
92 Forensic Engineering Fundamentals
provide sampling in real time where gravimetric measurements do not. ese optical
devices make use of the scattering of light that interacts with a sensor that produces a
voltage pulse when so excited. ere are a variety of standards both from ASTM and
ASHRAE that pertain to this technology. e third commonly utilized method is a con-
densation nucleus counter that can discern particles as small as 0.01 μm. A clean room
may appear to have very little airborne particulate matter. Typically clean rooms can
have as many as 10
6
particles per
3
. A smoky room may have 10 times the amount of
airborne particles.