Re: smoke sticks?

[dsimpson@unlnotes01.unl.edu]

Having taught a lab in air sampling that included the determination of air
flow patterns, let me add a few comments:

The dry ice is great in terms of expense and ease of production of smoke,
but my biggest complaint is that the smoke is so cold that it tends to sink
very rapidly, making it a little misleading if the air flow is relatively
slow.  Also, it tends to dissipate quickly once it warms up.

The "sticks" that were mentioned are relatively inexpensive and produce an
almost neutral bouyancy smoke that is abundant enough  to indicate even
moderately fast air flows.  Also I never had a problem with glass breakage
since the ones we used were contained in tygon tubing material  But as
previously indicated a residue can be left and the smoke can be very
irritating to some people.  I have had to excuse people from the lab
because of this at times.

Another very cheap method we used was incense sticks.  They don't produce
much smoke but are very effective around door openings and for determining
relatively slow moving air currents (hoods with the fans turned off, etc).
The smoke rises at first due to temperature but seems to cool quickly to
ambient temperatures.  Again, I suspect some people will react to the
smoke, but I never had it happen.

Finally, another method that I have seen suggested in the literature is
soap bubbles.  A little Karo syrup added to a soap solution produces long
lasting soap bubbles, but I strongly recommend against this method.  When
we have tried it, it leaves a slippery residue and the bubbles tend to be
heavier than air and sink to the ground when other methods indicate no
downward flow.

Dave Simpson
RSO, University of Nebraska - Lincoln
dsimpson1@unl.edu


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