The sash should never be raised above this level except to add or remove equipment from the hood. Under no circumstances shall a red-tagged hood be used and it is the responsibility of every Researcher, PI, Lab Supervisor, or Instructor to ensure this. When it has been repaired Facilities Division will notify OSEH so the hood can be recertified. The hoods will be inspected when they are installed, or modified and annually thereafter. The adjustable back baffle device in a hood provides more control of the exhaust system by more evenly distributing the air across the face of the hood.
Baffles usually have movable slot openings at both the bottom and top, and sometimes in the center.
The relationship of openings at the top and bottom has a major and deciding role on the manner in which the hood operates. The floor, or work surface sweep, is the zone from the work surface to approximately 8 inches above the floor of the hood. The semi- neutral zone is from the 8 inch height to 20 inches above the work surface. The vortex is from 20 inches above the floor to the top of the chamber. If the baffle slots are not properly adjusted, the vortex can move the generated fumes from the back of the hood to the front.