(2) Nature of the system. A blast gate system will require more frequent
checks than other systems.
(3) The level of maintenance. Airflow systems can be used to indicate the
need for more frequent and improved maintenance.
4-12. EVALUATING THE PERFORMANCE OF AIRFLOW SYSTEMS
a. There are several reasons for evaluating the performance of air-flow systems.
To assure adequacy of design and performance.
To assure system performance is maintained.
To determine the feasibility of expanding (adding to) the system.
To establish improved design parameters for new systems.
To assure compliance with Federal, state, or other regulations.
b. Just as there is numerous reasons for evaluating air flow systems, there are
differing degrees to which they may need to be evaluated. Instruments and techniques
are available which may provide only a cursory evaluation of a part of the system or an
in-depth survey of the total system.
c. Visualization is a technique that can be employed to make a cursory estimate
of the performance of a local exhaust system. It employs various methods of
generating visual "clouds" which can then be observed to evaluate airflow patterns and
air velocities at exhaust entries and supply outlets. There are several chemical devices
available for use in visualization of a system.
(1) Smoke tubes is a descriptive term applied to glass tubes containing
titanium tetrachloride absorbed on a granular medium. When the ends of the glass tube
are broken and air passes through the tube, the moisture in the air reacts with the
chemical to generate hydrochloric acid "smoke."
CAUTION: Direct inhalation of the "smoke" should be avoided, as it is extremely
irritating to the respiratory system. The same effect can be obtained by
using glass ampules of liquid titanium tetrachloride, available through
standard chemical supply companies.
CAUTION: These fumes and the liquid are corrosive to the skin, and irritating to the
eyes and respiratory system.