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
Gas meter prover Gas meter prover A gas meter prover is a device which verifies the accuracy of a gas meter. Provers are typically used in gas meter repair facilities, municipal gas meter shops, and public works shops. Provers work by passing a known volume of air through a meter while monitoring the gas meters register, index, or internal displacement. The prover then displays a proof, a value expressed as a percent which compares the volume of air passed with the volume of air measured to determine the meters accuracy. Since the early 1900s, bell provers have been the most common reference standard