> It also makes the point I have trouble getting people to understand--that heavier than air does not mean put the ventilation exhaust at the floor! Once airborne and mixed well with air, vapors will disperse and will not resettle quickly.. It's why heavy chlorinated solvents like the Freons end up in the stratosphere.
This is an important point. I heard a recent discussion with a PhD chemist who intuitively assumed that acetone and chloroform would move differently in the lab atmosphere. After all, he said, acetone is lighter than air (it isn't - it's vapor density is around 2) and chloroform isn't. My guess is that this sort of ad hoc reasoning is common among chemists who haven't had the occasion to think through macro properties of the chemicals they work with.
Ralph Stuart, CIH
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