In any type of production facility, fire control encompasses a wide range of equipment or systems from building sprinklers to plant site fire departments. A spark detection/extinguishing system must be thought of as part of a plant’s overall security and safety network. Just as a residential alarm system provides protection to a homeowner, a spark detection system provides preventive protection against potential loss of human life, production facilities, equipment and costly downtime.
Where do Spark Streams appear?
Spark streams in dust collection systems are a very common danger. They are not easily detected and this means that they may exist but are 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 with industrial machinery, sparks are created very quickly. A blunt tool, a damaged bearing in the fan, an overheated motor or foreign body within the material can be the cause.
Sparks are a constant danger in 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 a plant at greatest risk. Foreign bodies in the conveyed material, defective parts of the production machinery, friction processes as well as electrical sparks are all identified as fire generating. Here are the main danger areas known:
- Fiber and Particle Board Industry: The fiber and particle board processing as well as the further processing of the panels by sawing and sanding
- Wood-Working Factories: Working of materials by means of saws, planers, mortisers, hoggers, sanders and other wood working machines
- Chemical Industry: Pneumatic conveyors of dusts and powders
- Foodstuff Industry: e.g. Coffee roasting, tobacco processing and pneumatic conveying of powders
Why is it so Dangerous?
The spark itself is not dangerous. Here’s why: For the creation of fires or explosions there must be three elements that are combined simultaneously: a combustible material, oxygen and an ignition source. Removal of one of the elements will prevent a fire or explosion.
In today’s production plants, we have to cope with all elements 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 of the plant. The danger is when two of the three elements necessary for the creation of fires and explosions are transported, namely: air and ignition sources (sparks).
When this conveyed danger meets combustible materials (filter cloth, deposited and combustible dust in a separator or silo) it becomes more and more likely that a reaction will happen.
Environmental protection measures regarding dust emissions and tightened regulations for air pollution led to an increased use of filter systems, but the danger of dust explosions has not been reduced. In the process of drying, the dryer capacities have been steadily increased so that prevention of fires in these systems has become more important than ever.
What happens after a filter fire? Environmental regulations prohibit plant operation without the filter system. The plant will not only have the cost of repairing the damaged filter system caused by fire but also absorb the extremely high loss of a production shutdown.
According to individual reports, these production losses can exceed the damage costs many times over.
The risk of fire can be efficiently reduced or eliminated by means of modern spark detection and extinguishment systems.
Returned air to the plant also requires spark detection and extinguishment systems. Due to the high amount of material now collected in the dust filter systems, in certain circumstances clean air is allowed to be returned to the production buildings. Enormous savings in heating energy are achieved in this way. A filter fire, however, could quickly be transferred to the production area with devastating consequences.
To protect such a system, all extraction ducts as well as the conveying duct to the material storage should be equipped with spark detection and extinguishment systems.
How can you take Preventive Measures?
Protection can be achieved by installing a modern spark detection and extinguishment system. The sensors detect sparks and glowing embers immediately after their creation. Upon detection and evaluation, countermeasures are induced immediately in order to eliminate the causes of a fire or an explosion.
Let’s compare fire extinguishment systems with spark detection and extinguishment systems. Fire extinguishing systems combat fire after it has come to life, consuming material and air thus producing smoke and damage. A spark detection and extinguishment system eliminates one of the three elements (the ignition source) before it becomes a fire. In this way there is no fire, no smoke, and no damage.
Spark detection and extinguishment systems are able to detect even the smallest of sparks or hot particles in extraction ducts, drop chutes or mechanical conveyors, and to instantly trigger countermeasures. Countermeasures can be: activation of an extinguishing system, diverting the transport path or interrupting the production. All these measures are taken within a split second.
Detection of the ignition source 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. The sensors give alarm signals to the control console, which processes the signals and activates the appropriate countermeasures automatically. Normally an extinguishing device is triggered, which is installed downstream from the spark detectors. This device releases a mist of water in the duct section where the sparks are transported. When no additional sparks are detected, the extinguishment spray is automatically stopped. While the extinguishment takes place, the production process can continue unless otherwise desired. Due to this special operation principle, spark detection and extinguishment systems are classified differently than sprinkler systems, deluge systems, or even explosion suppression systems.
The Control Console
The centerpiece 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 microprocessor. The extinguishing devices of the affected areas are activated without any delay.
A practical fire protection concept also considers the demand for an almost uninterrupted production. The use of microprocessor technique including the corresponding software results in new possibilities 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 then possible.
For example, single sparks are only extinguished, but for heavy flow of sparks or when single ignition sources are detected over a longer period, further measures like machine shut down of the affected plant sections have to be taken. Diversion of the material transport is also possible using fast-acting abort gates.
The microelectronics has many other advantages.
Ease of Operation
Where once little lamps indicated a flow of sparks, the trouble message is now displayed in clear text. Important functions and all alarms are displayed clearly. The buttons on the keypad light up and provide visual information.
Integrated Memory
Thousands of events are stored so that important information is not 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 answers to these questions can be found in the memory of the control console and the danger spots can be identified very quickly. The display field not only shows the alarm itself, but also informs about the measures that have been taken. The memory content can be printed out at any time to an external or internal printer.
Automatic Function Checks
To ensure cables are functioning correctly, they are constantly checked for open and short circuit conditions. In addition, spark sensor function tests are performed regularly and automatically. Extinguishing device function tests can be performed manually from the control console.
The Spark Detector
The most important component of a spark detection and extinguishment system is the spark detector. To suit the different and often very severe applications, three different types of sensors are used. All three sensor types have highly sensitive electronics which detect even the smallest of glowing particles.
Spark Detector FM 1/8
The FM 1/8 detector features reliable function even in very dense material flow or when a dust layer covers the optical element. It can be used at material temperatures up to 149°F (65°C), which corresponds to a temperature range of extraction systems for woodworking machines like saws, planers, sanding machines, etc.
Spark Detector FM 3/8
The FM 3/8 detector is used in applications with operating temperatures above 149°F (65°C) as can appear in drying processes, for example. Spark radiation is carried through fiber optic cables to the detector.
Daylight Spark Detector DLD 1/8
For the most reliable detection of glowing or hot particles, no ambient light can be present at the sensor location. However, where an absolute dark surrounding cannot be guaranteed, sensors that aren’t sensitive to daylight or ambient light are used. These sensors operate only in the infrared spectrum of light so they can be installed 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 areas, like filter and silo systems. Its task is to monitor these areas for self-ignition of the material being conveyed or stored.
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 that prevents re-ignition of the combustible materials.
To obtain an optimal extinguishing efficiency, the area covered by the water must be kept as big as possible. This is accomplished by a fine atomization of the water. Atomization is achieved through a special nozzle and sufficient operating water pressure. With high atomization, the amount of extinguishing water can be minimized so that filter elements are not damaged by an excessive amount of water. This allows production to continue while extinguishing takes place.
The operating pressure of the extinguishing device should be at least 60 PSI at a flow rate of 24 GPM per nozzle. If this pressure is not available, a pressure-increasing unit must be used. Because extinguishing nozzles are spring loaded and flush-mounted, they are contamination-free and do not obstruct the material flow.
Not all extraction ducts of the plant are located inside the production building. Sometimes the extinguishing devices are required to be installed outside. Heat tape and insulating material is used to protect water pipes and extinguishing devices from freezing in areas exposed to frost. Special insulating bags are available for the extinguishing devices.
Alternatives to Extinguishing Means
In some production and processing systems, water cannot be used as an extinguishing means because it would have too much influence on the subsequent process. This is particularly true for the food industry where extremely high accuracy in respect to the material’s moisture must be observed. There are also other industries where water is not allowed as an extinguishing agent. There are alternatives: Diversion gates, shut-off gates, fire traps and even the actuation of a C02 or other inert gas system.
Diversion Gates, Shut-off Gates, Fire Traps.
In these industries, diversion gates to abort 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 spark threshold is exceeded, the installed device is activated from the control console.
CO2 Extinguishment
If parts of the plant, complete machines or sensitive filter systems are to be extinguished, a C02 system can be activated by a spark detection system. For this application, spark sensors monitor the ducts leading to these areas. Upon detection of sparks, an alarm message is transferred to the CO2 system through voltage-free relays 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 flood the contained area.
Central Visualization Software
Events recorded by several consoles that are installed in different areas of the plant are accessible through the visualization software. Such an application offers many advantages: Central actuation and processing of all spark alarms on one monitor is possible. The central acquisition of all events provides the operator with meaningful and comparable data. The remote control of the individual spark extinguishing systems make it possible to react rapidly on each alarm event and allows time and cost savings and shorter production interruptions.
Spark Detection and Extinguishing Systems Insurance Premium Rates
Fire insurance companies have acknowledged the minimized risk when automatic spark detection and extinguishment systems are installed, and may grant discounts on insurance premiums. Precondition for achieving discounts on premium rates is the use of an extinguishment system that is approved by a commercial and industrial property insurance and risk management organization. Factory Mutual is one such organization and the only North American organization to test spark detection and extinguishment systems. Factory Mutual requires stringent manufacturing standards and technical reliability that not only applies to the system, but also to the planning, installation and after-sales service.
Conclusion
Spark detection and extinguishing systems are among the most efficient fire prevention systems, which is a result of their highly developed technique and reliability. The use of these systems for various applications is even prescribed by Factory Mutual. All these factors lead to considerable investment reductions and improved safety for your plant, people and production.
