The science and art of sealing a mine fire

Mining Science and Technology, 5 (1987) 221-246

221

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

THE SCIENCE AND ART OF SEALING A MINE FIRE R. Morris Johannesburg Consolidated Investment Company Limited, JCI House, 28 Harrison Street, Johannesburg, 2001 (South Africa)

and T. Atkinson Mining Engineering Department, University of Nottingham, University Park, Nottingham (U.K.)

(Received October 15, 1986; accepted January 5, 1987)

ABSTRACT

The authors detail the objectives to be considered prior to sealing a fire, followed by the factors and the problems associated with fire seals. They conclude with three examples of shaft or adit sealing, and three practical exam-

ples of sealing underground fires. The paper describes numerous seals which have been used sucessfully on mine fires and which are believed to be useful to the mining engineer involved in similar crises.

INTRODUCTION

must prepare for the possible re-opening while sealing.

Statistics show that the odds are one in two that unless a fire is extinguished within a few minutes, more than eight hours will be required to control it. The odds are one in twenty that such a fire will not be controlled at all by underground attack, necessitating that the mine or at least a portion of it, will have to be sealed [1]. Often hundreds of thousands of tonnes of coal become lost to the mining c o m p a n y on sealing the spontaneous heating. Thus, the mine manager must bear in mind, while preparing an area for sealing, that he may need to re-open the same area one day, and he

THE OBJECTIVES OF SEALING A MINE FIRE Stoppings are erected in mine workings mainly for the following reasons: (1) to prevent the access of air to a fire or heating, so that the oxygen in the vicinity of the fire is consumed; (2) to provide an explosion-proof barrier in the event that mixtures of gas, or coal dust, with air are ignited by the active fire;

222

(3) to minimise changes in the composition of the atmosphere within the sealed area, which result from changes in barometric pressure and the contraction due to a cooling of the fire area; (4) to control the de-gassing of sections of mine workings during recovery of a sealed-off district; (5) to seal off abandoned workings; and (6) to effect a temporary diversion ,of the ventilation [2]. King stated that there are a number of objectives in sealing off old workings, not all of which necessarily apply in each case [3]. The practice at collieries is to judge each situation, decide which objectives are appropriate, and then to act accordingly. The degree of effectiveness of the seal can thus vary enormously, depending upon what was trying to be achieved. The following list indicates the main objectives of sealing and the means to make them effective. The objectives are: (1) to prevent access by persons into abandoned workings; (2) to minimise airway inspections; (3) to direct as much of the available ventilating air as possible into current workings; (4) to reduce the load of toxic and inflammable gases which have to be diluted; (5) to prevent a sudden outflow of accumulated gases during periods of falling atmospheric pressure; and (6) to build up an asphyxiating non-flammable atmosphere in the sealed area which will neither explode nor support spontaneous cumbustion. However, neither references [2] or [3] mentioned the importance of sealing a fire area in order to prevent it from spreading uncontrollably through the mine workings and thus depleting the coal reserves of a mine. The employment of workmen for long periods underground may of itself, be dangerous. If air is to be excluded from the fire, then the sooner a seal is erected, the more quickly will

the fire extinguish itself. Old workings may be particularly inaccessible so that the erection of stoppings presents great difficulty with the loss of valuable time. The building of a stopping by traditional methods may take 24 hours or more before the seal is complete and the air finally cut off; during this time the fire may have developed considerably, thus increasing the hazard. Moreover, in a gassy mine the danger of an explosion taking place increases with time. This may be especially true as the explosion-proof stopping nears completion and the ventilation is restricted. Indeed, the history of mining disasters contain many instances of men being killed while working on the stoppings. At the H o m i n g Mine, near Pittsburgh, U.S.A., an explosion killed all the 20 men building a seal, and during a further a t t e m p t to complete the stopping a second explosion took place [2]. Haldane et al. in a m e m o r a d u m submitted to the Council of the Institution of Mining Engineers itemized certain precautions to be taken while building stoppings [4]. They stated that to prevent the risk of a gas explosion while men are present during the operations of shutting off a gob-fire or heating, certain precautions are desirable. These precautions include: (1) The seat of the stoppings should be so selected, and the ventilation if necessary so modified, with the help of air-pipes or bratticing, that air which is as free as possible from firedamp, (or from carbon monoxide on the return side of the heating), is supplied to the out-bye sides of the stoppings both before and after the stoppings are closed. By this precaution three points will be secured: (a) if a stopping is blown out by an explosion of gas, the spread of the explosion out-bye will be checked rapidly, provided, of course, that the roadway is well stone-dusted; (b) There will probably be a fairly extensive cushion of non-flammable air be-

223 hind the stopping through the pores and cracks at which air is entering; and this will help to save the stopping; and (c) access to the stoppings will not be difficult since there will be no presence of firedamp, carbon monoxide, or blackdamp. (2) The stoppings should be so constructed that free air-passages or openings, sufficient to reduce to a harmless percentage the gas in the open workings of the section to be sealed off, should be left until the last moment, and the openings then quickly closed by doors, packs, or other ready means. The stoppings on intake and return sides are then closed simultaneously by trustworthy men, who will afterwards withdraw at once to a safe position. By this means the risk to life during the erection of stoppings will have been reduced to a minimum. If, unfortunately, an explosion sufficiently violent to damage a stopping should occur, it will probably be at only one stopping, leaving the air-supply sufficiently restricted to prevent the air from again becoming inflammable. A period varying from about 24 hours when the space shut off is very large, to an hour or less when it is small, ought to elapse before the stoppings are again examined after closure, or after an explosion, since a second explosion might follow. A sample, obtained through a pipe in the stopping, should then be taken on the return side to ascertain that the air inside is no longer inflammable, and a water gauge attached to the pipe should be read. The stoppings may now be completed in a more permanent manner. After some 60 years from the time the above items were included in the Memorandum to the Council, the authors of this publication cannot fault the steps which were advised.

PREPARING A SITE FOR THE FIRE SEALS In mines liable to spontaneous combustion in South Africa, it has been found advantageous to have a system of preparatory stoppings. By this is meant that the floor, roof and sides of the pillars are cut to the solid. These are hitched in a distance of 0.6 m, until the ground is settled and has no cracks. In addition, bricks, sand, pipes, etc. are placed near by the position of the seal. The value of this was stressed by Haldane et al. as follows: "consequently, in seams liable to spontaneous combustion I recomm e n d that sites for stoppings should be selected and some preparatory work done while the unit is still in production. In fact, in some seams where spontaneous heating is frequent, such preparatory work has been traditional practice" [4].

THE FACTORS AFFECTING THE SITE OF A SEAL The factors affecting the site of the fire seals may be itemized as follows: (i) The urgency of the situation, and the time the mine manager determines that he has before the fire becomes out of control. (ii) Factors such as the closeness of main haulages or conveyor roads. (iii) The gradients in the area. (iv) The pressure of water. (v) The normal make of firedamp in the district, and the location of its main emission in relation to the site of the fire. (vi) The quantity and distribution of the ventilation and the likely variation by restrictions arising during the construction of the stoppings. (vii) The effect of the above factors (v) and (vi) in permitting an accumulation of firedamp where it might become ignited.

224

(viii) The possible effect of the fire on the ventilation which as previously stated might slow, or even reverse, the general ventilation. (ix) The coal-dust hazard. If there is the possibility of a coal-dust explosion the means provided for arresting such an explosion, must be provided, e.g. stone dust or stone-dust barriers. (x) The site of the seal must finally be decided upon in terms of logistics, i.e. the distance from a transport roadway, since much time can be lost transporting materials " b y hand" into old workings [5]. Haldane stated that: "Cutting off the ventilation by sealing the workings into which firedamp is being given off is evidently an operation attended by the risk of an explosion. Hence this operation is never undertaken as a means of dealing with a fire or a suspected fire in a gassy seam except where all other means have failed or are impractical. Cases occur, however, in which there is no alternative but to seal off a considerable space if a pit is to be saved, though the area sealed off is, in view of the danger, limited to the utmost possible extent" [4]. When the ventilation is shut off in a gassy section, the percentage of methane in the air will, of course, increase rapidly. At the same time, the percentage of oxygen in the air still present will diminish owing to the absorption of oxygen by the coal and any other oxidizable material present. As soon as the percentage of methane exceeds about 5.4% the air becomes inflammable if none of the oxygen has been absorbed, or about 6.0% if, as probable, a good deal of oxygen has been absorbed. On the other hand, an upper limit of inflammability is reached when the methane percentage reaches about 15.0% if no oxygen has been adsorbed. If, however, as is probable, a good proportion of the oxygen in the air has been absorbed, this upper limit is correspondingly lowered, and if there is so

much absorption as to lower the oxygen percentage in the mixture to 12.4%, the upper limit meets the lower limit (which is raised to about 6.5%), so that continued inflammation is impossible. In a section where little gas is given off, an inflammable mixture will probably never be formed, since the oxygen percentage will fall to 12.4% before the methane percentage rises to 6.5%. But if a fair amount of gas is given off, the methane percentage will have reached about 6.0% before there has been any very great absorption of oxygen. Hence there will be an inflammable mixture as long as the methane percentage in the body of the air is between about 6.0% and a certain higher limit, which cannot be higher than 15%, but may be a good deal lower. When the percentage of methane has risen to about 15%, or that of oxygen has fallen below 12.4%, the risk of a gas explosion has passed. It hardly seems possible, however, to avoid the risk of a gas explosion during the critical period while the air is inflammable, if the ventilation is cut off from a gassy district with a fire present in it. Before stone-dusting was introduced, the risk existed of a gas explosion, however small, causing a coal-dust explosion. This might wreck considerable parts, or even the whole, of the roadways of a pit, and cause serious loss of life, if men were present. Such coal-dust explosions, sometimes accompanied by heavy loss of life, but sometimes also with little or no loss of life, have occurred again and again in the past. W i t h thorough stone-dusting, however, the risk of these occurrences is greatly reduced. Hence heavy stone-dusting all round the seat of a gob-fire or heating, and the roads leading to it, should always be done at once, and the proportion of stonedust present should be raised high above the statutory limit.

Type of Seals Having finalized the position of the seal or seals, it is necessary to have it examined by

225

an experienced official to determine the exact position(s). In a return or a contaminated airway, it is usual to have this examination m a d e by trained rescue men. Obviously, broken ground must be avoided, and the site chosen should be the one requiring the least amount of work to erect the stopping, i.e. small cross sectional areas should be chosen in preference to roadways having a large cross sectional area. Willett et al. stated that: " T h e sites selected for fire seals usually require to have the roof and sides trimmed and the floor cleared of loose debris to enable the sealing materials to be fitted closely and so to avoid air leakage"

[6]. Speed of erection is essential, and any operation which unnecessarily slows up this process should be avoided. If the site has a made up floor, it m a y be sufficient to clear only the in-bye end over a length of about 4 ft down to a hard bottom. In a roadway supported by

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steel arches and cover boards, the latter should be removed, one section at a time, as the work of building the seal proceeds in order that the site can be packed solidly. Where the supports are girders and legs, it may be better to remove the girders as well as the covering boards, though if there is a possibility that the removal of supports might results in a fall of ground, they should be left undisturbed. It is not intended to detail the erection of stoppings, however, Fig. 1-10 inclusive are felt sufficient to give the reader an indication of a seal, which must be of such construction that the ventilation into the fire area is cut off as quickly as possible. However, in the final seal that is being erected a ventilation tube (24 in), or a steel door is left. This serves two purposes: (i) In the event of a recovery operation into the sealed area, an access is readily available for the proto team to enter the sealed area and to investigate the state of the extinguished heating.

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(ii) To change the atmosphere from a free flowing ventilation circuit into a sealed area is extremely dangerous and numerous explosions have occurred at this point. The mine manager must never forget that his prime consideration must be towards the safety of his workmen. Usually when the final seal, or 24 in. diameter pipe or steel door is being closed, all men

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229

prolonged periods of time due to the leakage of oxygen into the fire or it could cause an old sealed area to develop a new fire as a result of spontaneous combustion. Several techniques such as shotcreting and grouting could be used to improve the quality of the final seal. Pressure equalization chambers could also be used under certain circumstances.

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walls and on the inner face of the stopping, can then be erected in safety and in the fresh air.

THE PROBLEMS FIRE SEALS

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Several problems are associated with fire seals, as outlined below [5].

Leakage Almost no fire seal may be regarded as absolutely airtight, mostly because of the fact that the strata surrounding the seal is, in itself, not airtight. This problem is aggravated by high pressure differentials across the seals as is the case in most " t h r o u g h " panels. The leakage resulting from such pressure differentials could cause a fire to remain active for

Fire "jumping" the seals This could very well happen when conditions are such that the seals have to be constructed close to an active fire. This problem is, once again, more acute under conditions where a unidirectional leakage into the fire due to large pressure differentials is present. If the fire is active, the solid coal in the roof and side will usually burn as well, and such burning will propogate very easily along leakage paths in the coal. Water sprays usually offer some protection against this hazard.

Explosions This is one of the concomitant hazards of sealing that should always be considered especially if the fire is very active. This hazard comes about through a combination of two factors, namely: (i) a build-up of explosive gases during a fire; and (ii) a decrease of oxygen immediately after sealing. The build-up of explosive gases is due to the natural emissions from the surrounding strata accelerated by the heat from the fire. In addition, the application of water to an active fire may often lead to a water-gas reaction in which the excessive heat ( + 1000 ° C) m a y lead to water being broken up into hydrogen and oxygen, thus leading to a further build-up of hydrogen, i.e. 2 H 2 0 + Heat ~ 2H 2 + 02

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The gases emitted from the strata are usually methane and hydrogen together with traces of other hydrocarbons. The concentrations of hydrocarbons other than methane are usually negligible in terms of affecting the explosiveness of the atmosphere although not to the same extent as hydrogen and methane. From this discussion it should become clear that certain precautions should be taken during the sealing operations in order to ensure the safety of workers and to safeguard the rest of the mine. Recommendations, stemming from the experience of the authors include the following: (a) During sealing operations the flow of ventilation should be kept undisturbed as far

as possible until a final seal may be effected very quickly. It has become standard practice to build a large diameter steel pipe (e.g. 300 mm) into the wall of the seal. This pipe is kept open until the seal is completed and dried. After that, the final seal is effected by putting a blank flange onto the pipe. This operation is carried out with a minimum number of people, while other people are removed to the surface. The danger is particularly acute when a significant uni-directional flow is present before sealing, as an interruption of the airflow could cause gases to build back over the fire, thus leading to an explosion. This sentiment is shared by the Committee

231 appointed by the Council of the Institution of Mining Engineers in the United Kingdom to investigate the sealing of underground fires [4]. They formulate the action to be taken as follows: "As a consequence of the danger, where fire gases are concerned, of even momentary reversal of the air over the fire it is desirable that unduly sudden stopping or unduly sharp reduction in ventilation should be avoided, to prevent surges of air". Additionally, "Wherever there is the possibility of such accumulation near the fire or of migration of firedamp to the seat of the fire, it follows that, unless there are weighty reasons to the contrary, the ventilation should be maintained as nearly as possible at its normal rate, or at least reduced under control only to a still safe rate, during the operation of building the seals." (b) As the danger period of a fire, or a heating, usually follows soon after a final seal has been effected, it is imperative that the composition of the atmosphere behind the seals be monitored regularly, or preferably continuously. During such monitoring note should be taken of either barometric pressure fluctuations or fan pressure differentials, or both, depending on the circumstances. (c) After the seals have been constructed every effort should be made to minimise leakage. This may be done by means of vermiculite plaster on the seal surface, shotcreting, grouting, pressure chamber, etc., depending on circumstances [7]. (d) As the danger of explosions always exists after sealing, it is conceivable that, given the right circumstances, such explosion could destroy the seals and propagate by normal processes. To prevent the propagation of such an explosion, it is essential to take adequate counter measures, such as the liberal application of stonedust out-bye of the seals, the erection of stonedust barriers at strategic points, etc. It is also advisable to use stonedust as a filler between double walls of seals.

(e) Adequate provision by means of spray pipes should be made to prevent the fire from "jumping" the seals. This is particularly important where a substantial uni-directional leakage is present.

SOME EXAMPLES OF SEALING AT A SHAFT OR AT AN ADIT When the management of a mine attempt to seal a mine at the shaft they are in one respect admitting that all previous attempts to extinguish or seal a smaller portion of the mine have failed. However, even while sealing at the shaft there must be certain steps taken which enable the mining company to re-open the mine at some future date if they so desire.

Felling Colliery (1812) The first attempt recorded of sealing a mine occurred with the shaft sealing after the Felling disaster of 1812 which claimed 92 lives. On May 25th, 1812 there occured the first great colliery explosion for which we have any accurate records. It was, moreover, a disaster of historic importance, for its aftermath marked the earliest attempt of any properly coordinated movement to enlist public opinion in the service of mine safety and to arouse scientific interest in the cause of accident prevention [8]. Felling Colliery, was situated between Gateshead and Jarrow. Two shafts were in use: the William Pit and the John Pit. This latter shaft, 602 ft deep, was used as the downcast pit and for winding. It was here that the first explosion occurred at about 11:30 a.m. An excellent description of it, written by John Hodgson, fortunately survives. " T h e subterraneous fire," he writes, "broke forth with two heavy discharges from the John Pit, which were almost instantaneously followed by one from the William Pit. A

232 slight trembling, as from an earthquake, was felt for about half a mile around the workings; and the noise of the explosion, though dull, was heard to three or four miles distance, and much resembled an unsteady fire of infantry. Immense quantities of dust and small coal accompanied these blasts and rose high into the air in the form of an inverted cone" [8]. Around the colliery itself a shower of wrecked corves, pieces of timber and small coal fell in all directions. The tops of the headgear of both shafts were destroyed, the pulleys at the William Pit being completely blown out. The wooden frames were set on fire, though luckily the winding pulleys of the John Pit, which were slung on a crane outside the force of the blast, remained intact. It was up this shaft that those who survived were wound to safety about half an hour after the explosion. Althogether, thirty-two men and boys were brought to the surface. By noon all the known survivors had been drawn from the pit and volunteers stood by to descend. The accident had occurred during the relief of the morning shift by the afternoon shift and therefore the death toll, it was realised only too well, was likely to be abnormally high. At 12:15, nine miners bravely descended the John Pit. Because of the imminent danger of a second explosion they used the faint light of steel-mills to guide them into the interior. Unfortunately, the men were able to make very little headway. The workings were found with afterdamp, and reluctantly the explorers had to retreat to the pit bottom and decided to ascend. Five had reached the bank safely and two were in the shaft when the mine exploded a second time. The men on the rope felt an unusual heat surge past them, but the blast lacked enough force to dislodge them. Their comrades below "threw themselves on their faces and kept firm hold of a strong prop" and also escaped without serious injury. But clearly the coal had ignited somewhere in the workings; unless fairly prompt

action was taken the underground fire would quickly spread. One or two further attempts at rescue were made, but no one doubted any longer the utter hopelessness of the situation. There was simply no question of being able to penetrate those fiery workings to any distance. Nor was it at all likely that anyone else could have survived the poisonous gases produced by the explosion. On May 27th, both the shafts were sealed in order to extinguish the fire and it was only some six and a half weeks later, on July 8, that the melancholy task of recovering the bodies, " b y the light of steel-mills," began. The Oaks 1866

In December 1866, a pit at The Oaks exploded which eventually took the lives of 361 men and boys. Of the 340 persons in the pit on Wednesday, December 12th, only six ultimately survived. Twenty seven were killed on the following morning, of which twenty three were volunteers from other collieries. This disaster is recounted here because the details of the shaft sealing is believed by the authors of this paper to be the first recorded in such detail. Owned by Messers, Firth, Barber and Company, the Oaks Colliery was situated on the Manchester, Sheffield and Lincolnshire Railway about a mile south of Barnsley. The colliery was ventilated by two furnaces, side by side and fed with fresh air which sent the return air into the upcast shaft some 70 yd from the fires. The total air current descending the downcast pits was 152,000 ft3/min, of which the "working" 135,000 ft 3 (17,000 ft 3 fed the furnaces) was divided into nine main splits. A serious issue of firedamp from a fault at the end of the dip north level was piped to the bottom of the downcast shafts and used for lighting the lamps there. Elsewhere, and certainly on the coal faces or in return airways, safety lamps

233 only were the rule. From the technical viewpoint, The Oaks was considered an efficiently managed mine. The first and most deadly explosion of a series of no fewer than seventeen ignitions took place at about 1:20 p.m. on Wednesday, December 12th, 1866. A loud report was heard throughout the vicinity to a distance of 3 miles. According to the Barnsley Chronicle " t h e convulsion shook the whole neighbourhood as if the earth had been rent by an earthquake." Volumes of dense black smoke and clouds of black dust arose from the pits "like that from a suddenly ignited volcano" [9]. At the pithead the shaken officials hastily examined the headgear. They discovered that the cage in number 2 shaft had been blown away and that the one in number I pit was broken and disconnected from the rope. The winding engine had also suffered some slight damage. But as the smoke continued for several minutes to pour ominously from the downcast shafts, it was principally human life, and not machinery, that the horror striken surface workers thought of. A warning that something serious might be amiss came to a number of the explorers the next morning at about 8:30 a.m. A party of about sixteen under William Sugden, one of the Oaks under deputies, was some 750 yards from the pit bottom at the time. Suddenly the men perceived an unmistakable disturbance to the air current. All the men save Sugden were drawn to safety; as an official he considered it his duty to remain behind. Another deputy, Matthey Haigh, had also noticed the "suck", which he attributed to a slight ignition of gas, and had also given the alarm. It was a few minutes later, at about 9 a.m. and just as a thermometer was being lowered into the shaft, that the pit fired with great violence for the second time. At 7:40 p.m. on the same Thursday, December 13th, a third explosion occurred. Dense black smoke billowed forth from num-

ber 2 pit after " a violent blast of wind" had been felt. Flames and sparks later discharged freely at the surface and it was clear that the mine was well and truly on fire. One of the effects of the explosion was to derange the ventilation hopelessly, the air current now being sucked down number 1 Shaft and the furnace pit. Smoke and sparks continued to be emitted by number 2 throughout the night. Later that day, a further meeting of colliery viewers and the government inspector was held. It was unanimously accepted that the mine probably now contained serious standing fires and that any attempts to examine the underground workings were futile. At this and subsequent meetings a plan emerged for putting out the conflagration. This was essentially to stop up the shafts so as to exclude all air, yet to revive the pumps to prevent the whole colliery from flooding. From 4:45 a.m. on Saturday, December 15th, to 3.20 a.m. on Tuesday, December 18th, no fewer than fourteen fresh explosions shook the Oaks Colliery. Some were very slight or at only one of the shafts; others were violent and issued from two or three pits. Filling operations could clearly not be delayed. On December 17th, the first load of soil and stone was tipped into the furnace shaft, and on the following afternoon the filling of number 1 commenced. A speciallyconstructed scaffold or platform, was lowered on the shaft guides down number 2 between January 7th and 9th 1867 to a point just below the Melton coal. Here it was suspended and loads of clay were cast down upon it. Piercing the platform's center and extending up to the bank was a 10 in. malleable iron pipe, from which gas could escape and which permitted measurements of pressure, temperature and so on, to be periodically made. In fact, readings of the barometer and pressure gauge were recorded hourly from January 30th, to November 5th, at which time clearing of the spoil from the pits began. The authors of this paper stated earlier that

234 when a mine manager commences the sealing of an area, he must also plan the reopening of such an area, if it is expedient to do so. The reader must therefore note a "platform was lowered" so that the reopening would be easier.

The Wilberg Mine (1984) The fire at the Wilberg Mine in the State of Utah started on December 19th, 1984, apparently caused by either a compressor or a diesel front-end loader catching fire. Twenty seven people lost their lives in the fire. By December 23rd 1984, the fire had developed to such an extent that the mine was abandoned for three days. During these three days the fire overran a large part of the mine and it eventually had to be sealed at the adit entrances. The Wilberg Mine supplied coal to the Hunter Power Station, a 1350 MV facility near Castle Dale. During 1984 its output amounted to approximately 2:2 million tons, but is was planned to increase this figure to 2.5 million tons during 1985. The Wilberg production infrastructure consisted of two 500 ft longwalls panels with Hemscheit shields and Eickhoff shearers, two Joy 12 CM continuous miner sections, and one Joy 14 CM (low seam) continuous miner section. All this equipment is now inside the sealed area of the mine. The mine was ventilated by a single main fan supplying about 500,000 ft3/min to the Underground workings. The fan had a back-up diesel generator which came in automatically when the electrical supply to the fan was interrupted. Access to the underground working was via adits or portals in the side of the mountain. A total of 15 portals existed at the time of the disaster. One served as a fan portal, another as the main beltway while the other 13 served as travelling ways a n d / o r intake airways. The production cycle for all sections con-

sisted of two 8-hour production shifts and one 8-hour maintenance shift. Production shifts rotated on a 2-week cycle. By December 25th, 1984, flames about 150 ft. were seen coming from some of the portals. A start was quickly made with the installation of temporary seals. Construction of temporary seals at all portals was completed by December 30th, 1984. Some of the portals had collapsed due to the heat of the fire and the falls were gunnited, i.e. sprayed with water, to effect the seals. Installation of the permanent seals was completed by January l l t h , 1985. Monitoring of the fire at the Wilberg seals, as well as in the Deer Creek Mine continued. Operations at Deer Creek were consequently stopped, as about 100 p p m of carbon monoxide was monitored in the return airways coming from the worked-out longwall panels. This was due to leakage induced by the Deer Creek fan through the Wilberg workings. When a fire in a mine is out of control, as mentioned in the three previous disasters at Felling colliery, The Oaks and at The Wilberg Mine, the mine has to be sealed. However, the mine management should always bear in mind the enormous loss of reserves to the mining company, and should always plan to reopen the sealed areas.

SOME EXAMPLES OF SEALING UNDERGROUND FIRES Northfield Colliery, South Africa (1969) The fire was discovered on February 5th, 1969 during blasting operations in the righthand barrier of Section 17, at the beginning of the afternoon shift at about 3:40 p.m. This section was prone to methane emissions during the development stage, but gas had only been found once during the previous six months while stopping was taking place. Tests done periodically with a methanometer indi-

235

cated that a large quantity of methane was present high up in the goaf [10]. On the afternoon of February 5th, 1969 no methane was found during the initial examination tests that were done with a flame safety lamp. Ten drill holes were drilled and charged up with Monobel explosives in a new lift in the right-hand barrier road. As no coal cutter was operating in this section the sliping method of blasting was used. Tests for methane were carried out before the 1st, 2rid and 3rd rows of holes were blasted. A miner reported that just before he turned the handle to blast the 3rd row he heard a fall occur in the goal. As the shots went off a bright orange flash was seen at the face being blasted. Flames were seen in the goaf of roadway 6 (see Fig. 11), and fire extinguishers, water and stonedust were used to try to put the flames out. On two occasions everyone present felt that the fire had burnt itself out and that there was no further danger. On the first occasion a fire hose was being used to spray water on the goaf in roadway 6 when an orange flame rolled out into the roadway. The second occasion was during the inspection of the face in roadway 7 by four officials, and again the flame rolled into the roadway. On this occasion it went approximately 9 m along the return side of the brattice before it rolled back into the goaf. On both occasions the flame was preceded by a deep rumbling high in the goaf and a distant bump from either a fall or a methane explosion. Members of the proto team reported that while they were busy working in the section, a sound similar to that made by a waterfall could be heard coming from the goaf. When it became obvious that it was impossible to get the fire under control by the application of water, it was decided to seal the area at points X, Y and Z (Fig. 11). X and Y were in intake roadways, and Z was in the return. All the seals were to be 360 mm-thick walls hitched into the floors and side walls

EO VOLUME OF E IN GOAF IS :

NTAKE AIR AREA: 9,4 rn3 / s

Fig. 11. Plan showing No. 17 Section of Northfield Colliery [10].

914 mm

1"306 mm

I i -'T--~Smm MILDSTEEL DOOR I ~mm [L,57mmx762mm)

HANDLE

--7--

51ram xl3mm FLAT

BAR

--203rnmx 152mmR,S.J. i

_J I

FRONT VIEW

"

~ ' ~ BLOCKS

HANDLE IBmm MILD STEEL DOOR 203 mm x 152 mm

REAR VIEW

Fig. 12. Explosion door [10].

236 with sandbags packed on the in-bye side. Two steel doors, (refer to Fig. 12), of very strong construction were available underground and were to be built into seals Y and Z, to be closed simultaneously once all persons not required to close the doors had been removed from the district. The final building of explosion-proof seals took place after the area had been left for two or three days, during which time regular sampling of the return air from the district had been carried out.

Acadia No. 7 Colliery, Nova Scotia (1946) Nicholson, [11] wrote that mining in the Pictou coalfield has, from early times, been accompanied by underground fires and explosions. Some of these have caused little damage, but many of them have resulted in heavy losses in both life and material. Once such lost area in the Cage and Third seams lay close to the outcrop and was bounded on the east by the Albion workings in these seams and on the west by the inferior coal on the fringes of the basin. In 1935, the Acadia No. 7 Colliery was sunk in the Cage seam to extract the coal left in that area. When the coal in the Cage seam became exhausted in 1940, the Third seam was opened by means of cross-measure tunnels from the slope in the Cage seam, and extraction was carried on in the Third seam to the east, mainly by the longwall method. The Cage seam had been extensively worked from the Cage pit prior to 1880, when an explosion, followed by a fire, caused its abandonment. The workings were never recovered and the fire continued to smoulder for many years and became active as soon as any oxygen penetrated the workings either by cave-ins to the surface or by other ways. The seam to the dip of these abandoned workings was entered by cross-measure drifts from the Third seam. Following the loss of the Cage pit, an opening was made on the Third seam at the

Albion Colliery and workings were driven to the west beneath the fire area in the Cage seam. In 1887, some pillar-drawing work was started in the Third seam workings. Before much of this was done, the pillar falls broke through into the overlying Cage seam workings, which were on fire at that point, and heated materials came into the Third seam working and caused an explosion, followed by a fire, which resulted in the abandonment of the Third seam workings in that area. From 1887 until the opening of No. 7 colliery, these abandoned areas in the Cage and Third seams had not been entered. Although it was known that the workings in the Cage seams near the crop were warm and that they fired whenever and wherever oxygen was admitted, it was not realized that any great amount of residual heat was left at any considerable depth, since no recent workings in the Cage or Third seams in the Albion colliery indicated the presence of such heat. However, as the longwalls in the Third seam from No. 7 colliery approached the original workings in that seam driven from the Albion colliery, it was found that both the coal and the strata overheat were warm and that the strata had at one time been greatly heated and, as a result, had become weakened and fell unless closely supported. It had not been realized until then why the roof in the main counter-level of the No. 7 workings broke up as readily as it did under comparatively shallow cover. The roof in the roadway had broken and fallen and had been ribbed instead of having been cleaned out and re-timbered, as might have been done had an adequate labour force been available. As it was, the roadway was kept in good condition by ribbing and other maintenance until, on May 1st, 1944, a fall occurred in a head between the counter-level and a longwall level at the point marked on Fig. 13. This fall, which broke away just to the dip of a fire stopping fell to such a height that it opened communication with the overlying

237

J

•

,,, ~ - ~ .............. ~ ,, ............... .~,

BROKEN LINES: WORKINGS IN CAGE SEAM SOLID LINES t WORKINGS IN THIRD SEAM

..........

'-.

Fig. 13. Area of fires and location of fire stoppings in Acadia, No. 7 Colliery [11].

Cage seam, Fig. 14. Almost immediately, the resulting hole filled with a light smoke which quite rapidly became dense, and a slight pull was noted on the ventilating current through the hole up to the Cage seam. The roof of the head to the dip of the fall was very tender and was supported by skeleton cribs which could not be drawn without extending the fall. In addition, there was

-

practically no room in the head to the dip of the fall in which to build an adequate fire stopping. It was, therefore decided to build a seal across the mouth of the head and to key it into the in-bye rib, and, since the counterlevel had been ribbed to the high side, out-bye the head, it was planned to extend the stopping along the out-bye rib of the counter-level for a distance of 15 ft to cover up a number

-a\Z

STOI~ING.

@ Fig. 14. Head in which fire occurred in Acadia No. 7 Colliery on May 1st, 1944, at point "A" in Fig. 13 [11].

238 of existing cracks and provide a tight seal. To cut the air from the fall as rapidly as possible, it was decided to put in a sand-fill stopping, eighteen inches thick, against the mouth of the head. This was done by flushing in sand between one-inch boards set eighteen inches apart. Because of difficulties in getting the necessary materials to this head, and because of the close timbering at the site of the stopping, the seal was still not complete after the lapse of twenty-seven hours. Then, just before the closure was finished, the whole of the sealed area suddenly burst into flames and enough oxygen was pulled through the uncompleted part of the stopping to permit the wood and coal behind the stopping to burn freely. Apparently, by this time, the original fall communicated with the Cage seam and extended to such a height that a free opening existed between the seams. Very fortunately, just a short time before this fire occurred, a roadway connecting the No. 7 and Albion collieries had been driven between the two slopes in order to provide a more economical transportation system. It so happened, too, that the compressed-air system of the two collieries had been interconnected. It was therefore possible to break the airline near the fire and to use that part of it coming from No. 7 colliery as a water line, while the line coming from the Albion was retained for compressed air. Within a short time after the fire borke out, these changes were made, and water piped in from No. 7 to a manifold at the site of the fire permitted three streams of water to be played on the burning area. By the use of these water lines, it was possible to keep the fire behind the seal under control until the seal itself could be completed. Leakages around the edges of the sand-fill were plugged with moistened Stone dust, which was the most suitable material readily available. The present stopping, owing to its unusual position, was nearly forty feet long and in some places reached a height of fifteen feet.

Because the fire frequently crept over it and had to be driven back by water, a great deal of difficulty was experienced in building the permanent seal. Time after time, the water used to extinguish the fire which had crept over the sand-fill washed out the grout from between the blocks of the permanent stopping. As a consequence of these difficulties, it took seven days to complete the permanent seal. In the mines of the Acadia Coal Company, a special technique has been developed in the building of fire stoppings. They are constructed of six-inch-square softwood blocks, five feet long, all placed as headers and laid in a cement grout. These blocks are not deeply keyed into the roof, ribs, and bottom, but are laid against the surface after all loose material had been dug away. When the block stopping has been built into place, the ribs, roof, and bottom surrounding it are sealed by grouting. This is done by boring holes twelve inches deep and about two feet apart into the surfaces close to the stopping. In these holes, pipes fitted with quick release valves are cemented. The holes are then bored to a depth of two feet through the valves. A mixture of cement and water in the ratio of one part of cement to two and a half parts of water, by weight, is then pumped into the holes. Should the holes encounter cracks through which the cement grout can pass very readily, the mixture is thickened by the addition of hardwood sawdust in such quantity that the easy flow of the grout is stopped. Each hole is pumped to a pressure of 125 pounds or to a lesser pressure if the grout flows very freely away through some crack cut by the hole. The valves are then shut and the grout allowed to set for twenty-four hours. When it is set, the valves are opened and the holes re-bored to a depth of five feet. They are then pumped at that depth to a pressure of 125 pounds, again closed, and the cement permitted to set for a further twenty-four hours. Following this, the holes are drilled to

239

a depth of ten feet and a third and final pumping is carried on. With this final pumping, no hole is considered tight unless it has been p u m p e d to a pressure of at least 125 p.s.i. In special cases, longer holes may be used and s o m e up to fifteen feet in length have been grouted in the vicinity of fire stoppings where the ground had been open. In the case of the fire under review, fiftyfive holes were bored around the stopping, some of them 14 ft in length, and they were p u m p e d to pressures up to 165 pounds per square inch. Two hundred and eighty-five bags of cement were required to close completely the cracks encountered by the holes. The heat behind the stopping had been so intense, apparently, fire was eating its way through some of these cracks, for, when the grout was p u m p e d through a n u m b e r of the roof holes, the water from it, flowing back through some of the cracks in the roof, left them at a scalding temperature. Because it was questionable whether the stopping built at the site of the fire could be completed in time to be effective, or could even be completed at all, it was decided to build a second ring of stoppings, seven in number, to reinforce the stopping being built near the fire. These were built while the main stopping was being constructed and, when both had been completed, the whole area was closed off.

Dominion No. 16 Colliery, New Waterford, Nova Scotia (1952) Frost, [12] writes of a fire in the Dominion No. 16 Colliery which occurred in October 6, 1952 (see Fig. 15). So far as can be ascertained, the fire was first noticed in the roof of No. 7 East Lateral, after a brushing shot had been fired in the pavement. There appears to be no doubt that this shot blew out, igniting a small feeder in the roof. However, in the week preceding the fire,

the mine examiner on four occasions had reported small feeders of gas at the face of the brushing in No. 7 East Lateral. Figure 16 is a diagram of the working place where the shots were fired. The face brushing had been shot down at 3:45 p.m. and cleaned up. Two " h u r d l e screens" had also been erected, one close to the face brushing and the other fifteen feet from the face. Three holes were bored in the pavement in order to level off the high side of the roadway. Figure 16 shows the direction and location of the holes. Holes No. 1 and 2, each of which was charged with 6 ounces of Monobel No. 7, were fired without incident. The brushers were stowing the stone from the first two shots, and as the outside hurdle screen was interfering with the removal of the stone, it was taken down. At about 5.30 p.m. the high side hole was charged with 9 ounces of Monobel No. 7 and fired. When the workmen went back to the face, the face of the brushings was on fire. It must therefore, be assumed that the shot blew out and ignited a small gas feeder at the face. During the active period, the flames travelled out the level a distance or nearly 150 feet. However at 6:30 p.m. the fire was reported out. The brushing was loaded into boxes, and the vicinity of the fire was heavily stone-dusted. However, at 12:45 a.m. the fire again broke out in the roof of the level and it was 3:15., or approximately 2 1 / 2 hours, before it was extinguished. However, as a precaution, the mine was kept idle on the 7 a.m. to 3 p.m. shift, on October 7th. As conditions in the affected area appeared to be normal during the early part of the day, it was thought possible to work the mine on the afternoon shift. A very careful inspection was carried out of the section between 11:30 a.m. and 1:00 p.m. on October 7th. Temperature readings taken in all cracks in the roof and sides

240

_OI~I_CB9£ _o_~z-~-",~

DOM ,NO15CCLLY WORKED OUTAREA

/ 0 C~

4TL4RT I

SCALE I'= I000 FT 0,500

2OO0

4O00

I

SCALE OF FEET

Fig. 15. Phelan seam, Dom. No. 1 Colliery [12]. HIGH

FACE0 F - ~ . l'IM / -" ROOFm.~i~ ~,~I I / I

SIDE

i_ I~4"~ ~ -r.~

~IL~¢-~--~ ~7;" r~ ~-~ ~.71

Fig. 16. Cross-sectionAB [12].

•

.....

/

241

showed that the average temperature of the strata was 7 6 ° F . The highest temperature noted was 78 ° F, and, as there was no evidence of drying in the roof or sides, it was concluded that the fire had been completely extinguished and orders were given to work the afternoon shift. The officials who had examined the fire area had no sooner reached the surface than word was received from the mine that the fire had again broken out at 2:00 p.m. This third outbreak was not extinguished until 3:00 p.m. In the meantime, the orders to work were rescinded and preparations were made to provide boring equipment to bore long holes in the roof of the top lateral because it was apparent b y this time that gas was burning in cracks at some point over the roadway, and it was though it could be extinguished b y the application of water at that point. However, in order to prevent a flash from finding its way downhill into the wastes through the roof cracks (see Fig. 17), it was decided to bore a number of vertical holes on the line of the low side rib of the roadway and apply water under pressure to cool off the strata. NIGH SIDE BAGS OF"---,-~ STONEDUST I

\,

FACEROOF BRUSHING

{

7

BORENOLESI

!

~

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Fig. 17. Cross-section CD [121

''"

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~

This was done, and three vertical holes were bored on the low side of the roadway, approximately three feet apart, to a depth of 6 ft and close to the brushing face of the level. Water was applied to these holes to cool off the strata and, as the roof strata was cracked, this water found its way down into the waste at the back of the face conveyor line. During this period, diamond-drill holes were bored to the high and low side of the roadway to strike the high side rib of the coal, close to the brushing face, above the high side pack and, on the low side, over the waste in line with the brushing face. These holes were set at angles of approximately 34 ° and 23 ° to the horizontal and reached a vertical height of 18 ft and 20 ft respectively. A third hole was drilled in the center of the roadway at an angle of 31 ° to the horizontal, so as to strike a large crack in the roof about 3 ft from the brushing face. This hole reached a depth of 20 ft and a height of approximately 15 ft in the roof strata. Water was applied to these holes also b u t since the strata were badly broken 'did not reach very far into the roof. During this period there was much concern over the possibility of an explosive mixture gathering in a space which existed along the high side coal rib and above the high side roadway pack (Fig. 17). In order to prevent an accumulation of gas, packing of this space with stonedust was started. At 10:30 p.m. on October 7th, the fire again broke out in the centre of the roadway and lasted for a period of two minutes, being extinguished mainly by blowing carbon dioxide into the fire and cooling off the strata with water. In an attempt to smother the fire and to prevent air from seeping through the cracks in the roof and sides, stonedust was mixed into a paste and all the cracks were plastered over. This in some measure helped to delay the formation of an explosive mixture along

242 the high side rib until the stonedust packing had been completed. The fire was inactive from 10:35 p.m. on October 7th until it flashed at 1:45 p.m. on October 8th, a period of 15 hours and 10 minutes. This time it flashed in the center of the place and lasted about a minute. As the water applied to the center hole was ineffective due to the broken character of the roof, it was decided to insert a one-inch pipe into this hole to its full depth. However, due to the movement of the broken strata, the pipe could only be inserted to a depth of 12 ft. When water was turned into this pipe, it forced the burning gases down through the cracks in the roof, into the center of the roadway. This flash occurred at 2:15 p.m. and lasted an appreciable time. As long as the water was forced into this hole, the fire continued to burn strongly along the roof and high side rib. In spite of the application of water to the flames, burning continued until the water was turned off and the fire extinguished with CO 2 extinguishers. This clearly indicated that the gas was burning high up in the strata, and that the application of water to the seat of the fire might force the flame into the waste with disastrous results. Under these circumstances, the officials in contact with the underground operation decided that is was not possible to extinguish fire by cooling off the strata, and that it would be necessary to seal off the section. The fire again broke out at 4:05 p.m. and 4:50 p.m., and from this time on it broke out at frequent intervals, of which a record of time was not kept. An inspection of the area, to decide on the steps to follow in sealing of the fire, was carried out. It was decided to seal off the east side of the mine. Preparations were started immediately to build fire seals in No. 10 East, 9 East, 8 East levels, and in the material road leading from No. 7 East lateral to No. 7 level (see Fig. 18).

The stoppings were to be made of tightly packed stonedust bags, filled with stonedust, to a depth of 6 feet, with 6 ft by 6 ft openings to be left in the stoppings in No. 10 East and No. 7 East for closure. In front of the stonedust stoppings, a sand seal approximately 12 inches in depth, behind a double-play thickness of board, was to be built. Included in each stopping was a sampling pipe 3 / 4 in. in diameter and 20 ft long (Fig. 19). Every effort was made to speed up the building of the stonedust stoppings, but is was not until Friday, October 10th, at 5:30 a.m., that the stoppings were sufficiently complete to permit closure. No. 8 and No. 9 levels were completely sealed, while No. 10 and No. 7 had 6 ft by 6 ft openings left in them to permit an uninterrupted flow of air through the section during the fire-fighting operations. The only effective medium for putting out the flashes of flame as they appeared was by blowing CO2 on them. The burning gases, as they appeared, would cover long stretches of the roadway and would sometimes burn in isolated patches away from the cracks. Water used by itself had little or no effect on these flames. On October 9th, during the 7 a.m. to 3 p.m. shift, flashes occurred at frequent intervals, but were not of long duration. These flashes continued with increasing frequency throughout the afternoon shift and up to the time of withdrawal of the firefighting crews at 5.30 a.m. on October 10th. At 5.30 a.m., orders were given to seal off the openings simultaneously in No. 10 and No. 7 stopings, and telephonic communication between these points permitted each crew to know how work was progressing at the other stopping. In No. 7 lateral, the water hoses used in fire fighting were left running and the carbon dioxide cylinders were turned on near the face to hold back the fire while No. 7 stopping was closed.

243

Fig. 18. Part plan showing East side of Dominion No. 16 Colliery and location of fire stoppings [12].

The closing was successfully completed at 6.30 a.m. and all the men were withdrawn. The power was then cut off the mine. The fan ventilating the east side of the mine was stopped and the speed of the west side fan was reduced to give about half the normal ventilation. On October 12th at 1.00 a.m., after a rest period of approximately 36 hours, the east side fan was restarted with a reduced volume and only 10,000 ftB/min was circulated through the main air courses of the east side of the mine. At 9:30 a.m. on October 12th, officials of the company, accompanied by mine rescue crews, entered the mine to inspect the fire seals and found that No. 7 stopping (see Fig.

18) had been blown out. Samples were taken and the condition of the outside end of No. 7 lateral was examined. The lateral appeared to be in good condition a n d had not been seriously affected by the explosion. Other than the blown stopping, there was little evidence of violence. The stoppings in No. 8, 9 and 10 levels were examined and found to be intact, indicating that the disturbance had taken place only at the upper end of the section. Before leaving the mine, the stopping in No. 7 material road was lightly repaired by the officials who conducted the examination. At 4:00 a.m. on October 14th, the east side fan was again started, preparatory to an in-

244 55~.

GROUTING HOLES.

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Fig. 19. Dominion No. 16 Colliery fire stoppings built in No. 7, 8, 9 and 10 East levels [12].

spection of the mine, and 10,000 f t ~ / m i n of air was circulated through the east side of the mine. At approximately 10:00 a.m. an inspection party again entered the mine. This inspection indicated that there had been no further disturbance. Samples were taken and the blown out section of No. 7 stopping was permanently repaired by filling in the opening with bags of stonedust to a depth of 13 ft. Samples taken on October 12th and 14th, as well as all subsequent samples, showed no trace of carbon monoxide. However, the first samples at 10:35 a.m., drawn off on October 14th through the sampling pipe in No. 7 stopping before the stopping was tightened

up, showed a concentration of 16.05% of C H 4 , 0.40% C O 2 and 15.15% of 0 2. A second sample, taken at 2:45 p.m., showed that the C H 4 at the sampling point had increased to 49.70%, with 0.50% CO 2 and that the O 2 content had dropped to 10.95%, indicating that there was no fire in No. 7 East Lateral, where it was assumed the explosion had occurred. U n d e r these conditions, it was decided to work the west side of the mine, and it was opened for work on October 28th. Preparations were made to tighten all the east side fire stoppings by cement grouting around them to prevent air leakage through the strata surrounding the stoppings, in order to establish an inert blanket over the whole area.

245

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Ir V

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Fig. 20. Dominion No. 16 Colliery fire stoppings built in No. 7, 8, 9 and 10 East level [12].

During the grouting of the stoppings, there was a steady increase in the CO2 content of the samples taken from No. 8 stopping. This increase reached a maximum of 3.10% on December 7th. However, with the high concentration CH 4 and the low oxygen content, it was apparent that insofar as No. 8 was concerned, no active fire existed. In spite of the groutings, the stoppings were "breathing" with every change of the barometer, and an inert atmosphere was not being built up with satisfactory speed behind the stoppings. Therefore, in order to maintain a negative pressure on the stoppings, a plywood stopping was built on the outside of every stopping except No. 7. A fan was installed in the stopping and so arranged that, when the fan was running, it would produce a suction on the stonedust and sand stopping in the level (Fig. 20). In this way, an endeavour was made to maintain an even, negative pressure on all the stoppings so as to reduce the outward leakage at No. 7 stopping and to assist in drawing downhill the inert blanket which already existed in No. 7 and No. 8 levels. No. 7 stopping, however, continued to leak off CH 4 at approximately 60 ft3/min. As the ground in the location in which No. 7 stopping was built was severely broken, the tightening of this stopping presented quite a seri-

ous problem and was only accomplished with extreme difficulty. Although the grouting around No. 7 stopping reduced the leakage of C H 4 t o about 35 ft3/min, the stopping was still not tight enough to permit a sufficiently rapid building-up of the inert blanket in the section below No. 8 level. In order, therefore, to limit as far as possible the amount of C H 4 coming off No. 7, it was decided to apply a positive pressure against this stopping. A plywood stopping was therefore built in front of No. 7 at a distance of approximately 3 ft, and a blower fan installed with the discharge of the fan blowing through the plywood stopping onto No. 7. The plywood stopping was completed on December 22nd and the fan, which was started on December 23rd, produced a positive pressure of 2 in. of water gauge against the front of the main stopping. This naturally reduced the leakage and assisted in the buildup of the inert blanket behind the stopping. Between December 24th and 26th, there was a sharp drop in the barometric pressure, in a period of 48 hours the barometer fell from 30.46 inches to 29.44 inches, a little over one inch. The result of this drop in the barometer and the reduction of the leakage of CH 3 at No. 7 stopping permitted a sharp build-up of C H 4 in No. 9 and No. 10. By

246

January 1st, the CH 4 content at No. 10 stopping had risen to 12.06% and the 0 2 had dropped to 7.8%. With this analysis, it was clear that any fire that may have existed was definitely out. It was decided to re-open the east side of the mine. This particular fire has been detailed in order that the reader obtain an insight into the steps taken to fight what appeared initially to be a simple straighforward fire. That it was eventually controlled in the above manner, indicates a measure of the professionalism of the personnel of Dominion No. 16 Colliery.

CONCLUSION The authors have deliberately detailed the paper with practical examples of crises in the mining industry in order to aid the mining engineer with steps to be taken in the event of an occurrence of such incidences on his own mine. The examples of sealing discussed in the paper are by no means the only forms to be used, however these have been used successfully in numerous instances by the authors.

REFERENCES 1 D.W. Mitchell and J. Nagy, Problem in fire control in coal mines. Conf. on the Underground Mining Environment. Univ. Missouri, Rolla, MC, Oct. 1971.

2 G. Coles and N.M. Potter, Inflatable air seals for mine roadways. Colliery Guardian, 196 (5039) (Feb. 13, 1958). 3 P. King, A proposed code of practice for the sealing of old workings in collieries. J. Mine Vent. Soc. S. Afr. (May 1982). 4 J.S. Haldane, The shutting off of gob fires in gassy seams. Trans. List. Min. Eng., LXIX (1924). 5 R. Morris, Spontaneous Combustion in Coal Mines and the Interpretation of the State of a Mine Fire Behind the Stoppings. Doctoral Thesis, Univ. Nottingham, England, 1986. 6 H.L. Willett, J. Blunt, A.J.G. Coulshed and F.V. Tideswell, Sealing Off Fires Underground. Inst. Min. Eng., 1962. 7 R. Morris and T. Atkinson, Recommended ventilation techniques to be used in coal mines which are subjected to the adverse mining conditions of a mine fire. In: A.B. Szwilski and M.J. Richards (Eds.), Proc. Int. Symp. Underground Mining Methods and Technology, Nottingham, England, September 8-13, 1986. Elsevier, Amsterdam, 1987, pp. 75-102. 8 A. Duckham and B. Duckham, Great Pit Disasters in Great Britian: 1700 to the Present Day. David and Charles, Newton Abbot, U.K. 1973. 9 Barnsley Chronicle, 13 December, 1866. 10 D.P. Ayliffe, Sealing off an underground fire at Northfield Colliery. Mine Vent. Symp. on Colliery Fires and Explosion Hazards. Johannesburg, March 10th. 1977. 11 R.P. Nicholson, Recent mine fire in Acadia No. 7 Colliery. Can. Min. Metal. Bull. Sept., 1946. 12 L. Frost, Fire in Dominion No. 16 Colliery, New Waterford, Nova Scotia. Ann. Meet. Min. Soc. N. S., Can. Min. Metall. Bull., June 1953. 13 G.W. Grove, F.E. Griffith and H.R. Burdelsky, Procedure used in Fighting and Sealing a Fire in an Ohio Coal Mine and Recovery of the Mine by Air-locking Methods. Bureau of Mines, IC 17418, 1947. 14 D. Coatesworth, Prevention of fires in mines. Colliery Guardian, Nov. 22, 1929.