Every operation to be carried out underground requires suitable protection and safety devices to safeguard operators from gases that may be there.
Oxygen (O2): in a limited area, often remaining closed for years, lack of oxygen is highly probable. Flammable gases: flammable gases are most likely to be found either due to leaks of underground piping or spillage from ducts nearby.
Carbon oxide (CO): even if generally produced by combustion, this gas can also be found in rooms which have been remained closed for a long time.
Hydrogen sulphide (H2S): it is naturally found in particular in sewages, as it forms by decomposition of organic matters.
O2: both excess and lack of oxygen may cause important diseases, sometimes death.
Inflammable gases: in smaller concentration even than LEL with regard to the volume they explode in presence of a minimum flash source often resulting in serious consequences for people and things.
CO: carbon dioxide is a compressed colourless, odourless, tasteless and poisonous gas. Even short exposures to carbon dioxide may reduce oxygen concentration in brain so the victim falls unconscious and dies.
H2S: colourless gas stands out for its characteristic smell of rotten eggs. A low-concentration exposure causes eye and throat irritation, cough, acceleration of breathing and fluid formation in the respiratory ways. High concentrations kill the olfactory nerve so making impossible to smell its disgusting odour, and may cause unconsciousness in few minutes.