Burnley, Lancashire. 22nd March 1962
Mr. F.J. Hartwell, the Senior Principle Scientific Officer in charge of the S.M.R.E. examination summarised the point of ignition and the spread of the explosion. These were based on three facts.
- First, none of the fibrous material had been exposed to flame for more than a very short time.
- Second, at no point in the explosion area was there evidence of slow burning by rich firedamp
- Third there had been a rapid moving of flame accompanied by considerable violence although not so great as would have been expected from the most explosive mixture of firedamp and air with a relatively ‘quiet zone’ between 180 yards and 280 yards outbye of the return gate ripping.
These three facts led to the belief that the explosion originated in the ‘quiet zone’.
The signs were, that the flame had travelled outbye from this area with some violence to a point about 550 yards from the face ripping and possibly less violence inbye to the return gate stable. Here it was probable that there had been added firedamp which would have added to the violence sufficiently to raise some coal dust along the face contributing to the spread of the flame and blast in that direction.
Mr. Hartwell added that there might have been firedamp in the return gate stable and that flame from such an ignition could have blown out onto the face causing a minor coal dust explosion there. If this did occur, flame from the stable could have been propagated down the return gate in a ‘trail’ of firedamp along the roof to a body of firedamp which would have exploded with flame and blast in both directions.
Either possibility would have required a presence in the return gate of a reasonably well mixed volume of firedamp and air. The violence of the explosion was of 8 per cent mixture of gas and air. He estimated that about 2,000 cubic feet of firedamp would have had to be present to have remained undispersed it would have appeared rather quickly.
There was no scientific evidence to show where the firedamp came from but he thought that the most probable place was along the face or the return gate stable. Dr. Willett for the N.C.B. thought that it came from ‘either the sold coal in the vicinity of the stable or the waste’. Mr. Clough, H.M. Divisional Inspector of Mines was firmly of the opinion that it came from waste because neither the face nor in the return gate stable where the strata breaks or displaced coal were there more common signs of a rapid emission.
All were of the opinion that only frictional heat and explosives need be considered as the means of ignition. Mr. Crawford of N.A.C.O.D.S. suggested that the firedamp had been ignited by a frictional spark or thermite reaction as a result of vehicles running uncontrolled down the return gate. No other form of frictional heat was considered as a possible source of ignition.
Mr. J. Gormley for N.U.M. and Mr. Clough were both of the opinion that the shot fired in the return stable was responsible for ignition. Shotfiring operations were in progress when the explosion occurred. Some of the men that died were grouped some little way down the return gate as if sheltering from shotfiring and Madden and Fisk thought that the explosion followed a shot. However if the explosion occurred after a shot the shotfirer must have had time to return the firing key to his pocket and this was found not to be the case.
Mr. Clough thought the ignition was in the stable would have been from the gas from broken coal and that this flame in turn ignited gas passing from the face into the return gate after being emitted from the waste. In these circumstances it was concluded that Halstead would have had time to return the firing key into his pocket and to begin returning to the shotholes before he realised that gas was burning in the stable.
In conclusion the commissioner was not able to give an entirely satisfactory explanation either of the source of the firedamp or of the means of ignition.
It was accepted that the explosion was caused by firedamp present in the return gate. The possibility that this was caused by an interruption of the ventilating current would mean that the ventilation would have to be stopped for two minutes and there is no evidence that this occurred.
In considering the possibility of a rapid emission of firedamp into the return gate stable it was possible that the required explosive mixture could have been formed in the return gate. On ignition the blast ahead of the flame travelling up the return gate could have dispersed and rich firedamp in the stable as to cause it to flame and continue the explosion with the help of coal dust along the face.
Firedamp from the high level in the waste could have been pushed out onto the face but it was felt this would have required a heavy strata movement which would be audible but there was no evidence of this. An emission from the waste could however have taken place quietly had the firedamp been hanging close to the edge of the waste but after the explosion efforts to establish the location of the firedamp were unsuccessful even though probes were pushed up into the waste to a distance of 7 to 8 feet above the seam roof level.
Two other possible sources of firedamp were considered. The first is the return gate ribside. A sudden emission of gas would normally be accompanied by breaks in the coal and surrounding strata. The fact no such breaks were found after the explosion is not however conclusive proof that they did not exist. They could have been near the ribside but concealed by packed material. The second possibility was that there could have been some unplugged methane drainage holes. There were five such holes in the return gate between 200 and 350 yards outbye from the face. Separation of the upper beds resulting from the working of No.5 face could have made rich firedamp available to these holes. Relatively high pressures would have been needed to emit the firedamp but it was not thought that this had occurred.
As to the possible causes of ignition other than explosives and frictional heat all others could be dismissed. The use of explosives have long been the possible cause of ignition of gas and there was ample evidence that there was shot firing in the return gate stable at the time of the explosion. It was clear that shots in the stable were fired from a point immediately outbye the ripping debris. The position in which the body of the shotfirer was found that is on top of the debris, face downwards with his head pointing outbye and with the shotfiring key in his pocket suggests that after the explosion occurred he was either going towards or returning from the stable. At the time Fisk was sheltering in the return gate outbye of the ripping said in evidence that the blast came from the stable.
The commissioner was satisfied that the rate of emission of the firedamp could have been such as to create adverse conditions in the vicinity of the stable between the shotfirers examination and the firing of the shot.
If shot firing had been the cause of the initial explosion, it would have required a flame from firedamp ignited in the stable to communicate with and explode a mixture farther down the gate. The pattern of the blast showed marked signs of movement towards the face does not rule out this possibility as blast from a minor explosion in the return gate stable would have been masked by the effects of a much larger explosion down the gate. This is of course presupposes two explosions and it is supported by a witness who gave evidence that the doors at the Cut-back opened and closed twice.
A great many pieces of foil of the type commonly used in the wrapping of confectionery and chewing tobacco were found in the return gate including some in the ‘quiet zone’ referred to by Hartwell. The S.M.R.E. showed that if this material was laid on rusty steel and struck a glancing blow with a hammer a thermite reaction, capable of igniting firedamp may result. Two pieces of foil found immediately on the outbye side of the zone showed signs of fusion which would result from the thermite reaction. No pieces showing signs of fusion were found in the zone but this was not proof that none was present.
In considering whether the firedamp was ignited by frictional heat it must be remembered that, at the beginning of the shift there were empty tubs at the top of the return gate waiting to be taken down to the return wheel. There was evidence that three supplies lads had been sent down early in the shift to collect tubs and that the rope itself, which was to be lengthened, was found to be fully extended after the explosion.
The rope would not have been drawn by hand down the gate solely for recapping by the mechanic. It was more likely that the supplies lads used it to lower the tubs as far as possible and in this event the tubs would then have been at a point not more than a few yards from the outbye fringe of the zone. Had the tubs run uncontrolled from this point and ignited firedamp either by running over aluminium foil or by violent impact with other material the resulting ignition would not have produced the flame and blast pattern described by Hartwell.
The conclusion was that there was either one explosion predominantly of firedamp in which coal dust played a little part initiated at a point 180 yards outbye of the face by thermite flash from aluminium foil or two explosions, a minor one of firedamp and coal dust initiated by shotfiring in the return gate stable followed almost immediately by a major explosion of a large body of firedamp/air mixture in the return gate.
The danger of sparking from aluminium alloys had been known for some ten years and steps had been taken by the N.C.B. to limit as far as possible the use of equipment made from these alloys to situations underground where the danger of gas was remote.
In view of the evidence from this disaster it was felt that a revision of the instructions, with particular reference to aluminium equipment should be made. Portable drills should certainly be considered since I understand that manufacturers can now produce them constructed of steel or brass.
The use of metallic foils in wrapping confectionery and tobacco is not clearly within the control in the N.C.B. or the mine owners. Dr. Willett in his submission suggested that various associations and organisations in the industry should jointly consider steps which might prevent aluminium foil wrappings from being taken underground.
It was recommended that-
The several associations and organisations in the industry should consider ways.
- “The N.C.B. should undertake further investigations into the effect of borehole drainage on the movement of firedamp where total caving is practised, including the possibility of using lower inclination boreholes aimed at exhausting from the waste cavitation in addition to boreholes into relaxed strata and the continuous monitoring of the firedamp content in return airways from such faces.
- Mangers of collieries should ensure that stables are always ventilated.
- Managers of collieries where shotfiring forms one of the principle face operations should review current shotfiring practice and ensure that not only explosives used are efficiently but that the circumstances are such that the shotfirers are not tempted to disregard the requirements of safety.
- Every effort should be made to hasten the development of a robust automatic firedamp detector which is easily maintained and gives a strident audible alarm.
- The N.C.B. should further revise the restrictions imposed on the use of aluminium based alloys so as to exclude them from the face workings from the return roads and from within 300 yards of the face in all other roadways.