News Column

Patent Issued for Method and Device for Fire Detection in Enclosed Environments

August 13, 2014

By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Russwurm, Manfred (Bad Schwartau, DE); Westphal, Torsten (Lubeck, DE); Mendle, Thomas (Timmendorferstrand, DE); Klischat, Olaf (Elmenhorst, DE); Ziems, Bernd (Zarpen, DE); Dittmer, Hauke (Fehmarn, DE); Lenkeit, Kurt (Sulfeld, DE), filed on November 28, 2011, was published online on July 29, 2014.

The assignee for this patent, patent number 8791826, is Minimax GmbH & Co. KG (Bad Oldesloe, DE).

Reporters obtained the following quote from the background information supplied by the inventors: "Device and method for fire detection in enclosed environments are suitable for storage rooms, silos, bunkers, and other enclosures, which are, among other things, subject to regulations on explosion protection and from which air is aspirated, checked for typical fire criteria and, if necessary, a fire alarm is triggered.

"The present disclosure is especially suitable for enclosed environments such as silos or bunkers for combustible and/or dust forming bulk goods or storage areas for combustible materials from which air samples have to be taken for the purpose of using fire parameters to generate a fire alarm.

"Enclosed environments in the sense of the present disclosure can be silos or bunkers as well as other storage areas and transport areas which are subject to explosion protection requirements and in which easily combustible material and dust forming bulk goods such as wood shavings, wood chips, wood pellets, grain, powdered fodder, fertilizer, or other such goods are stored or transported. An explosive air-dust mixture can form due to an appropriately high concentration of dust from these materials. Sources of ignition can then be, for instance, warm or hot parts or surfaces. In the following sections these enclosed environments are also referred to as storage areas. These storage areas/enclosed environments, which are subject to regulations for protection against explosion, are also referred to in the following sections as 'ex-zones'. In the following sections, 'dust' is understood to denote small particles of the materials which are being stored or transported/poured.

"Discharge systems, conveyor belts, or processing devices are the primary potential sources of ignition in this context. Through friction or overheating of material being conveyed in the region of the discharge worm drive a deep lying fire can start in a silo or a storage area without being noticed. Ignition sources introduced from outside through the entry opening also constitute a fire hazard. In addition, spontaneous combustion can occur through biological decay processes in piled up materials. A smoldering fire that starts in this way can spread to the surface of the piled up material and, as a result of the access to oxygen, quickly develop into an open fire which destroys the entire storage area or machinery. The difficulty of detecting incipient fires in storage areas, bunkers, or silos is due to the fact that there is often a high proportion of fine dust and carbon monoxide or high relative humidity. Serious problems exist in such ex-zones regarding early detection of fires. Conventional fire detection systems without any technical modifications and without approval for use in ex-zones are not appropriate for use here.

"Fire detection systems such as aspirating smoke detector systems with sensors/detectors for detecting fires which are installed to detect fires in ex-zones are required to satisfy the requirements for protection against explosions such as the set of standards EN 60079 or IEC 60079 or the appropriate national requirements such as NEC 500 to NEC 516. Such systems are not permitted to contain any parts which could become so hot that they constitute ignition sources.

"Devices which meet these requirements are tested and approved by appropriate national certifying agencies. They are then recognized as devices or machines with ex-approval for specific classified ex-zones such as zones 20, 21 or 22. Devices with ex-approval are technically more complicated and are more costly in comparison with standard machines.

"In EP 1 542 188 B1 a device and a method for detecting incipient fires is described according to which samples of air are continuously extracted from spaces or from electrical devices and tested for fire detection characteristics. In order to direct the air flow to be extracted, the aspirator opening must have a specified size and shape.

"The filter is for keeping dust concentrations low. No provision is made for monitoring the filter for defects or the air flow for exceeding the explosion limit.

"DE 197 81 749 T5 describes a system for monitoring the functioning of the dust filter of a fire detection system in areas which are not potentially explosive for blockage of the filter where, if a specified threshold value is exceeded, a warning signal is generated after which the filter is replaced.

"DE 101 25 687 B1 describes a device for detecting fire sources or gas contamination in one or more monitored spaces which has a main detector for detecting a fire parameter value or a gas contamination level which is connected by means of an aspirating unit with a pipe fitted with an intake opening which is required in every space being monitored.

"The devices described above are not suitable, nor are they permitted, in particular for cost-effective fire detection in enclosed environments which are subject to explosion protection regulations.

"For fire detection equipment such as aspirating smoke detector systems without ex-approval, which extract and analyze air from such enclosed environments, it must be ensured that dust concentrations of the aspirated air-dust mixture sucked in the aspirating smoke detector system are below the limits of the maximum allowable concentration for a potentially explosive atmosphere."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Consequently, the purpose of the present disclosure is to develop a method and a device for detecting fires in enclosed environments which satisfies the explosion protection regulations without an explosive air-dust mixture entering the fire detection system while also preventing transfer of the explosive atmosphere from the ex-zone into the fire detection system and enabling the use of cost-effective fire detection systems which do not satisfy the requirements for potentially explosive areas.

"The solution in this disclosure proposes a method and a device for detecting fires in enclosed environments such as material warehouses, silos, bunkers, or similar structures which are subject to the requirements for prevention of explosions and from which an air-dust mixture is extracted which can contain burning characteristics in the air flow.

"'Burning characteristics' are understood to be all indicators such as smoke, heat and flame radiation as well as combustion gases which indicate an incipient or actually burning fire. They are derived from the measurement of physical variables such as temperature, electromagnetic radiation, light scattering in smoke aerosols, or evidence of combustion gases such as CO, NOx or long chain carbohydrates or other substances indicating a smoldering fire.

"Aspiration of the air-dust mixture is carried out by a smoke aspiration system which is not approved for use in ex-zones.

"An aspirating smoke detector system is a fire detection system which extracts air from an area that is to be monitored. It contains at least one, as a rule several sensors for fire detection. It may also contain combustion gas sensors. In addition, among other things, components for monitoring the air flow and for generating an alarm signal, as well as a signal processing unit and an aspirator are elements of the aspirating smoke detector system. Instead of an aspirator a pump can also be used in the system.

"Aspirators or pumps can also be operated outside the aspirating smoke detector system.

"An air-gas mixture is extracted from the monitored enclosed environments which constitute an ex-zone by means of a suction pipe into an aspirating smoke detector system and passed through a filter. The purpose of the filter is to reduce the dust concentration in the dust-air mixture sucked into the aspirating smoke detector system below the explosive level.

"Decisive for this disclosure is that a filter monitoring unit with a malfunction monitoring sensor is located between the storage area for combustible materials (ex-zone) and the aspirating smoke detector system, which is not approved for use in explosion risk areas and is positioned in the non-ex-zone where there is no danger of an explosion. Preferably, the malfunction monitoring sensor should be positioned at the filter or in its immediate vicinity.

"The malfunction monitoring sensor continuously monitors the operability of the filter. A malfunction exists in the filter/filters if, for example, the concentration of dust in the airstream beyond the filter is inadmissibly high. This can occur because of leaks in the filter or because the filter is destroyed. In the following sections this will be referred to as destruction of the filter.

"The filter monitoring unit measures and records increases in dust concentration in the aspirated air stream behind the filter and generates a malfunction signal if the measured dust concentration values exceed specified threshold concentration values or threshold slope (gradient) values.

"The malfunction monitoring sensor is connected to a signal processing unit which contains stored threshold values for ignitable dust concentrations and/or advance warning threshold values and/or slope (gradient) values.

"The term 'signal processing unit' denotes a signal-processing and control unit with a memory. Preferably, this is the signal processing unit of the aspirating smoke detector system. It can also be integrated into the filter monitoring unit separate from the aspirating smoke detector system.

"The threshold value for an explosive wood dust concentration for instance is more than 30 g of dust per cubic meter of air with the corresponding range of particle sizes. It can, however, be advantageous to specify values below the explosive concentration, for example, early warning thresholds of 90%, or 80% or 70% of the explosive dust concentration.

"In addition, it is advantageous to specify maximum levels for changes in the increase of dust concentration (threshold slope (gradient) values), especially in the case of sudden sharp increases. A sudden sharp increase in dust concentration is measurable when a sudden leak or an isolated or complete rupture of the filter occurs. This is regarded as a malfunction and the filter is no longer capable of functioning.

"It can be advantageous to use a combination of threshold concentration values and threshold values of the slope change to generate a malfunction signal.

"A malfunction signal is generated whenever the exceeding of specified threshold value is measured and determined by the malfunction monitor sensor and the signal processing unit. This malfunction signal indicates that the filter is not functioning correctly. For the sake of simplicity, in the following sections the concepts malfunction signal from the malfunction monitoring sensor or filter monitoring unit are used to refer to analysis of signals and measurements from the malfunction sensor by a signal processing unit, in comparison with stored threshold values carried out by the signal processing unit, and generation of a malfunction signal by this unit.

"If the filter is destroyed, a signal (malfunction signal) is generated by the malfunction monitoring sensor which initiates subsequent actions to prevent ingress of an aspirated air-dust mixture with elevated ignitable dust concentrations into the aspirating smoke detector system.

"Under these conditions it is advantageous for the malfunction signal of the filter monitoring unit to switch off the aspirator in the aspirating smoke detector system or switch off the entire aspirating smoke detector system so that no more air is extracted from the enclosed environments being monitored. This shutdown prevents carry-over of a potentially explosive mixture into areas in which it could become an incalculable risk. In particular, the ingress of a combustible air-dust mixture into the aspirating smoke detector system is prevented. Electrical equipment such as aspirating smoke detector systems, which are not approved for use in ex-zones, could contain ignition sources such as ignition causing hot surfaces.

"It is also advantageous for the length of the suction pipe between the filter and the entry into the aspirating smoke detector system to be calculated and measured in such a way that after the aspirator or the entire aspirating smoke detector system is switched off the transport velocity of the aspirated air-dust mixture in the suction pipe is reduced to 0 m/s prior to entry into the aspirating smoke detector system. This prevents ingress of an explosive atmosphere into the aspirating smoke detector system.

"It is also advantageous for the malfunction signal of the signal processing unit to control one or several flaps and/or one or several valves which prevent the aspirated air-dust mixture from entering the aspirating smoke detector system. A convenient structural measure in this regard is to install a valve or flap which isolates the aspirating smoke detector system from the suction pipe in terms of air flow and/or diverts the aspirated air-dust mixture from the suction pipe into the surroundings or a container. A 3/2-way valve can be installed.

"In an additional design variant of the method the signal from the malfunction monitoring sensor controls a flap or valve through which the aspirated air-dust mixture is diluted by adding uncontaminated air, or the explosive threshold in the enclosed environment of the aspirating smoke detector is reduced by mixing in an inerting gas, allowing ongoing detection of burning characteristics.

"It can be advantageous to combine diversion of the aspirated air-gas mixture and/or the closing off of the entry to the suction pipe into the aspirating smoke detector system with the unit shutdown.

"It can also be advantageous to integrate the flap or valve into the filter monitoring unit, which can be exchangeable.

"A person skilled in the art can conceive of various reasons for detecting instances where a dangerous concentration level has been exceeded. Only a few instances are specified here. The process mostly involves measurement methods whose values are compared with each other over time and where deviations are the primary signal for the malfunction monitoring sensor. The malfunction monitoring sensor is the device that turns a deviation of a measured value into a response.

"It is advantageous to monitor the dust concentration in the gas stream by means of a light transmission or scattered light system. The light transmission or light dispersion system can be carried out using UV light, visible light, or IR beams. To maintain functioning of the scattered light or light transmission system the devices can be automatically reset in the event of visible soiling.

"It is also advantageous to clean the lens of the light transmission or scattered light system automatically. This can be done using, for example, an air flushing device.

"It is also advantageous to monitor the dust concentration in the gas stream by means of a microwave system.

"It is advantageous to fit the filter with a separator.

"Another possible solution is to monitor the dust concentration in the gas stream by means of a separator which traps the dust which is present so that the amount of dust per unit of time can be monitored. If this is too high, a signal is generated, i.e., the malfunction monitoring sensor switches off the aspirator in the aspirating smoke detector system and/or the entire detection system. The amount of dust behind the filter can be determined by weighing it or optically by means of a liquid level indicator or laser measurement of the level.

"Another possibility for measuring the dust concentration in the gas stream involves installing an electrostatic monitoring unit.

"It is also advantageous to separate out liquid from the air-dust mixture using a filtering procedure or by means of a separator.

"It is also advantageous to return the filtered air-dust mixture to the closed environments for combustible materials.

"In addition, it is advantageous if the sensor for detecting burning characteristics is connected to an alarm and/or a fire extinguishing system so that the fire can be extinguished immediately.

"The solution proposed in the present disclosure has the advantage that enclosed environments such as material warehouses, silos, or bunkers for combustible materials which are subject to explosion prevention regulations can be monitored for typical fire criteria without the maximum possible concentration for an explosive atmosphere being exceeded, because in this case the equipment is automatically shut down or alternative subsequent actions are implemented, so that no explosive air-gas mixture can enter the aspirating smoke detector system. As a result, fire detection is possible in enclosed environments which are subject to explosion prevention regulations using low-cost standard components which are not approved for use in potentially explosive areas.

"In the following sections, the present disclosure will be presented in greater detail by means of an implementation example."

For more information, see this patent: Russwurm, Manfred; Westphal, Torsten; Mendle, Thomas; Klischat, Olaf; Ziems, Bernd; Dittmer, Hauke; Lenkeit, Kurt. Method and Device for Fire Detection in Enclosed Environments. U.S. Patent Number 8791826, filed November 28, 2011, and published online on July 29, 2014. Patent URL:

Keywords for this news article include: Electronics, Signal Processing, Minimax GmbH & Co. KG.

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Source: Electronics Newsweekly

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