In some such manner the fire-damp is ignited, and then there follows the fiery blast, which, sweeping through the narrow galleries and passages which constitute the workings, simply licks up the life of the men whom it encounters. Others, in byways and sheltered corners, escaping the burning cloud of flame, are poisoned by the deadly fumes of carbon monoxide which it leaves when its force is spent. While others, perchance the most unfortunate of all, are saved for a time, but, being imprisoned by falls from the roof and walls, die a lingering death of hunger and slow suffocation. A colliery explosion is one of the ghastliest events imaginable, the only relief from which is the noble heroism with which the survivors, from the mine managers to the humblest workmen, crowd round the pit-mouth, eager to risk their own lives for the faint chance of saving some below. Not infrequently these brave volunteers only share the fate of the men they would rescue. Now all that, as I have said, used to be put down to the effect of the fire-damp. But it dawned upon men's minds some years ago that the damage seemed to be out of proportion to the power of the gas. Modern mines are well ventilated by large fans, which impel great volumes of air through all the workings. The air currents are cunningly guided by partitions or "brattices," so that every nook and corner shall be scoured out by the plentiful draught of pure fresh air. Consequently the amount of explosive gas which can collect in any one place is but small. How, then, can so small a volume of gas do so large an amount of damage? Coupled with this was the fact that explosions take place in flour mills, where there is no gas, and experimenters had found in their laboratories that almost any burnable substance, _if ground up finely enough_ and blown into a cloud, would explode. Coal-dust would naturally do this. Indeed anyone throwing the dust from the bottom of the coal-shovel upon a fire will see for himself how, quickly such dust will burn, and, as has been pointed out in an earlier chapter, an explosion is but rapid burning. So the blame was largely transferred from the shoulders of the fire-damp to those of the clouds of coal-dust which collect throughout the workings of a mine. But then a difficulty arose from the fact that there is dust in all mines, yet some districts are quite free from explosions. And such districts are those where there is little or no fire-damp. These two facts seem to be explainable in one way, and in one way only. It must be that the gas first of all explodes feebly, and so, stirring up the dust lying along the roads and passages, prepares the way for the powerful, deadly explosion of coal-dust which follows.