What was Gas Smell?

Reports came in overnight of a gas smell in Perth’s SW suburbs.
What was it? Well, the gas companies say it wasn’t them – and I believe them.

Here’s what I think happened. Both natural gas and LPG are odourless. But this represents a safety hazard, as if there is a gas leak you want people to be able to smell it. So for that reason, a chemical is added to the gases to give it a smell. The chemicals they use for this are mercaptans.

Mercaptans possess the unique quality of being the smelliest chemicals in existence. The human nose can detect them at tiny, tiny concentrations- far too low to present any health concerns.

So people associate the smell of mercaptans with gas (LPG or Natural).

But mercaptans can come from other sources as well, most notably rotting organic matter in anaerobic environments. And the most common place for this is rubbish tips. As putrescible matter (ie food scraps) is bulldozed into the ground it starts decaying anaerobically. This produces mercaptans which make their way up through the soil and into the atmosphere.

Under normal circumstances they get blown away and you never smell them, but if there are the right circumstances – warm weather, still air, and temperature inversions, they can accumulate to the level where you can smell them.

A few days ago Perth was blanketed in a smoke haze, with smoke from as far away as Albany apparently. This was due to a temperature inversion, and I’m betting the same thing has happened in this case.

Is it toxic? In a word, no – these gases have an intense smell, and can be detected by the human nose at very, very low concentrations – far too low to present a toxic hazard

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