SU1574829A1 - Method of automatic detection of fires in mine workings - Google Patents

Abstract

The invention relates to mining and can be used in coal mines in fire alarm systems. The purpose of the invention is to improve the reliability of detecting a fire source while reducing the cost of the method. A thermosensitive cable (TC) is attached to the wall of the mine for the entire duration of the control zone. TCs are made in the form of two metal conductors encased in a sheath of heat-shrinkable material. At normal ambient temperatures, the conductors are electrically isolated from each other. The conductors TK are connected to an ohmmeter, according to the indications of which they monitor the temperature state of the mine. When a fire occurs, the heat shrinkable shell is compressed and the metallic conductors are closed. The moment of occurrence of a fire is determined by the moment of the short-circuit of the conductors, and the place is determined by the resistance value of the closed electric circuit of the pair of measuring conductors. The distance from the ohmmeter to the closing point is equal to the resistance of the electric circuit divided by the resistivity of the pair of conductors. The method allows to significantly reduce the cost of fire detection in the mine workings. 3 il.

Description

The invention relates to safety in the mining industry and can be used in coal mines in automatic pre-emptive fire extinguishing systems, in fire alarm systems.

The purpose of the invention is to improve the reliability of detecting a fire source while reducing the cost of the method.

FIG. 1 shows the layout of the detector cable; in fig. 2 is a section through a pair of wires in the sheath A-A in FIG. one; in fig. 3 - the same, section BB in FIG. one.

The method is carried out as follows.

A heat-sensitive cable is attached to the wall 1 of the mine workings. The measuring wires 2 and 3 of the cable are placed in an insulating sheath 4 of a heat-shrinkable material. Wires 2 and 3 in sheath 4 are attached to wall 1 with staples 5 and nails 6. To prevent wires 2 and 3 in sheath 4 from closing, the latter is made with a longitudinal corrugation 7 between wires 2 and 3 (see Fig. 2) . The ends of the metering wires 2 and 3 are connected to an ohmmeter 8

In the normal state, when there is no fire and the shell 4 has a temperature of the mine workings wall 1, the wires 2 and 3 are insulated from each other by a longitudinal

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corrugated 7 in the sheath 4. Ohmmeter 8 shows the insulation resistance of the sheath 4 If, for example, a sheath of a heat shrinkable polyethylene composition with a shrink temperature of 160 ° C, an inner diameter of 6 mm is used as the sheath 4, and wires 2 and 3 have a diameter of 1 5 mm, the insulation resistance of the sheath 4 with the length of the measuring wires in the sheath of 100 m is 200 MΩ

When a fire site occurs, sheath 4 is heated, dramatically reduced in diameter (4-7 times) and tightly presses wires 2 and 3 to each other (as shown in Fig. 3). By a sharp change in resistance (from hundreds of millions to fractions of ohms), the moment of occurrence of the source of fire, i.e., the moment of heating of the shell 4 to the shell shrinkage temperature, is determined.

After closing the wires 2 and 3 with an ohmmeter 8, the resistance of the circuit is measured and the distance from the ohmmeter to the fire site is determined. The distance is equal to the resistance of the electric circuit divided by the resistivity of the pair of wires

Example. A heat-sensitive cable has been laid in the mine. The cable was attached with staples to the wall of the mine, and its measuring conductors were connected to an ohmmeter. The heat-sensitive cable is made of a heat-shrinkable polyethylene composition with a shrinkage temperature of 160 ° C. The inner diameter of the shell is 6 mm. As a pair of wires, copper conductors with a diameter of 1.5 mm were used, the resistance of each meter of a pair of conductors was 19, Ohm. The heat-sensitive cable section was heated to a temperature above 160 ° С. The cable sheath at this place sharply decreased in diameter and tightly squeezed the copper conductors. After closing, the ohmmeter showed a resistance of 0.4 ohms. Taking into account the resistivity of a pair of conductors, the distance from the ohmmeter to the heating point — 20.8 mm was calculated. The calculated magnitude satisfactorily coincided with the actual distance from the ohmmeter to the heating section of the cable.

Claims (1)

Invention Formula A method of automatically detecting fires in mines, including laying a pair of metering wires in an open space along a control line and measuring resistance between a pair of wires, characterized in that, in order to increase the reliability of detecting a fire center while reducing costs, a pair of metering wires are placed into one a common insulating sheath of thermo5 shrinkable material with the possibility of short-circuiting the metering wires on the superheated part of the worked-out space, while ate dissolved time of occurrence of fire by short-circuiting time metering wires, as mes0 the occurrence of a fire is determined by the magnitude of resistance of a closed electrical circuit wire pair  Heat B flow  Fig 1 FIG. 2 R 4 2 Fig.Z