Robert M. Rioux & William A. Elliott, Pennsylvania State University, University Park, PA Fume hoods and laminar flow cabinets are engineering controls that operate under similar principles. Both use a constant flow of air to prevent contamination of the laboratory environment and its inhabitants. Fume hoods prevent hazardous substances from exiting the hood workspace, whereas laminar flow cabinets prevent contaminants from entering the cabinet workspace. Fume hoods are ventilation systems designed to minimize exposure to hazardous vapors, fumes, and particles. A constant flow of air is drawn into the hood opening, limiting the escape of vapors, fumes, and particles, and then is pulled out through the exhaust. Laminar flow cabinets are used to maintain a sterile/clean environment by constantly flowing high-efficiency particulate arrestance (HEPA)-filtered air outwards, minimizing contaminated air entering the cabinet workspace. The HEPA-filtered air reduces the opportunity for harmful chemicals or particles from entering the laboratory. A HEPA filter removes 99.97% or greater of 0.3 µm particles.