Page III - 46 
Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
See Schoeb, Davidson and Lindsey (1982) who indicated that NH3 concentrations above 25 ppm 
promote the growth of infective agents in the respiratory tract of rats in cages. 
In cases 25-27, in which sealed edge cages with particularly poor ventilation are used (the only 
airflow is through the filter), the mean concentration did not rise above 25 ppm until day 7 for 
any of the rooms studied. The “maximum” part of the table shows that the worst cage in the 
room did go over 25 ppm on day 6 (see cases 73, 75, 77 and 78). By day 7 most rooms have at 
least one cage with NH 3 concentrations over 25 ppm. 
As indicated previously, a supply rate of 0.85 cfm (4.01e-4 m 3 /s) per iOOg mouse body weight 
will provide good room conditions up to day 4 or day 5. To go beyond this time before changing 
the bedding the flow rate must be increased to 1.28 cfm (6.04e-4 m 3 /s) per IOOg, although a few 
rooms will be 1 ppm, on average, by day 7. Even increasing to 1.70 cfm (8.02e-4 m 3 /s) per IOOg 
will only extend this to eight days, although even then the maximum NH 3 concentration in the 
breathing zone will rise to 3 ppm and some parts of the room will be noticeably smelly. 
Even at 1.70 cfm (8.02e-4 m 3 /s) per IOOg (20 ACH in the double density rooms) the cages are 
unacceptable by day 8 as the NH 3 concentration is around 25ppm. The very small amount of 
improvement that 20 ACH gives over 15 ACH for the cages makes it unlikely that further 
increases in supply flow rates will change this situation. 
Tables 3.05 and 3.06 are repeats of 3.03 and 3.04 with the cage temperatures increased by 3.0 °C 
(5.4 °F). The increase in temperature reduces the relative humidity as well as the NH 3 generation 
rate leading to lower NH 3 concentrations. 
Increasing the temperature is also recommended by Gordon, Becker and Ali (1997) who indicate 
that the “standard housing temperature of 22.0-24.0 °C (72.0-75.0 °F) is significantly below the 
thermoneutral zone of groups of mice suggesting that they are subjected to varying degrees of 
cold stress under standard housing conditions.” 
The increase in temperature shows the rooms improve in approximately one day. Considering the 
average NH 3 concentration, the rooms are acceptable up to day 7 apart from the very low flow 
rates that fail on day 6. The maximum NH 3 concentration shows an improvement with many 
more rooms acceptable on day 5 with most starting to fail on day 6. 
The cages show nearly a two day improvement with the average cage going over 25 ppm on day 
10, although the worst cages with the maximum NH 3 concentration start to fail in a few rooms on 
day 8, with most failing on day 9. 
Note on use of tables 3.03 to 3.06: 
The tables show mean NH 3 concentrations for the cages and scientist's breathing zone (1.5m- 
1.8m, 4’ 11” - 5’ 11 ”) and the maximum value (in one cage or one spot in the room breathing 
zone). The color coding allows both good (black) and poor (red) cases to be quickly identified. It 
