Blackdamp or Stythe.
These names were given originally by miners to a mine atmosphere which had the property of reducing the illuminating power of a candle or a flame safety lamp, or of completely extinguishing such flames, and which could be dangerous to life.
Such an atmosphere, as found in the unventilated parts of a mine, on being analysed is found to contain carbon dioxide, oxygen and nitrogen in abnormal proportions.
Dr. Haldane, by determining the amount of nitrogen required to give the oxygen present a fresh air equivalent, and regarding the remaining nitrogen and carbon dioxide together as blackdamp, eliminated the synonymous use of the names blackdamp and carbon dioxide for atmospheres which are irrespirable and non-supporters of combustion.
The actual composition varies widely from 0.5% to 21% of CO2 together with 99.5% to 79% of nitrogen. As much as 83% of blackdamp has been found in mine air samples. It is important to appreciate that a given accumulation may have a comparatively safe fringe, but that the oxygen content will continue to decrease with depth of penetration. Penetration should not be attempted once the flame safety lamp is extinguished, as death may result.