|
|
|
|
|
 |
 |
|||
V. - GENERAL OBSERVATIONS
In describing the ventilation I pointed out that the quantity of air circulating this 160 yards long Plough Face had gradually fallen from the time the face started until three weeks before the explosion when, in the return airway, it was measured at 1,232 c.f.m. (1 .58 per cent, of the total quantity entering the undersea workings of the Low Main Seam) with a firedamp content of 0. 25 per cent. As no steps had been taken to counteract the diminution, it may well be that the quantity of air circulating at the time of the explosion was even less than that which had last been ascertained by measurement.
The chief reason for the reduction in quantity was that, owing to exhaustion of the Hutton Seam, face room in the Low Main Seam was rapidly expanded despite the fact that the quantities reaching the farthest inbye faces, including the Plough Face, were not more than marginal due to restrictions in and losses between the main airways. The management, who were fully aware of the state of affairs, unfortunately did not take any immediate action with regard to the diminishing air quantities, but awaited a proposed installation of inbye booster fans as a short term remedy until a more permanent solution, involving the provision of new and larger airways, could be carried out.
As regards the ventilation of the Plough Face in particular, the position was further aggravated by leakage between its intake and return airways due to failure to provide effective means of separation between them, contrary to the requirements of Regulation 10 of the Coal Mines (Ventilation) General Regulations, 1947: there being only one door provided to the east of, and only one brattice screen to the west of, the intake at stenton 24, and the two doors east of the return in stenton 20 being set so that they opened with, instead of against, the pressure of the ventilation. Thus, the ventilation of the Plough Face was such that there was little if any margin for contingencies and the management's acceptance of the conditions, which they had inspected and which were shown in the records of ventilation, is difficult to understand. If their standards were based on the quality of the air as shown by its firedamp content - and such seems to have been the case - then clearly the fact escaped them that no margin was available for dealing with an extra emission of firedamp, which could and should have been anticipated under the system of working. Firedamp determinations required by the Ventilation Regulations should never be taken as the sole criterion. The under officials, including the deputies, were lax because they failed to ensure that effective means of separation between intake and return were provided and maintained. If full use had been made of the available ventilation, the chances of an explosion taking place would have been materially reduced, because the volume of firedamp involved was not large.
The only evidence of firedamp having been produced in the Plough Face was that obtained from the statutory record of the monthly determinations, but this information and that relating to air quantities was not made available to the under officials and deputies concerned. Such vital details are not the prerogative of managements. If under officials and deputies are supplied with them they will be encouraged to take a fuller and keener interest in the subject and its problems. This vitally important first line of defence against explosion would thereby be materially strengthened.
The face had travelled some 34 yards from the back rib and the individual wastes between the strip packs had started to fall: hence the nether roof spanning the solid sides was reaching that stage when it would fracture and settle on the packs, the normal and well known effect with such a system of working and one which often gives rise to a sudden increase in the emission of firedamp. As this was a retreating face with solid sides, there was no avenue of escape for the firedamp in such an eventuality other than by entering the air current travelling the face and so being carried away in the return air. In his report on the circumstances attending the explosion which occurred at Easington Colliery, County Durham, on the 29th May, 1951, H.M. Chief Inspector of Mines rightly drew attention to this feature of retreating systems as normally practised in this country and recommended that means whereby such firedamp could be drained off should be investigated. This was a face to which the recommendation applied, and I feel that if a means of drainage had been provided this explosion would not have occurred.
Coal dust blown from the face and its neighbourhood may have assisted the spread of the explosion away from the face. However, as the flame died out and only slight blast was felt, the first explosion failed to establish a propagating coal dust explosion in the intake airway. That the dust cloud raised was inadequate, in quantity or composition to do so, was due in part to the mild character of the original firedamp explosion and in part to the absence of coal from the belt conveyor. A propagating coal dust explosion was not established in the return airway, undoubtedly because of the inert dust conditions existing there in compliance with the Coal Mines General Regulations (Precautions Against Coal Dust), 1939. In the second explosion it is likely that coal dust played a similar or perhaps slightly larger part in its propagation along the intake airway, but again there is no evidence to suggest that conditions favourable to establishing a propagating coal dust explosion had been set up. Therefore, while it is uncertain how far this explosion would have propagated had there been no stone dust barrier, it is worthy of record that the explosion did in fact stop at, or very near, the barrier and that despite the very mild explosion the barrier was satisfactorily destroyed and a substantial amount of its stone dust was dispersed.
I have analysed in some detail the occurrence with a view to assessing the part played by barriers as a defence in limiting the spread of explosion, but I must stress the greater importance of prevention, viz, adequate ventilation constantly maintained and high standards in clearing up coal dust and in stone dusting. Stone dust barriers can play an important part in limiting the spread of an explosion, but it should be clearly understood that they are a last line of defence and are not an alternative to the classical requirements of prevention, suppression, collection, removal and treatment of coal dust.
This explosion has strongly emphasised the inherent dangers of light alloys and hence it is necessary that research into this problem should continue. Moreover, until any particular alloy is proved to be incapable of giving rise to incendive sparking, its use in mines should be limited to those places where inflammable gas is not a hazard, and I recommend accordingly.
Contains public sector information licensed under the 
