| There are four types of Class II cabinets: Class II Type A1 (formerly designated Type A): It exhausts approximately 30% air back into the laboratory and re circulates the remainder. May have positive pressure contaminated ducts and plenums that are not surrounded by negative pressure plenums. Class II Type A2 (formerly designated Type B3): It exhausts approximately 30% air through a HEPA filter back into the laboratory or to the environment through an external exhaust duct. It has all biologically contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums. Class II Type B1: It exhausts 70% air through a dedicated duct exhausted to the atmosphere after passing through a HEPA filter and re circulates the remainder. It has all contaminated ducts and plenums under negative pressure or surrounded by negative pressure ducts and plenums. Class II Type B2: (sometimes referred to as "total exhaust"): It exhaust 100% air through an exhaust duct after passing through a HEPA filter and contaminated positive pressure plenums must be surrounded by a vacuum. Class III: The Class III cabinet is a totally enclosed ventilated cabinet of airtight construction. Operations within the Class III cabinet are through attached rubber gloves. When in use, the Class III cabinet maintains negative air pressure. Supply air is drawn into the cabinet through HEPA filter. The cabinet exhaust air is filtered by two HEPA filters installed in series, before it is discharged outside the facility. The exhaust fan for the Class III cabinet is generally separate from the exhaust fans of the facilities ventilation system. | 
Pune, Maharashtra, India
