One important trend is the integration of gas detection into smoke detection systems. Combining gas detection with heat and/or smoke sensors can help avoid false alarms and allow multicriteria detection systems to more effectively analyze a given situation. For example, the system may react differently if heat alone is rising rather than if it detects both rising heat and an increase in CO or other gases from combustion.
Gas detection sensors are commonly used in multicriteria units and in advanced systems that combine smoke detection and air quality monitoring. The combined benefits can be significant.
Many different temperature-sensitive technologies are used to detect fire, often based on an alloy or other material that will change shape, form or electrical properties as temperature changes.
Thermal detectors typically fall into one of four categories:
Fixed temperature — These sensors trigger once heat passes a certain point. They have been used for decades, especially in conjunction with auto-extinguishing systems and in very harsh environments that affect other detection technologies.
Rate-of-rise thermal/thermistor-based — These units are far more sophisticated and apply a type of computer logic to the situation based on the dynamics of the speed and degree of temperature increase. They are often combined with other technologies in systems operated by algorithms to most accurately determine the scope of the threat and desired response.
Linear heat detection — This typically consists of a cable with a combination of polymer and/or digital technologies that can detect heat conditions anywhere along the length of the cable. The cable is normally comprised of tri-metallic conductors individually insulated with a heat sensitive outer layer that is designed to break down at various selected fixed temperatures. This technology has historically been used in freezer warehouses and storage facilities where other detection technologies may not be ideal.
Multicriteria — These units integrate thermal sensors and can be quite sophisticated. For example, one manufacturer offers a detector that integrates advanced signal technology software with two optical sensors, two thermal sensors and one CO sensor. It allows for the earliest and most reliable detection, with highest immunity against false alarms. It can also be programmed for independent (life-safety) CO monitoring or cooperative functionality.
Video Paces Leading-Edge Methods
Specialized surveillance software has been developed that now enables video cameras to be used for fire detection purposes. Using video image detection (VID), the cameras monitor the area and are programmed to detect specific visual signals such as flickering flames or rising plumes of smoke that indicate the presence of fire. In recent years, complex algorithms have been integrated to make the systems highly accurate and effective.
Video systems are particularly effective in very large open buildings where smoke or gases are more difficult to detect. They can be very useful for industrial environments where radiant heat and smoke make other detection systems harder to implement. To date, VID systems are listed and approved by Nationally Recognized Testing Laboratory (NRTL) as supplemental fire detection and not primary life-safety systems. In most cases, the monitored area must be illuminated for video imaging technology to work effectively.
Video is also increasingly popular in commercial settings that combine security needs with fire detection. In such systems, video signals can be transmitted simultaneously to the building security center and fire panel. Automatic flame detection technology can be combined with live video for immediate verification. And, by automatically recording video images for a prescribed period before and after an event, the systems are very valuable for investigation and future legal or security actions.
Future smoke and fire detection systems may also be responsible for ongoing monitoring of air quality to direct heating, air conditioning and ventilation (HVAC) systems for utmost energy efficiency. In a fire, such systems could use voice commands and other means to automatically direct occupants away from danger and toward the best escape routes, rather than simply sounding a general alarm.
Ron Ouimette is a Business Development Manager for Siemens’ Building Technologies Division.
5 Stages of Fire Progression
The exact science, technology and application of smoke detection systems vary. But the one consistent factor is a quick and accurate assessment of the danger, and an effective warning to all occupants in the building. Fires may develop very quickly or somewhat more slowly, depending on the combustible material involved. In any case, there is a relatively small window of opportunity early in the development of the fire to extinguish the flames and/or safely evacuate.
Most fire professionals agree that the ultimate protection of lives and property comes from a combination of the early warning of smoke detection and fire suppression. Following is the typical sequence of fire development:
1. Early stage — The small fire can easily be extinguished with water or other means. Little visible smoke occurs, although it is often sufficient to trigger a smoke alarm.
2. Smoldering phase — Visible, partly dense smoke occurs and large amounts of carbon monoxide (CO) may be produced by the incomplete combustion. The fire may still be easily controlled by a fire extinguisher.
3. Flaming phase — The open fire leaves precious little time for evacuation, and must effectively be fought by fire professionals. As combustion becomes more complete, less CO is produced, but relatively large amounts of carbon dioxide ensue.
4. Flashover — This is the transition between an open, flaming fire and a total fire. This explosive fire spread is caused when gases and aerosols produced in earlier phases ignite and spread the fire into all rooms already penetrated by the smoke gases.
5. Total fire — Once the
flames reach larger building parts, there is little fire professionals can do and they typically concentrate their efforts on protecting neighboring buildings and fire sectors.
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