The intensity and type of sounder or beacon chosen for the area in which they will be used, will be dependant on the application i.e. sounders for certain applications in the Food Industry may not be suitable for similar applications in an industrial area. A sounder used in a Manufacturing Company (Heavy Industrial) may not be suitable for a similar application at a School.
Industrial, Mining and Manufacturing
Included in this category is not only factory premises but also equipment and facilities used in factories, such as cranes, mechanical handling vehicles, diesel generating sets and control panels. Also included in this category, are industrial hazardous locations such as coal mines and the petro chemical industry.
Building: Commercial and Public
Hospitals, Schools, Offices, Building sites, Houses, Military sites and Airports can be classified under this category. Due to continuous product research and developement some products may vary from the specifications in this catalogue.
Priority and Public Service Vehicles
Police vehicles, Fire departments and Ambulances
Dock and Ship installations, including any other hazardous sites (oil terminals etc.)
The frequency is the identication of note and is usually defined by the number of vibrations per second. To measure frequency one should use a frequency meter. In cases where the electrical contractor does not have such a meter, it is usually sufficient for the ambient noise frequency in an environment for our purposes to be identified. For example, the noise in a machine shop in which a grinder is being operated would be of a high frequency, while that of forge with a drop hammer would be of a low frequency.
Account must be taken of the time cycle over which the alarm is required to operate and a signal has to be selected which has an adequate time rate. It should be noted that sounders used as evacuation alarms are required to be continuously rated. Sirens for example, are products available on the market which have time ratings of either one minute or more,
but these products are not accepted by the Fire Authorities. The contractor should keep this in mind when modifying or inspecting existing installations.
Noise Level required
Having established the ambient or background noise and frequency level, the sound pressure level needs to be defined in order for the sound to be heard over the distance that the sound is required to travel. Tests show that the ear can distinguish a warning signal which is ten decibels below that of the ambient noise level, provided that there is an adequate frequency differential.
In selecting the correct sound pressure level required to cover an application, it is necessary to appreciate that as a “rule of thumb” sound is absorbed and reduces at the rate of 6 decibels as the distance from the signal is doubled. This factor is known as attenuation. Where the operating conditions are difficult, for example where there is a likelihood of high winds or where there are solid objects in the noise path, attenuation of 8 to 10 decibels should be allowed for to avoid “blind spots” or inadequate coverage. Before finally choosing the signal to be used, ensure that the same or similar sound is not used in an adjacent system for other applications. Should the sounder be installed outdoors and be subjected to exterior elements, then a weather proof version must be selected. It should be remembered that there are also in-door situations that require weatherproof enclosures. Explosion or flameproof signal devices are essential if the sounder is required to be sited in a location where there are explosive or fire hazard conditions.
Sirens are low frequency devices usually continuous rated and are electric motor driven. Air is pulled in through a multi bladed impeller and pushed out through radial vents. The combination of motor speed and the number of impeller blades, with the number and spacing of the radial outlets determine the frequency. The siren is used extensively for disaster warning but also has many other applications. These include, uses as fire alarms, anti-theft/security alarms, process control, time signalling, fault indication and machinery stop-start alarms. Most individual requirements are covered by sirens rated from 100 W to 7.5 KW, which have sound outputs from 95 dB to 145 dB at 1 metre distances and giving an audible signal over a range of 100 to 15000 metres.
Buzzers �and Hooters
These are electro-mechanical devices where the diaphragm is deflected by an electro magnet. In general, hooters are
low cost and robust. Their applications include fire and security alarms in Industrial and Marine applications, truck horns, process control, time signalling, telephone signalling, boat horns and public vehicle attack alarms. Buzzers can be used with projectors to give more directional sound and are used as general industrial alarms, crane warning alarms, control panel warning alarms, industrial truck alarms and boat alarms.
The electronic sounder is by far the most versatile device available and has many distinct advantages as far as the design engineer and contractor is concerned. Not least of these is the low current consumption and relatively high sound output, which make the electronic sounder ideal for use in conjunction with battery powered systems. Consequently, this type of sounder is also used extensively for fire and security alarm systems, as well as industrial mining, process control, marine and hazardous area applications.
The beacons can assist by adding additional visual attraction by means of a flashing, static or rotating format. These units are normally available in RED, AMBER, GREEN and BLUE, but other colours are available on request. The LED beacon can be set to flash at up to 120 flashes per minute or remain static.The Xenon flasher is avaliable in all the colours and the
LED flasher usually only in RED or AMBER, other colours available on request. When beacons are used in conjunction with sirens or sounders, the unit can be connected to set the siren and beacon off simultaneously or with the siren sounding for a short period and the beacon flashing until the condition for alert has been rectified.
These are motor driven or coil driven devices mainly used for School alarms, Fire and Security alarms and time signalling. These units have high frequencies and low current consumption. Of particular interest to the contractor is that models have been designed to make installation very simple.
When selecting a siren, a careful study of the specific project is required. Although Kama Industries will always be prepared to give advice, it is first of all necessary that each of the following points be considered:
1. The nature of the proposed warning signals, including sequences, duration of blasts, intervals and length of signal. Each type of hazard should be given its own code to ensure the correct response. On-site warning signals must not be confused with off-site warning signals.
2. Area and range of audibility to be covered by the system. The signal must be clearly audible to all persons, inside and outside the plant likely to be affected.
3. The nature of the terrain and construction and heights of the buildings and structures on the site. Uneven ground and enclosed or noisy areas must be taken into account.
4. The type of system to be installed. Plants with high levels of machine noise – or covering large areas – may be better covered by a series of smaller sirens than by one large unit.
5. Local meteorological conditions. For example, temperature, fog, mist, wind, snow or rainfall must also be taken into account.
6. The nature of other signals in the area. Hazard signals must not conflict with emergency services or civil defence signals.
7. Test facilities. Siren motors, shutter and signal sequences should be regularly tested to ensure that they are still functioning properly.
8. Availability of an adequate power supply, or a power back-up system.
9. The positioning of sirens. The ideal height above ground level for a siren depends on the individual type and sound output of the instrument. Sirens should not be mounted too high above ground level: 4 m to 6 m are usually recommended. Installing sirens on top of high buildings often has the effect of deflecting the sound wave upward because of negative temperature gradients. Sirens should not be located close to tall buildings. There should be adequate clearance around each instrument to allow sound distribution.
Similar to general-purpose sirens, but incorporating sound damping shutters that enable them to be used for making clearly defined coded signals i.e. succession of short or long blasts, a mixture of short or long blasts, etc. This enables one instrument to be used for a number of different signals. Shutter mechanisms are operated by a solenoid and are quoted as accessory items, according to individual requirements.
Situations may arise where a signalling device is installed on a site with a power source available at or close to the mounting position of the siren. To trigger or switch the siren from a control room or distant site on the plant, a separate cable may be required to be installed for this application. We offer a remote control switching system to accommodate this. A transmitter is supplied to be installed at the control point and a receiver at the siren. This will allow more than one siren to be triggered by one central transmitter.
Decibel vs Distance Chart
Sound attenuation at higher frequencies
- Determine the sound output of your device
- Determine the sound frequency of the unit and see the dB variance
- Subtract the dB variance of your device from the sound output at one meter.
- Now go down the column to determine the sound output at a given distance.
- The ideal sound level can be between 40-60 dB depending on the observer’s hearing.
Examples of industry noise levels in dB(A)