Class III BSC: Performance Testing Standards

There are several prominent industry accepted standards for performance testing of Class III Biosafety Cabinet in the US.  These standards contain some areas of overlap, and in many cases one standard contains performance related information not contained in the other standards.  The information below provides a brief summary of the highlights as they apply to criteria for US performance testing.  A subsequent blog will address international performance standards.

1. National Sanitation Foundation Standard 49, 2008:

• It is a gas-tight (no leak greater than1x10-7 cc/sec with 1% test gas at 3 inches pressure wg) enclosure with a viewing window that cannot be opened without the use of tools or locks.
• Access for passage of materials into the cabinet is through a dunk tank, that is accessible through the cabinet floor, or double-door pass-through box (e.g., an autoclave, rapid transfer port, pass through chamber)
• Both supply and exhaust air are HEPA filtered on a Class III cabinet. Exhaust air must pass through two HEPA filters, or a HEPA filter and an air incinerator, before discharge to the outdoors.
• Airflow is maintained by an exhaust system exterior to the cabinet, which keeps the cabinet under negative pressure (minimum of 0.5 inches of water gauge.)
• The exhaust fan for the Class III cabinet is generally separate from the exhaust fans of the facility ventilation system.

 2. American Glovebox Society, 2007 :

•  Airflow monitoring: should be provided i.e. magnahelic guage
• Differential pressure is industry specific: maintained at 0.2-1.5 inches wg
• Glovebox flow rate through an open glove port: 125 +/- 25 linear ft/min
• Glove inspections should be performed: no firm guidance on frequency
• Leak detection: internal pressure is stabilized at -1.5 inches wg and temperature, pressure and time are recorded until pressure drops to -0.6 inches.  Leak rate can not exceed 0.5% glovebox volume per hour.
• There should be qualified trainers and operator training.

3.  Laboratory Safety Monograph: A Supplement to NIH Guidelines for Recombinant DNA Research, 1979:

• The Class III biological safety cabinet is a totally enclosed ventilated cabinet of gastight construction.
• Class III cabinet is maintained under negative air pressure of at least 0.5 inches water gage. Supply air is drawn into the cabinet through HEPA filter. The cabinet exhaust air is filtered by two HEPA filters installed in series.
• The exhaust fan for the Class III cabinet is generally separate from the exhaust fans of the facility ventilation system.
• Material transfer through double-door sterilizers and dunk baths with liquid disinfectants.
• Should be certified (i) after a new cabinet has been purchased and installed, but before it is used, (ii) after it has been moved or relocated, and (iii) at least annually.
• Negative pressure inches wg: >0.05
• Leak tightness:  leak rate <1 x 10 ^-5 cc/sec at 3”wg pressure using halide tracer gas
• Small leaks can be detected by soap solution testing
• HEPA certification: annual or as needed above
• Verify and calibrate magnahelic gauge and test audible alarm

Class III BSC:  Best Safety Practices & Engineering

Taken together there are a few recurrent points and statements that reflect best safety practices and engineering.  The Class III Biological Safety Cabinet must be leaktight (this implies very solid construction, durability and seals), and operate at -0.05 " wg relative to the lab.  Exhaust air is filtered through 2 HEPA filters in series, with supply air filtered by 1 HEPA filter.  Alarms should be present to warn the user of BSC failure, and the user should be trained in te correct operation of the unit.  The BSC and its HEPA filters should be field tested annually, but components that are prone to wear (i.e. gloves, gaskets, etc) should be inspected as part of a pre-operational inspection.  As perfromance tests in the field are not codified by NSF 49, recomendations on what types of field testing should be perfromed annually will be provided in a later blog.

References:

1. NSF 49 Class II (Laminar Flow) Biosafety Cabinetry, NSF/ANSI 49-2008,  Edition: 11th

2. Guideline For Gloveboxes, Third Edition AGS-G001, February 2007

3.  Laboratory Safety Monograph: A Supplement to the NIH Guidelines for Recombinant DNA Research, 1979 (PDF)