Summary of Tornado Siren Data
Eyewitness News surveyed officials in the nine-county metropolitan area, including Boone, Hamilton, Madison, Hendricks, Marion, Hancock, Morgan, Johnson and Shelby, for locations of tornado warning sirens. We used that information (some counties had more authoritative information than others) to pinpoint the sirens in a mapping program to show how well the area is covered by sirens.
The data includes 348 sirens: 26 in Boone, 57 in Hamilton, 16 in Hancock, 48 in Hendricks, 23 in Johnson, 22 in Madison, 139 in Marion, 10 in Morgan and 7 in Shelby. The range of the sirens, under ideal conditions, varies from about a mile for the older ones to about a mile and a half for the newer ones. For the purposes of our analysis, we calculated each siren at a range of a mile and a half.
To determine how many people live in areas not covered by the sirens, we used 2000 Census block data, counting only those blocks completely outside the one and a half mile buffer zone around each siren. Marion County was the only county to have virtually complete coverage. Elsewhere, a total of 184,508 people live in the blocks without siren coverage. The totals by county:
Comprehensive siren activation data was not available for all counties. For Marion County, we reviewed test and warning data for 345 dates beginning December 13, 1999, and ending April 2, 2006. For the 139 active sirens, the data show failures 4,689 times, or about 10 percent overall, with another 762 partial failures (about 2 percent). There was at least one siren failure on 327 of the 345 dates. There were four dates – all test days – on which more than half of the on-line sirens failed, but most dates had 30 or fewer failures (the average number was 15).
Twenty-four of the Marion County sirens failed more than 20 percent of the activations. Two failed more than half the time – one in Beech Grove, at 59 percent, and another at Fort Harrison, at 50 percent. The Fort Harrison siren also had partial failures 24 percent of the time.
Sirens recently placed in off-line status had poor performance as well. A siren on Harding Street, now scheduled for removal, failed 152 out of 222 times that it was supposed to be on-line – a rate of 68 percent. But a siren on south Illinois Street had the worst performance – 81 failures out of 104 activations – a failure rate of 78 percent. (For individual siren performance, click here.)
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