Lum: from hearth to headframe

To most people, a lum is simply a chimney, the passage that carries smoke upward from a fireplace or stove to the open air above a roof. The word is especially common in Scotland and northern England, where it remains everyday vocabulary for something so familiar that few bother with the Latin-derived term chimney in casual speech.

In mining, a lum is the top of a shaft that connects underground workings to the surface. More precisely, it is the collar or mouth of the shaft at ground level, where fresh air enters or foul air exits, depending on whether the lum serves as an intake or return. The lum is where the mine's entire ventilation system begins and ends. If the lum is too small, or clogged by debris, coal dust, or ice, the mine cannot breathe: air cannot flow down to replace the stale, dangerous atmosphere at depth. If it is blocked, the only path for gases and heat to travel is shut off.

The term came naturally. Both a chimney and a mine shaft lum rely on the stack effect, the buoyancy-driven movement of air through an open vertical passage. Heat rising through a chimney creates pressure that pulls fresh air in at the base and sends exhaust up and out the top. In a mine, the temperature difference between the warm depths and the cool surface, combined with the miners' work and any heating equipment, creates natural draft. The lum is the engine intake and exhaust port in one.

Mining engineers refer to different kinds of lums: the downcast lum, through which fresh air descends into the workings; the upcast lum, through which heated, fouled air rises and escapes. A mine must have at least two distinct shafts to create circulation. The efficiency of a lum depends on its diameter, height, and whether it is fitted with furnaces, fans, or other devices to accelerate flow. A well-designed lum can move thousands of cubic feet of air per minute; a neglected or poorly sited lum creates dead zones where gas accumulates and men suffocate.

The word itself has roots in Scots and Northern Middle English, where it was used for chimney long before industrial mining made ventilation a matter of life and death. Mining simply inherited the term and put it to work on a grander and more critical scale. Today, the lum remains a fixture of mining vocabulary, especially in coal-mining regions where the word has never fallen out of use, and where the sight of a tall stone or metal lum rising above the pit headgear is as iconic as the pumps and wheels that once drew water from deep shafts.