Researchers at the University of Corsica off the coast of France released information regarding development efforts they have been conducting dealing with using wireless sensor networks as a reliable solution for capturing the kinematics of a fire front spreading over a fuel bed. This work was financed by the Territorial Community of Corsica to provide reliable information in fire studies and support fire fighting strategies. To do this a wireless sensor network must be able to perform three sequential actions: 1) sensing thermal data in the open as the gas temperature; 2) detecting a fire i.e., the spatial position of a flame; and 3) tracking the fire spread during its spatial and temporal evolution.
Researchers at University of Corsica took on this challenge as the Mediterranean area is a region experiencing strong ecological variations due to global climate change. Wildland and forest fires represent an important cause of natural hazards and disasters for assets and human lives every year. Early detection and accurate tracking of the fire front propagation are key points in fire fighting strategies to minimize the damage and possible casualties. According to fire managers, the delay in detecting a fire ignition in the open is considered as one of the main factors increasing the response time of the first fire fighting actions. The resulting size of the fire to be managed as the final burning area strongly depends on this response time of the first fire fighting action.
One of the great and obvious challenges in performing fire front tracking with WSNs is to avoid the destruction of the Motes by the fire. This effort shows the ability and performance of a Wireless Sensor Network, when the Motes are protected with a thermal insulation dedicated to track a fire spreading across vegetative fuels on a field scale. The resulting experimental WSN was then used in series of wildfire experiments performed in the open in vegetation areas ranging in size from 50 to 1,000 m².
Using Crossbow's MICA motes and MTS420 GPS enabled sensors, researchers designed the Firesensorsock. The goal of this protection was to dampen the thermal impact from the fire on the Motes during the fire spread and contact. This shield also had to allow both a continuous emission of data and the temperature and the hygrometry inside the sock to vary on short time scales for locating the fire’s position. This innovative technique packaged the Mote and sensors to be thermally protected, preventing their destruction and extending their lifetime beyond the fire event. With this thermal insulation, the network could be reused for subsequent events. The key was to provide a protection able to preserve continuous flow of data from sensors embedded in a thermally destructive environment, namely a large scale natural fire. When sensors were covered with Firesensorsock the temperature and humidity measured during fire experiments was relative to what was measured inside the protection. The Firesensorsock consists of several layers of thermal insulation materials: a layer of simple Zetex fiber, a layer of ceramic wool and a final layer of aluminized Zetex fiber. These layers are fixed to one another with Kevlar thread. This level of protection allowed the sensor to support prolonged fire contact and also wireless communications without any disturbance. The sensing of any significant change of thermal data in the protection, due to the change of external thermal medium governed by the fire allowed for fire detection and tracking.
The sensors were triggered by the arrival of the fire and enabled the researchers to distinguish exactly the direction of the fire’s spread. The estimation of the rate of fire spread was possible because no node was destroyed by the fire in these experiments. It should be noticed that the computed rate of spread is not the same over the whole grid. This feature is consistent with real fire dynamics: indeed, according to infrared video imaging of the horizontal plot, the fire front propagates with a strong asymmetry. The sensing of the thermal data inside the sock which suddenly varies according to the presence of a strong thermal environment, i.e., a flame, leads to the opportunity to detect the presence of a fire. This point was very important for managing fire alerts in a specific areas because it determined the action of the first fire rescue team.
Because it has not been possible to follow the evolution of a fire with current systems available, this new solution was created - the double system (sensor + Firesensorsock) provided an adapted tool for natural fire scenarios. Results illustrated that the temperature and humidity variations in the socks allowed users to relevantly determine the presence of a fire and becomes a measurement system for the rate of fire spread in the open. The different tests performed during these fire experiments illustrate the ability of the Firesensorsock system to track the fire's evolution!
