Residents and visitors within 10 miles of the Shearon Harris nuclear plant will be treated tomorrow to a full blast of the plant's emergency sirens.

Progress Energy will conduct an annual full-volume test of all 83 sirens between 10 a.m. and 11 a.m. The annual test will sound very much like a real emergency, except that the sirens will wail only 3 minutes at a time.

All U.S. nuclear plants are required to have emergency warning systems within a 10-mile emergency planning zone. Shearon Harris conducts four tests a year for about 5 seconds and one test for 3 minutes.

The sirens used by Raleigh-based Progress Energy, which operates the plant, sound like air raid warnings. At 100 feet, they generate 127 decibels, comparable to a human scream or a marching band.

In a periodic ritual familiar to residents who live near a nuclear power plant, Progress Energy will sound the emergency warning sirens for the Shearon Harris plant at full blast tomorrow morning.

The Raleigh-based power company will conduct a full-volume test for about 5 seconds between 10 a.m. and 11 a.m. The Shearon Harris nuclear plant has 83 warning sirens within 10 miles of the power plant.

The nuclear siren, which resembles an air-raid warning, is not likely to be mistaken for the afternoon bell at the local schoolhouse.

Progress is required to have a notification system in place in the event of an accident that results in a radioactive release. In past years, the sirens have failed the test, but since then the utility has replaced them at a cost of $2.5 million.

A violent storm disabled several dozen emergency warning sirens at a Duke Energy nuclear plant in South Carolina.

The loss of 40 sirens at the Catawba nuclear plant is reminiscent of the mishaps at the Shearon Harris plant several years ago before Progress Energy installed new sirens with backup battery power at a cost of $2.5 million. The batteries can operate the sirens for several days.

Raleigh-based Progress lost use of all 81 sirens on three separate occasions in 2007 and 2008 at the Harris plant in southwestern Wake County. Disabled sirens typically don't trigger federal penalties, but they can be an embarrassment to companies that pride themselves on public safety and public confidence.

The Nuclear Regulatory Commission requires sirens or some other warning system within a 10-mile radius of all U.S. nuclear plants.