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July, 1939

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Recent regulations call for the provision of suitable fire-fighting equipment at the machine-got coal face, and when a coalcutting machine is in operation it is especially stressed that means to deal with any likely ignition of gas shall be provided either on the machine or at suitable intervals along the working lace.

The provision of a suitable type of extinguisher and whether it shall, or can, be attached to the coalcutter presents a problem. In the majority of seams there is little clearance for the cutter and certainly orthodox cutter design leaves little room for the attachment of a fire extinguisher of practical size. On the other hand, no statement is made as to what constitutes a suitable interval along the coal face for the placing of extinguishers; and the most essential part about first-aid fire-fighting is to have the extinguisher on the spot and in operation within the first few seconds of the outbreak. The ideal solution would be the provision for carrying a suitable extinguisher in a specially-designed recess on the coalcutter, and it may be that coalcutter manufacturers have such an arrangement in mind for future machines.

Apart from the position chosen for extinguishers at the coal face, opinion is by no means unanimous as to the most suitable type of fire-fighting appliance to instal. In the past, fires in the "cut" have been extinguished simply by throwing shovelfuls of gummings into the outbreaks, and based on this idea some collieries have provided their machine men with bags of stone dust. In spite of the apparent difficulty of propelling it under, or into, the "cut," the writer knows of several cases where such stone dust has been successfully used to extinguish an outbreak of fire.

Under the new regulations it is very doubtful if a sack would be termed a "proper container" for sand or stone dust, while to fit a sand box to an ordinary cutter would be almost impossible and not altogether wise from the mechanical point of view.

Portable extinguishers

Under the regulations there are four suitable types of portable extinguishers, viz., water, carbon dioxide, foam, and dry powder. Bracketed, for the sake of convenience, with water, is the soda-acid type of extinguisher, as the same remarks apply. Types of equipment liable to give off poisonous or noxious fumes when operated are expressly excluded, this ruling out carbon-tetrachloride and methyl-bromide extinguishers. The soda-acid extinguisher is simple to operate and cheap to recharge, also the jet produced is capable of penetrating loose burning material; it has the further advantage of being produced in a variety of shapes, i.e., cylindrical or conical and with or without a flat base. Installed at a coal face equipped with compressed air machines such an extinguisher should be cheap and efficient. The same remarks apply to an extinguisher charged with water only and expelled by a built-in pump, a drawback in this case being that manual effort is required to operate the pump, a possible gain being that in this type there is no need to expel the whole of the charge at once. It might be mentioned that in some cases the water-charged pump-operated extinguishers are simply carbon-tetrachloride extinguishers filled with water instead of the liquid that gives them their name. Should it be desired to experiment along such lines, old carbon-tetrachloride extinguishers should not he used as the mixture of water with the original charge sets up corrosive acids. Also it should be made clear on the labels that such extinguishers are charged with water only and must not be used on any electrical gear.

Electrically driven machinery

The possibility of the operator receiving an electrical shock through the use of an extinguisher on, say, a faulty trailing cable or plug-end, renders the use of a water or soda-acid extinguisher, at a face, worked by electrically driven machines, unwise to say the least. This leaves carbon-dioxide, foam and dry powder extinguishers as suitable alternatives. The use of carbon-dioxide as a fire-fighting medium in conjunction with coalcutters is not new. Various ideas have been suggested and tried out in the past. One idea was to have a stream of carbon-dioxide constantly fed into the "cut," but apart from the expense of such a system being excessive, the outlet nozzle is very liable to freeze-up and choke. A modification of this idea is to use instead of a cylinder of carbon-dioxide under pressure, a box containing frozen carbon-dioxide, the gas being driven off on evaporation.

The standard portable carbon-dioxide extinguisher simply consists of a steel cylinder, or bottle, containing carbon-dioxide under high pressure, a suitable control valve, and a length of high-pressure rubber tubing terminating in a fibre wide-mouthed nozzle. Recently the writer carried out a number of tests with such extinguishers on a layout of bricks and wooden sheeting designed to represent as far as possible a 5 ft. undercut in a coal face. The normal ventilating current, it is true, was lacking, but it was thought that fire itself would produce almost the same degree of air flow as occurs under the average undercut. The actual fire consisted of coke and waste soaked in petrol. As would be expected this mixture burnt very fiercely, but was extinguished in just as long as it took to walk from one end of the "cut" to the other, the nozzle being placed just under the "cut." A second test was made in which the fire had been allowed to burn for some little time; the carbon-dioxide extinguisher was again applied and the flames quickly extinguished. The sheeting was then removed, thus opening-up the "cut," and the fire examined; as was anticipated, a certain amount of the coke and the remainder of the waste smouldered freely, proving that to obtain the full benefit of carbon-dioxide as a fire extinguishing medium it is very necessary for it to be undisturbed by ventilation. Should it be decided that the most likely type of fire to be met with under the "cut" would be of a gaseous nature with little or no chance of solid matter being involved, then, providing reasonable sized cylinders are used, carbon-dioxide extinguishers should receive careful consideration. Carbon-dioxide is, of course, a complete insulator and can be used freely on any electrical gear. It is also non-toxic and can safely be used underground.

Foam extinguishers

Foam as a coal-face fire-extinguishing medium has several advantages but also one big disadvantage. A jet from a foam extinguisher can be played on live electrical gear, from a reasonable distance, two yards, and no fumes are produced; the foam is neutral to any substance and an expansion ratio of at least eight to one is obtained, i.e. , a one-gallon foam extinguisher will produce eight gallons of foam, and the bubbles are distended with carbon-dioxide. The disadvantage foam possesses compared with water or a jet from a soda-acid extinguisher is its lack of penetrating power when required to extinguish a fire under a "cut" containing a lot of fine, loose material. On the other hand it does not require a tremendous amount of foam to fill an undercut for a distance of several yards and so act as a fire barrier. Several colliery concerns in this country are successfully using small foam extinguishers for coal-face fire protection. Compared with carbon-dioxide extinguishers, foam extinguishers can be quickly re-charged at the colliery.

Dry-powder extinguishers require some source of propellant; it can either be carbon-dioxide under pressure or some form of percussion-cap. Up to the present little has been heard of them for coal-face work.