In biological safety cabinets (BSC's), fume hoods, and other biocontainment enclosures such as clean benches and pharmaceutical filling stations, air is the principal medium of containment. There is a growing trend to continuously monitor, measure, and control the air to provide optimal containment, reduce energy costs, and to track airflow deterioration to ensure sterility.

Most containment equipment and minienvironments have regular testing and certification of air velocity with portable hand-held anemometers. Many users, however, do not continuously monitor airflow. If a BSC or pharmaceutical filling station fails its routine QC check, there can be expensive consequences for the end user. The user will not know at what point in time the airflow containment failed and the reason for the failure. Pharmaceutical manufacturers and other regulated laboratories need to be especially sensitive to airflow containment failures, as they can result in the disposal of manufactured goods worth thousands of dollars.

Airflow failures can be caused by a blocked or clogged HEPA filter, a failure of the fan or blower, and other equipment issues. Continuous monitoring of aseptic processing areas can alert the user to airflow deterioration immediately rather than waiting for a routine certification check with a portable instrument. An immediate notification of airflow failure allows the user to correct the problem instantly, thus preventing the destruction of valuable research and manufactured goods. Also, continuous monitoring can provide a database if quality control issues arise with FDA inspectors.

FDA aseptic processing guidelines discuss an optimal airflow rate of 90 fpm. The airflow must also be laminar. Thus, it is important to understand if there is any risk of the airflow reversing if the velocity rate changes or if an unforeseen object creates turbulence.

Sensors are now available which will allow for accurate, continuous measurement of airflow at 90 fpm with a linear output in either a voltage or current output. In addition, bi-directional sensors exist which can tell you if the airflow direction has reversed. These sensors are in a price range similar to low differential pressure sensors. The sensor head is mounted remotely, either alone or on a stainless steel rod, with the sensor electronics located typically 1-2 meters away via a thin cable (Photo 1).