If you were to ask a group of people how they can tell when an emergency vehicle is approaching, they would probably immediately say the “lights and sirens.” The use of visible and audible warning devices to distinguish emergency vehicles dates back to the days of early motorized fire apparatus, when the colored lenses of the apparatus lanterns and the urgent clanging of the bell warned people to get out of the way.

Today the lanterns have been replaced by an array of electrical warning lights and the bell has been replaced by a siren (and sometimes an air horn). The principle is still the same, however. Apparatus warning devices help an emergency vehicle travel through traffic quickly and safely. In many respects, they are some of the most important components on the vehicle.

Up in lights

NFPA 1901, Automotive Fire Apparatus, defines four zones around an apparatus: front, rear and each side. Each zone is divided into an upper level and a lower level. For each of these eight areas, the standard defines the mounting location, allowable colors, minimum flash rate and optical power for warning lights. The standard further divides these requirements into whether the vehicle is moving (“calling for right-of-way,” also called “clearing right-of-way”) or stationary (“blocking right-of-way”). To further complicate matters, these requirements vary depending on the length of the vehicle and the height of the warning lights from the ground. Got that?

The KKK-A-1822D Federal Specification for Star of Life Ambulances defines similar criteria for ambulances, including a requirement that the warning lights must flash in a certain sequence. The upcoming KKK-A-1822E specification is expected to have more stringent requirements. This standard applies to all ambulances purchased through the federal General Services Administration and has been widely adopted by many states.

Before you give up in despair, you should know that many warning light manufacturers have light packages that are specifically designed and tested to meet these standards. Some manufacturers even have printed guides that allow departments to choose various combinations of components to meet the standards, rather than taking a single package. Before you start loading your apparatus with unnecessary warning lights, it's recommended you consult one of the manufacturers listed at the end of this article. (See Manufacturers on page 13)

There are three types of apparatus warning lights commonly used today: halogen, strobe and light-emitting diode. Each type has its own advantages and disadvantages.

Halogen warning lights are brighter than older filament lights and have the lowest initial cost. They produce a flashing pattern by using either an on-off interrupter circuit or, more commonly, a rotating or oscillating parabolic reflector. Halogens produce good light intensity in all colors, but they are best in red. On the negative side, halogen bulbs are susceptible to vibration, moisture and extreme temperatures. As a result, they have a bulb life of about 300-600 hours. They also use significantly higher current than other types of warning lights.

Strobe warning lights have a higher initial cost than halogens, but use less current. They use a programmable power supply to vary the flash rate and intensity. On some strobe lights, each flash is actually a burst of several closely spaced flashes that the human eye perceives as one long flash. Strobes have good light intensity in all colors, although they are best in white, amber and blue. They have a much longer bulb life than halogens, usually about 2,000 to 5,000 hours, although the light intensity degrades with time. Some manufacturers recommend replacing bulbs at the 50% point, or about 1,000 to 2,500 hours. On the down side, strobe bulbs are more expensive to replace than halogens. Strobes with slower flash rates can also be distracting to the apparatus driver when the flashes are reflected off falling snow or fog, producing a jerky “silent movie” effect.

LED warning lights have come a long way since they were first introduced for stop/turn/tail light applications several years ago. They have the highest initial cost of any warning light, especially in blue, although the price has been falling steadily. Like strobes, LED lights use a programmable power supply to vary the flash rate and intensity. The biggest advantages of LED lights are that they aren't affected by vibration or moisture and have an estimated life of 100,000 hours. They also use the least amount of electrical current. The disadvantages, in addition to the higher cost, include a certain degradation of intensity over time and the fact that the illumination is more focused in a straight-ahead direction than it is off to the sides. Despite the disadvantages, LED lights are expected to continue to grow in popularity as their price falls and their intensity increases.

Many departments use a combination of lights for various functions on an apparatus. For example, they might use the sweep of rotating halogens and the pulse of flashing strobes on the upper level for good long-distance visibility, with the variable flash pattern of strobe or LED lights on the lower level for good short-distance recognition.

To supplement a vehicle's required warning lights, some departments also specify rear-facing directional arrows or message boards to direct traffic around emergency vehicles.

Wails and yelps

Although warning lights visually distinguish an emergency vehicle from surrounding traffic, it's not always possible for other drivers to see those lights. The emergency vehicle may be approaching from a side street, coming around a blind curve, over a hill or may simply be blocked from view by larger vehicles on the road. To give other drivers adequate warning, emergency vehicles also rely on audible warning devices, such as sirens and air horns.

NFPA 1901 requires an electrical (electro-mechanical) or electronic siren. The KKK standard for ambulances has similar requirements. Each type of sirens has its advantages and disadvantages.

Many departments feel that traditional electro-mechanical sirens have a “commanding” sound spectrum, including a blend of rich harmonics and penetrating low frequencies, that is more easily recognized by other drivers. These sirens also continue to produce sound after the electrical motor is turned off and the siren is coasting down. On the down side, electro-mechanical sirens require a lot of electrical power to operate. One popular model requires 100 amps or more. Other somewhat smaller models require 45-60 amps. Larger electro-mechanical sirens are also heavy and must be mounted on a sturdy base.

Traditional electronic sirens can produce the same sound intensity as electro-mechanical sirens, but are lighter weight and require far less electrical power. They can also be programmed to produce a variety of sounds from wails to yelps, as well as double as a public address system. On the down side, many departments feel electronic sirens do not produce the same sound spectrum as electro-mechanicals and aren't as recognizable. Some testing has also shown that certain electronic siren configurations can project sound in a non-uniform pattern that produces lower levels of sound pressure angles ahead of the vehicle on either side.

Within the last few years, several manufacturers have introduced electronic sirens that duplicate the sound spectrum of electro-mechanical sirens, thus combining the advantages of both types. These new sirens have a current draw of only 10-30 amps, which may make them an attractive alternative to electro-mechanicals for some departments.

Toot your own horn

Although NFPA 1901 only requires an automotive horn, usually electrical, an air horn can be a valuable supplement to a siren. Many sirens project sound in all directions around the vehicle. While that's useful to alert other drivers in the vicinity, it also makes it difficult to determine the location of the emergency vehicle. “I could hear the siren, but I couldn't tell where it was coming from” is a common complaint of motorists. Because an air horn is designed to project most of its sound directly forward, its location is easier to determine (left, right, ahead and behind) and it makes an effective warning device when approaching intersections.

Some emergency vehicle air horns are designed to produce a unique sound that is immediately distinguishable from other truck horns. A few air horns include optional under-hood air compressors for use on vehicles that don't have air brake systems. Others produce an air-horn sound from an electrical horn.

No amount of lights, sirens and air horns can protect you from a collision with vehicle operated by someone who is impaired by alcohol or isn't paying attention. Warning devices don't make an emergency vehicle invincible. All fire departments should train their vehicle operators in defensive driving tactics and techniques. This includes proceeding with caution when crossing against a traffic light or in situations where other drivers may not be able to see or hear the warning devices.

In some cases, a department may even want to define certain response situations where an emergency vehicle doesn't use its warning devices at all, but simply proceeds with the normal flow of traffic. These might include lockouts and other public service calls; minor vehicle accidents not involving fires, injuries or hazardous materials; or confined fires not threatening structures, such as dumpster fires.

And whenever you drive, always be safe. Wear your seat belts at all times.

Manufacturers

B&M Siren Manufacturing (sirens)
562-623-0020

Buell Air Horns (air horns)
800-422-8355, <www.buellairhorns.com>

Cast Products (lights and sirens)
800-468-2278, <www.getcpi.com>

Code 3 Inc. (lights and sirens)
314-426-2700, <www.code3pse.com>

Federal Signal Corp. (lights, sirens and and air horns)
800-832-5908, <www.fedsig.com>

Grover Products (air horns)
323-263-9981, <www.groverproducts.com>

ATC Lighting and Plastics Inc./KD Lamp (lights)
440-466-7670, <www.atc-lighting-plastics.com;

Lumastrobe (lights)
800-775-luma, <www.precisionmulticontrols.com>

PowerArc, the Fire Products Co. (lights)
800-990-8455, <www.powerarclights.com>

Signal Vehicle Products (lights and sirens)
800-875-8003, <www.svp-inc.com>

Timber Wolf Sirens (sirens)
877-788-7473, <www.timberwolfsirens.ws>

Tomar Electronics (lights and sirens)
800-338-3133, <www.tomar.com>

TriLite Mars Inc. (lights)
800-322-5250, <www.triliteinc.com>

Unitrol (sirens)
800-854-3375

Unity Manufacturing Co. (lights)
312-943-5200

Vectra Corp. (sirens)
508-430-1600, <www.vectracorp.com>

Weldon Technologies Inc. (lights)
800-989-2718, <www.weldoninc.com>

Whelen Engineering (lights, sirens and air horns)
860-526-9504, <www.whelen.com>

Standards and requirements

Sections 11-8 and 11-9 of NFPA 1901 define standards for warning lights, sirens and air horns on fire apparatus that have a gross vehicle weight rating of 10,000 pounds or greater. NFPA 1906 defines standards for smaller wildland fire apparatus.

The General Services Administration KKK-A-1822D Federal Specification for Star of Life Ambulances (and the upcoming revision E — see Shop News) defines standards for warning lights, sirens and air horns on ambulances. This federal standard has been adopted in many states.

The new SAE j2498 standard provides a performance-based specification for warning lights and may be incorporated into other standards.

Some states have their own unique requirements for warning systems, such as California's Title XIII. These state requirements may limit such factors as warning light colors or may require that one or more lights be constantly illuminated without flashing.

State and federal osha requirements limit both the maximum and the time-weighted sound intensities experienced by persons riding inside the vehicle or working outside in the vicinity of the vehicle. These limits may affect the placement, operation and sound output of audible warning devices.