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Usually, thiols such as ethanethiol are added to fuel gases to warn the user of a leak. Why is a few percent of ammonia not used instead?

  1. Ammonia is flammable so it will burn to nitrogen and water in the flame.
  2. Ammonia has a strong smell, and causes a stimulation effect which may wake sleeping people in the event of a gas leak.
  3. Ammonia produces no sulfur oxides when it burns (although the usual amount produced with ethanethiol is insignificant).
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    $\begingroup$ Ammonia can be toxic also maybe corrosive. $\endgroup$ – Greg Dec 31 '16 at 6:46
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In principle, you could use ammonia, but there are practical disadvantages.

The sulfur-based odourants are some of the smelliest compounds known and are detectable in very low concentrations. In practice, they are used in concentrations of perhaps 30ppm. Several percents of ammonia would be thousands of times more than this concentration implying greater expense. At this level, the concentration of ammonia would be problematic because of the corrosive nature of certain types of pipe and would probably create other safety concerns (it might even be a direct safety hazard at the concentrations where it is readily detectable by smell).

Typical sulfur-based odourants are detectable at such low concentrations that they are not a direct safety hazard. Nor is there much worry about the combustion products at such low concentrations.

Ammonia is also much more reactive than the typical sulfur-based odourants and would be much more likely to be stripped from the gas during transmission which defeats the purpose.

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  • $\begingroup$ I think I should start a campaign to retain the proper (but deprecated) spelling of sulphur. $\endgroup$ – matt_black Jan 15 '17 at 16:56

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