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I live in Australia, where both electricity and natural gas are common forms of household energy. An odour is added to the natural gas as a safety precaution since it is otherwise almost undetectable. I haven't been able to find what gas/mixture of gases is used in Australia, with all the sites I've checked just saying "an additive" or "an eggy smell".

The Wikipedia article on natural gas says that both tert-Butylthiol and tetrahydrothiophene can be used as an additive, and the article on tetrahydrothiophene says:

It is also used as an odorant for natural gas, usually in mixtures containing tert-butylthiol.

Whenever I've used natural gas (i.e. burning it for heating or cooking) I've noticed that there is no smell afterwards. Are all the additives completely flammable? Presumably, their combustion products are odourless, but I haven't been able to find any information on that either.

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  • $\begingroup$ Yes, they burn completely and turn into SO2 and whatever else. While most certainly not odorless, SO2 smells much weaker, so we don't feel it at all. $\endgroup$ – Ivan Neretin Nov 26 '16 at 6:44
  • $\begingroup$ The odourants are used in very small quantities as their smells are very intense. But, of course, some is emitted before the natural gas catches fire so there may be some residual smell because of that. This doesn't usually last long as the amounts are very very small. $\endgroup$ – matt_black Nov 26 '16 at 11:23
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On looking it up on Google and a few more places, it turns out that natural gas is primarily methane, along with a few other hydrocarbons. Well, I have found out through some searches online that in the case of propane based fuel, like LPG (Liquid Petroleum Gas) in India, ETHYL MERCAPTAN is a popular option. It's smell is described as a

strongly disagreeable odor that humans can detect in minute concentrations

And that it's smell resembles that of

leeks, onions, durian or cooked cabbage, but is quite distinct.

(source :Wikipedia)

And also, most important point of all, it is highly explosive.

This is what the New Jersey Department of health and safety has to say:

This is what the New Jersey Department of health and safety has to say

(Source : This document)

So yeah, You're right. Based on this example, I think it logically follows that these "additives" are flamable and result in products that are ODOURLESS.

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