Interesting, thank you! I was surprised by this, as it's the major component of natural gas (as used widely for cooking here), and this has a distinct smell. I

Interesting, thank you! I was surprised by this, as it's the major component of natural gas (as used widely for cooking here), and this has a distinct smell. I went looking however, and discovered that's actually because Ethyl Mercaptan is added specifically to make it detectable by humans. I never realised this, and does indeed explain why it's plausible no-one would have noticed such a large effect.