Blackdamp (also known as stythe or choke damp), sometimes found in enclosed environments such as mines, sewers, wells, tunnels and ships' holds, is an

asphyxiant An asphyxiant gas, also known as a simple asphyxiant, is a nontoxic or minimally toxic gas which reduces or displaces the normal oxygen concentration in breathing air. Breathing of oxygen-depleted air can lead to death by asphyxiation (suffocation) ...

, reducing the available

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

content of air to a level incapable of sustaining human or animal life. It is not a single gas but a mixture of unbreathable gases left after oxygen is removed from the air; it typically consists of

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and

water vapour Water vapor, water vapour, or aqueous vapor is the gaseous phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Water vapor ...

. The term is etymologically and practically related to terms for other underground mine gases such as fire damp,

white damp Whitedamp is a noxious mixture of gases formed by the combustion of coal, usually in an enclosed environment such as a coal mine. The main, most toxic constituent is carbon monoxide, which causes carbon monoxide poisoning. Hydrogen sulfide, also ca ...

stink damp Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist Carl ...

, and

afterdamp Afterdamp is the toxic mixture of gases left in a mine following an explosion caused by methane-rich firedamp, which itself can initiate a much larger explosion of coal dust. The term is etymologically and practically related to other terms for ...

Etymology

The meaning of "damp" in this term, while nowadays understood to imply humidity, presents evidence of having been separated from this meaning at least by the first decade of the 18th century; the original meaning of "vapor" derives from a Proto-Germanic origin, ''dampaz'', which gave rise to its immediate English predecessor, the Middle Low German ''damp'' (with no record of an Old English intermediary). The proto-Germanic ''dampaz'' gave rise to many other cognates, including the Old High German ''damph'', the Old Norse ''dampi'', and the modern German ''Dampf'', the last of which still translates as "vapor".

History

Choke damp was documented in 37 BC by

Varro Marcus Terentius Varro (116–27 BCE) was a Roman polymath and a prolific author. He is regarded as ancient Rome's greatest scholar, and was described by Petrarch as "the third great light of Rome" (after Virgil and Cicero). He is sometimes call ...

, who stated "Those who keep their grain under ground in the pits which they call ''sirus'' should remove the grain some time after the pits are opened, as it is dangerous to enter them immediately, some people have been suffocated while doing so."

Sources

Blackdamp is encountered in enclosed environments such as mines, sewers, wells, tunnels and ships' holds. It occurs with particular frequency in abandoned or poorly ventilated

coal mine Coal mining is the process of resource extraction, extracting coal from the ground or from a mine. Coal is valued for its Energy value of coal, energy content and since the 1880s has been widely used to Electricity generation, generate electr ...

s. Coal, once exposed to the air of a mine, naturally begins absorbing oxygen and exuding carbon dioxide and water vapor. The amount of blackdamp exuded by a mine varies based on a number of factors, including the temperature (coal releases more carbon dioxide in the warmer months), the amount of exposed coal, and the type of coal, although all mines with exposed coal produce gas.

Hazards

Blackdamp is considered a particularly pernicious type of damp (especially in a historical context), due to its omnipresence where exposed coal is found, and slow onset of symptoms. It produces no obvious odor (unlike the

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is toxic, corrosive, and flammable. Trace amounts in ambient atmosphere have a characteristic foul odor of rotten eggs. Swedish chemist ...

of stinkdamp), is constantly being reintroduced to the air (instead of being released in pockets from actively mined sections), and does not require

combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion ...

in order to be released (unlike

whitedamp Whitedamp is a noxious mixture of gases formed by the combustion of coal, usually in an enclosed environment such as a coal mine. The main, most toxic constituent is carbon monoxide, which causes carbon monoxide poisoning. Hydrogen sulfide, also ca ...

). Many of the initial symptoms of oxygen deprivation (dizziness, light-headedness, drowsiness and poor coordination) are relatively innocuous and can easily be mistaken for simple fatigue, given the physically strenuous job of coal mining. The time between the onset of initial symptoms and the start of frank

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects all the tissues and organs, some more rapidly than others. There are m ...

tion (and rapid unconsciousness) can be as short as seconds. Consequently, if the warning signs are missed, a large number of miners can be rapidly incapacitated in the same short period of time, leaving no one to summon help. In addition to the danger inside the mine, blackdamp can be "exhaled" in large quantities from mines (especially long-abandoned coal mines with few outlets for escaping gas) during sudden changes in atmospheric pressure, potentially causing asphyxiation on the surface.

Disasters

The gas mixture has been responsible for many deaths among underground workers, especially miners—for example, the 1862

Hartley Colliery disaster The Hartley Colliery disaster (also known as the Hartley Pit disaster or Hester Pit disaster) was a coal mining accident in Northumberland, England, that occurred on 16 January 1862 and resulted in the deaths of 204 men and children. The beam o ...

, when 204 men and boys were trapped when the beam of an engine suddenly broke and fell down the single shaft, damaging the ventilation system and blocking it with debris. Despite rescuers' efforts, they could not be reached before they suffocated in the blackdamp atmosphere.

Detection and countermeasures

Historically, the

domestic canary The domestic canary (''Serinus canaria'' forma ''domestica''), often simply known as the canary, is a domesticated form of the wild canary, a small songbird in the finch family originating in the Macaronesian Islands. Over the past 500 years ...

, a conveniently small bird very susceptible to toxic gases, was used as an early warning against carbon monoxide. In active mining operations, the threat from blackdamp is addressed with proper mineshaft ventilation as well as various detection methods, typically using miners'

safety lamp A safety lamp is any of several types of lamp that provides illumination in places such as coal mines where the air may carry coal dust or a build-up of flammable gases, which may explode if ignited, possibly by an electric spark. Until the d ...

s or hand-held electronic gas detectors. The safety lamp is merely a specially designed lantern with a flame that is designed to automatically extinguish itself when oxygen concentration drops to approximately 18% (normal atmospheric concentration of oxygen is c. 21%), before it becomes dangerously low. This detection threshold gives miners an unmistakable warning and allows them to escape before any potentially incapacitating effects are felt.

References

* JS Haldane and JG Priestley, ''Respiration'', Oxford University Press, 2nd ed. (1935)

External links

* http://www.healeyhero.co.uk/rescue/glossary/blackd.htm {{Damp Coal mining Carbon dioxide Nitrogen Gases