Experience has shown us that survivors of a collapse can hear us but we can not hear them from the outside of the rubble pile.Slideshow Images:
After a building collapse or a disaster wreaks havoc on the structures of your community, the search for survivors is truly a race against time. A seismic or acoustic type of listening device can help us locate victims that are still able to indicate they are alive by tapping, movement or calling out.
Often victims trapped in a collapse can hear the rescuers but the rescuers cannot hear the victims due to the amount of debris and rubble that blocks the sounds they make in an attempt to contact us. The wood, brick, concrete and building contents tend to block the sounds from traveling more than a few feet. The Delsar Life Detector is one of several on the market (see photo 1). With the use of this type of listening device, we can locate trapped victims by use of its seismic/acoustic omni-directional sensors. It is the one I know and have trained on, so that is what we will talk about. This is a great tool and you must research the different manufacturers if you are looking to purchase one.
As stated, experience has shown us that survivors of a collapse can hear us but we can not hear them from the outside of the rubble pile. This device employs sensors that convert any vibrations or noise in to audible and visible signals. By visible I mean that the device has sequential lighting by use of a signal amplitude display that visibly shows you the amount of sound/vibration that a particular sensor is receiving.
The main unit of the device has a sensor selection giving you the opportunity to select any of the six sensors placed strategically around the work area. It runs on six "C" cell batteries, that will give approximately 24 hours of use, or it can be plugged in to an outlet with an attachment similar to a laptop computer; in addition it has an adapter that can be used off a 12 volt vehicle battery (see photos 2 & 3). Although the system is somewhat water resistant, every effort should be made to try and keep it dry to protect the microprocessor and other electronic technology.
On the main unit we have two selector switches that say "sensor", each being dedicated to channel "A", or channel "B". Using these switches we can scroll through the numbers which will indicate the sensor that you are listening to. If the display indicates "A", you will be listening to all of the sensors at once. Each sensor has a number making it easy to know which sensor you are getting a vibration or sound from (see photo 4). It is recommended that you hook up the sensors sequentially but it is not necessary to use all of the sensors at once. In certain situations you may not need to run the sensors in a sequential string, for this there is a t-cable junction (see photo 5) enabling you to run two sensor strings in different directions if needed. Also on the side of the main unit is an input for headphones (see photo 7). This gives you the ability to listen closely to the sounds emanating from the rubble pile. There is a splitter to allow two people to listen at once, (see photo 6), but you must be aware that using the splitter (also called the stereo Y plug) may give you some acoustical feedback if the second set is not used. The volume control will increase or decrease the volume in the headset.
There is a filtering function on the unit (blue switch on lower left of unit of photo 1). This is used to reduce interference and change the clarity of the sounds you may be receiving. The "rumble" filter reduces low frequency noise and will reduce the detection range. The "PWR" filter cuts out a very narrow band of frequencies and will not reduce the detection range. The "HISS" filter cuts off the higher frequencies but at the cost of reducing the sounds of scratching. And to the immediate right of the filter switch on the main unit is the "TALK" switch. This is used in conjunction with the intercom probe (see photo 8).