Asphyxiant gas can smell the odorants, and assigning a different smell to each gas may be impractical. Another difficulty is that most odorants (e.g., the thiols) are chemically reactive. This is not a problem with natural gas intended to be burned as fuel, which is routinely odorized, but a major use of asphyxiants such as nitrogen, helium, argon and krypton is to protect reactive materials from the atmosphere. The dangers of excess concentrations of nontoxic gases has been recognized for centuries within the mining industry. The concept of black damp (or "stythe") reflects an understanding that certain gaseous mixtures could lead to
Bottled gas some variation due to intermolecular force and molecule size compared to an ideal gas. Normal high pressure gas cylinders or bottles will hold from 200 to 400 atmosphere (unit)s. The atmosphere units pressure held by the bottle is equivalent to the number of volumes of standard temperature and pressure of the gas held by the bottle for an ideal gas. Because the contents are under high pressure and are sometimes hazardous, there are special safety regulations for handling bottled gases. These include chaining bottles to prevent falling and breaking, proper ventilation to prevent injury or death in case of leaks