November 2005, Issue 184

Water Pressure Sensor
ZigBee-Based NozzleMon Aids Firefighters

FUTURE MODIFICATIONS

The design I’ve described in this article is truly a prototype—more of a proof-of-concept than a ready-for-production model. Although the firefighters who have seen the NozzleMon work have been enthusiastic about using it, it isn’t ready yet for real scenarios. It wouldn’t be practical to enter a burning structure with a hunk of plumbing and a plastic box hanging from your nozzle. And although using only the on-board antennas on the SARD and evaluation board gives fine reception over a modest distance under good conditions, a real fire scene may involve significant distances and suboptimal conditions.

To be practical, the nozzle unit has to be incorporated in the nozzle itself. The handle of most fire nozzles is a solid stem just waiting to be stuffed with electronics. Incorporating the pressure reduction/water isolation in the body of the nozzle would be easy, and, of course, the local pressure gauge and external plumbing would be eliminated.

Integrating electronics in the nozzle body would enable even more functionality. You could implement a handle grasp indicator with a Freescale MC33794 e-field imaging IC. This would help determine if the nozzle is out of control. For example, if the accelerometers indicate rapid motion and there is nothing gripping the handle, that’s a pretty good indication of a loss of control. With nozzle-mounted electronics, other operational parameters could be sent back to the pump panel unit such as the position of the valve and the selection of the stream type.

To increase the radio’s distance and improve reliability in hazardous environments, you can use an inexpensive hose-coupling repeater. Typical fire hoses are 50¢ long. Incorporating a ZigBee router node in the female hose couplings would ensure that the next network node would be no more than 50¢ away. Leveraging ZigBee’s self-organizing network topology (with the pump panel unit as the ZigBee coordinator and the nozzle units as reduced function devices) makes for a fast, flexible, and reliable fire scene network.

With repeaters already scattered around the fire scene, other ZigBee devices could be developed to leverage the network infrastructure. ZigBee devices could monitor things such as the performance of a self-contained breathing apparatus (SCBA—an air pack), a firefighter’s health (e.g., blood pressure, temperature, and respiration rate), and fire conditions (e.g., temperature and air composition). It even may be possible to incorporate pressure sensors in the hose-coupling devices, allowing for the immediate determination of the location of a hose line problem within 50'. Having live data from inside the fire scene would be a powerful tool for making tactical firefighting decisions. And, most importantly, it would make the fire environment safer for firefighters. Figure 2 shows how the ZigBee devices would be placed around the fire scene.

Power management is another thing needing modification to prepare the design for real-world scenarios. One of the original design goals was to have the NozzleMon function transparently for the interior firefighter. A firefighter shouldn’t have to go through extra steps to enable the NozzleMon’s functionality. He should be able to use the nozzle (and other equipment) just as before.

In order to avoid having a power-on switch that must be activated manually, a pressure-activated switch would be used to conserve battery power when the system isn’t in use. This would ensure power is applied when the nozzle is active. Having the nozzle unit and the intermediate routers power on automatically when the hose line is charged to at least a few pounds per square inch would satisfy the transparency requirement and conserve battery power.