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Ventiiation Design Handbook on Animal Research Facilities Using Static Microisolators 
Figure 3.32 Comparison of Mean Breathing Zone NHj Concentrations (ppm) 
Switching off the change station seems to decrease slightly the CO2 and NH3 concentrations in 
both the cages and the room for the radial and low induction supplies. The slot diffuser shows a 
small increase in both CO2 and NH3 concentrations in the cages, although the room values show 
a large decrease. This indicates the difficulty in making generalizations because the effect of 
making a change is very dependent on the case under consideration. 
The change station produces a strong airflow upwards when active (see figure 3.33), which acts 
to mix dirty air from the cages with the fresh air from the supplies. 
