It was natural that Stephenson should devote his attention to the causes of these deplorable accidents, and to the means by which they might, if possible, be prevented. His daily occupation led him to think much and deeply on the subject. As engine-wright of a colliery so extensive as that of Killingworth, where there were nearly 160 miles of gallery excavation, in which he personally superintended the working of inclined planes, along which the coals were sent to the pit entrance, he was necessarily very often under ground, and brought face to face with the dangers of fire-damp. From fissures in the roofs of the galleries carbureted hydrogen gas was constantly flowing; and in some of the more dangerous places it might be heard escaping from the crevices of the coal with a hissing noise. Ventilation, firing, and all conceivable modes of drawing out the foul air had been tried, while the more dangerous parts of the galleries were built up. Still the danger could not be wholly prevented. The miners must necessarily guide their steps through the extensive underground ways with lighted lamps or candles, the naked flame of which, coming in contact with the inflammable air, daily exposed them and their fellow-workers in the pit to the risk of death in one of its most dreadful forms. One day in the year 1814, a workman hurried into Stephenson's cottage with the startling information that the deepest main of the colliery was on fire! He immediately hastened to the pit-head, about a hundred yards off, whither the women and children of the colliery were running, with wildness and terror depicted in every face. In a commanding voice, Stephenson ordered the engine-man to lower him down the shaft in the corve. There was danger, it might be death, before him, but he must go. He was soon at the bottom and in the midst of the men, who were paralyzed at the danger which threatened the lives of all in the pit. Leaping from the corve on its touching the ground, he called out, "Are there six men among you who have the courage to follow me? If so, come, and we will put the fire out." The Killingworth pitmen had the most perfect confidence in their engine-wright, and they readily volunteered to follow him. Silence succeeded the frantic tumult of the previous minute, and the men set to work with a will. In every mine, bricks, mortar, and tools enough are at hand, and by Stephenson's direction the materials were forthwith carried to the required spot, where, in a very short time, a wall was raised at the entrance to the main, he himself taking the most active part in the work. The atmospheric air was by this means excluded, the fire was extinguished, most of the people in the pit were saved from death, and the mine was preserved.