Almost fourteen years ago, in December of 1999, the Worcester (MA) Fire Department lost six brave men in a fire in an abandoned cold storage warehouse. Two of the men had gotten lost; the other four perished in a valiant effort to rescue them. This is particularly relevant to VDC and to me; the firm is located only 23 miles from the disaster site and, in a “former life,” I worked for a company that manufactured personal lighting equipment for mining and other hazardous occupations, including the Fire Service. The Worcester FD was one of our customers.
At the time, there was very little in the way of personal safety equipment available to firefighters. True location systems were large, clumsy, inaccurate and very expensive. “State of the Art” comprised Personal Alert Safety Systems, or PASS, devices. These units, which could be integrated into a firefighters’ breathing apparatus, personal lights, or attached to turnout gear as discrete devices, comprised a small battery back coupled with a loud piezoelectric alarm. Mercury switches were used to sense movement (or, more properly, a lack of movement) to activate the alarm, which could also be activated by hand. Worcester’s firefighters were equipped with these. However, they were not adequate to prevent the tragedy. The noise level inside the fire and the labyrinthine construction of the building made them ineffective (see http://www.usfa.fema.gov/downloads/pdf/publications/tr-134.pdf, “Lessons Learned,” nos. 9 & 10). But even now, in 2013, no reliable, accurate and cost-effective system exists.
The Department of Homeland Security and WPI (Worcester Polytechnic Institute) have each developed systems that show some promise. DHS’s entry is called GLANSER (Geospatial Location Accountability and Navigation System for Emergency Responders). One WPI system is called the PPL (Precision Personnel Locator). Both utilize MEMS-based gyroscopes and accelerometers to sense both motion and position in component devices called IMUs (Inertial Measurement Units). Ranging and internal position estimates would be sent via VLF (Very Low Frequency) pulsed transmissions to external receivers mounted on fire apparatus or incorporated into ladders. VLF signals between 170 and 200 kHz are more easily able to penetrate steel and concrete structures than are higher frequencies. ULF (Ultra Low Frequency) signals, in the range of 20 Hz, offer even better penetration; these are used to locate miners trapped underground and for communication with submarines. However, frequencies this low require large, cumbersome antenna systems and thus are not practical for use on the fireground.
The ranging signals and IMU internal position estimates would be combined by the receiving system using a synthetic aperture imaging algorithm.
Although these systems do show promise, there is still a long way to go. The IMUs have a tendency to drift, making location somewhat problematic. Cost is also an issue. But at least progress is being made, and MEMS suppliers can help by working with both DHS and WPI to improve the accuracy of the IMUs. We believe that development of viable systems should be a national priority, especially in view of today’s threats of terrorism.