Design and modeling of outdoor alerting and warning systems

Public alert and notification in a 10-mile radius EPZ, for nuclear emergencies off-site of nuclear plants, are required after the Three Mile Island accident in 1979. Sirens have been the primary device deployed to provide the alert. NRC/FEMA requires the system to provide adequate alert signals to all the population within the EPZ, accounting for site topography and weather condition. A practical outdoor sound propagation model was developed and used as a tool for siren alert system design and evaluation. The model relies upon the use of 3 different frames of reference for treating the three critical aspects of outdoor sound propagation; namely, UTM coordinates for geometry, Above Ground Levels for vertically stratified weather effects, and source-receptor ground profile for impedance terrain effect. Applications of the model have shown satisfactory results. Extension to outdoor voice messaging and speech intelligibility was implemented with the use of ANSI S3.5. Current electronic loudspeaker-type SASs are not specifically designed for voice messaging under FEMA-REP-10 Rev. 1; the effectiveness of these systems as voice messaging or warning systems must be separately evaluated. The model presented provides a tool to assess the intelligibility of the siren warning system.