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Journal List > AMIA Annu Symp Proc > v.2006; 2006

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AMIA Annu Symp Proc. 2006; 2006: 846.
PMCID: PMC1839626
Copyright This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose.
A WiFi Public Address System for Disaster Management
Nicholas Andrade, Douglas A. Palmer, PhD, and Leslie A. Lenert, MD
Jacobs School of Engineering and the California Institute for Telecommunications and Information Technology, University of California, La Jolla, CA
Abstract
The WiFi Bullhorn is designed to assist emergency workers in the event of a disaster situation by offering a rapidly configurable wireless public address system for disaster sites. The current configuration plays either pre recorded or custom recorded messages and utilizes 802.11b networks for communication. Units can be position anywhere wireless coverage exists to help manage crowds or to recall first responders from dangerous areas.
 
In disaster settings sometimes shouting is the best form of communications. If background noise levels are impractically high, amplification often via “bull horns” is proven solution. However, sometimes at disaster sites, one might need to make announcements or broadcast instructions over a very large area without any kind of pre-existing public address system. As part of the Wireless Internet Information System for Medical Response to Disasters (WIISARD) we developed a WiFi disaster bullhorn broadcasting system. The unit used the mesh 802.11b network deployed at the scene to create ad hoc wide area public address system.
The WiFi Bullhorn is wireless Linux computer coupled to a sound amplifier, a batter source and two “bullhorn style speakers. It is controlled by a web page served by the device. The web page offers stored messages (Eg. “Please proceed to the nearest exit.”), warning alarms, soothing music, as well as the ability to record and broadcast custom messages.
The web server is Apache2 with PHP4 and the web server controls am audio player (mpg123); the operating system is Debian GNU/Linux running a custom 2.6 kernel. The kernel runs on a Soekris net4521; it is essentially a motherboard with a 133MHz 486, 64MB RAM, two PCMCIA slots, a CompactFlash slot, and a type III PCI slot. The operating system was stored on a 512MB CompactFlash card which was set to read only to allow quick power downs without damaging the file system. This posed as a challenge for storing custom messages; we solved this by writing custom messages to a tmpfs (RAM disk) at the cost of being limited to one custom message at a time which is lost when power is cut or a new message is recorded. The soundcard used is the MP878-S by Commell; We used off the shelf 802.11b PCMCIA cards to connect to the network.
Since rapid deployment is essential in disasters, a design requirement for the WiFi bullhorn was that it would be light and simple to set up. We used a standard aluminum engineering tripod as the base. The bullhorn chosen is the BDT30A by Bogen Horns. The bullhorn uses a Jenson UPA224CS amplifier which is lightweight and could fit in the same container as the Soekris board and battery (a 10,000mAh NiMH 12V battery). In addition to being lightweight, the unit needed to be weatherproof, so damageable parts were put into a waterproof Pelican case. The case was retrofitted with weatherproof audio jacks and antennas, as well as a power switch and LED's.
The device was tested at a Southern California Disaster Drill held at the Del Mar Fair Grounds. This event simulated explosion of a large car bomb with resulting a pesticide release. Contaminated victims were rescued by emergency response-teams. Two bullhorn units were deployed; one at the location of the bomb (to potentially play a warning message about contamination), and the other near the treatment areas (about a kilometer apart). At the drill we received positive feedback from emergency workers who generally said they could see the potential uses for such a device. There were some limitations resulting from a design that required pre-recording and transmission, rather than streaming of audio messages.
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Figure 1
Figure 1
Figure 1
Deployed WiFi “Bullhorn” unit
Acknowledgements
Hung-Chun Lin, Elisa Schoenmackers, and Ryan Nichimura also contributed to the development of this device. This work was support by a contract from the National Library of Medicine.
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