These sirens are designed to alert citizens, who are outdoors, to an eminent threat in the community. When sounded, citizens should seek shelter immediately in a stable structure. Once secure, citizens should listen to a radio and/or television for emergency warning details and further instructions.
While tornado warnings are the most common cause for siren activation, the sirens should not be considered to be "tornado sirens." They are intended as an "all-hazards" alerting system and may be activated for any type of emergency situation. The sounding of the sirens does not necessarily mean that a tornado warning has been issued. In fact, it means only that an emergency event has occurred or is about to occur and you may need to take action to protect yourself. If you hear a siren, you should immediately seek additional information through local radio and television stations. In all cases, the siren warning signal is a three minute steady blast.
Sirens will be activated for:
• A tornado warning issued by the National Weather Service
• Tornado or funnel cloud reported by a reliable source
• Sustained winds in excess of 60 mph
• Reports of hail larger than one inch
• Chemical spill emergency
• State or national emergency declared by the governor or president
• Other emergencies as appropriate
The most important thing to know about these sirens is that they are designed to alert individuals who are outdoors. Sirens are not intended to alert people who are in cars, homes, or other buildings. Hearing sirens indoors may have been possible in the past; however, this should no longer be expected. Energy conservation practices and better insulation have effectively reduced the sound penetration into these areas. In addition, many homes and businesses are air-conditioned. Very few buildings have open windows in the summer when it is hot and humid – the very time when severe weather is most likely to occur.
A number of factors affect the range of the siren- sound output, atmospheric conditions, topography and ambient noise levels. Very simply, some sirens are designed to be louder than others. A louder siren will have a greater range. Atmospheric conditions, such as wind speed and direction, air stability, and relative humidity, all affect the distance that the sound will travel. Your ability to hear the siren will change as these conditions change. It is very possible that from your location, in some cases you will be able to hear the siren, while in other cases, you won't. Topography and background noise levels will also have an effect on your ability to hear the sirens. Hills, trees, and buildings can be barriers that block the sound. High background noise levels from highways or industrial areas can mask the sound of the siren. These conditions will effectively limit the warning range of the siren.
Sirens can also be very susceptible to disruptions in the electrical power supply. A majority of the sirens operate on power supplied by local utilities. Power failures, which are common during thunderstorms, can disable a siren. In addition, lightning striking a nearby power line can blow fuses in the siren itself. This will also disable the unit until the fuses can be replaced.
How They Work
The primary activation point of the outdoor warning sirens is in the City of Garland Emergency Operations Center, with backup capabilities in the City’s Dispatch Center. When the Office of Emergency Management (OEM) staff is notified of a potentially dangerous situation that may warrant activation of the siren system, the first call is to activate the Skywarn Storm Spotters. The storm spotters respond by going out to monitor the conditions and report back to staff via amateur radio (HAM radio). OEM staff then heads in to the office to listen to the amateur radio reports and activate the sirens if the reports meet an established threshold. If staff is unable to make it to the office in time, a designated storm spotter is responsible for calling the OEM duty officer and notifying them that the situation has met the threshold for activation. The OEM duty officer then calls the Dispatch Supervisor and requests that they activate the sirens.
While most storms allow enough advance notice for OEM staff to make it in to the office, sometimes that does not happen. In those cases, activation of the sirens may be delayed by several minutes. For this reason, and the limitations listed above, outdoor warning sirens should be regarded as a notification system of last resort.
New Outdoor Warning Siren System
The City of Garland will begin installation of the 15 new outdoor warning sirens approved by the Garland City Council in the 2012 Capital Improvement Program later this Spring. The existing siren system was taken offline in 2011 due to lack of reliability with the aged equipment. Once completed, the new Garland Outdoor Warning System will consist of 15 sirens strategically-located to warn those in public outdoor gathering spots throughout the city.
During the next few weeks, residents may notice signage at the potential sites of the new sirens. These signs will be placed to notify citizens where the new sirens will be installed, as well as provide contact information for citizens who have questions or concerns about the placement of the siren.
To reduce costs and traffic disruptions to citizens, city officials have arranged for the old sirens to be removed at the same time that the new sirens are being installed. Construction is set to begin sometime in late February or early March (depending on weather conditions), and it is expected the system will be fully functional by late April 2013.
During this system upgrade, the Office of Emergency Management will continue to monitor severe weather conditions and provide warnings via CodeRED, Weather Warn and Twitter. Remember that the outdoor warning sirens are not intended to be heard indoors and emergency officials urge all citizens to remain alert to changing weather conditions and to have multiple means of receiving emergency warnings.