Patent ID: 7014674

Claim:
A biological safety cabinet having a makeup air inlet comprising: a) a work chamber having an air inlet and a contaminated air discharge opening; b) a fan enclosure having an exhaust port; c) a conduit extending from said contaminated air discharge opening to said fan enclosure, said conduit including a makeup air inlet; d) a first HEPA filter downstream of said contaminated air outlet and said air inlet and upstream of said fan enclosure; and e) a fan within said fan enclosure to draw air through said conduit from said contaminated air outlet and said makeup air inlet through said first HEPA filter into said fan enclosure, said fan being the only means for conveying air through said conduit and said first HEPA filter and into said fan enclosure, whereby a positive pressure is created downstream of said fan so that a portion of the air is exhausted through the exhaust port and a portion of the air is returned to the work chamber, said fan being isolated from contaminated air by said first HEPA filter.