Volume I - Section III - Evaluation of Results and Recommendations 
Page III - 69 
3.4 Recommendations 
There were a total of 101 typical animal room and ventilation configurations analyzed by CFD 
simulation and subjected to rigorous quantitative post-processing. The analysis focused on CO 2 
and NH 3 concentrations in the scientist’s breathing zone (4’ 11”- 5’ 11”, 1.5m to 1.8m) and in the 
cages occupied by mice. As stated in section 3.2, the nominal pass/fail limits chosen were 1 ppm 
NH 3 in the breathing zone and 25 ppm NH 3 in the cage. 
The results of the CFD simulations performed in this study show that no particular room layout 
or ventilation system produces consistently good or bad results. Indeed, often improvements in 
the room are accompanied by poorer ventilation in the cages. The CO 2 concentration values are 
representative of any airborne contaminants, whereas the NH3 concentrations that are related to 
the CO 2 concentrations also depend on temperature and relative humidity. 
• The level of CO 2 concentration in the room breathing zone depends on both the flow rate into 
the room and the number of cages, and mice present in the room. Doubling the number of 
cages leads to approximately double the amount of CO 2 . Rooms with low stocking density 
could be operated with lower flow rates; 
• Acceptable day 5 NH3 concentrations are produced by supply flow rates of 0.85cfm (4.01e-4 
m 3 /s) per lOOg body weight of mice (equivalent to 5 ACH for single density racks, 10 ACH 
for double density racks); 
• Acceptable day 6 NH3 concentrations are produced by supply flow rates of around 1.28cfm 
(6.04e-4 m 3 /s) per lOOg body weight of mice (equivalent to 7.5 ACH for single density racks, 
15 ACH for double density racks); 
• Changing bedding every four to five days will produce acceptable rooms (at supply flow 
rates of around 0.85 cfm (4.01e-4 m 3 /s) per lOOg body weight of mice) and acceptable cage 
environments for the mice; 
• Increasing the cage temperature by 3.0 °C (5.4 °F) could extend the period for changing to six 
or seven days, and can provide a better environment for the mice; 
• Ceiling level exhausts often provide poor ventilation for cages, compared with low level 
exhausts; 
• Although increasing the ventilation rate reduces the concentration of contaminants in the 
occupied zone of the room by increased dilution, the same cannot be said for cage 
concentrations. In fact, with single cage density, the cage concentrations of NH3 were seen to 
rise with ventilation rates increasing from 15 to 20 ACH; 
• Higher temperatures in the room and cages reduce the relative humidity, and NH3 generation 
and concentrations. Although this can be achieved by low level exhausts (which consistently 
