David C. Bursell
More industrial facilities are finding ways to prevent fire damage by connecting infrared imaging and other fire detection sensors via the internet of things (IoT). By having systems in place to alert building occupants about fire ignition, facility managers can avert costly and potentially life-threatening fires before they start and spread.
There are various fire detection sensors available with varying response times. The following chart shows the relative detectability of fire detection devices at different stages of fire development with corresponding damage levels.
Infrared (IR) Camera Systems
Infrared (IR) cameras operate on the heat transfer principle of radiation. The infrared camera has a focal plane array of detector elements that sense infrared light from object surfaces. The radiation captured by the infrared camera detector is digitized, converted to data, and displayed as a viewable image. Calibrated IR cameras can report temperature measurements from specific spots, lines, and areas on live or recorded images.
IR cameras are the first to alert before a fire develops. They “see” a warming-up of material early in the fire development process before forming smoke particles or flames. These warming materials appear as hot spots in a thermal image and are measured with regions of interest (ROIs) like spots, lines, or areas that report temperature values. Applying multiple ROIs to an image and setting temperature thresholds per ROI allows monitoring and alarming multiple locations within the camera’s field of view. When the threshold condition of an ROI is satisfied, alarms trigger notifications to the appropriate personnel.
PROs: Can detect and alert at the earliest stages of potential fire development. Are accurate and can precisely pinpoint the position of a hotpot.
CONs: Can only detect surface temperatures and require a clear line of sight to the target of interest.
Aspiration Smoke Detectors
Aspiration Smoke Detectors (ASDs) draw air samples to the detector using a sampling pipe with multiple holes. The air sample is filtered and processed by a sensitive laser detection unit. If smoke particles are detected, the system’s alarm is triggered. ASDs are more precise than passive smoke detectors and typically incorporate multiple alarm levels. For example, users can program ASDs to alert at the earliest smoldering stage to prompt investigation with other alarm levels configured to provide fire and suppression system inputs.
PROs: Flexible installation options due to active sampling. Detect smoke activity in large open spaces where smoke dilution can occur. Incorporates integrity monitoring and alerts when the ability to detect smoke is compromised.
CONs: Poor performance in dirty environments where fouling can occur.
Ionization Smoke Detectors
In an ionization smoke detector, a small amount of radioactive material between two electrically charged plates ionizes the air, causing a current to flow between the plates. When smoke enters the chamber, it interrupts the flow of ions, which reduces the flow of the current and triggers the alarm.
PROs: High responsiveness to the flaming stage of fires.
CONs: More susceptible to giving false alarms from steam or dust particles.
Photoelectric Smoke Detectors
In a photoelectric smoke alarm, a light is aimed into a sensing chamber but away from the sensor itself. When smoke enters the chamber, it causes the light to be reflected onto the sensor, activating the alarm.
PROs: More responsive to slow smoldering fires that emit larger particles. Less susceptible to false alarms.
CONs: Slower at responding to fast-forming fires.
Fire Sprinkler Systems
Fire sprinkler systems have strategically placed sprinkler heads with glass bulbs containing a glycerin-based liquid. Sprinkler systems detect a fire through rising temperatures. As the temperature at the sprinkler head increases to between 135 to 165 degrees Fahrenheit, the liquid inside the glass bulb expands and breaks the glass, thus activating the sprinkler head. There are various liquid colors in these glass components, each indicating a different threshold of heat required to break the glass.