My best training in preventing contamination came from handling thiophenol. The smell is detectable at sub-ppb levels. Everything that touches it has to be immersed in diluted Chlorox before it can leave the hood. Failure to do this will quickly bring down the wrath of one's coworkers (sometimes from quite a distance away). I developed what I term an "airlock mentality" -- the kind of mental habit that keeps you constantly aware of what has touched PhSH, just as someone entering or exiting a spacecraft or submarine is intensely aware of whether or not the airlock is secured. After a while, you can't accidentally remove PhSH-contaminated materials from the hood -- it's just reflexive, automatic.
When I was first learning to handle PhSH I had one day when I had transferred a syringeful into a reaction and successfully cleaned everything afterwards without allowing any detectable traces to escape the hood. Everything seemed fine, and I quit thinking about it for the rest of day. Late at night, after I turned out the light and lay down in bed, I rolled over so that my hands on my pillow were close to my face -- and caught the faintest whiff of thiophenol ! That stuff is really pervasive.
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