Practice question

HEPA, High Efficiency Particulate Air filter, is fibrous mat of randomly arranged borosilicate fibers that captures airborne particles via interception, inertial impaction, and Brownian diffusion. In Class II biosafety cabinets, laminar flow hoods and CO2 incubators, HEPA filters provide 99.97% efficiency for most penetrating particle size of 0.3 micrometer, with even higher capture for smaller and larger particles including bacteria, fungal spores, dust and aerosolized cell fragments. In BSC, intake and exhaust HEPA filters deliver product protection for cultures and personnel protection by filtering exhaust before release to laboratory or outside. Filtration is purely physical; microorganisms trapped on filter matrix remain viable until filter is decontaminated by formaldehyde fumigation or hydrogen peroxide vaporization during cabinet certification. HEPA does not kill microbes by chemistry, does not control humidity, temperature, or gas composition, which are governed by humidifiers and infrared CO2 sensors. Periodic integrity testing using dispersed oil particulate challenge and measurement of face velocity at 100 lfpm ensures protection.