62k and All,
one thing to consider in all of this, is the performance of the human nose. When trying to detect these odours/fumes one is susceptible to de-sensitization, i.e. the olfactory sensing system slowly 'get's used to' the smell. Like when you splash on your Brut 33 aftershavein the morning, and 5 minutes later you can't smell it, but women are fainting at your feet all day.
We have noticed this a lot when investigating events of oil smell. Crew will return to base and en-route radio in a report of oil smell, then on arrival perhaps 30 mins later, we open the a/c door and get knocked over by the fumes, but the crew by this time are desensitized due to continuous exposure and they say that the smell has almost gone!
My two-penneth,
N1 Vibes