Nevertheless, we can draw some general conclusions about how long you can expect a HEPA or ULPA filter to last based on field tests Baker has performed with the help of our customers.
But first, here’s a little background.
Filter Loading and Airflow in a Biosafety Cabinet
As filters become “dirty” with particles (known as “loading”), the filter’s resistance to airflow increases. Every biosafety cabinet has an internal fan to compensate for this resistance. Class II Type A1 and A2 biosafety cabinets have a fan and a balancing damper that compensate for loading of both the supply and exhaust filters. The internal fans in Class II Type B1 and B2 cabinets only compensation for supply filter loading. The exhaust filter resistance is actually compensated for by a building’s exhaust system.
Maintaining Constant Airflow as a Biosafety Cabinet Filter Loads
NSF/ANSI Standard 49 requires a biosafety cabinet’s internal fan be capable of handling a 50% decrease in pressure across the filter with no more than a 10% decrease in airflow. (You can test this by applying an artificial load to the suction side of the biosafety cabinet fan and measuring any resulting decrease in airflow.) The best biosafety cabinets incorporate technology that automatically maintains constant airflow even when the filter is loaded by far more than 100%.
Laboratory Field Test Results
Biosafety cabinet filter replacements are expensive, both in terms of the replacement itself and cabinet downtime. Extending filter life is the best way to reduce those costs. We wanted to see how our customers were faring with our airflow management system, StediFLOW, which self-adjusts the fan speed to compensate for filter loading. We compared the resistance, airflow and loading percentage of filters in SterilGARD III cabinets used in laboratories of various air cleanliness.
The data (available upon request) show that after 10 years of use in a typical laboratory setting, neither the supply nor the exhaust filters warranted replacement. Even the cabinet containing the filter with the highest load percentage – an exhaust filter more than 75% loaded – still maintained an acceptable airflow velocity. But the most exciting data is the range of load percentages. Supply filter loads ranged from about 3% to 17%, and exhaust filter load percentages were as low as 5.8%.
Based on this data, the life expectancy of a HEPA or ULPA filter in a cabinet with self-adjusting motor technology would most likely far exceed 10 years.
