Even with proper selection and usage, a fume hood must be tested on a regular basis to insure that it is maximizing it safety value. The most common and inexpensive form of testing are airflow measurements. This allows an air velocity profile to be obtained for the face (front opening) of the hood and for an average airflow and flow uniformity factor to be calculated. Visual smoke tests are used to supplement the airflow measurements and show overall fume hood containment. There are two guidance documents for chemical fume hood velocities; ANSI/AIHA Z9.5- Lab Ventilation Standard and SEFA 1- Lab Fume Hoods Rec. Practices. These documents are also excellent sources for a wealth of information on lab ventilation and fume hoods and are highly recommended reading for the fume hood manager. ANSI/AIHA recommends a nominal 80-120 feet per minute (fpm) average airflow with 20% uniformity with a maximum average range of 80-150 fpm; SEFA recommends 75-125 fpm (this applies to variable air volume hoods only).
The meeting of the above criteria is a good but not absolute measure of hood containment. ASHRAE 110 is a test method that allows for direct measurement of hood containment by the release of a tracer gas in the hood. It is a more complex and expensive form of testing but yields a wealth of valuable data and allows for optimization of hood containment. An alternative to ASHRAE 110 testing is to perform chemical exposure monitoring on personnel using the fume hood to insure that no overexposures are occurring during the work procedures. While this yields less data on specific hood operation than ASHRAE 110 testing , it does complement the airflow testing and can help document the effectiveness of the fume hood(s). LTS does not provide either of these two forms of testing at the current time.
The fume hood manager should have an established testing frequency for hoods and also ensure that individuals testing the hoods are properly trained, used calibrated equipment, and have a system of quality control and review for their testing data. For these reasons, many facilities use an outside firm to test and certify their fume hoods.