Wier (1983) describes distribution system design for research facilities that house animals.
Proper distribution of air in the animal rooms is very important. The velocity of air hitting the animals must not be excessive; drafts can cause undesirable effects such as snuffles and pilar erecta (hair movement) on animals. The proper velocity varies with the animals and the types of cages, i.e., whether they are wire or solid "shoe boxes." Other factors -- temperature, humidity, noise, and objectionable ammonia vapors -- may vary greatly between rooms and cage types (Yamauch, Takahaski and Audo, 1965; Bernstein and Drew, 1980).
One style consists of a cage support system that includes an exhaust-air connection to each individual cage, allowing the removal of dander, hair, odors, particulate matter and pathogens without exposing other animals or personnel. This arrangement uses room air for makeup air and keeps cages drier by increasing urine evaporation rates. Rack and cage systems that include both a supply and an exhaust plenum in the rack are also available from laboratory equipment manufacturers. This unit uses room air or a supply air duct for supply air. Exhaust from ventilated cages may require treatment depending on the substances in the air stream.
Supply diffusers and grilles are still widely used as an economical trade-off, but their high induction rate requires that caution be exercised in preventing drafts and cross-contamination in a given room. Such cross-contamination can result in dosed animals contaminating non-dosed (control) animals in the same room. A design in which two supply registers and return grilles are placed high at the end of the room has been found to provide an acceptable solution to the cross-contamination problem at a reasonable cost (Neil, 1982). However, low-level returns do a better job of removing particulates because the density of such materials causes them to settle to the floor... .
The clean/dirty (supply/return) corridor concept is a combination of the containment and barrier designs. In this design, a clean-corridor pressure is maintained sufficiently above the animal-room pressure to cause airflow into the animal-room that may contain pathogenic or toxic test substances. The dirty-corridor pressure is maintained at approximately 0.1 inch of water [gauge] below that in the test rooms. Animals, contaminated material, and personnel exit the animal rooms into the dirty corridor. These pressure differentials can be established and maintained with various levels of sophistication in instrumentation, or, if, the facility has a properly designed air-handling system, by using manual balancing dampers and reading differential-pressure gauges. Manually operated systems must be checked regularly because conditions change, with variables such as supply and exhaust filters becoming loaded with hair.