APPARATUS WARNING DEVICES PRESENT AND FUTURE
The successful family man was duly proud of his new luxury sedan that possessed every creature comfort available. Driving this automobile was a pleasure, as it put the occupants in a world of their own. All of the manufacturer’s literature and advertising touted the smooth ride and silent comfort of the passenger compartment.
One afternoon the family was out for a drive with the air conditioner on, the compact disc player at a comfortable level, the kids laughing in the back seat, and the driver and his companion engaged in conversation.
Suddenly the atmosphere was disturbed—the music stopped and a serious-sounding synthesized voice loudly announced, “Caution, emergency vehicle approaching.” The announcement was repeated continuously.
As the driver looked around and checked his mirrors, he detected a bright, piercing white light flashing across his rear window, followed shortly thereafter by red lights, a siren, air horns, and the unmistakable form of a large red fire truck approaching.
He pulled to the side of the road and allowed the responding unit to continue on its critical mission. As the apparatus passed, the automobile’s voice-warning system cut out, and the CD player picked up right where it had stopped.
Is this fictitious scenario a possibility? 1 believe it is. Is it available? The answer is no.
In today’s world of electronics, you can hardly walk through the parking lot of a large store without hearing the “chirp” of vehicle alarms being set or disarmed by miniature transmitters on drivers’ key rings. Another system in full use today implants a small homing transmitter that can be remotely triggered when a vehicle is reported stolen, allowing the police to locate the stolen auto. Some auto rental companies in resort areas are experimenting with a device that indicates to the driver his/her exact location on an “electronic map” in the car.
The thought of having an automobile equipped with a device that overtakes the car’s radio speakers and announces the presence of an emergency vehicle in the immediate area is not farfetched. The device could be activated by a short-range transmitter mounted to the front of an emergency vehicle. The unit could be programmed to operate in conjunction with the apparatus siren to avoid blanking out radios when it is not responding. In addition, the transmitter could be further arranged to project the signal to the rear when the apparatus is stopped on a busy roadway, to give ample warning to approaching automobiles.
As we attempt to create safer apparatus and a more healthful response environment, cabs have become more insulated against noise. The fully enclosed open area-type cab adds the element of several firefighters dressing in turnout gear and possibly discussing assignments and strategy as the unit responds. The enclosed cab also has greatly increased the use of air conditioning to maintain the interior temperature of the riding compartment. This, in turn, has led to responding with the windows closed and the cab insulated from the outside environment, including the sound of other apparatus responding to the same call.
Data from the National Fire Protection Association indicate that during the 1980s, 179 firefighter deaths (IS percent) resulted from accidents involving fire apparatus that were en route to alarms.
The radio-controlled receiver 1 described in this article also could be a valuable asset if installed in emergency vehicles. Receiving advanced warning that other apparatus are approaching conceivably could reduce intersection accidents while responding.
Of course, if this idea were to be embraced, it would take miles of bureaucratic red tape and many years to implement. A phenomenal amount of cooperation would be needed from automobile manufacturers, the producers of signaling equipment, the government, as well as the general public.
With the full knowledge that this concept is far off in the future, let’s examine the signaling equipment presently available and the best ways to warn the public of our presence.
AUDIO WARNING DEVICES
Warning devices generally fall into two categories, audio and visual. The audio warning devices to which we have become most accustomed are the apparatus’ siren and horns.
Hie NFPA 1901-04 (Apparatus) series indicates that apparatus shall be equipped with an electronic or electromechanical siren that complies with the Society of Automotive Engineers (SAE) J1849 (Emergency Vehicle Sirens) and at least one automotive traffic horn.
As with all sound-producing sources, sirens and horns create vibrations or disturbances that travel through the air and reach the inner ear—sound. Being familiar with two concepts relating to sound, frequency and pressure, will help you better understand issues relating to audio warning devices.
SOUND FREQUENCY
One unit of sound measurement is frequency, expressed in hertz (Hz), the number of vibrations generated per second. In simple terms, it is the tone of the sound. Hie human ear can hear from 15 to 20,000 Hz, but it is the most sensitive in the 1,000to 2,000-Hz range. Because of the fact that people detect sounds at different frequencies, the most effective audible signals cross the sensitive range of human hearing.
The SAE requirements call for the siren sound to rise and fall in the frequency range of between 650 and 2,000 Hz in the “wail” and “yelp” as well as the manual modes. The difference between these two sounds is that the cycle rate per minute of wail (10 to 30 cpm) is much slower than that of yelp (150 to 250 cpm), but both sweep the normal hearing spectrum. The rapid pulsations of the yelp tone convey a more urgent message than the steady rise and fall of the wail or manual setting.
Note also that other tones may be available on your electronic siren control, but they are not recognized in the SAE standards as sirens that call for the right-of-way by an emergency vehicle. The “hi-lo” two-tone European-type siren operates at approximately 800 and 1,000 Hz and fails to sweep the spectrum. Also, the newer ultra fast (phaser) tone is not yet recognized. Be careful when using these auxiliary signals, as their validity might present a legal challenge if your responding apparatus is involved in an accident.
SOUND PRESSURE
Another measurement of sound is the decibel (db), a measurement of sound pressure and generally understood as a comparative degree of loudness. Decibels are rated at a given distance, usually 10 feet for warning devices.
A comparison of decibel ratings at 10 feet is as follows:
- 0 db: Threshold of hearing.
- 90 db: Average street traffic noise.
- 140 db: The threshold of pain.
For an audible warning device to be considered effective, it must be heard over the 90-db level of street traffic. An approved siren must produce 118 db of sound at 10 feet directly in front of the device. This surely would overcome the traffic noise, but the element of distance reduces the sound level when the source is farther away. Visual signals provide better longdistance warning than audible signals.
One misconception is that dual speakers are twice as loud as a singular speaker. The polar plot (illustrated at right) compiled by one signal manufacturer, compares a singlevs. dualspeaker system. The two speakers projected slightly farther ahead of the vehicle but left critical “hollow” areas at the 45-degree angles, where intersection warning is most necessary. The best coverage probably could be gained by using a single 200-watt speaker instead of dual 100-watt speakers.
Most people would agree that nothing is more effective for audible warning than a large electromechanical siren. This type of unit is unsurpassed in decibel output (128 to 140 db) and coasting ability. Its obvious disadvantages are the space needed for mounting and the large current draw (up to 100 amps) necessary to drive the siren motor.
(Photos by author.)
Air horns, especially those with valves that cause the horn’s note to rapidly pulse or stutter, also are effective warning devices. Apparatus drivers must be cautioned against causing civilians to panic when air horns suddenly are sounded while responding.
NFPA 1901 also requires that all audible warning devices be mounted as low and as far forward on the apparatus as practical. Sirens and horns no longer are allowed to be mounted on the roof of the apparatus.
VISUAL WARNING SIGNALS
The minimum number of warning lights each apparatus must have, according to NFPA 1901-04, is as follows:
- One or more rotating, oscillating, or flashing lights, visible through 360 degrees in a horizontal plane, mounted on the cab roof or as high as practical.
- A pair of flashing, oscillating, or rotating warning lights affixed on the front of the vehicle facing forward and below the windshield level.
- Another pair of these lights affixed at the rear of the vehicle, facing to the rear.
- An intersection light affixed between the front wheel and front of the vehicle on each side.
All warning lights must be Class 1 as defined in the current SAE requirements and be included on the current list of the American Association of Motor Vehicle Administrators.
The color of these lights is not specified, but a combination of red and blue is strongly recommended, where such combinations are allowed by state and local law.
ELECTRONIC SIREN POLAR PLOT SINGLE vs. DUAL SPEAKERS
Sound meter readings taken at various locations with an electronic siren operating disclosed that a single speaker produced a relatively uniformed pattern. The dual speaker system had slightly more reach; however, there were ”hollow” areas at the angles where intersection warnings are most needed.
(Illustration courtesy of Federal Signal Co.)
These are the minimum requirements for warning lights. Other areas on the apparatus, such as those listed below, also would serve as good locations for additional signaling devices:
- The midsection of an aerial unit or the broad side of a large rescue truck—especially for increasing visibility when crossing an intersection.
- A center-mounted, clear, oscillating light below the windshield level produces a good, long-range signal. In addition, the figure “8”or “M”shaped pattern these lights produce catches the attention of automobile drivers in front, as the light flashes across the rearview mirror.
- Driving with the headlights on attracts attention even in daylight. Adding a flash sequence to the highbeam circuit makes these lights even more noticeable. Note that some states prohibit flashing headlights as a warning device.
- Rear-facing, traffic-directing arrow lights are important additions for vehicles that might block traffic at the emergency scene. Warning lights mounted to the interior of the trunk lid could help avoid an accident when the open trunk blocks visibility of the roof-mounted light bar.
State or local regulations also might require additional warning lights. The state of California, for instance, has a law mandating a steady burning lamp to the front and a flashing lamp to the rear of every emergency vehicle.
IDENTIFYING VISUAL SIGNALS
The three components of visual warning signals are detection, recognition, and response.
Detection. The threshold of observation or the point at which the observer first sees the warning signal. It is the first area to consider when choosing a visual signal system. The obvious goal is to achieve the earliest possible detection of your approach or presence.
Recognition. The time when the observer attempts to identify the source of the detected warning signal. Several factors influence recognition. Color is one major factor. Drivers in various areas of the country associate signal colors with specific emergency services.
In most locations, for example, amber usually indicates “caution” or a nonemergency vehicle warning, such as that of a tow truck, a highway maintenance vehicle, or even a roadside barricade used to direct traffic.
Red usually denotes “danger” and normally is used to request the rightof-way or indicate “stop” to the observer. Drivers usually identify red with fire and police vehicles.
Blue signifies a police vehicle or a volunteer firefighter, depending on the geographic location. In some states, blue is the primary warning color used by police.
The frequency or flash rate of the warning signal also conveys a message during the recognition phase. A fast flash indicates more of an urgency than a slow, “lazy” signal such as that used for roadside barricades or trafficpattern arrows. Special high-output, fast rotators (160 to 180 flashes per minute) are very effective as attention-getting signals, especially in the clear mode. When specifying this unit in a lightbar, however, the number and location of these rotators might be limited because they have a high heat output and require a significantly high rate of current.
Another recognition factor is pattern. Warning lights with a synchronized pattern provide a consistent signal that allows the observer to focus and judge the size and speed of the signal’s origin. Many light bars are programmed to flash out from the center in a “V” pattern, which indicates a clearing pattern. Traffic-warning strips, which are very effective when placed on the rear of a vehicle, can be programmed from the vehicle to select a pattern indicating the direction the traffic is to take. Random flashes, on the other hand, are more difficult to focus on, analyze, and identify.
Response. The response to an emergency signal is the course of action the observer takes after recognizing it. This reaction could be anything from moving to the side of the road to slowing down to stopping to completely ignoring it. The sight and sound of emergency signals cause some drivers to experience elevated pulse rates or to become nervous and confused. These responses could adversely affect reaction time and even cause the drivers to take improper actions. Drivers of emergency vehicles must maintain a calm disposition when approaching civilian traffic, since civilians may not always display rational behavior. If the apparatus driver becomes emotional and loses patience, die likelihood of an accident is greatly increased.
LIGHTING CONCEPTS
When evaluating lighting concepts, you must consider several factors. The first is the candlepower or candela of the light source. One candlepower, used as a reference, is the amount of light that will he produced by one specific type of candle burning. When a light source is surrounded by a parabolic reflector, all of the light energy is focused in one direction. A 50-watt halogen bulb produces 150 candlepower w’hen it is illuminated. Adding a reflector concentrates the light and produces 70,000 candlepower from the same bulb.
Although candela measures light intensity, it is not a very effective method of comparing the visual performance of warning lights. The amount of time the light is visible to the observer’s eye also must be considered when evaluating effectiveness. The strobe flash has a much higher peak candela than rotating lights, but it is of a shorter duration. To address this issue, strobe manufacturers have included multiple highenergy pulses per flash burst. This increases the “on” time, which helps in the recognition of the lighting signal and its color.
LENS COLOR
Several conditions affect the transmission of light through domes and color filters. Light projecting straight through a clear lens transmits almost 90 percent of its energy when leaving the device. As the light source rotates, the light striking the inside of the lens reflects back into the source, and the refraction (bending) of the light rays by the dome causes an additional loss. When a light bar is viewed straight ahead, it delivers more effective flashes than when the observer is off at an angle. To counter this effect and to direct more warning flashes into the intersections, some choose to mount two light bars at angles to the corner of the cab roof in a V-shaped configuration.
Lens color also has a great effect on the transmitting of light from a warning signal. A naked bulb transmits 100 percent of its light; however, various dome colors and light sources affect the amount of light ultimately delivered.
The color of the original light source depends on the temperature at which it burns. The halogen bulb burns at a temperature at which a good deal of red is generated in its color content. The strobe tube has a much higher color temperature and a bluish tint.
When comparing the percent of light being transmitted through a colored filter, the source of the light directly affects the transmittance (see chart below).
As can be seen from these figures, clear and amber perform about the same in each type of light. Note, however, that red performs better with a halogen light source and that when blue is used with a strobe source, it far outperforms a blue halogen.
Many jurisdictions now are using clear and amber in combination with red or blue on emergency vehicles because of the far-reaching light energy these combinations transmit. This helps increase the chances of early detection of the warning, and the standard red or blue facilitates recognition as the observer identifies the source.
Visual examination is the best way to evaluate the most effective warning light combination. The major warning light manufacturers offer a variety of colors and configurations of strobe, rotating, flashing, and oscillating lights in the same lightbar to satisfy customers’ needs.
Another important consideration when specifying warning lights for a vehicle is the electrical load the system will require. The manufacturers’ literature shows the number of amps each component will use. Compare products and systems, as they all do not have the same electrical rating.
Making warning devices louder and brighter in an attempt to alert the driving public could be counterproductive to the goal of safely moving through traffic to the scene of an emergency. Overly bright warning lights would be seen at greater distances, but they could temporarily blind an oncoming driver, which might result in loss of control.
To reduce firefighters’ hearing loss, NFPA 1901 stipulates that the sound inside the cab of a responding vehicle be no greater than 90 decibels without warning devices in operation. Louder audio signals, which would be environmentally unacceptable, could void the entire intent of this important health consideration.
In my opinion, the only way to penetrate the new breed of “silent” automobile passenger compartments or overtake a pounding stereo system to announce our impending arrival is through the use of space-age technology such as that described at the beginning of this article. Increasing the physical aspects of the present signaling systems might do more harm than good.
Ultimately, no amount of warning devices can compensate for the attitude and skill of the driver of an emergency vehicle. Chauffeurs must understand that they are only “requesting” the right-of-way with a siren and light, not “seizing” it! The issues of negligence and liability will always surface when an apparatus is involved in an accident. I’m quite sure that no firefighter wants to be the subject of this type of inquiry.
To test the feasibility of my proposals for warning motorists of the approaching of fire and other emergency apparatus, I consulted with a leading manufacturer of traffic control equipment. Following are some of his comments and observations:
- The preemption system his company now has on the market uses a short-range radio transmitter of the type proposed in the article to broadcast from the emergency vehicle to the intersections. In a similar fashion, the radio could allow the emergency vehicle to broadcast directly to the motorists.
- Broadcasting warning signals from emergency vehicles to all motorists, as proposed in the article, is more difficult. All cars would have to be equipped with a special radio that can interrupt the normal entertainment audio on receipt of a coded message. The idea, however, is not as farfetched as it may appear, since related highway-to-vehicle communications currently are being investigated with federal funding under the Advanced Traveler Information Systems (ATIS) category of the Intelligent Vehicle Highway Systems (IVI1S) program, a multiyear, multibillion-dollar project involving government, industry, and universities.
Fart of the ATIS/IVHS program is to develop communications technology and interface standards that allow real-time audio and visual communication from the highway system to motorists. Much of ATIS deals with information on congestion, navigation, location, incident location, average speeds, land restrictions, and recommended routes. Will communications from emergency vehicles to motorists be far behind? 1 think not.
- My own opinion is that the ground is fertile to bring about a radio communication system of the typeproposed in the article by the 21st century. The firefighter community, however, will have to make its voice heard by the traffic engineering community and the Federal Highway Administration in Washington, D.C.
