Fire-setting

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Fire-setting is a method of traditional mining used most commonly from prehistoric times up to the Middle Ages. Fires were set against a rock face to heat the stone, which was then doused with liquid, causing the stone to fracture by thermal shock. Rapid heating causes thermal shock by itself—without subsequent cooling—by producing different degrees of expansion in different parts of the rock (and in other materials). In practice, rapid cooling may or may not have been helpful to produce the desired effect. Some experiments have suggested that the water (or any other liquid) did not have a noticeable effect on the rock, but rather helped the miners' progress by quickly cooling down the area after the fire.^[1][2] This technique was best performed in opencast mines where the smoke and fumes could dissipate safely. The technique was very dangerous in underground workings without adequate ventilation. The method became largely redundant with the growth in use of explosives.

Although fire-setting was frequently used before modern times, it has been used sporadically since then. In some regions of the world, notably Africa and Eurasia, fire-setting continued to be in use until the 19th and 20th centuries.^[3][4] It was used where rock was too hard to drill holes with steel borers for blasting or whenever it was economic because of cheapness of wood.^[3]