From the Document: "These Non-Weather Emergency Message (NWEM) event codes are available to state, local, tribal and territorial Alerting Authorities for use with the Integrated Public Alert & Warning System (IPAWS). The weather-related event codes, not listed here, are reserved for the National Weather Service. Use of these event codes by Alerting Authorities depends on established IPAWS permissions. The codes may be used with EAS [Emergency Alert System], WEA [Wireless Emergency Alert], and/or NWEM except where indicated."
U.S. Federal Emergency Management Agency: https://www.fema.gov/