Emergency Alert System

The Emergency Alert System, or EAS, is a national system put into place in 1997, superseding the Emergency Broadcast System and is administered by the Federal Communications Commission (FCC). The EAS covers both radio and television, including low-power stations.

EAS messages are handled by specialized equipment called EAS encoder/decoders. The decoder component receives and interprets EAS messages, and the encoder component transmits relayed messages. Low-power stations are only required to have the decoder components, but all other stations must have both decoder and encoder components.

In the EAS system, messages are originated in four parts. The first part is the FSK header code, repeated three times. FSK stands for Frequency-Shift (K)Carrier, and is an encoding method for encrypting and condensing data in rapid bursts. The header code contains:

• Information about the originating station of the signal
• Areas affected, usually designated by county (or parish in Louisiana, or borough in Alaska), but which may be designated for the whole state
• Event type
• Duration of alert

See below for a complete breakdown of the header.

Each station must have installed an EAS decoder which then interprets these data bursts. Two of the three bursts must be found to be identical by the decoder for the message to be valid. The decoder then decides, based on programming, whether to ignore the message as not pertaining to the local area, or whether to relay it on the air. Every station must monitor at least two other source stations, one of which must be designated a local primary.

The FSK header bursts are followed by an eight-second alert tone that carries no information. This is in turn followed by a voice message giving details of the alert.

The message is ended by three bursts of the FSK EOM, or End of Message.

All EAS equipment must be tested weekly. The RWT, or Required Weekly Test, consists only of the three FSK header bursts and the three FSK EOM bursts. Monthly tests, or RMT for Required Monthly Test, are transmitted with all four parts. These are the ones that state that they are just a test.

The number of events in the national system has grown by several increments, and is now forty-nine events. At first, they were almost all weather events with only one to three possible categories for civil emergencies, but several classes of non-weather emergencies have now been added.

In most states, the Amber Alert System[?], for child abductions, has now been added as well.

Stations are required by law to keep full logs of all received and transmitted EAS messages.

Table of contents 1 Full Header Breakdown 2 EAS Headers 2.1 Required Headers 2.2 Optional Headers

Full Header Breakdown

The EAS header contains these elements, in this transmitted sequence:

1. (Preamble) ZCZC-ORG-EEE-PSSCCC+TTTT-JJJHHMM-LLLLLLLL
2. Attention (two-tone) signal
3. Message - audio, video image or video text
4. (Preamble) NNNN (EOM)

• (Preamble): Signal that clears and resets the receiving system; factory-programmed
• ZCZC: Start of ASCII code; factory-programmed
• ORG: Originator code; programmed per unit when put into operation
• EEE: Event code; programmed at time of event
• PSSCCC: County-location code; programmed at time of event
• TTTT: Duration of alert; programmed at time of event
• JJJHHMM: Date/Time-of-Day; encoded automatically, based on settings
• LLLLLLLL: Eight-Character ID; programmed per unit when put into operation
• Attention signal: Sent if any message is included (normally sent with all messages except RWT, EAT, and EOM); must be at least eight seconds long
• NNNN: End-of-message code (EOM)

EAS Headers

There are two types of headers, four that are required to be encoded in every unit used, and forty-nine optional headers that users may program

Required Headers

1. RWT: Required weekly test
2. RMT: Required monthly test
3. EAN: Emergency alert notification
4. EAT: Emergency alert termination

Optional Headers

1. ADR: Administrative message
2. AVA: Avalanche watch
3. AVW: Avalanche warning
4. BZW: Blizzard warning
5. CAE: Child abduction emergency
6. CDW: Civil danger warning
7. CEM: Civil emergency message
8. CFA: Coast flood watch
9. CFW: Coast flood warning
10. DMO: Demonstration message
11. DSW: Dust storm warning
12. EQW: Earthquake warning
13. EVI: Evacuation Immediate
14. FFA: Flash-flood watch
15. FFW: Flash-flood warning
16. FFS: Flash-flood statement
17. FLA: Flood watch
18. FLW: Flood warning
19. FLS: Flood statement
20. FRW: Fire warning
21. HUA: Hurricane watch
22. HUW: Hurricane warning
23. HLS: Hurricane statement
24. HMW: Hazardous materials warning
25. HWA: High wind watch
26. HWW: High wind warning
27. LAE: Local area emergency
28. LEW: Law enforcement warning
29. NIC: National Information Center
30. NMN: Network message motif
31. NPT: National periodic test
32. NUW: Nuclear plant warning
33. RHW: Radiological hazard warning
34. SMW: Special marine warning
35. SPS: Special weather statement
36. SPW: Shelter in place warning
37. SVA: Severe storm advisory
38. SVR: Severe thunderstorm warning
39. SVS: Severe weather statement
40. TOA: Tornado advisory
41. TOE: 911 telephone outage emergency
42. TOR: Tornado warning
43. TRA: Tropical storm watch
44. TRW: Tropical storm warning
45. TSA: Tsunami watch
46. TSW: Tsunami warning
47. VOW: Volcano warning
48. WSA: Winter storm watch
49. WSW: Winter storm warning