Spark Extinguishing System BS 7

Filters may burn or even explode because of sparks within exhaust ducts. GreCon Spark Extinguishing Systems are designed to prevent this. They detect small sparks within the ducts and extinguish them in a split second. Spark sensors detect the infrared radiation of glowing particles. Immediately, a dense water mist spray which extinguishes passing sparks is created in a specified distance downstream from the spark sensors. The production process can continue without interruption during the whole procedure.

Fire insurance companies have noticed the minimised risk when installing spark extinguishing systems and may grant discounts on insurance premium rates of up to 15 %. The regulations of the German Association of Property Insurers (Richtlinien der VdS Schadensverhütung), form 2106, specifically stipulate all requirements on spark extinguishing systems. Precondition for achieving discounts on premium rates is the use of an extinguishment system that is approved by this association.

Spark extinguishing systems are amongst the most efficient fire protection systems as a result of their highly-developed technique and their reliability. The use of these systems for various applications is even prescribed by the employer's liability insurance associations and by national factory inspectorates. The German Association of Property Insurers (Verband der Schadenversicherer e.V.), Cologne, have published recommendations on premium rate discounts. All these factors, i.e. discounts on premium rates and technical innovations, help to justify the investment required.

Where do Spark Streams appear?

Spark streams are a very common danger. They cannot be easily detected and this means they are existing but not known! Consequently attention is paid to a spark stream only when it is too late, namely when there has been an explosion or a fire. When working combustible materials sparks are created very quickly. A dull tool, a damaged bearing in the fan, an overheated motor or a foreign body within the material can be the cause. This is a constant danger for all those factories where combustible materials are being worked, exhausted, transported, filtered or dried. The damage statistics provided by the insurance companies point out that filters, dust collection bins, silos and even complete production lines are the areas of plant at greatest risk. Foreign bodies in the conveyed material, defective parts of the production machinery, friction processes as well as electric sparks and self-ignition are all identified as fire-generating. Here are the main danger areas known:

Fibre and Particle Board Industry: The fibre and particle board processing
as well as the further processing of the panels by means of sawing and
sanding

Wood Working Factories: Working of materials by means of saws, planes,
mortisers, hoggers, sanders and other wood working machines

Chemical Industry: Pneumatic conveyors of dusts and powders

Foodstuff Industry: E.g. coffee roasting, tobacco drying and pneumatic conveying of powders

Why is it so Dangerous?

The spark itself is not dangerous because for the creation of fires or explosions there have to be simultaneously a combustible material, air and an ignition source. When at least one of these preconditions is eliminated, fire and explosion have been prevented.
In today's production plants we very often have to cope with all components that can lead to fire damage or cause an explosion. Extraction systems and pneumatic conveyors increase the danger of fire. Once sparks and glowing embers are created, the pneumatic extraction system conveys this danger very quickly to other, subsequent areas at risk.
The concrete danger is now that two of the three preconditions for the creation of fires and explosions are transported, namely:
air and ignition sources (sparks).
Wherever this conveyed danger meets combustible materials (filtre cloth, deposited and combustible dust in a separator or silo) it becomes more and more likely that the feared reaction will happen.
Environmental protection measures regarding dust emissions and tightened regulations for air pollution at work led to an increased use of filter systems but the danger of dust explosions has not been reduced. Besides, in the field of drying, the dryer capacities have been steadily increased so that protection for prevention from fires in these systems has become more important than before.
The risks of fire can be efficiently combatted by means of modern spark extinguishing systems.

As, for environmental reasons, the owners of production plants are not allowed to go on with the production without having an operative filter system they have not only to cover the real damage to property but also the extremely high losses due to long production interruptions.
According to individual reports, these losses exceed the damages many times over.

Returned air also requires spark extinguishing systems.
Due to the high amount of material now collected in the dust filter systems, in certain circumstances, it is allowed that the clean air be returned to the production halls. In this way enormous savings of heating energy are achieved. A filter fire, however, could be quickly transferred to the production area with devastating consequences.
To protect such an extraction system all extraction ducts as well as the conveying duct to the silo have to be equiped with spark extinguishing systems.

How can You take Preventive Measures

By installing modern spark extinguishing systems. They detect sparks and glowing embers immediately after their creation. Upon the detection and evaluation, countermeasures are induced at once in order to eradicate the causes of a fire or an explosion. Here's the difference to other fire extinguishment systems: spark extinguishing systems combat the beginning causes and not the beginning fire.

Spark extinguishing systems are in a position to detect even the smallest of sparks or hot particles in extraction ducts, drop chutes or mechanical conveyors, like for example screws or elevators, and to start countermeasures instantaneously. These can either be: activation of an exinguishing system, shutting off the way of transport or interrupting the production. All these measures are taken within a split second.
Detection of the ignition sources is made by means of spark sensors recognizing the infrared radiation of sparks and glowing particles. These sensitive spark sensors are even capable of detecting sparks through layers of dust or through the conveyed, dense material flow. They give alarm signals to the control console which processes the signals and releases automatically well-aimed countermeasures. Mostly an extinguishing device is triggered which is installed downstream from the spark detectors.

This device releases a water mist spray in the duct section into which the sparks are transported. Once no spark stream is detected, the extinguishment spray is automatically stopped. While the extinguishment takes place, the production process can be continued unless otherwise desired. Due to this special operation principle, spark extinguishing systems have to be classified differently than for example sprinkler systems, deluge systems, or even explosion suppression systems.
These fire protection measures are required for the protection of buildings and facilities which cannot be dropped even when a spark extinguishing system is installed.

The Control Console

The centrepiece of a spark extinguishing system is the control console. All signals given by the spark sensors installed in different plant areas are being accumulated and processed by a micro-processor. The extinguishing devices of the affected areas are released without any delay.
A pratical fire protection conception also considers the demand for an almost uninterrupted production. The use of microprocessor technique including the corresponding software results in new possibilites to react on sparks. Integrated counters and time recording systems allow an exact assessment of the spark stream. A graded use of the existing countermeasures is possible.
Single sparks, for example, are only extinguished; but for a heavy flow of sparks or when single ignition sources are detected over a longer period, further measures, like machine and fan shut-downs of the affected plant sections, have to be taken. Deviation or shut-off of the material transport is possible, too.

The microelectronics has got many other advantages:

Operator's Ease

Where once little lamps indicated a flow of sparks, the trouble message is nowadays displayed in clear text. Important functions and all alarms are of course displayed clearly.
The buttons on the key pad light up and provide visual information when relevant. A misoperation is almost impossible - and operating instructions unnecessary.

Integrated Data Memory

Up to 2.500 events are stored, so no important information is lost. This enables analysis of alarms at any time:

When exactly did the spark stream happen?
How heavy was the spark stream?
How long did the extinguishment action last?
Where exactly did the spark stream appear?
When was the system out of action?
When and where did troubles appear?

The replies to these questions can be found in the data memory of the control console. The danger spots can be recognized very quickly.

The display field does not only show the alarm itself, but also informs about the measures that have been taken.
The memory content can also be printed out at any time (external or internal printer).

Safe Function

To ensure correct functioning all signal cables are checked as to wire rupture and short circuit.
In addition, the automatic testing equipment enables regular function tests of all connected spark sensors from the control console.
By means of a manual activation it is also possible to check each extinguishing valve from the control console.

The Spark Detector

The most important component of a spark extinguishing system is the spark detector.
To suit to the different and often very severe operating places, three different types of sensors are used:

Spark Detector FM 1/8

All three sensor types have high-sensitive electronics which detect even the smallest of glowing particles. The detector FM 1/8 features reliable function even in very dense material flow or when the optical element is covered by a dust layer. It can be used at material temperatures up to 60 °C which corresponds to a temperature range of extraction systems for woodworking machines, like for example saws, planes, sanding machines etc.

Spark Detector FM 3/8

The detector FM 3/8 is used for operating temperatures up to 360 °C as they can appear for drying processes for example. Spark radiation is led through fibre optic cables to the detctor itself.

Daylight Spark Detector DLD 1/8

For a reliable detection of glowing or hot particles it has to be assured that no ambient light is present at the inspection place. Where an absolute dark surrounding cannot be guaranteed sensors which aren't sensitive to daylight or other ambient light are used. These sensors only operate in the spectrum of infrared light so they can be installed even at open transfer points or on conveyor belts.

Thermo Detector TM 1/8

The thermo sensor TM 1/8 is used for the additional inspection of large rooms, like filter and silo systems. Its task is to monitor these areas as to self-ignition of the material conveyed or in stock.

The Extinguishing Device

Water is the best extinguishing agent. Its excellent extinguishing efficiency mainly results from the high ability of heat absorption. For this reason it has a strong cooling effect.
At the same time a new flaring up of the combustible materials is prevented.
To obtain an optimal extinguishing efficiency the surface covered by the water has to be kept as big as possible which is gained by a fine atomization of the water.
This is achieved through a special nozzle and sufficient operating water pressure. Due to the high atomization the amount of extinguishing water can be minimized whereas the filter elements are not endangered by too much water. In this way production can go on while extinguishing takes place.

The operating pressure of the extinguishing device should be at least at 7 bar. If this pressure is not available a pressure increasing unit will be connected. The extinguishing nozzles are contamination-free because they are flush-mounted and spring-loaded.
Not all extraction ducts of the plant are located inside the production halls. For this reason it may be necessary to install the extinguishing devices outside. To protect the devices from frost they are equiped with standardized insulating bags.

Alternatives to Extinguishing Means

For some branches of industry water is not suitable as extinguishing agent but there are alternatives: Diversion gates, shut-off gates, fire traps and even the actuation of a CO2 system.

Diversion Gates, Shut-off Gates, Fire Traps

In some production and processing systems water cannot be used as extinguishing mean because it would have too much influence on the subsequent process. This is particularly true for the foodstuff industry for which extremely high accuracy in respect of the material's moisture has to be observed. There are also other plants where water is not allowed as an extinguishing agent.
In these plants, diversion gates to deviate the material flow or shut-off gates and fire traps to stop the material flow are used.

When the spark sensor detects a spark, or when the preset sparks threshold is exceeded the above-mentioned devices are activated from the control console.

CO2 Extinguishment

If parts of the plant, complete machines or sensitive filter systems are to be extinguished a CO2 system can be activated by a spark detection system.
For this application the ducts leading to these areas are monitored by spark sensors. Upon detection of sparks an alarm message is transferred to the CO2 system through voltage-free outputs of the control console. The corresponding parts of the system are simultaneously shut-off by activating shut-off gates so that the incoming CO2 can now react.

GreCon Safety Information System

In big industrial plants, such as wood based panel productions, there are often more than 100 spark detection and extinguishment zones. If an alarm is triggered, it is usually of short duration. The operation staff register this short incident and acknowledge it. Production usually continues uninterrupted. Even if the incidents become more frequent within one shift, they are often neither allocated nor checked for plausibility. Only if severe incident occurs and a production standstill or even a fire or an explosion are the result, it will be investigated, and the reason is often found afterwards. It would be nice if there was a permanent overview, showing the numerous incidents at a glance. In many cases, the signs could have been recognised in time and countermeasures have been taken before a damage occurred.

With the GreCon Safety Information System SIS the operator will receive comprehensive information about the distribution of alarms and alarm frequency in its production. It clearly represents all incidents of the individual zones for every control console on one screen page. One can see at a glance where danger zones are concentrated, whether there are deviations from standards and whether interventions are necessary. The GreCon SIS visually depicts the trend of alarm frequencies and graphically indicates an increase in spark generation. Thus, management and system operators are always up to date.