A system based on low-power radio transponders and associated analog and digital electronic circuitry has been developed for locating firefighters and other emergency workers deployed in a building or other structure. The system has obvious potential for saving lives and reducing the risk of injuries.
The system includes (1) a central station equipped with a computer and a transceiver; (2) active radio-frequency (RF) identification tags, each placed in a different room or region of the structure; and (3) transponder units worn by the emergency workers. The RF identification tags can be installed in a new building as built-in components of standard fire-detection devices or ground-fault electrical outlets or can be attached to such devices in a previously constructed building, without need for rewiring the building. Each RF identification tag contains information that uniquely identifies it. When each tag is installed, information on its location and identity are reported to, and stored at, the central station. In an emergency, if a building has not been prewired with RF identification tags, leading emergency workers could drop sequentially numbered portable tags in the rooms of the building, reporting the tag numbers and locations by radio to the central station as they proceed.
Each RF identification tag periodically transmits a short-burst, low-power signal containing its unique identifier code. The intervals between these transmissions are made pseudorandom to minimize interference among transmissions from different RF identification tags. Each emergency worker wears a transponder unit, which receives the codes transmitted by one or more RF identification tag(s) and measures their relative signal strengths. Each transponder also transmits a unique identifier code, which makes it possible to distinguish its wearer from other emergency workers.
The central station periodically transmits a polling command, in response to which each transponder transmits its identification code plus all of the RF-identification-tag information it has received during the preceding 5 seconds. For each such polling cycle, the central station issues only one polling command, and each transponder responds during a unique assigned time slot after that command, as determined by its code: this arrangement minimizes the "handshaking" needed to establish communication with transponders and reduces the cycle time for the location updates. On the basis of the relative strengths of RF-identification-tag signals reported by each transponder and the locations of the tags that transmitted those signals, the central-station computer calculates the location of the transponder and, hence, of the emergency worker who carries it. Thus, the locations of all emergency workers are repeatedly updated and displayed in real time at the central station.
The power for prewired RF identification tags is derived from the main AC power of the building by means of a rectifier/voltage-divider circuit, which also maintains a charge in a miniature, large-capacitance capacitor. The power demand of the RF identification tags is so low that in the likely event of loss of AC power during an emergency, the tags can continue to operate for at least 72 hours from the charge stored in the capacitor.
The design of the RF identification tags is based on a microcontroller chip. This design is amenable to easy and inexpensive integration of sensors. For instance, digital temperature sensors could be included within the RF identification tags. In that case, the information provided to the central station could also include the temperature of the wall, roof, or other portion of the structure where the tag is located. The temperature would be an additional indication of the integrity of the structure and progress of a fire through the building. The RF identification tags can be encapsulated for protection against water, smoke, and shock, and can be made from components that withstand extremes of temperature.
Most of the hardware and software of the system have been tested in a laboratory, and limited field tests have been performed. At the time of reporting the information for this article, several fire departments had expressed interest in this system.
This work was done by William Larson of Kennedy Space Center and Pedro Medelius, Stan Starr, Guy Bedette, John Taylor, and Steve Moerk, of Dynacs Engineering Co. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Computers/Electronics category. KSC-12079