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Colliery Engineering

May, 1948

Cause of the explosion

After the explosion a thorough search for contraband in the district was made by two Inspectors of Mines, accompanied by the Manager and undermanager and two representatives of the workmen. Cigarettes, matches and one pocket petrol lighter were found, some in the pockets and clothing belonging to the persons killed in the explosion, some in tins hidden near the working places, 26 spent matches and three cigarette ends beneath and behind the deputies' kist, and other contraband lying exposed on the floor near the delivery end of the Straight East gate conveyor. The points in the district where contraband was found are marked in Fig. l. All other likely igniting causes of the explosion can be eliminated. No shotfiring was being carried on at the time; in fact, the exploder and shotfiring cable were found stored at the kist, and here the two drillers were discussing with deputy Estell the shots to be fired later by him, when the explosion occurred.

Conclusions. — It was thus concluded that during the night shift of Friday, August 22, 1947, there was an emission of firedamp from the strata below the Hutton Seam, which created an inflammable mixture of firedamp and air on the East face line and the Straight East gate; that shortly before midnight a lucifer match struck about the loading point on the Straight East gate for the purpose of lighting a cigarette ignited this mixture and initiated a very mild firedamp explosion, which developed additional force as it progressed and which was propagated by coal dust along the mechanised roadways, both existing and disused, throughout the district; and that the explosion was finally extinguished by stonedust on the South Heading and the Main Drift.

Matters arising out of the explosion

Coal Dust. — The Hutton Seam in the 4th North District is not a very dry and dusty seam, and wet conditions are met with at times, but the air picks used by the hewers produce coal dust, the finest of which is air-borne and deposited at the return ends of the faces, where the loading points in both conveyor gates were placed. This dust, added to that deposited during coal loading operations, would thus increase the difficulty of maintaining these places constantly in compliance with the Coal Dust General Regulations, 1939.

There was evidence to show that the management were alive to the importance of dealing with the coal dust at these points. On August 16, 40 bags (4 tons) of shale stonedust were spread in the district, and after the roadways had been cleaned up on the nights of August 19 and 20, a further 40 bags of stonedust were spread throughout the roadways, including the two loading gates, on the following night of August 21; but it is to be noted that subsequent to the treatment the Straight East face had been worked on the first shift and the 2nd East face on the second and third shifts; and the cleaners-up were just about commencing their work in both gates when the explosion occurred.

Four days after the explosion, nineteen samples of the dust on the roadways in the district were collected by an Inspector of Mines, and the details of the results of the analyses of these samples are given in Appendix II. Admittedly, in view of the blast which had swept the district these results do not represent the conditions obtaining before the explosion, but they indicate that the floor of the conveyor roadways as a whole was in doubtful compliance with the Regulations at the time. However that may be, the disquieting fact remains that a coal dust explosion swept throughout all the existing and disused conveyor roadways in the district, with the contrasting difference that neither of the conveyor faces nor the handworked faces and roadways were affected; and this exemplifies the additional hazard from coaldust brought about by mechanised mining. Furthermore, a sample of the coal dust ground from the Hutton Seam was found on test for inflammability at the Research and Testing Branch at Sheffield to require 69 per cent, total incombustible matter content to prevent inflammation, as compared with the 65 per cent, minimum required for this seam by the Regulations.

The stonedust in use was ground at the colliery from shale from the underground workings and a sample tested at Sheffield for fractionation and dispersability was found satisfactory. The accumulations of dust apparently rich in coaly matter found on the floor after the explosion in all the disused conveyor gates indicate that these roads should have been cleaned up more thoroughly. In this connection it should be pointed out that No. 3 of the Coal Dust Regulations 1939, in requiring the taking of such measures "for the prevention, suppression, collection and removal of coal dust and for treating it with incombustible dust or in any other manner approved" includes "every road or part of a road which is accessible" and that No. 7, in calling for the systematic clearing of the dust on the floor of every conveyor road, includes "the space beneath the conveyor."

The arrangements in respect of frequency of treatment in the 4th North District of the working roadways in the district were good up to a point, but it may well have been that after two coaling shifts had been worked there since it had been last treated the 2nd East gate was not up to the required standard.

Dust sampling had been carried out in accordance with the Coal Dust Regulations, but monthly sampling on conveyor roadways, especially in the vicinity of the loading point, where the conditions can deteriorate considerably in the course of a loading shift, clearly gives no real guide to the position in respect of coal dust. Under the existing Regulations conveyor roadways are not necessarily sampled each calendar month ; and therefore, in effect, treatment is decided on the result of a visual inspection. It is true that in many instances where very dusty conditions prevail the treatment is systematic, but this may well be not sufficient, and managers should make it a rule to have these roadways sampled at very frequent intervals to provide themselves with a truer picture, of the position and so enable them to decide on the extent and frequency of treatment necessary to ensure compliance at all times with the Regulations.

In this connection, however, it is necessary to point out the danger of exposed layers of coal dust. Experiments carried out at the Research and Testing Branch with a highly inflammable coal dust (similar to the Hutton Seam) have established that a mild explosion, initiated by an igniting source of low violence — the conditions which obtained in this explosion — may be propagated by a coal dust which it raises from a surface layer only 4/100ths of an inch thick, even where the coal dust rests on a stonedust deposit nine times its own weight; and this result was obtained on separate tests with three different types of stonedust. This danger can be countered only by the frequent application of stonedust in small amounts. There is no immediate remedy other than the continual cleaning up and application of stonedust at these places, except that the amount of breakage and spillage of the coal while being conveyed and transferred should be reduced to a minimum; and shrouding the delivery and transfer points, and the use of water sprays, should be adopted more generally. But there is no doubt that the only solution (known at present) to the problem lies in the application of water for the suppression of coal dust at the source either in the form of infusion of the coal face, wet cutting or spraying; including, where used, the fitting of water feed to air picks, which is now a practicable proposition. The chain type of conveyor used in 4th North District undoubtedly created additional coal dust, due to the grinding action of the chain on the conveyor pans and to the escape at the pan joints of some of the dust on to the roadways.

Searching of Workmen. — It is doubtful if safety lamps were legally required in any part of this mine, but in any event Section 35 of the Act was applied in its entirety to all sections or districts in which safety lamps were in use, including the 4th North District, as a voluntary precaution by the management; and the standard selective system, with a quarterly general search (which was last carried out throughout the mine on July 28), had been in force since 1941.

The general arrangements for searching have since been checked and found satisfactory, but the usual complications arising from "mixed" lights were present in respect of the Morrison North shaft, where the 4th North District workmen using safety lamps intermingled with other workmen of the open light areas. This difficulty was overcome by fixing warning notice boards along the haulage road leading to the 4th North District, beyond which open lights and contraband were prohibited, and many of the workmen were searched at this point by the overmen, who were responsible generally for searching all the main shifts of workmen at the mine.

The method of searching was clearly much too perfunctory in respect of the 4th North District, but admittedly no degree of searching can be really effective without the co-operation of the workmen concerned. In this instance, it is difficult to avoid drawing the conclusion that there was connivance in this matter of smoking between the deputies and the workmen. This deplorable state of things was certainly not consistent with the high standard of safety and discipline which has always been the aim of the management of this group, and this lack of discipline in the 4th North District can be attributed to the "mixed light" conditions.

Ventilation Arrangements. — The single cloth on the Straight East gate to separate the main intake from the North Heading return airway was bad practice and not in compliance with No. 10 (1) (b) of the new Ventilation General Regulations which came into force on August 1 last. Arrangements for splitting the air were practically completed and this would have cut out the North Heading as an airway, but owing to its proximity to the main intake this connection with the return airway should have been dispensed with at a much earlier stage in the development of the district. It is true the Wembley connection had, meanwhile, established the ventilation of the 2nd East face and the other inbye faces, but it had the effect of placing the Straight East between two very heavily regulated airways and any disturbance of the cloth would therefore have a more serious effect on the ventilation of this part of the district; and this aspect of the position does not appear to have been fully realised by the officials. Admittedly, the cloth was found apparently unaffected by the explosion, but it may, nevertheless, have had some bearing on the occurrence of firedamp in this part of the district. The uncertain character of the regulating arrangement at the Wembley connection is also open to criticism. The availability of an abundant supply of fresh air (due to the proximity of the district to the upcast shaft) doubtless accounted for the fact that canvas cloths only were in use for coursing the air current around the district.

Observations and recommendations

(1) The disquieting feature of this explosion was the ready propagation of the flame by coal dust along roadways on which conveyors had either been used or were in use; and there seems little doubt from the evidence left by the explosion that after having been initiated by firedamp it received its main "kick-off" by a coal dust explosion about the loading point on the 2nd East gate. The treatment of coal dust on conveyor roadways in seams where the coal is friable and the natural conditions are dry, so maintained as to be at all times in compliance with the Coal Dust Regulations, is admittedly a difficult problem and one for which the only effective remedy is prevention of dust at the source by means of water. It was therefore recommended that more active steps should be taken at the more dusty collieries to adopt this method in one or more of its different forms at the coal face. These measures are now being taken at many collieries more especially in South Wales, in an endeavour to reduce the hazard from pneumokoniosis, and in curtailing the explosion hazard from coal dust they serve a dual purpose in health and safety.

(2) The danger from coal dust on disused roadways was demonstrated by this explosion and this stressed the necessity for adequate treatment of such roads so long as they remained accessible, as required by the Coal Dust Regulations ; also, when these roads become untravellable, they should either be sealed off or otherwise protected by a substantial barrage of stone dust at each end.

(3) In view of the increased hazard from coal dust brought about by mechanised mining, it was further recommended that in respect of No. 10 of the Coal Dust Regulations the modification Order of 1939 made under the Defence Regulations, 1939, be revoked to allow the minimum percentages of incombustible matter laid down by the Schedule to Regulation 3 to have full application in the case of coals having a volatile matter content exceeding 27 per cent.

(4) The igniting cause of this explosion can, in the last analysis, be attributed to "mixed light" conditions, and it was consequently recommended that unless the different sections of workmen are completely segregated from the surface inbye the use of open lights should be prohibited in any mine where safety lamps have been introduced into any part (other than as a temporary precaution).

(5) The potential danger of an emission of firedamp from the intervening strata due to the concurrent working of a lower seam or seams needs to be emphasised and a careful watch should be kept for such a contingency, especially in that part of the workings overlying the abutment areas of coal ribs in the lower working, to enable suitable precautions to be taken in time.

(6) The searching of persons for contraband should be made compulsory in all mines or parts of mines in which safety lamps are used, whether or not they are required by the Coal Mines Act, 1911.

(7) Lastly, the question of inculcating a safety-lamp outlook amongst the miners of North West and Mid Durham in particular remains to be tackled. Many of these men have at some time or other worked under open-light conditions, and following a change of mine or the later adoption of safety lamps at mines previously on open lights, they find it difficult to give up old and ingrained habits of smoking while at work; hence their apparent indifference to, and disregard of, rules prohibiting the taking of contraband below ground. It is a sad reflection on Durham that four explosions of firedamp, each involving loss of life, which have occurred in the county during the past eighteen months have been due to contraband and in the case of a fifth explosion, in 1944, probably due to sparking at coal-face switchgear, contraband was found on the body of the victim.