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.
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).
The intercom probe is used to detect airborne sounds in voids and can be used to talk to a victim. It is connected just like the sensors but once connected you can not scroll through the sensors, the display will indicate "0", and all filtering is turned off automatically. The intercom probe can be lowered or inserted in to a void to listen and/or talk to a victim that is trapped (see photo 9). It isolates high frequency sounds such as breathing and groaning. To communicate with the victim, push the talk button and speak in to the microphone indicated by the four small holes next to the talk button.
Additional accessories include a metal spike (see photo 10) that screws on to the bottom of a sensor for placement in to soil (see photo 11) where needed and a magnetic disc which also screws on and can be used to attach the sensor to metal objects (see photo 12). Be aware that when attaching the sensor to metal it will pick up many different sounds. The metal transmits noise from greater distances, and, although that could be an asset or a detriment, it may take longer to get a more accurate fix on the source. Metal tends to transmit wind noise, airborne sounds and may give general interference.
When setting up for a search, connect the end of the sensor cable that says "To Life Detector" to the main unit, or to a sensor that is already connected to the unit. The other end attaches to the next sensor. This is done sequentially from each sensor to the next until all that will be used are attached (see photo 13). Although it is not imperative to place the sensors in numerical order, it makes it a little easier to keep track of sensor location and calculating a triangulation formula.
You cannot use two of the same numbered sensors in any string. Select suitable locations for the sensors and try to obtain a solid contact with the surface. Select hard materials like concrete, wood or brick. You can attach the sensors to any remaining walls or floors and if you need to you can tape them in place. Clear off as much surface dirt and debris as possible to get good contact and avoid things like carpet, insulation, roof membranes, or soft soil like sand. If necessary secure the cables near the sensors with tape or "soft" debris to avoid the cables from vibrating and giving "false" reading due to vibration.
Once the sensors are placed, put on the headset, and listen to channel "A". In an "All Quiet" environment attempt to establish a baseline on the sounds. Increase the volume a notch or two to get a good base. Now toggle through the sensors using the switch on the main unit, listening to the sounds and watching the display, keeping track of which sensor receives the highest levels of sound. Relocate any sensor that is giving excessive interference. Large amounts of interference may mask a victim trying to signal us, especially in the "A", ALL mode.
If there is a know victim in a collapse, place the sensors strategically around the area and try to communicate with the victim, perhaps with a bull horn. Ask the victim to tap an object 3 times and listen. If no noise is heard, move the sensors and try again. If noise is heard, leave the sensor that has the greatest noise in place and move the remaining sensors in an attempt to "close in" on the victim and isolate the sounds. Once the victim's location is narrowed down we can begin with the other technical disciplines necessary to remove them.
This is a great tool and its use by USAR teams is well known. The above explanation is just a brief version of the full capabilities of this tool. As I said, there are a few different types systems out there. Call the manufacturer and test them all to see what is the best for your department. Stay Safe.
Captain Tony Tricarico has been a member of the fire service since 1977 and was hired by the FDNY in 1981. Tony has served in the South Bronx, Brooklyn and Manhattan. Since 2002 he has been assigned to the Special Operations Command and currently serves as Captain of Squad 252.
Tony is a nationally certified instructor as well as a New York State Certified Fire Instructor, is an adjunct instructor at the FDNY Technical Rescue School, a Deputy Chief Instructor at the Suffolk County Fire Academy, and additionally instructs and lectures throughout the country on a Engine, Truck, RIT and Special Operations tactics and procedures. He has been featured in FETN and American Heat training video's on collapse, elevator operations and SCBA emergencies. He is an active member of the Mount Sinai Volunteer Fire Department on Long Island and a former Chief of Department.
