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
Most common words in English Most common words in English Studies that estimate and rank the most common words in English examine texts written in English. Perhaps the most comprehensive such analysis is one that was conducted against the Oxford English Corpus (OEC), a very large collection of texts from around the world that are written in the English language. A "text corpus" is a large collection of written works that are organised in a way that makes such analysis easier. In total, the texts in the Oxford English Corpus contain more than 2 billion words. The OEC includes a wide variety of writing samples,