Evaluation of a one-way airflow system in an animal room based on counts of airborne dust particles and bacteria and measurements of ammonia levels.

Air cleanliness in the working area of an animal room equipped with a conventional turbulent flow air distribution systems was compared with that in a similar room fitted with a one-way-flow air distribution system; in this, the supply air flowed from the working area through the racks of cages and was removed from the exhaust side. Before the introduction of animals, the air in the working and exhaust areas of both rooms was ascertained to be Class 100. With animals in situ, however, whereas in the turbulent airflow room both the workspace and exhaust air reached about Class 10,000 (with particle counts, bacterial counts and ammonia levels being almost the same) in the one-way-flow room, the air in the work space only went up to about Class 1000. With the addition of sliding doors or curtains in front of the rack in the one-way-flow room the work space air was maintained at Class 100 with almost no dust particles over 1 microns in size, airborne bacteria or ammonia being detectable. A comparison of all factors measured showed that whereas in the turbulent flow room the contamination of the work space air was 91% of that of the exhaust air, in the one-way-flow room it was only 47%, with curtains added this was reduced to 7% and with sliding doors to only 2%. In the latter case, contamination levels increased markedly on both sides during and immediately after cage changing, but recovered to the pre-cage changing levels within 30 min in the personnel working area and within 60 min on the exhaust side.