US3684021A

US3684021A - Mine explosion suppression method and apparatus

Info

Publication number: US3684021A
Application number: US114608A
Authority: US
Inventors: Edward J Poitras
Original assignee: Fenwal Inc
Current assignee: BLOOM-1 Inc A CORP OF; Fenwal Inc; Kidde Fenwal Inc
Priority date: 1971-02-11
Filing date: 1971-02-11
Publication date: 1972-08-15
Anticipated expiration: 1989-08-15
Also published as: GB1364754A; AU462718B2; AU3885072A

Abstract

A method and apparatus that ignores possibly harmless radiant energy sources such as flames or sparks that occur directly adjacent the working face in a mine tunnel but detects and suppresses potentially dangerous flame fronts moving through the tunnel away from the face.

Description

0R 3,684,021 SR United States Patent Poitras [451 Aug. 15, 1972 1 MINE EXPLOSION SUPPRESSION METHOD AND APPARATUS Edward J. Poitras, Holliston, Mass.

Fenwal, Inc., Ashland, Mass.

Feb. 11, 1971 [72] Inventor:

Assignee:

Filed:

Appl. No.:

[52] US. Cl. ..169/2 R, 169/19, 169/28 Int. Cl. ..A62c 3/00 Field of Search ..169/1 R, 1 A,'1'B,' 2 R, 2 A,

References Cited UNITED STATES PATENTS Mathisen .,.....169/2 R Mitchell et a1 ..169/1 R 3,515,217 6/1970 Jamison 169/2 R FOREIGN PATENTS OR APPLICATIONS 547,179v 5/1956 Belgium ..169/2 R 1,131,233 10/1968 Great Britain ..169/2 R Primary Examiner-M. Henson Wood, Jr. Assistant Examiner--Edwin D. Grant Attorney-John E. Toupal ABSTRACT A method and apparatus that ignores possibly harmless radiant energy sources such as flames or sparks .that occur directly adjacent the working face in a mine tunnel but detects and suppresses potentially dangerous flame fronts moving through the tunnel away from the face.

19 Claims, 4 Drawing Figures PATENTEDMJB 15 1972 A SHEET 1' 0r 2 Edward J Pair/"a5 MINE EXPLOSION SUPPRESSION METHOD AND APPARATUS BACKGROUND OF THE INVENTION of either methane gas or coal dust adjacent a working face of a mine tunnel.

Although modern mining techniques have substantially reduced the hazards to the underground mining of coal, certain dangers are still recognized. The most serious of these dangers are the mine explosions resulting from the ignition of either coal dust or methane gas produced during mining operations. A common wellknown method for preventing mine explosions entails the application of rock dust, such as powdered limestone, over exposed tunnel surfaces on which coal dust tends to collect. This process reduces the incidence of airborne coal dust within the tunnel and consequently reduces the danger of coal dust fed explosions. The effectiveness of rock dusting is somewhat reduced in modern mines that employ mechanized equipment such as the well-known continuous miners with rotating cutter wheels that remove coal from the working face of a mine tunnel. Because of the speed at which a mine face is advanced by such machines and because of their tendency to generate a high volume of coal dust, it is difficult to maintain a rock dust covering on newly exposed surfaces. Another problem associated with continuous miners is their tendency to produce sparks despite the fact that water spray equipment is generally mounted at the cutting ends of the machines to both quench sparks and settle coal dust. I

A rock dusting method and apparatus disclosed in US. Pat. No. 3,333,896 was developed to alleviate the problems noted above. According to that method rock dust is directed in an air suspension, preferably from a device mounted on the mining machine, so as to comingle with coal dust being produced. The continuous co-mingling of rock dust and coal dust results in a settled mixture from which the coal dust component is not easily separated should an explosion occur. The interspersion of rock dust and coal dust also reduces the possibility of the air suspension propagating an explosion.

The aforesaid method, although cumbersome both mechanically and procedurally, is relatively effective for arresting mine explosions fed by coal dust. However, as disclosed in US. Pat. No. 3,515,217, explosions induced by the accelerated burning of methane gas are an even more serious problem in that a methane-air mixture can be ignited by a lower energy source. An abrasion spark created by a cutter striking a pyritic particle, for example, can have sufficient energy to ignite a methane-air mixture. To provide for the suppression of either gas or coal dust fed explosions, the method disclosed in the aforesaid US. Pat. No. 3,515,217 entails the discharge of a flame extinguishing material in response to the sensing of flame. A suitable flame sensor mounted on a mining machine detects the existence of flame at the mine face and in response to such flame activates a detonating mechanism that releases the extinguishing agent from suitably positioned containers, also mounted on the mining machine. Because of the tremendous effectiveness of modern flame extinguishing agents, this system can be made highly reliable with respect to any explosions initiated by flames generated at the mine face. However, a significant drawback of the system is that the flame extinguishing mechanism is activated in response to detection of any flame at the mine face regardless of whether the prevailing conditions will support a destruction explosion. The requirement to replenish costly extinguishing agent supplies and unnecessary interruptions of mine operations can result, therefore, from the detection of flames that would not produce catastrophic explosions.

The object of this invention, therefore, is to provide an improved and more efficient method for reliably preventing destructive explosions in the work tunnels of coal mines.

SUMMARY OF THE INVENTION The present invention relies upon known and inherent characteristics of mine explosions to provide a method and apparatus that distinguishes between harmless and potentially dangerous flames ignited near the working face of a mine tunnel. Studies of mine explosions have indicated that prior to either a coal dust or methane-air explosion, a flame initially ignited adjacent the mine face first propagates along the mine tunnel for a substantial distance. As the flame moves, accelerated burning generates increased heat and gas expansion that ultimately precipitates a destructive explosion. Experience has shown that a flame front ignited at the mine face will generally have progressed as far as 30 to 50 feet down a mine tunnel before a catastrophic explosion actually occurs. Furthermore, the initial velocity of the flame front is relatively slow so that a finite time period elapses between initial ignition of the flame and the actual explosion. According to the method of this invention, flame present at the mine face itself is ignored while any flame front progressing a finite distance down the mine tunnel from the mine face is detected and results in the discharge of a flame extinguishing agent. Since light emanating from the mine face is ignored, harmless sparks or small transient flames occurring thereat do not produce a discharge of extinguishing agent. Conversely, any potentially dangerous flame front moving away from the mine face down the mine tunnel is detected and results in discharge of a flame suppressing agent to thereby prevent a destructive explosion.

A featured apparatus of the invention detects the radiation produced by sparks or flame with an ultraviolet sensor preferably mounted on a mobile mining machine. The sensor is oriented so as to sense radiant energy emanating from a detection zone that extends in lateral directions from the machine but is shielded from radiation emanating from an obscured zone in front of the machine. During mining operations, the obscured zone lies directly adjacent the mine tunnel face being worked by the machine. Thus, harmless short duration sources of radiation at the mine face are ignored while potentially destructive flame fronts propagating down the mine tunnel are detected.

A preferred apparatus embodiment also includes a plurality of sealed containers that can be ruptured to release a flame suppressing agent. Explosive squibs for effecting rupture of the containers are detonated in response to detection of radiant energy by the ultraviolet sensors. The agent filled containers also are mounted on the mining machine and are oriented so as to release suppressing agent into a discharge zone that v DESCRIPTION OF THE DRAWINGS These and other objects and features of the invention will become apparent upon a perusal of the following description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic representation of the invention operatively positioned in a mine tunnel;

FIG. 2 is a schematic view, partially in cross section, illustrating in greater detail one of the detector units shown in FIG. 1;-

FIG. 3 is a schematic view, partially in cross section, illustrating in greater detail one of the suppression agent filled containers shown in FIG. 1; and

a FIG. 4 is a schematic block diagram showing the circuit connections between the detector units and suppression agent containers shown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is shown a mobile mining machine 11 located within a tunnel 12 of a coal mine. The machine 11 is of the type commonly known as a continuous miner with a cutter head assembly 13 that rips chunks of coal from a working face 14 of the tunnel 12. As the machine 11 advances in the tunnel 12, the face 14 is continuously advanced and dislodged coal is conveyed out of the mine by conventional equipment (not shown).

Mounted on the front half of the machine 11 are a plurality of detection units 15 each possessing a sensor head 16 responsive to ultraviolet radiation. As described in greater detail below, each of the sensor heads are arranged so as to receive only that radiation that emanates from an annular fan-shaped volume extending laterally into the shaft 12 as indicated by the dashed lines 17. The individual volumes defined by the lines 17 together form a detection zone A that comprises a lateral section of the mine tunnel 12. Similarly mounted on the rear portion of the machine 11 are a plurality of suppression units 21 that are operatively connected to the detection units 15. As also described in greater detail below, each of the suppressor units 21 is arranged to discharge a flame suppressing agent into an annular fan-shaped volume extending laterally into the mine shaft 21 as indicated by the dashed lines 22. Again, the volumes defined by the dashed lines 22 together form a discharge zone B that comprises a lateral section of the mine tunnel 12. Longitudinally adjacent to and straddling the detection zone A are obscured zones C and D that also comprise lateral sections of the mine tunnel 12. Obscured zone C is located ahead of the machine 11 and extends from the front surface of the detection zone A to the mine face 14 while the obscured zone D extends rearward of the detection zone A.

FIG. 2 shows in greater detail one of the identical detector units 15 shown in FIG. 1. The sensing head 16 comprises a conventional ultraviolet detector tube 31 enclosed by a transparent dome 32 made, for example, of quartz. Supporting both the tube 31 and the dome 32 is a housing 33 that encloses detection circuitry and a power supply. The detection circuitry (not shown) is conventional and provides a signal output in response to detection of ultraviolet radiation by the tube 31. Examples of suitable circuits of this type are disclosed in US. Pat. Nos. 3,189,743 and 3,191,036. Coated over a hemispherical portion of the dome 32 is an optically dense mask 34 that shields the tube 31 from ultraviolet radiation emanating from the obscured zone C located ahead of the mining machine 11 as shown in FIG. 1. Similarly coated on the base of the dome 32 is an optically dense annular mask 35. This mask 35 together with the housing 33 shield the tube 31 from ultraviolet radiation emanating from the obscured zone D behind the mining machine 11 as shown in FIG. 1. Thus, as also illustrated in FiG. 1, the sensors 16 together detect only that ultraviolet radiation emanating from the detection zone A that encompasses the individual volumes defined by the dashed lines 17.

FIG. 3 shows in greater detail one of the identical suppressor units 21 shown in FIG. 1. The unit 21 comprises a cylindrical container 41 partially filled with a flame suppressing agent 42 preferably a liquefied gas such as methyl bromide or a similar halogen suppressant. Coaxially extending from one end of the container 41 is a discharge tube 43 having one end closed'by a frangible diaphragm 44. The opposite end of the tube 43 opens into the bottom portion of the container 41. Mounted on the closed end of the tube 43 is a deflector unit comprising a cylindrical screen 45 and a hemispherically shaped deflector plate 46. An explosive squib and detonator assembly 47 projects into the tube 43 adjacent the frangible diaphragm 44.

Although the suppressor unit 21 does not, per se, form a part of the present invention, a brief description of its operation will be presented in order to clarify the overall operation of the disclosed system. In response to an activating signal on line 48, the squib 47 explodes to rupture the frangible diaphram 44 forming a discharge opening in the tube 43. Gas pressure within the container 41 then forces the contained agent 42 upward through the open end of the tube 40 and out of its opened mouth 44. The released agent is deflected by the plate 46 into a discharge pattern that is defined by the dashed lines 22 and which helps form the discharge zone B shown in FIG. 1. Further descriptions of explosive suppressor units of this type appear in US Pat. Nos. 2,742,094 and 3,523,583.

During operation of the machine 11, small pockets of either methane or coal dust are occasionally ignited adjacent the mine face 14. Such ignitions can result, for example, from sparks produced by contact between the cutting head 13 and pyritic particles embedded in the coal being removed from the mine face 14. Because these ignitions occur in the obscured zone C provided by the shielding masks 34 (FIG. 2) they are not sensed by the detector units 15 and, consequently, do not result in activation of the suppressor units 21. This is desirable in that most of the flames ignited adjacent the mine face 14 terminate quickly and are therefore harmless. Occasionally, however, conditions are such that an initially small flame will grow into a flame front that propagates from the mine face 14 back into the mine tunnel 12. Should this occur, the flame front upon reaching the detection zone A is immediately detected by at least one of the sensors 16 each of which is electrically connected by lines 48 to all of the suppressor units 21 as shown in FIG. 4. Output signals produced by the detection units in response to the sensing of ultra violet radiation detonate each of the squibs 47 (FIG. 3) effecting release of extinguishing agent 42 into the discharge zone B (FIG. 1). Because the discharge zone B encompasses a complete lateral section of the mine shaft 12, the propagating flame front is completely quenched to prevent a potentially destructive explosion. The longitudinal spacing of the detection zone A and the discharge zone B is useful in that it assures that the zone B will be completely filled with suppressing agent when reached by a flame front detected in the detection zone A. Thus, the method and apparatus disclosed herein is effective to prevent potentially catastrophic coal mine explosions initiated at the mine face but ignores harmless, quickly terminated sources of radiation.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is to be understood, therefore, that the invention can be practiced otherwise than as specifically described.

What is claimed is:

l. Explosion suppressing mining apparatus comprismg:

a. a movable unit adapted for longitudinal movement through a mine tunnel;

b. radiant energy detection means comprising energy sensing means disposed on said unit so as to sense radiant energy emanating from a detection zone of the tunnel, said detection zone encompassing a lateral section of the tunnel;

c. shielding means for shielding said sensing means from radiation emanating from an obscured zone longitudinally spaced from said unit along the tunnel; and

d. suppression means for discharging a flame suppressing agent into the tunnel in response to detection by said detection means of radiant energy emanating from said detection zone.

2. Explosion suppressing mining apparatus according to claim 1 wherein said suppression means is mounted on said unit.

3. Explosion suppressing mining apparatus according to claim 2 wherein said suppression means comprises container means filled with said suppressing agent, explosive means for rupturing said container means, and detonator means for detonating said explosive means in response to detection output from said detection means.

4. Explosion suppressing mining apparatus according to claim 1 wherein said sensing means comprises an ultraviolet radiation sensor.

5. Explosion suppressing mining apparatus according to claim 1 wherein said shielding means is disposed so to claim 1 wherein said movable unit is a mobile mining machine for dislodging coal from a continuously advancing face of the mine tunnel and said shielding means is disposed so as to shield said sensing means from radiation emanating from in front of said mobile mining machine.

7. Explosion suppressing mining apparatus according to claim 6 wherein said shielding means is disposed so as to also shield said sensing means from radiation emanating from behind said mining machine.

8. Explosion suppressing mining apparatus according to claim 6 wherein said sensing means comprises an ultraviolet radiation sensor.

9. Explosion suppressing mining apparatus according to claim 6 wherein said suppression means is disposed so as to discharge said agent into a discharge zone spaced from said detection zone in a direction from the front toward the rear of said mining machine.

10. Explosion suppressing mining apparatus according to claim 6 .wherein said suppression means is mounted on said mining machine.

11. Explosion suppressing mining apparatus according to claim 10 wherein said suppression means comprises container means filled with said suppressing agent, explosive means for rupturing said container means, and detonator means for detonating said explosive means in response to detection output from said detection means.

12. Explosion suppressing mining apparatus according to claim 11 wherein said shielding means is disposed so as to also shield said sensing means from radiation emanating from behind said mining machine.

13. Explosion suppressing mining apparatus according to claim 12 wherein said detection means comprises a plurality of spaced apart ultraviolet sensors and said suppression means comprises a plurality of spaced apart individual containers each filled with said agent and opened by an explosive charge in response to detection of radiation in said detection zone.

14. Explosion suppressing mining apparatus according to claim 13 wherein each of said ultraviolet sensors are covered by sealed transparent housings and said shielding means comprises optical masking applied to said transparent housings.

15. Explosion suppressing mining apparatus according to claim 14 wherein said suppression means is disposed so as to discharge said agent into a discharge zone spaced from said detection zone in a direction from the front toward the rear of said mining machine.

16. A method for suppressing explosions in a mine tunnel comprising the following steps:

a. providing a sealed container filled with an explosion suppressing agent near the face of the tunnel; b. providing a radiation sensor means in the tunnel near the tunnel face; 0. orienting said sensor means so that it is impinged by radiation emanating from a detection zone separated from the tunnel face by an obscured zone;

shielding said sensor means from radiation emanating from said obscured zone; and

tion sensor means on a mobile mining machine adapted to dislodge coal from the tunnel face, and wherein said shielding step comprises shielding said sensor means from radiation emanating in front of said mining machine.

19. A method according to claim 18 including the step of shielding said sensor means from radiation emanating behind said mining machine.

Claims

1. Explosion suppressing mining apparatus comprising: a. a movable unit adapted for longitudinal movement through a mine tunnel; b. radiant energy detection means comprising energy sensing means disposed on said unit so as to sense radiant energY emanating from a detection zone of the tunnel, said detection zone encompassing a lateral section of the tunnel; c. shielding means for shielding said sensing means from radiation emanating from an obscured zone longitudinally spaced from said unit along the tunnel; and d. suppression means for discharging a flame suppressing agent into the tunnel in response to detection by said detection means of radiant energy emanating from said detection zone.

5. Explosion suppressing mining apparatus according to claim 1 wherein said shielding means is disposed so as to shield said sensing means from radiation emanating from diametrically opposed directions so as to establish said obscured zone on opposite sides of said detection zone.

6. Explosion suppressing mining apparatus according to claim 1 wherein said movable unit is a mobile mining machine for dislodging coal from a continuously advancing face of the mine tunnel and said shielding means is disposed so as to shield said sensing means from radiation emanating from in front of said mobile mining machine.

10. Explosion suppressing mining apparatus according to claim 6 wherein said suppression means is mounted on said mining machine.

16. A method for suppressing explosions in a mine tunnel comprising the following steps: a. providing a sealed container filled with an explosion suppressing agent near the face of the tunnel; b. providing a radiatioN sensor means in the tunnel near the tunnel face; c. orienting said sensor means so that it is impinged by radiation emanating from a detection zone separated from the tunnel face by an obscured zone; d. shielding said sensor means from radiation emanating from said obscured zone; and e. releasing said agent from said container in response to detection by said sensor of radiation emanating from said detection zone.

17. A method according to claim 16 including the step of mounting said sealed container and said radiation sensor means on a support adapted for longitudinal movement through the tunnel.

18. A method according to claim 16 including the step of mounting said sealed container and said radiation sensor means on a mobile mining machine adapted to dislodge coal from the tunnel face, and wherein said shielding step comprises shielding said sensor means from radiation emanating in front of said mining machine.