Technical Bulletins published by the FDIA
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The FDIA has had growing concerns of the different types of cables, at great variances in price, being sold into the industry.
Based on this concern, the FDIA made arrangements to conduct tests on the cables claiming compliance with EN 50200.
EN 50200 provides the test requirements to ensure PH 30 cables remain operational in fire conditions for 30 minutes or more.
International cable standards specify cable sheaths to be halogen free. The result of burning cables that are not halogen free is the production of noxious gases and fumes, which therefore becomes an important factor for fire alarm cables.
Cable core sizes and drain wires were inspected.
Cable samples were collected from contractor’s stock. FDIA committee members witnessed the two sets of tests conducted on a test rig in Johannesburg.
The competition for cable sales is fierce and by leaving certain elements out of the cable structure allows them to be price competitive, but we wish to remind everyone that these cables are for life safety systems. Should we be looking to cut corners with cable selection?
The FDIA is not promoting any one cable over the other, or making recommendations, but the tests were undertaken to provide information to the industry as to the performance of these cables.
The results reflected below are for information purposes only and do not form any sort of approval or disapproval by the FDIA.
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Various national standards are used in the gas suppression industry. Each standard has a section on the use of audible and visual alarms. However, there is no conclusive sequence of operation, they all request alarms to be audible and visual but are not clear as to which alarms should be installed where.
This has led to contractors adopting a variety of methods of operation.
Investigations by the FDIA revealed that many contractors differ in the operational methods of audible and visual alarms for gas systems.
Designers within the same consultancy practice specify different sequences of operation. Inspectors report that gas suppression systems on the same site differ in operation from one room to the next.
This leads to confusion for all concerned.
Internationally there is no published common method of operation in any country. The FDIA compared local and international standards to formulate uniformity of audible and visual warnings to be used throughout the country on all gas protected rooms.
The FDIA are urging all designers and installers to adopt the following philosophy to achieve uniformity of alarms throughout the country.
AUDIBLE AND VISUAL WARNINGS FOR GAS PROTECTED AREAS |
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Bell inside | Siren inside | Strobe inside | Siren outside | Strobe outside | |
| First detector activates | ON | ON | ON | ON | Standard/ house fire alarm | |
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Second detector activates & timer starts |
ON (intermittent) | ON | ON | ON | ON | Intermittent sound |
| Timer expires / Discharge | ON (solid) | ON | ON | ON | ON | Solid sound |
NOTES AUDIBLE AND VISUAL WARNINGS
The image below shows the implementation of 2 sounder-strobe devices each on a separate sounder circuit as the 1st stage alarms devices on a gas protected area.
A bell is shown inside of the room connected to the second stage alarm (End Of Line resistor must be connected at the last device to ensure active monitoring).
The bell will be pulsed pre-discharge and remain on upon discharge.
Operational Process
- 1st stage (both first stage outputs activate continuously)
- 2nd stage Pre discharge – 2nd stage output pulses (intermittent)
- 2nd stage Discharge – 2nd stage output is on solid
- 2 separately wired first stage alarms required (for compliance).
- There should be a clear distinguishing between 1st and second stage alarm sounds.
- The first stage alarm will be continuous and accompanied by a visual indicator.
- The second stage alarm should be pulsed in the pre discharge countdown mode and active (on) post discharge.
- Any relays or 3rd party timing devices should be avoided as these may not be certified, may affect monitoring circuits and introduce a difficulty in implementation, which may result in failure of the system upon discharge.
- A certified panel should be used which caters for this operation. Any modification to panel electronics must be avoided.
- EN12094-1 compliant panels cater for the pulsed second stage alarm pre discharge as standard.
- In areas where there are several sounder devices and status units are deployed, current consumption on the outputs must be taken into account and testing of the discharge signal must include firing of the actuation device (or equivalent load during testing).
Ensure that the power being supplied to the system is sufficient to support simultaneous discharge of all outputs associated with the control panel. Don’t just test to a discharge relay interface point, activate all outputs with equivalent discharge loads during testing to confirm the operation of the system.
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AUDIBLE AND VISUAL ALARMS FOR FIRE SYSTEMS
The selection and location of audible and visual alarms in an installation is a key factor in design as it ensures that the alarms will be heard or seen by all in the affected areas. SANS 10139 Part 8.9 to part 8.12 provides guidelines on the requirements to be met.
Audible Alarms
It is essential that alarm signals are sufficient in nature and extent to warn all persons for whom the alarm signals are intended. The alarm signal needs to be capable of alerting all occupants of the building regardless of their location.
The sound pressure level and frequency of alarm signals must be adequate to provide unambiguous warning of fire. Particular care needs to be taken to ensure adequate sound pressure levels in small cellular spaces, such as cellular offices, toilets and plant rooms.
If the alarm signal comprises of a speech message, it is also necessary to ensure that the message is intelligible.If people sleep in the building, the alarm signal needs to be sufficient to rouse them from sleep.
Traditionally, a sound pressure level of 65 dB(A) has been regarded as the minimum acceptable. The minimum sound level of a sounder device should be 65dB(A) or 5dB(A) above a background noise (if lasting more than 30 seconds) and at a frequency between 500Hz and 1000Hz.The maximum sound level should not exceed 120dB(A).
For areas where people are sleeping, sounder devices should produce a minimum 75dB(A) at the bed-head with all doors shut. In buildings likely to provide sleeping accommodation for the hearing impaired, consideration should be given to the incorporation of both audio and visual devices.
Decibel loss occurs through doors: Approximately -20dB(A) through a normal door, and approximately -30dB(A) through a fire door. Unless a sounder is installed in a bedroom, it is unlikely that 75dB(A) will be achieved.
Sounder device cabling should be arranged so that in the event of a fault at least one sounder located within the vicinity of the control and indicating panel will remain operational.
A mixture of bells and electronic sounders should not be used in the same building as fire alarm devices. The fire alarm sounders should be distinctive in sound. The system should incorporate at least two fire alarm sounders, even if the recommended sound pressure levels could be achieved with one sounder. At least one sounder should be provided in each fire compartment.
In order to prevent excessive sound pressure levels, which can cause disorientation or even damage to hearing, a larger number of quieter sounders is preferable to a few very loud sounders.
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There are various types of detectors available for fire detection system designers and each type is suitable for a particular use. The type of fire / smoke being detected will determine the choice of detector. Section 8.14 of SANS 10139 gives a guide on selection criteria and factors to consider when carrying out a design.
Below are the various types of detectors available.
1. Point Smoke Detectors. These detectors utilize one (or both) of two principles below;
a. Ionization Chamber Smoke Detectors. This type detects smoke by change in current flows between electrode when smoke enters the chamber of an ionization detector. This detector is particularly sensitive to smoke containing small particles, such as are produced in rapidly burning flaming fires, but may be less sensitive to the larger particles found in optically dense smoke of similar mass, such as can result from smouldering fires, including those involving polyurethane foam, or overheated PVC.
The ionisation detectors contain a small radioactive element that exists in the detection chamber. This has led to most manufacturers stopping the production of these devices. Stringent procedures need to be followed when disposing of this type of detector, which ends up being a costly process.
b. Optical smoke detectors. This type detects smoke by means of the light scatter principle. When smoke enters the chamber the small LED light source within the detector is deflected towards the receiver to trigger the detector. Optical smoke detectors are sensitive to optically dense smoke, but are less sensitive to the small particles found in clean-burning fires that produce little visible smoke.
2. Multisensor Fire Detectors. This type of detector contains more than one sensor, each of which responds to a different physical and/or chemical characteristic of fire. The purpose of combining sensors in this way is to enhance the performance of the system in detection of fire by means of smoke, heat or CO gasses. These detectors can reduce certain categories of false alarm.
3. Point Heat Detector. There are two types of point heat detectors.
a. The first type is the Rate of Rise heat detector which reacts to abnormally high rates of temperature change and provides the fastest response over a wide range of ambient temperatures. A fixed temperature limit is also incorporated in these detectors.
b. The second type is the Fixed Temperature which reacts to a pre-determined fixed temperature rather than a rate of rise temperature. The fixed type is suitable where sudden large change in temperature is considered normal for example in boiler rooms and kitchens.
4. Linear Heat Detector. This type comes in the form of length of wire or tube. Ideally suitable for cable tunnels, cable trays, transformer bays, etc. there are two types of linear heat detectors:
a. The Non – Integrating type consists of an electric cable with an insulation of fixed melting point which is suspended over the area to be protected. The melting of the insulation when there is a fire causes a short circuit which causes the system go into alarm mode.
b. The Integrating type is similar to the Non-integrating except in this type the insulation does not melt but electrical resistance is temperature dependent. The average temperature is taken over the whole length of wire rather than sections of it.
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SYSTEM TYPE AND ZONING
One of the key decision to make when installing a fire alarm system is whether to utilise an addressable or conventional system. The size / layout of the premises to be protected, user requirements, category of risk and budget will be the main factors that will drive the decision.
Conventional Systems
Conventional detection systems offer a good basic system, ideal for small applications, or projects that are tight on funds.
The detectors in a zone of the building are all connected to the same pair of wires. If any of the detectors report an alarm, only a zone indication is shown on the control panel, meaning that the exact location of the alarm is not shown. There could be say 10 detectors in that zone and one cannot tell from the control panel which detector has triggered. Only the zone will be shown.
The visual audio devices are wired on a separate circuit.
Advantages of a Conventional Fire Alarm System over an Addressable Fire Alarm System are:
- No sophisticated configuration is required and the setup is simple.
- Control panel and field devices are comparatively cheaper.
- There is compatibility of devices within a wide range of manufacturers.
Addressable Systems
Addressable fire alarm systems are usually for larger, more complicated applications and will be generally more expensive than conventional systems.
Detectors, sounders, Manual Call Points and interfaces are all connected to the same loop /cable.
Each device communicates directly with the control panel, therefore the control panel will be able to indicate the exact location of any alarm reported.
All the devices are individually addressed i.e. given a unique address and description of the area it is installed in to help identify the device. An example would be “device number 1021, Optical Smoke Detector, Finance manager’s office”. The customised message will be displayed on the control panel in a text format or in a graphical display alongside the visual detection zone indicators.
The detector continuously sends data to the control panel. The Control Panel then uses this data to decide the condition of the device, Fire, pre-alarm or fault. This feature allows some panels to increase or decrease the sensitivity of individual detectors.
Detectors are assigned to zones by software program, which allows for easier zone changes if the building layout is altered at a future date.
Addressable panels usually have an event log to recall past system events.
Addressable panels allow for Cause & Effect Programming, where outputs are only triggered by certain detectors / inputs.
Whether one opts for a conventional or addressable system there are some recommendations as stipulated in SANS 10139 that one needs to consider and one of these is zoning.
Read more: Conventional and Addressable Fire Detection Systems
