Exercises

I. Answer the following questions orally:

1. What is the main classification of modern methods of working coal-seams ?

2. What is a pillar ?

3. Are the pillars extracted?

4. What is referred to as packing?

5. By what means is the roof near the working face supported?

II. Answer the following questions in written form:

1. What does the board and pillar method consist of?

2. What are the general principles of longwall advancing work­ing?

3. What does longwall retreating working consist of?

The ventilation of mines

Amongst the many requirements for the safe and efficient operation of coal-mines none is more important than the provision of adequate ventilation. Ventilation is necessary for the following purposes, namely: (a) diluting gases that are inflammable and noxious so as to render them harmless and removing them; and (b) providing air containing a sufficien­cy of oxygen.

The provision of ventilation adequate in a mine presents engineering and scientific problems of no mean order.¹ In large modern coal-mines it is found necessary² to circulate quan­tities from 300,000 to 600,000 cu. ft. per min. The weight of air circulated by some mine fans is enormous, being three to twelve times larger than the weight of coal produced from the mine.

The atmosphere, the composition of which is practically constant over the whole surface of the earth, is comprised principally of the two gases: oxygen and nitrogen, with small traces of carbon dioxide, moisture and the so-called rare gases (neon, helium, krypton and xenon).

Normal air always contains a certain amount of aqueous vapour.

The atmosphere of a coal-mine is subject to contamination from a variety of causes.³ Amongst these are gases given off from the coal and associated strata, fumes from blasting, the products of oxidation and spontaneous combustion, mine fires, and explosions. In addition oxygen is absorbed by respi­ration, oxidation and other causes.

The term “mine gases” is applied to the gases found in mines which do not form part of the normal atmosphere. The four most important of these are methane or firedamp, carbon dioxide (in percentages in excess of that found in normal atmospheric air), carbon monoxide and sulphuretted hydrogen.

The term firedamp was originally used somewhat loosely to denote any gas or mixture of gases capable of giving rise to an explosion.⁴ Thus the term was applied equally to the natural gas issuing from the strata or to mixtures of that gas with air. Nowadays the term firedamp is confined to the nat­ural gas itself and' mixtures of this gas with air are designat­ed firedamp-air mixtures.

Notes

1. problems of no mean order — немаловажные проблемы (большой важности)

2. it is found necessary — считается необходимым

3. from a variety of causes — по целому ряду причин

4. capable of giving rise to an explosion — способных при­вести к взрыву

Exercises

I. Answer the following questions:

1. What is one of the most important requirements for the safe and efficient operation of the miners?

2. What quantities of air are circulated in modern mines?

3. What is the atmos­phere comprised of?