Class I Bio Safety Cabinet is defined as a totally enclosed, ventilated unit of airtight constructions. The front panel can be opened, allowing room air to enter the cabinet, sweep the inner surfaces, and exhaust-out through the duct. A front sash with glove ports may be installed. If glove are installed, air is drawn through a secondary opening equipped with a primary filter. A laboratory hood could be considered a class I BSC, the exhausted air is passed through HEPA filter before released in to the atmosphere. The Cabinet unit is maintained under negative pressure.