RU2022250C1 - Method of pre-fire situation diagnostics and device designed to realize it - Google Patents

Abstract

FIELD: prevention of fire. SUBSTANCE: pre-fire situation is determined by infra-red spectroscopy method by the effect of thermal destruction on products within three ranges of wavelengths characterized by the absorption of carbon-containing, chlorine-containing and oxygen-containing radicals and molecules. The device has an optical unit including a radiation source, multiway vessel, gas-and-air medium pumping facility, shadow and mirror modulators, slits, narrow-band filters, measurement result receivers, and single processing circuit with a source data unit. EFFECT: more reliable pre-fire diagnostics. 4 cl, 2 dwg

Description

 The invention relates to the prevention of fire in premises of various purposes and classes, including inhabited deep-sea vehicles, ship's premises, nuclear power plants, coal mines, space and aircraft compartments, in granaries and storages of biological masses, warehouses and chemical industries, hotels, museums, art galleries , banks, pawnshops, etc.

 A known method for the early detection of fire [1], based on fluorescence spectroscopy.

 The purpose of the invention is to increase the reliability of detection of pre-emergency - pre-fire situation by applying the method of infrared spectroscopy.

 The disadvantage of this prototype method is that the control of the presence of thermal degradation products is carried out in the wavelength range of 0.3-0.5 μm, in which a small group of organic materials (polymers) absorb radiation, which does not allow the detection of thermal degradation products of various organic materials .

 The second disadvantage of the prototype is that when the signal is formed during the early detection of a fire, it does not take into account the influence on it of the presence of the background level of thermal degradation products formed in the protected premises under normal operating conditions from hot technological equipment, sparking brushes of electric DC machines, etc., which significantly reduces the signal-to-noise ratio characterizing the reliability of the method.

 The third disadvantage is that the named method allows you to control the presence of decomposition products in the local area of the gas-air environment of the room, and not in its entire volume, which significantly increases the time of detection of a crisis situation (reduces efficiency).

Experimental studies have shown that the products of thermal decomposition of a variety of organic materials formed both under the influence of an abnormal heat source or overcurrent of cable routes, and an electric arc (sparking in cable routes) consist of a common radical like С-Н, which has a strong band X are absorbed in the mid-infrared range of the spectrum in the region of wave numbers 3000-2700 cm ^-1 An analysis of infrared absorption spectra showed that the common gas components released during thermal degradation of various organic materials (fuels, lubricants, paints, electrical insulation materials, etc.) also include molecular fragments of the CX type, which include the methyl group CH _3, having a pronounced double asymmetric oscillation of the CH bonds of wave number 2965 cm ^-1, a methylene group CH ₂ with an asymmetric oscillation of the CH bonds with wave number 2926 cm ^-1 (L. Swerdlow et al. Vibrational spectra of many languid molecules / M .: Nauka, 1970, pp. 155-175, 179), and a variety of other radicals of this type. Oscillations of the aforementioned group of radicals (С-Н bond) have a strong intense absorption band in the IR spectrum (J. Grassel. Application of Raman spectroscopy in chemistry. M: Mir, 1984, p. 52), which allows one of detect gas components by the absorption spectrum of a crisis.

 A common cause of a fire is a decrease in insulation resistance, which is accompanied by the occurrence of arcing with subsequent heating and the potential for the formation of an electric arc and ignition of electrical insulation materials.

 As a result of overheating associated with the action of an electric arc, the following thermal decomposition products are formed: hydrocarbon radicals of the form С-Н; chlorine radicals of the form C-Cl; also a large number of components that can be characterized as containing a peroxide group (or oxygen-containing radicals).

...

CH₂CH

CH₂CH

CH₂CH

...

и т.д.The first group of gas components includes hydrocarbon radicals discussed above. The second group includes chlorine-containing radicals (C-Cl bond), which have a very strong absorption intensity in the wave number range 720-760 s ^-1 and are formed as a result of thermal degradation of chlorine-containing organic materials:
polyvinyl chloride (...- CH ₂ CHClCH ₂ CHCl -...) _n ;
polyvinyl chloride (-C ₂ Cl ₄ -) _n ;
rubber products obtained by vulcanization of chloroprene rubber

...

CH ₂ CH

CH ₂ CH

CH ₂ CH

...

etc.

 (see P. Carrer. Course of Organic Chemistry, L .: 1960, p. 932-933).

Identification of gas components formed during thermal decomposition of chlorine-containing materials shows that these are:
methyl chloride (CH ₃ Cl), C-Cl bond, lane 720-740 cm ^-1 ;
tetrachlorethylene (C ₂ Cl ₄ H ₂ ), C-Cl bond, lane 750-760) cm ^-1 ;
ethylene chloride (C ₂ H ₄ Cl ₄ ), C-Cl bond, lane 725-740 cm ^-1 ;
vinyl chloride (C ₂ H ₃ Cl), C-Cl bond, band 720-740 cm ^-1 , etc.

 (see Gordon A., Fort R. Chemist Sputnik. M: Mir, 1976, pp. 191-192; Cases and vapors. HiGH Resolution infrared srectra. Sadtler Research Laboratories, In.C., Subsidiary of Block Engineering, Inc 1972 (GS77, 75, 69).

 Hydrocarbon and chlorine-containing radicals are formed as a result of thermal degradation of organic materials both under the influence of a heat source and the action of an electric arc.

C

, 2843, 1169 см^-1;
муравьиная кислота, НСООН, -О-О-, 1105, 1033 см^-1;
перекиси, R-O-O-R', 820-890 см^-1;
гидроперекиси, R-O-O-OH, 920-800 см^-1;
озониды,

_;

1064-1042 см^-1 и т.д. (см. Свердлов Л.М. и др. Колебательные спектры многоатомных молекул. М.: Наука, 1970, с. 429, 431, 432, 439); Беллами Л. Инфракрасные спектры сложных молекул. Каррер П. Курс органической химии. Государственное научно-техническое издательство химической литературы. Л., 1960, с. 65-66; Infrared Characteristic Group Freguencies, G.Sockates. JoHN WILEY, 80, p 52).The third group of gas components, which is characterized as oxygen-containing, includes oxygen-containing radicals formed as a result of sparking and the appearance of an electric arc. These radical compounds are formed as a result of ozone oxidation of thermal decomposition products to oxygen-containing compounds. This group includes gas components with the following absorption frequencies:
ozone, O ₃ , the bond-O-O-O-, 1103, 1042 cm ^-1 ;
formaldehyde,

C

, 2843, 1169 cm ^-1 ;
formic acid, HCOOH, -O-O-, 1105, 1033 cm ^-1 ;
peroxide, ROO-R ', 820-890 cm ^-1 ;
hydroperoxides, ROO-OH, 920-800 cm ^-1 ;
ozonides

_;

1064-1042 cm ^-1 , etc. (see Sverdlov L.M. et al. Vibrational spectra of polyatomic molecules. M: Nauka, 1970, p. 429, 431, 432, 439); Bellamy L. Infrared spectra of complex molecules. Carrer P. Course in Organic Chemistry. State scientific and technical publishing house of chemical literature. L., 1960, p. 65-66; Infrared Characteristic Group Freguencies, G. Socksates. JoHN WILEY, 80, p 52).

Thus, the ozone generated as a result of the electric arc intensively oxidizes the thermal decomposition products to peroxide radicals, which are found in the band of the average absorption intensity in the region of 800–900 cm ^–1 . An analysis of the results showed that a pre-fire situation can be detected at fixed frequencies in three absorption ranges.

I range - a fixed wave number ν _С-Н in the range of 3000-2700 cm ^-1 , in which all kinds of hydrocarbon radicals of the СН type are absorbed by infrared radiation, which are formed as a result of thermal decomposition of all existing organic compounds, including biomass, fuel and lubricant, electrical insulation, paint and varnish etc.;
II range - a fixed wave number ν _C-Cl in the range of 720-760 cm ^-1 , in which IR radiation is absorbed by all kinds of chlorine derivatives of the C-Cl type, resulting from the thermal degradation of chlorine-containing organic materials. In this range, when a short circuit occurs, some increase in absorption due to the formation of NO ₂ (750 cm ^-1 ) is possible;
III range - a fixed wave number ν _-О-О in the range of 800-900 cm ^-1 , in which all kinds of oxygen-containing (perikis-containing) -O-O-radicals, which are formed as a result of sparking and the action of an electric arc on organic matter, absorb infrared radiation materials.

The fixed wave numbers ν _С-Н , ν _C-Cl , ν _OO were selected from the calculation of the maximum absorption intensity in each of the generalized groups of radicals.

 A device for implementing the proposed method is an infrared system for detecting a leak of combustible gas and air control (see Fire safety on ships. Transl. From English. L .: Sudostroenie, 1985, p. 147-149).

 The disadvantage of such a system is that it is built on the discovery of a single gas component, in contrast to the generalized radical groups of the form CH, C-Cl; -O-O-, characterizing the thermal decomposition products of various organic materials.

 In addition, the named device has low reliability for determining a crisis situation, since the pumped gas of the controlled gas is very low, and it will take a very long time to monitor the entire gas-air environment of the room to interrogate the entire gas-air environment of the protected room. A significant drawback of this system is that when the signal is formed, the influence of noise (signal-to-noise ratio) is not taken into account, which significantly reduces the reliability of detection of a crisis situation. The noise for radicals in the CH band is higher than for radicals in the C-Cl band, due to the greater volatility and prevalence of hydrocarbons compared to chlorine derivatives. The amount of noise in the absorption band -O-O- is determined by the number of working collector electrical machines, DC / DC converters, etc.

In addition, to increase the reliability of detecting a crisis, it is envisaged to increase the optical path length of monochromatic radiation to 5 m using a deflecting system of mirrors, which significantly increases the sensitivity of the device for controlled thermal degradation products (Bouguer-Lambert law D = D _o exp ^-ζd d, where D _o , D is the intensity of monochromatic radiation before and after the measuring section; ζ is the molecular absorption coefficient; d is the optical path length).

 The aim of the invention is to increase the reliability of the device.

The purpose of the invention is achieved by the fact that to control the room environment using a standard ventilation system, a gas-air medium is pumped through the controlled space, followed by repeated (simultaneous) exposure to infrared monochromatic radiation at three fixed wave numbers ν _С-Н , ν _C-Cl , ν _О-О using a deflecting system of mirrors in the spectral ranges: band (3000-2700 cm ^-1 ), characteristic for the absorption of hydrocarbon-containing radicals of the form С-Н; band 760-720 cm ^-1 , characteristic for the absorption of chlorine radicals of the type C-Cl; a band of 960-800 cm ^-1 , characteristic of the absorption of oxygen-containing radicals of the -O-O type, absorption of radiation, fixing it by its radiation receiver, the noise at its frequency is subtracted from the obtained absorption spectrum, the difference is introduced through an analog-to-digital converter into a microcompressor, in which its absorption maximum is determined, followed by comparison with a threshold value and possible absorption values characterizing the different fire hazard of energy-saturated rooms (electrical equipment, etc.) or Stability of thermal destruction of crisis surfaces.

 The coincidence or excess of the resulting absorption at one of the fixed frequencies is used as a criterion for the pre-fire situation (PPS) with the output of information to the monitor and through a digital-to-analog converter to the display unit.

The proposed device differs from the prototype in that in order to increase reliability, the medium in the controlled space is irradiated simultaneously with three fixed wave numbers ν _С-Н , ν _C-Cl , ν _О-О , the gas-air medium of the room is pumped through the controlled space using a ventilation system having a high volumetric flow rate with subsequent repeated exposure to monochromatic radiation using a deflecting system of mirrors, etc.

This constructive solution has a number of significant advantages: it increases the reliability of the detection of PPS due to irradiation of the medium at three fixed wave numbers ν _С-Н , ν _C-Cl , ν _О-О (see figure 1); reduces the weight and size of the device, since air ducts of a standard ventilation system are used for interrogation-control of a gas-air environment; the performance characteristics of the system, namely the increase in the volumetric flow rate of the gas-air medium through the controlled space, significantly speeds up the interrogation of the entire environment of the room. So, with the free volume of the room V = 300 m ³ and the fan capacity Q = 6700 m ³ / h, the pumping time of the whole medium through the controlled space is τ = V / Q = 2.68 min. Multiple exposure to monochromatic radiation on the controlled space using a deflecting system of mirrors increases the sensitivity of the proposed device in proportion to the optical length of the controlled space.

 In FIG. Figures 1 and 2 show the absorption regions of decomposition products and the basic block diagram of a device that implements a method for detecting a pre-fire situation.

The device contains a fan 1 and pipelines for air intake from local volumes of the controlled room, a monochromatic radiation source 2 in the IR range, a controlled space enclosed in a multi-pass gas cell 3, a modulator 4 with an electric motor 5 (with a radiation modulation frequency of 12.5 Hz). Mirror modulators 6.7 (N 1 and N 2) with rotation frequencies of 12.5 and 25 Hz, respectively, deflecting mirror systems 8, input slots N 3, in each of the three measuring channels 9, interference narrow-band filters for operation on fixed wave numbers ν _С-Н , ν _C-Cl , ν _О-О, respectively 10, IR receivers 11, amplifiers 12, electric motor 13, potentiometer 14, data blocks on noise at wave numbers ν _С-Н , ν _C-Cl , ν _O-O, respectively 15, three-channel analog-to-digital converter (ADC) 16, microprocessor 17, monitor 18, digital-to-analog converter Indicator 19, alarm unit 20.

 The frequency of rotation of the modulators, both "shadow" 4 and mirror 6, 7, is selected taking into account the optimal characteristics of the infrared receiver and is 12.5 Hz for 4 and 6, and for the mirror modulator 7 - 25 Hz. The magnitude of the gap 9 in each of the three channels is selected taking into account the optimal operation of the optical system with controlled thermal decomposition products consisting of molecular radicals of the form С-Н, C-Cl, and О-О.

 Interferential narrow-band filters 10 provide stable operation of the optical circuit in each of the three channels at the indicated fixed wave numbers.

The device operates as follows. The pumping device (ventilation system) takes the room air from local volumes and the fan 1 pumps it through a multi-way gas cell 3. Source 2 sends monochromatic radiation through a controlled space 3, in which the radiation undergoes multiple reflection from the mirror system. When plot 3 of one of the types of radicals С-Н, C-Cl, О-О appears in the controlled space, the latter absorb radiation at their fixed wave number ν _С-Н , ν _С-Cl , ν _О-О , attenuating the flow of monochromatic radiation.

 The radiation stream passes through the "shadow" modulator 4, then enters the mirror modulator 6, on which in the first half-cycle of rotation the beam is reflected from the mirror surface and enters the channel N 1 (see Fig. 2) for measuring radicals of the form С-Н, in the second half-cycle of rotation, the beam passes to the second mirror modulator 7, rotating at a frequency doubled compared with the first mirror modulator 6, which during the passage of the flow through the modulator 6 makes a complete revolution, in the first half-cycle of which the radiation beam is reflected from the mirror 7 th surface and enters the channel 2 N radicals measuring type C-Cl, and in the second half 7 is held by the fixed mirror 8 is reflected from which enters the channel 3 N for measuring oxygen-containing radicals. Thus, the radiation beam simultaneously enters into each of the three channels in which it enters the slot 9, its own narrow-band interference filter 10 and the receiver 11 of infrared radiation. In the receiver 11, the signal is amplified and, with the help of an electric motor 13 and a potentiometer 14, in the form of a corrected variable signal is supplied to the analog-to-digital converter 16 of the analyzer 21, from which the signal converted in a convenient form for input is supplied to the microprocessor 17, from a signal characterizing the absorption spectrum of radicals C -N, C-Cl and O-O (potentiometer 14), the noise at the corresponding frequency is subtracted (block 15 of the initial data).

 The corrected signal (difference) in the form of an alternating signal enters the analog-to-digital converter 16 of the analyzer 21, from which the signal converted in a form convenient for input, enters the microcompressor 17, in which its absorption maximum is determined and then compared with the threshold value and possible absorption values characterizing various pre-fire hazard in the premises.

 Coincidence or excess of the resulting absorption of the threshold value for each of the frequencies is used as a criterion of the pre-fire - pre-emergency situation with the output of information to the monitor 18 and through the digital-to-analog converter 19 to the display unit 20.

 The algorithm for choosing the criterion for the diagnosis of PPP is that a crisis situation is detected by the presence of absorption of hydrocarbon-containing (C-H) and chlorine-containing (C-Cl) radicals, and by the presence of additional absorption of oxygen-containing radicals (band-O-O-), the occurrence of sparking or short circuit in electrical switching equipment.

Claims (3)

 1. A method for diagnosing a pre-fire situation in enclosed spaces, which consists in exposing the gas-air mixture in a room to monochromatic radiation at characteristic wavelengths and recording the intensity of radiation transmitted through the gas-air mixture, which determines the presence of components that characterize a crisis situation, characterized in that the gas-air mixture is exposed repeatedly by pulsed monochromatic radiation in the infrared range of the spectrum, a signal is simultaneously recorded The bands corresponding to the intensity of the transmitted radiation in the wavelength ranges of 3.22 - 3.84 μm, 12.82 - 14.28 μm and 10.98 - 12.65 μm, characteristic of the absorption of hydrocarbon, chlorine-containing and oxygen-containing radicals, respectively, of which the signals corresponding to the permissible concentration are subtracted, this difference is compared with the threshold value, and the occurrence of a fire hazard is judged by the presence of hydrocarbon, chlorine-containing or oxygen-containing radicals in the gas mixture above the permissible concentration.  2. The method according to claim 1, characterized in that the presence of oxygen-containing radicals in the gas mixture above the permissible concentration is used to judge the fire hazard of the situation due to a possible short circuit in the electrical switching equipment.  3. A device for diagnosing a pre-fire situation, containing an optically coupled radiation source and receiver connected to the first amplifier, and a processing circuit, characterized in that it further comprises a multi-pass optical system associated with a device for pumping a gas-air mixture, a shadow modulator located at the output of this systems, three optical channels, each of which contains a mirror modulator, a slit and an interference filter in the ranges 3.22 - 3.84, 12.82 - 14.28 and 10.98 - 12.65, respectively, and the processing scheme Natively contains two radiation detectors, the second and third amplifiers, which, together with the first amplifier, are connected through the appropriate blocks of permissible concentrations of fire hazardous components to an analog-to-digital converter, the output of which is connected through a microprocessor and a digital-to-analog converter to an alarm unit, while the second microprocessor output is connected to a monitor .

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