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28th April 1883

Sir,

I beg to report that I proceeded to the Ryhope Colliery and inspected at air receiver which exploded on the 1st ultimo ; I also made inquiries regarding the circumstances attending the case generally, and have to report as follows:

The exploded receiver was used as a reservoir for compressed air, which was conveyed to the workings of the colliery for the purpose of working the machinery employed in hauling coal. The air was compressed and discharged into the receiver by means of two steam engines, the air-compressing cylinders being 33 inches diameter, the stroke of the pistons 5 feet, and the number of strokes per minute about twenty-eight. The temperature of the compressing cylinders was reduced by a stream of cold water which passed through chambers surrounding them.

Principal Dimensions of Air Receiver

The exploded air receiver, which was cylindrical and with hemispherical ends was 5 feet 10 inches diameter and about 29 feet long. It was made of 3/8 inch wrought-iron plates and all joints were single lap riveted, the rivets, which were about 13/16 inch diameter, being spaced about 2 inches apart.

The plates are not materially reduced from their original thickness.

The receiver had, I was informed, been in use as such for about 12 years. From its appearance and the nature of the repairs it had undergone it would seem to have been an externally fired steam boiler.

Safety Valves on Air Receiver

All the fittings had been removed from the receiver when I visited the colliery, but there had, I was informed, been attached to it two safety valves 4 inches diameter, which were loaded by lever and weights to 60 lbs. per square inch ; besides these safety valves there were several others loaded to about the same pressure on smaller air receivers in the pit. As these were stated to have been directly connected with the exploded air receiver, being supplied with compressed air from it, the means for preventing over-pressure appear to have been quite sufficient under ordinary circumstances. It is stated that the safety valves were seen to be working on the day of the explosion.

Nature of Explosion

The explosion was caused by the bursting of the external shell of the air receiver, the rupture beginning at an unstrengthened man-hole. It extended across five belts of plating at one end of the receiver, and continued across the hemispherical end at the same extremity. The five belts of plating alluded to were by the force of the explosion blown from their cylindrical shape into one almost flat, and they were almost entirely separated from the remainder of the receiver.

Effects of Explosion

The explosion had evidently been very violent, for besides causing the destruction of the air receiver considerable damage was done to the engine house and other objects in the vicinity. The explosive force also extended down the 10-inch wrought-iron pipe which conveyed the compressed air to the underground workings. About two and a half feet in length of one of these pipes, which was about two hundred and forty fathoms down the shaft, was blown almost entirely flat ; another pipe had a large piece blown out, while one other burst at the weld. At other parts of the shaft the expansion joints of the air pipes were blown out. Besides the above, the explosive force liberated in the shaft did a considerable amount of damage to cage conductions and ventilating brattice.

General Remarks

The bursting pressure of the receiver was, I consider, about 200 lbs. per square inch, and of the small pipes in the shaft a much greater pressure ; it is therefore clear that the explosion of the receiver and pipes was not caused alone by the air compressed by the engine.

The explosion, by which fortunately no person was killed or injured, occurred at about 10.30 p.m. The air-compressing engines had been at work since 5 a.m. on the same day, and the pit was at the in full work. Nothing unusual had, I was informed, occurred on the day, the pit having been on full work the whole time. The man in charge of the air-compressing engines had, I was informed, just oiled the compressing cylinders when the explosion of the air receiver took place. He was stunned by the shock and noise at first, but upon recovering he shut the steam off the engines, and then noticed flames issuing from the receiver. Mr. Routledge, the manager, informed me that he was on the spot about three minutes after the explosion, and saw flames from the exploded receiver extending about 30 feet or 40 feet high. This continued for about half an hour, until they were extinguished by water. Mr. Wanless, colliery engineer, was also on the spot shortly after the explosion, and mentions having seen flames of the same height. The flames issuing from the exploded receiver as it lay wrecked, and which Mr. Routledge and Mr. Wanless observed brought the plates to a red heat, were attributed to the burning of a sediment at the bottom of the receiver, which consisted of coal dust drawn in with the air, together with portions of the lubricant carried by the air from the compressing cylinders.

Mr. Hall, the head manager of the colliery, informed me that until within rather more than 12 months before the explosion the air-compressing cylinders were lubricated by a mixture of animal oil, soft soap, and water, but whilst using this considerable difficulty was experienced owing to the pipes between the compressing cylinders and air receiver becoming choked. In consequence of this the engineer to the colliery at that time suggested the use of a mixture of a mineral oil, soft soap, and water for lubricating the air-compressing cylinders. This was tried for a time, and as the difficulty previously experienced respecting the stoppage of the pipes was not found to occur its use was continued.

On the occasion of my second visit to the colliery to inspect the small exploded pipes the air-compressing engines were at work discharging air into the new air receiver. The pressure of air in it at the time was about 43 lbs. per square inch, and the temperature of the receiver was about 195° Fahrenheit, the increase in the temperature of the air of about 145° being due to the heat evolved in its compression. The discharge pipes from the compressing cylinders were at the time immersed in a tank of cold water for the purpose of experiment. This I believe caused a marked reduction of temperature in the receiver; it is evident that, with the air at a pressure of 60 lbs. and without the pipes immersed in cold water tanks, the temperature of the receiver would be considerably higher than 195° Fahrenheit. I have not, however, been able to ascertain the exact temperature.

Mr. Hall declined to mention the particular name of the oil used, preferring only to state that it was a "mineral" oil. It is well known that there is a very great difference in the qualities of such oils and in the temperatures at which they will flash or give off inflammable vapours. With some the temperatures are very low, and, so far as I am aware, there are few ordinary mineral oils of which the flashing point much exceeds the temperature of 200° Fahrenheit.

If therefore, as is most probable, the flashing point of the oil used for lubricating the compressing cylinders was less than the temperature of the air-compressing cylinders and receiver, the latter would after the lubrication of the former be immediately filled with vapour of the oil. This when mixed with air in the proper proportions forms a powerful explosive, only requiring the presence of a flame to, ignite the gas and cause an explosion.

Difficulty is experienced in deciding how ignition of the mixture could take place. From the description given of the arrangement of the receiver, and the facts which I ascertained, it appears evident that ignition of the inflammable vapour could only take place from inside the receiver. There appear to be two ways in which ignition could occur, viz., (1) by flame arising from the spontaneous combustion of a piece of oily cotton waste or similar substance either left in the receiver or which had entered by the air valves of the compressing cylinders, or (2) by flame arising from the spontaneous combustion of the residuum of oil and coal dust at the bottom of the receiver. I have no reason to think that the latter could take place, and only mention it as the possibility was suggested at the colliery.

I have therefore arrived at the conclusion that the destruction of the receiver was caused by. the explosion of a mixture of the vapour of a mineral oil and atmospheric air, and that the ignition of the vapour was caused by flame arising from the spontaneous combustion of cotton waste or other similar substance inside.

In whatever way the ignition of the vapour of the mineral oil may have taken place, this explosion indicates very clearly that there is very great danger in using mineral oil as a lubricant for air-compressing cylinders.

I have referred to the destruction of air pipes in the shaft : one of the men, it is stated, saw a flash of light in the shaft at the time of the explosion and it is a matter of congratulation that the explosive force did not extend beyond the shaft. Had it been expended in the workings of the colliery a serious. explosion and loss of life would possibly have occurred there, where some hundreds of men were at work.

I should state in conclusion that Mr. Hall, the head manager of the colliery, informed me that the use of the mineral oil for lubricating the compressing cylinders had been discontinued. It is however, to be feared that it is in use for the same purpose at other collieries, the manager or proprietors being as ignorant of the danger as were those in charge of the Ryhope Colliery.

I am, &c.,

(Signed) Thomas J. Richards.

Since writing the above I have carefully experimented with some of the mineral oil kindly supplied me by Mr. Hall's directions as a part of that with which the compressing cylinders were lubricated. I found that it did not give off an inflammable vapour at 208° Fahrenheit, the highest temperature to which, with the appliances at my disposal, I could subject it. It appears, however, likely that the temperature of the compressing cylinders and air receiver was at times considerably in excess of this.

(Initialled) T. J. R.

The Assistant Secretary,

(Marine Department,) Board of Trade.