Background context for question

When I was young, we'd go fishing. And Dad would put a camper on the back of the truck. One time we came back in after fishing and the camper smelled like rotten eggs. He used that as an opportunity to teach us how some gases are tasteless/odorless. And as a result that sort of rotten egg smell is added as a safety measure.


My question is this: What are those gases that are odorless that then have that rotten egg smell added to them?

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    $\begingroup$ Propane is a colorless, odorless gas. Ethyl mercaptan is added as a safety precaution as an odorant and is commonly called a "rotten egg" smell. wikipedia.org - propane. Similar is done for natural gas, containing mostly methane. $\endgroup$
    – Poutnik
    Dec 27, 2023 at 18:33
  • $\begingroup$ @Poutnik Thanks. There was just enough doubt in my mind that I thought I should ask and make sure. Thanks for giving me the details. I had thought that Propane might have been one of those, but didn't know that natural gas had an additive too. $\endgroup$
    – Epimanes
    Dec 27, 2023 at 18:42
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    $\begingroup$ tert-Butyl thiol is also used as an odorant for natural gas en.wikipedia.org/wiki/Tert-Butylthiol $\endgroup$
    – Waylander
    Dec 27, 2023 at 19:16
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    $\begingroup$ BTW, many natural gas suppliers have "Scratch & Sniff" cards to remind the user of the odor. You can request cards from your local supplier, or ugi.com/forms/request-scratch-sniff-brochures , dominionenergy.com/safety/natural-gas-safety/… and outreach.ngridsafety.com/product/… . Some state a generic "mercaptan"is used. $\endgroup$ Dec 27, 2023 at 20:26
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    $\begingroup$ @Epimanes, relabel and sell as Parfum de Pepé Le Pew, and make a mint... or Symplocarpus foetidus, $\endgroup$ Dec 27, 2023 at 23:27

1 Answer 1


Rotten eggs happen much less frequently than 50-60 years ago because of better hen-consumer refrigeration. Most people today have not had the pleasure of smelling them. H2S and low molecular weight mercaptans [AKA thiols] have distinct more or less unpleasant odors tho at low concentrations they can smell sweet, and we can develop tolerances to many at higher concentrations when they can be deadly. H2S is supposedly the active ingredient in rotten eggs; Methylsulfide CH3SH the active gas in human feces, and thioglycolic acid in eau de skunk.

Manufactured gas, no longer used, was a mix of H2 and CO and is toxic. It was flavored with mercaptan at rather high levels; smelling gas then was almost a death sentence, we were trained to open windows and leave immediately. There was also the explosion hazard. Manufactured gas was replaced by "natural", really fossil fuel, gas that is mostly methane CH4. Methane is odorless, not toxic, but it can be soporific, and it can explode. A warning is still necessary tho it seems to me the odorant is now less noxious and less intense than before [It could be my sense of smell has waned.]. It is to protect from explosion, again evacuate and ventilate. Odorants are added to propane and LPG, I do not know about hydrogen. Perfumes are added to many products to overcome odors or enhance odors and Bitrex is added to some drugs to make them less palatable so it works both ways.

Gases in a laboratory or industrial, even a home, locations can be an unseen danger. They can be invisible and relatively odorless and gases such as nitrogen, carbon dioxide, argon, and low MW freons can displace oxygen in the atmosphere of confined spaces. A person entering such space can quickly become unconscious. Even oxygen can be a problem by making usually nonflammable materials flammable. This can be an under-appreciated aspect of Hazmat or fire situations.

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    $\begingroup$ This is some pretty fascinating context & details to add. Thanks. $\endgroup$
    – Epimanes
    Dec 28, 2023 at 12:42

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