Outdoor Warning Sirens
Outdoor Warning Sirens (OWS) are primarily used to warn citizens of approaching severe weather conditions while outdoors. However, they are also used for other emergencies such as a hazardous chemical spill, which may require sheltering in place or evacuating. People visiting our parks, in their yard, or at other outdoor locations in the City would hear the loud sound from the OWS. After hearing the OWS, please seek more information from local radio and television broadcasts.
How many outdoor warning sirens do we have and how do they work?
The City has 10 outdoor warning sirens strategically located and covering each neighborhood in Bedford. Each siren will produce a very loud 128 decibel (dB) (sound of a jet taking off) at 100 feet and 70 dB (the sound of vacuum cleaner or a hairdryer) at 5,571 feet with a 60 degree sound pattern rotating 360 degrees. Even though the sound is loud and steady, each siren will vary in levels of amplitude as the siren speaker bell rotates. Wind speed and direction, in addition to the changes in atmospheric pressures and factors of weather conditions, can also influence the quality of the siren sound.
All 10 OWS are activated electronically by radio control and can be sounded independently to alert sections of the City, as needed. There are three separate control stations at different locations to assure continuity of the OWS system. Each siren and control location has battery emergency power and emergency power by generators.
Again, Outdoor Warning Sirens are designed to alert people who are outside of a structure that pending and/or immediate danger is approaching our city and to seek information by ‘tuning in’ to their radio or television. Even though the outdoor warning sirens can be loud enough to be heard inside some nearby structures, they are not intended to warn people indoors.
How come we did not activate our outdoor warning sirens when other cities did?
There may be times when we do not activate our outdoor warning sirens when other cities in the area have. Based on the activation criteria, each threatening situation is carefully evaluated by a team of emergency management staff using up-to-the-moment information concerning how the threat will affect the people in Bedford. The sirens will only be initiated in the case of severe weather directly threatening Bedford as reported by the National Weather Service that meets at least one of the following criteria:
- Reported hail of 1.50” in diameter or greater (or smaller for areas or events where large numbers of people are outdoors)
- Rotation in a dangerous cloud or a tornado
- Straight-line winds over 70 mph
The emergency management teams of each city have worked together developing plans and guidelines in an effort to be consistent when activating their sirens during critical public emergency events. However, there will be conditions when our neighboring cities may activate their systems and be heard in Bedford and the event does not affect us, causing confusion. In most cases, all cities in our area use the guidelines listed above when activating outdoor warning sirens.
When do we test the sirens?
The City performs a system test on the first Wednesday of each month at 1 p.m., unless there is a severe weather warning or a dark overcast that day. The “loud test” is a full test of each siren checking all functions usually lasting up to two minutes. The “growl test” performs the same assessment as the “loud test” except the siren speaker bell only makes one full rotation with sound usually lasting less than 30 seconds. We also test each siren’s electronics twice daily notifying emergency management of the results and reporting any issues by pager and email.