RADIO COMMUNICATIONS: COMING IN LOUD AND CLEAR
DURING THE course of firefighting, vital radio communications are subjected to, and are all too frequently at the mercy of, the most adverse conditions imaginable. Noise in the area of the pump panel is louder than both the spoken and transmitted word. Line officers with radios may have difficulty hearing the portable receiver because of protective clothing and breathing apparatus, and transmitting is even more problematic. Even before personnel arrive at the fireground, they face the obstacles of engine and siren roar. It is truly a challenge to operate in this environment. However, there are tools available to help make the job of communicating a little easier.
The radio systems summarized in this article all are designed to improve radio communications, which in turn, increases the safety of personnel. Although not even the best equipment used in accordance with ICS procedures can guarantee successful communications, your chances are greatly increased when personnel are equipped with technology that’s equal to the task, are trained in its use, and understand that communications must be loud and clear—all the time.
ATTENUATING HEADSET WITH BOOM MICROPHONE
Fire departments have used noiseattenuating headsets complete with noise-cancelling microphones for years, especially after OSHA regulations increased the awareness of hearing damage caused by prolonged exposure to high levels of noise. Because attenuating headsets reduce the level of exterior noise entering the eardrum, they are becoming increasingly popular.
High-quality headset systems contain acoustical filtering, audio speakers, a microphone, and a radio interface module. The filtering protects the wearer against hearing loss by reducing the level of potentially harmful sounds entering the eardrum.
Whether the wearer is fully protected against hearing impairment depends on the environmental noise level and the protection rating of the headset. Hie protective element of a headset is measured by the noise reduction rating (NRR). Normal conversation reaches a level of 60 decibels. Up to 80 decibels is considered a safe environment. Any continued, prolonged exposure above 80 decibels can cause damage. A diesel engine puts out just over 100 decibels. Fain sets in at about 120 decibels. In some fire applications the ambient noise level is so high that even with a headset the level entering the ear canal is unsafe and can cause hearing damage with continued exposure. Check out the NRR before you buy.
Headsets also improve communications. Similar to a stereo headset, speakers in the earmuff bring the sound close to the user’s ear so the radio is heard. Furthermore, in the more technically advanced units the shape of the sound wave is modified so that frequencies at the high end—mostly from noise—are reduced, thereby making middle-range frequencies—voice messages—more audible above the noise. This feature also works for direct oral statements and not just radio transmissions; that is, if two firefighters are standing in front of a pump panel in full operation, the headset wearer will better hear the member next to him since the high-end pump noise is reduced. Headsets with two earmuffs are best for high-noise situations.
From highest to lowest pitch, the spoken human voice has a relatively narrow range compared with noise coming from many sources. The system’s noise-cancelling microphone eliminates the extremes and allows only the frequency range for the voice to be passed through to the radio and transmitted. This system still may transmit some noise, but it will be far less than the unfiltered sound, and the spoken voice is accentuated if the headset is equipped with such a microphone.
The headset has many uses in and around the fire apparatus. The particular application will determine how each headset is interfaced to your radio. A vehicular intercom system and radio link allow the driver and officer to communicate with dispatch while en route to the scene. Through hookups strategically located on the vehicle, other personnel can be wired either for receiving or for two-way communications. The intercom feature also can limit communications exclusively to the apparatus, so personnel can know what to expect and the plan of attack on the way.
Most systems have a module with a receptacle for the headset, a push-totalk (PTT) button, and a radio interface cable designed specifically for the particular portable or mobile radio used. By plugging directly into the vehicle’s radio system, transmissions are at the full wattage of the mobile. Also, the operator has an umbilical cord so he will not wander unnecessarily. If needed. quick disconnects are possible during which time the operator will be out of radio contact. Using a portable allows more room to roam.
Another application is with the aerial ladder. With either an extension of the intercom or a portable plus headset, the firefighter in the bucket can communicate with ground personnel.
Quality headsets have a relatively long service life, are simple to maintain, and are easy to use, making them an ideal accessory to ensure high noise protection for personnel and clarity of transmissions. Portables and mobiles vary in terms of their electronics, so you cannot necessarily interchange headsets from one system to another. Determine your needs and evaluate your operating procedures before you buy. An car microphone is a relatively new technology. laterally, it allows you to “talk through your ear”—and listen, too. A tiny device about the size of a hearing aid is placed in the ear. This is a transducer—capturing the vibrations of the ear canal, linking it to an electronic module where it is amplified, and sending it to the radio via a push-to-talk button. Press the PTT and whatever the wearer says, even a whisper, is transmitted. Release the button and it becomes a speaker. Being in the ear canal reduces the amount of outside noise entering the transducer, so the audio transmission quality is excellent.
In high-noise situations such as at the pump panel, using the ear microphone and a set of personal ear protectors is a viable alternative to a headset. It has very good noise attenuating characteristics but is not as easy to put on as a headset.
Ear microphones make communicating while wearing breathing apparatus safer. Often firefighters use the collar/ speaker microphones or the radio itself in the lift-to-talk mode, lifting radios to their face masks. But when transmissions are garbled, they may be tempted to lift the face mask as well. Ear microphones capture internal ear vibrations; they cannot be garbled by the mask. On the receiving side, the wearer has only one ear covered, so he can hear the environmental noises of the fire.
Haz-mat response teams can also benefit from ear microphones. Microphones are lightweight and do not further encumber a responder in an encapsulating suit. Most ear microphones have detachable radio interface cables for use with different brands of radios. Some haz-mat teams use specialized, low-wattage radios with their own unique connector.
To be effective, the ear microphone must be integrated with your radios and equipped for the intended use. The hazmat application, for example, requires access to the PTT button while in a fully encapsulating suit. For some models properly engineered with flexible options, this is no problem; for others, it definitely is.
Earpieces should be custom-molded for each radio user for the best fit. They will last longer if clearly made the specific responsibility of and considered the personal equipment of the user.
The throat microphone was used by pilots in World War II. A noise-cancelling microphone is strapped around the throat, where it picks up vibrations of the vocal cords. Headsets or earpieces are worn to hear the radio. Both are linked to a PTT or voice-activated (VOX) module. Although the microphone picks up lower, more gutteral sounds better than high, nasal ones, the sound quality is fairly good if the user talks clearly.
The system is basically designed for face masks worn by haz-mat and entryteams. The throat microphone fits below the seal of the mask without breaching its integrity. The strap is elasticized to contract and expand with breathing or weight loss from heavy perspiration in an encapsulating suit.
The main benefit is the system’s voice-activated capability. Without lifting a finger to key the microphone, the wearer speaks and the radio transmitter comes on. It is completely hands-free. There is a sensitivity adjustment to set the voice activation level to the wearer’s threshold. If set properly, false activation from grunting or heavy breathing is not a problem in quality units.
Some throat microphone systems with VOX have been designed as full duplex radios—the users on the system can speak and hear at the same time. This is designed for specialized teams needing to talk so quickly and freely that the standard, proper radio protocol (“over”) would cause unacceptable delay.
A bone microphone works on the principle of bone conduction. The sound waves that speaking creates are conducted through the skull, and these vibrations are picked up similar to vibrations in the ear canal or throat. The bone microphone is normally positioned on the top of the skull and is held in place by the webbing of a face mask or helment. You can hear several ways—through a small speaker held externally to the car by the face mask, an earpiece, or a headset. A PTT or VOX system is possible using a module as with the throat microphone. The module is linked to a portable radio via different cables.
The primary application of the bone microphone is for breathing apparatus. The mask has to be on the wearer to operate, unlike with a throat or ear microphone. Clarity is very good and the system is lightweight. The bone microphone must be held in place securely by the webbing of the mask, which may be a problem since some masks have a loose netting over the top. The list of vendors is very short and prices are somewhat high compared with other systems on the market, but this could change with the increase in hazmat teams.
BREATHING APPARATUS RADIO
This system works with a microphone worn inside the face mask itself. A wire passing through the mask without breaking the seal is connected to a module that contains a push-to-talk and a speaker. Typically, this is worn on the harness and is connected to the firefighter’s radio via detachable radio interface cables.
Transmission clarity on a quality unit is good. The speaker audio may be less than some other systems and more like a collar microphone. The system may be retrofitted to existing face masks or purchased new as a single assembly.
Safe and effective emergency scene operations can’t be accomplished without communication. Your know ledge of available technology, your ability to choose the technology that best fits the needs of your department, and the ability of personnel to employ the technology correctly under extreme conditions could well mean the difference between an effective and poor operation.