Occupational Asthma Reference

Hendrick DJ, Sizer KE, Breathing" coal mines and surface asphyxiation from stythe (black damp)., Br Med J, 1992;305:509-510,

Keywords: mine, stythe, asphyxiation, carbon dioxide, case report

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David Hendrick, Newcastle-upon-Tyne David Hendrick

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That disused coal mines "breathe" is well recognised within the mining industry, though the surprisingly close parallel with mammalian breathing may not be so widely appreciated. By contrast, the effect on surface communities living in the path of the expired mine air seems to have attracted scant attention. Though access shafts are often sealed when a coal mine is abandoned, the airways within the mine may remain patent, depending on the degree of subsidence, and a substantial volume of alveolar air (potentially as much as 500 million litres per km2 of shallow mined seam) may retain immediate contact with exposed coal faces, tunnel walls, and pit props. This allows metabolic oxidative processes to continue, thereby removing oxygen and replacing it (partially) with carbon dioxide. The process would be self limiting in the absence of ventilation, but some mines are connected by geological pores of Kohn to a natural positive pressure respirator-the earth's atmosphere. At times of stable weather and high atmospheric pressure fresh air is forced into these mines with a tidal volume which may reach several million litres per kM2, thereby allowing tissue respiration to continue. As atmospheric pressure returns (fairly quickly) to normal the mine expires a similar volume, which consists of its alveolar air mixed with the recently inspired fresh air. Such a mixture may pose little hazard, but when weeks or months later there is a storm and a rapid and profound fall in atmospheric pressure the mine may expire undiluted alveolar air with a dangerously low oxygen content at a forced expiratory volume in one second of several hundred litres per km2. This alveolar air is known locally in north east England as stythe or stythe gas but is more generally called black damp or choke damp-a reflection on the occupational threat it has posed to generations of coal miners. Far less commonly it may threaten overlying communities if it accumulates under impervious layers of rock or clay and then finds access to a limited area on the surface through fissures or faults. Such an event occurred recently in Newcastle upon Tyne.

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