(2) Smoke candles are available in a range of sizes and a few colors. They
are sized on the basis of volume (cubic feet) of smoke produced or the duration of
(3) There are other means of generating visible clouds to follow airflow. A
"heavier-than-air" cloud can be generated by placing dry ice in an alcohol bath. A
"lighter-than-air" cloud can be generated by blowing air through a smoldering mixture of
sawdust and oil.
d. Visualization devices are best suited for the evaluation of air-flow patterns
and velocities at exhaust entries and supply outlets.
(1) The industrial hygienist can carry smoke tubes with him as he conducts
surveys or inspections of industrial work areas. The tubes can be used best as an
immediate survey type tool in assessing the ability of a local exhaust system to capture
airborne contaminants. Smoke should be administered close to the hood entry initially,
and gradually the smoke source moved away from the entry to observe the sphere of
containment the exhaust system produces. Larger quantities of smoke can be
generated inside the hood or enclosure to estimate rate of clearance as well as to check
smoke can be used to estimate the force and direction of air from outlets as well as a
qualitative check of the performance of return air outlets.
(2) Titanium tetrachloride is best used by swabbing it along the periphery of
hoods as a check for eddy currents, reverse airflow, and lack of control. Once swabbed
inside a hood, the smoke will persist for several seconds, providing an opportunity for
prolonged observation or photographs.
(3) Smoke candles can be used to estimate clearance rates and
containment of large hoods such as paint spray booths, laboratory hoods, or other high
volume exhaust systems. The hygienist must ensure that the system is operating at
minimal performance levels before igniting a smoke candle to ensure reasonable
removal of the smoke. Smoke candles can be held by forceps and moved across hood
face openings to estimate the air distribution at the face. Colored smoke can be
introduced in ventilation systems to check for leaks.
(4) The fire department should be informed of the use of excessive amounts
of smoke to prevent false alarms.