Early Fire Detection and Fire Prevention Using Infrared Thermography

Early fire detection using LWIR thermography is accomplished by measuring the surface temperature of the object being monitored. This method enables the detection of heat build-up long before critical temperatures are reached. For this purpose, IR video images recorded with special cameras are electronically processed and analyzed and visually displayed or used to trigger an alarm.
Early fire detection based on this principle has significant system advantages as compared to all other detection and alarm technologies:

Contactless measuring across wide and long distances
LWIR video-based fire detection can be used across wide and long distances of up to several hundred meters. Using LWIR thermography, temperatures can be measured via each individual pixel of a video image. With this method, the person viewing the image is provided with a representation of the object, including precise temperature values for every point on its surface.
This information can be used to detect potential fire sources early and to initiate fire prevention measures.

“See through” smoke and fog
Two wavelength ranges of infrared radiation can be used in thermography. In the IR wavelength range (3-5μm), transmission strongly depends on the extent to which the atmosphere is contaminated with airborne particles. Consequently, this wavelength range is not suitable for providing the accuracy needed when measuring temperatures for the early fire detection, despite the availability of cost-efficient sensor technologies. In the LWIR wavelength range from 8-12μm, a large portion of the aerosols, such as fog or smoke that occur in many applications are almost transparent. In contrast to conventional monitoring cameras (CCTV) or the human eye, which both utilize much shorter wavelengths, this allows an LWIR camera to virtually “see through the smoke”. Even across distances of 500m and greater, the signal is not susceptible to any considerable attenuation. Moreover, wavelength fluctuations due to temperature changes do not cause absorption-induced fluctuations in the signal strength that might be mistaken for changes in the actual radiation intensity. As a result, this technology can also be used in environments with high aerosol concentrations and provides valuable support in fighting fires.

Sensitive, accurate measurements in all temperature ranges
Only the LWIR wavelength range presents optimal conditions for temperature measurement. The temperature measurement ranges can extend from below -20°C to much higher than 1000°C. The temperature can be determined to 1K. Increased or excessively high temperatures can be precisely measured, regardless of the ambient temperature. This provides ideal conditions for the prevention or early detection of fires.

Visualization of temperature values
The invisible LWIR radiation can be made visible using today’s video post processing methods. For this purpose, a color is assigned to every measured temperature value, resulting in a false color image, such as those known from the thermal inspection of facade insulations. “Warm” colors (e.g. red) indicate high temperatures, whereas “cold” (e.g. blue) colors are used for low temperatures. As a result, the distribution of the surface temperatures becomes visual and can be evaluated at a glance to immediately assess the situation.
In order to be able to visualize, in any situation, the relevant temperature range with the limited contrast range of both video technology and the human eye, this method recalculates and reassigns the temperatures and brightness values for every new image. Consequently, the temperature cannot be evaluated based on the video images, and therefore, selected alphanumeric temperature values are displayed in addition.

Hot spot detection and localization
Color images are not practical in terms of fire monitoring. With fire monitoring, the required information is reduced to visualizing the area to be monitored and signaling an alarm if threshold values are exceeded. For this purpose, a grayscale image is rendered. Increased brightness indicates rising temperatures. If the alarm threshold is exceeded, the affected areas are displayed as particularly bright or highlighted in color. The occurrence of alarm conditions and their localization within the area being monitored is thus visible at a glance. The method is particularly well suited for the quick visualization and localization of inhomogeneous temperature curves. This can apply to directly visible heat build-ups, e.g. on a conveyor belt, as well as to distinct temperature differences below the surface. These hot spots are typicalindicators of local overheating which, in most cases, would lead to the start of a fire. If the hot spot is located below the surface, the temperature measured on the surface is still significantly lower than the critical temperature, even if the hot spot has already reached the critical temperature. In these cases analyzing the trend of temperatures can provide indications of the presence of concealed hot-spots. Therefore, it is necessary to be able to take accurate and reliable measurements far below the critical temperature as well – a task for which LWIR thermography is ideally suited.