Choosing the Right Audible and Visual Signaling Devices for Different Applications

The type and intensity of sounders or beacons used in a particular area depend on the specific application. For example, sounders used in the food industry may not be suitable for industrial areas, and those used in heavy industrial manufacturing may not be appropriate for school environments.

  • Industrial, Mining, and Manufacturing Applications This category includes factory premises, as well as equipment and facilities used in factories such as cranes, handling vehicles, generating sets, and control panels. It also encompasses hazardous locations like coal mines and the petrochemical industry.
  • Building: Commercial and Public Applications Hospitals, schools, offices, building sites, houses, military sites, and airports fall under this category. Please note that due to continuous product research and development, some products may vary from the specifications in this catalogue.
  • Priority and Public Service Vehicles This category includes police vehicles, fire department vehicles, and ambulances.
  • Marine Applications Dock and ship installations, as well as other hazardous sites such as oil terminals, are covered under this category.

Frequency Considerations

Frequency refers to the number of vibrations per second and is used to identify the note of a sound. It can be measured using a frequency meter. In cases where a frequency meter is not available, identifying the ambient noise frequency in the environment can suffice. For example, a machine shop with a grinder will have a high-frequency noise, while a forge with a drop hammer will have a low-frequency noise.

Time Rating

The time cycle over which an alarm is required to operate must be taken into account when selecting a signalling device. It is important to choose a signal with an adequate time rate. Note that sounders used as evacuation alarms are typically required to be continuously rated. Some products on the market have time ratings of one minute or more, but these may not be accepted by Fire Authorities. Contractors should be mindful of this when modifying or inspecting existing installations.

Required Noise Level

Once the ambient or background noise and frequency level have been established, the sound pressure level needed for the sound to be heard over the desired distance must be defined. Tests show that the ear can distinguish a warning signal that is ten decibels below the ambient noise level, provided there is an adequate frequency differential.

Noise Attenuation

It is important to consider noise attenuation, which refers to the reduction in sound as the distance from the signal doubles. As a rule of thumb, sound is absorbed and reduced at a rate of 6 decibels. In challenging operating conditions, such as high winds or solid objects in the noise path, an attenuation of 8 to 10 decibels should be allowed for to avoid blind spots or inadequate coverage. Additionally, it is crucial to ensure that the same or similar sound is not used in adjacent systems for other applications before finalising the choice of signal. For outdoor installations exposed to exterior elements, a weatherproof version must be selected. Similarly, indoor situations that require weatherproof enclosures should also be considered. Explosion or flameproof signal devices are essential when the sounder is located in an environment with explosive or fire-hazard conditions.

Sirens: Powerful Low-Frequency Warning Devices

Sirens are electric motor-driven devices that operate at low frequencies and are typically continuous rated. They work by pulling in air through a multi-bladed impeller and pushing it out through radial vents. The frequency of the siren is determined by the motor speed, the number of impeller blades, and the spacing of the radial outlets. Sirens are widely used for disaster warnings, but they also have many other applications such as fire alarms, anti-theft/security alarms, process control, time signalling, fault indication, and machinery stop-start alarms. Sirens are available in various power ratings, ranging from 100 W to 7.5 KW, with sound outputs from 95 dB to 145 dB at a distance of 1 meter, and can provide audible signals over a range of 100 to 15000 meters.

Buzzers and Hooters: Electro-Mechanical Alarms

Buzzers and hooters are electro-mechanical devices that use an electromagnet to deflect a diaphragm and produce sound. Hooters are generally low-cost and robust, and they find applications in fire and security alarms in industrial and marine settings, truck horns, process control, time signalling, telephone signalling, boat horns, and public vehicle attack alarms. Buzzers, on the other hand, can be used with projectors to give more directional sound, and they are commonly used as general industrial alarms, crane warning alarms, control panel warning alarms, industrial truck alarms, and boat alarms.

Electronic Sounders: Versatile and Efficient Alarms

Electronic sounders are highly versatile devices with many advantages for design engineers and contractors. They have low current consumption and relatively high sound output, making them ideal for use in battery-powered systems. As a result, electronic sounders are extensively used in fire and security alarm systems, as well as in industrial, mining, process control, marine, and hazardous area applications.

Beacons: Adding Visual Attraction to Alarms

Beacons are visual alarm devices that can be used in conjunction with sirens or sounders to provide an additional visual alert. They are available in various colors such as RED, AMBER, GREEN, and BLUE, with other colors available upon request. Beacons can be set to flash at up to 120 flashes per minute or remain static, and they are commonly used in combination with sirens or sounders to provide synchronized alerts. LED beacons are typically available in RED or AMBER, while Xenon flashers can be obtained in all colors.

Bells: Motor Driven or Coil Driven Alarms

Bells are alarms that are either motor-driven or coil driven, and they are commonly used for school alarms, fire and security alarms, and time signalling. They produce high frequencies and have low current consumption. Some bell models are designed for easy installation, which can be of particular interest to contractors.

Selecting the Right Siren: Factors to Consider

Choosing the right siren for your project requires careful consideration of various factors to ensure that it meets your specific needs. While Kama Industries is always ready to provide advice, it is important to take into account the following points:

1. Nature of Warning Signals: Consider the nature of the proposed warning signals, including sequences, duration of blasts, intervals, and length of the signal. Each type of hazard should have its own code to ensure the correct response. On-site warning signals should not be confused with off-site warning signals.

2. Area and Range of Audibility: Determine the area and range of audibility that needs to be covered by the siren system. The signal should be clearly audible to all persons, both inside and outside the plant, who may be affected.

3. Terrain and Construction: Consider the nature of the terrain and construction, as well as the heights of buildings and structures on the site. Uneven ground, enclosed or noisy areas, and other factors should be taken into account when determining the optimal placement of the siren.

4. Type of System: Consider the type of system to be installed. For plants with high levels of machine noise or covering large areas, a series of smaller sirens may be more effective than one large unit.

5. Local Meteorological Conditions: Take into account local meteorological conditions such as temperature, fog, mist, wind, snow, or rainfall, as these can affect the audibility and performance of the siren.

6. Other Signals in the Area: Ensure that the hazard signals from the siren do not conflict with emergency services or civil defense signals in the area.

7. Test Facilities: Regularly test the siren motors, shutter, and signal sequences to ensure that they are functioning properly.

8. Power Supply: Ensure that an adequate power supply or power backup system is available for the siren.

9. Siren Positioning: Consider the ideal height above ground level for the siren, which depends on the individual type and sound output of the instrument. Sirens should not be mounted too high above ground level, typically recommended at 4m to 6m. Avoid installing sirens on top of tall buildings, as it may deflect the sound wave upward due to negative temperature gradients. Provide adequate clearance around each siren to allow for proper sound distribution.


Coded Sirens

Coded sirens are similar to general-purpose sirens but incorporate sound-damping shutters that enable them to produce clearly defined coded signals, such as a succession of short or long blasts, or a mixture of short and long blasts. This allows one siren to be used for multiple different signals. Shutter mechanisms are operated by a solenoid and can be quoted as accessory items based on individual requirements.


Remote Triggering

In some situations, a signalling device may be installed on a site where a power source is available at or close to the mounting position of the siren. In such cases, a separate cable may be required for remote triggering or switching of the siren from a control room or a distant site on the plant. We offer a remote control switching system that includes a transmitter to be installed at the control point and a receiver at the siren, allowing for multiple sirens to be triggered by one central transmitter.

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