Air Quality

The quality of air delivered to the facility is determined to a large extent by the source of the air and the degree of filtration. The source of the supply air must be selected to avoid contamination with exhaust air from other buildings or the same building, especially the animal faculty, incinerator smokestacks, vehicle exhaust fumes, etc. The quality of filters used for filtering incoming air varies from 85 to 99.97% high-efficiency particulate air (HEPA) filters depending on the type of facility or area of the facility. For example, the air being delivered to rodent barrier facilities and surgery rooms may be HEPA filtered, while the air to other areas of the facility may be filtered with 85 or 95% efficient filters. The need for HEPA air even in rodent barrier facilities is not well documented, and its cost-effectiveness is questionable. Task-directed HEPA filtering, e.g., using HEPA filters on ventilated racks and in cage change cabinets, may be more cost effective than HEPA filtering all the air coming into the facility.

Another use of task-directed HEPA filter air is in "mass air displacement (MAD) clean rooms," similar to but typically at a lower quality to that used in electronic fabrication plants. In MAD rooms, air is recirculated within the room through HEPA filters at volumes sufficient to change the air 150 (most common) to 600 times per hour, depending on the type of system and clean room class desired.34 Fresh air exchanges are superimposed over the recirculated air at a rate similar to that in a conventional room. MAD rooms effectively control the animal's airborne microbial environment, thereby reducing cross-contamination. MAD rooms may be "hard wall" or "soft wall" units, the size of rooms large enough to house multiple cage racks or soft wall units just large enough to house a single cage rack. Recently, there has been an increased interest in using multiple soft wall units in large open warehouse type spaces to gain maximum flexibility at a minimal cost.

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