lum

A lum is the vertical shaft or chimney that carries hot gases and smoke from a furnace, smelter, or mine workings up and away from the operation. In hard rock mining, the lum serves as the primary ventilation outlet, drawing air through underground passages by natural convection created by the temperature difference between the hot lum and the cooler outside air. The term is most common in Scottish and Northern English mining regions, though the structure itself appears wherever ore is processed with heat.

The lum must be tall enough to create adequate draft. A short lum produces weak convection and poor ventilation; operators learned that every additional metre of height substantially improves air flow through the workings below. Historically, lums were built from brick or stone and lined internally with clay or tile to withstand corrosion from acidic furnace gases. Modern lums may use steel casing or ceramic brick, especially where smelting produces particularly corrosive emissions.

Failure and maintenance

Lums are subject to both structural and chemical degradation. The internal surfaces erode from thermal cycling and chemical attack, eventually requiring relining. External damage from wind, frost, or subsidence can compromise the draft and allow fumes to escape into surrounding areas rather than rising through the top opening. A cracked or partially blocked lum reduces ventilation efficiency throughout the entire operation, making it a critical maintenance priority.

The name itself derives from Old English and Scots dialect, where it has meant chimney or flue for centuries. In mining contexts, the lum is distinguished from other ventilation structures by its reliance on natural convection rather than mechanical fans, making it a passive system that operates continuously as long as furnace temperatures remain above ambient.