosive threat or attack
Other: Other events


Immediate: Responsive action should be taken immediately
Expected: Responsive action should be taken soon (within next hour)
Future: Responsive action should be taken in the near future
Past: Responsive action is no longer required
Unknown: Urgency not known



 Extreme: Extraordinary threat to life or property
Severe: Significant threat to life or property
Moderate: Possible threat to life or property
Minor: Responsive action is no longer required
Unknown: Severity unknown


Observed: Determined to have occured or to be ongoing
Likely: Probability is greater than or equal to 50%
Possible: Probability is less than 50%
Unlikely: Not expected to occur
Unknown: Certainly unknown

Event Response:

Shelter: Take schelter in place or per instruction
Evacuate: Relocate as instructed in the instruction
Prepare: Make preparations per the instruction
Execute: Execute a pre-planned activity identified in instruction
Avoid: Avoid the subject event as per the instruction
Monitor: Attend to information sources as described in instruction only 

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