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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
through two diffuser stones that were spaced 0.08m (3.15") apart. CO 2 injector location varied 
with cage orientation (see figure 4.05 to 4.10 and 4.19). Two tracer gas methods were conducted 
simultaneously: the decay method and the constant injection method. 
All sample concentrations were measured using a Beckman CO 2 Analyzer. CO 2 samples were 
pulled into the Beckman Analyzer using the analyzer pump. Flow through the analyzer was 
monitored and controlled using a flow controller/monitor. The flow was held constant at 469 
mL/min (1.66e-2 ft 3 /min). Flow rate readings were checked using a digital flow meter 
(Humonics 650 Digital Flowmeter) once daily. To produce an effective average flow rate of 100 
mLVmin (3.53e-3 ft 3 /min), at 469 mL/min (1.66e-2 ft 3 /min) of air was pumped out of the cage for 
20 seconds with a 73.8 second waiting period during that background CO 2 concentration was 
measured. All wind tunnel exhaust air was ducted outside of the room. 
The analyzer was calibrated using 1.58 percent and 0.55 percent standard concentrations of CO 2 . 
The analyzer was calibrated by first adjusting the zero dial to match the lower concentration and 
then by adjusting the gain to match the higher concentration. This was done at the beginning of 
each experiment. 
Samples from a bag of standard gas were drawn at the beginning of each day from each of three 
points that corresponded to those used during the decay method (see figure 4.20) and analyzed as 
a means of detecting leaks within the system. A leak was present if the concentration pulled 
through the sampling lines did not correspond to the known concentration within the bag. These 
values were recorded on the strip chart. 
Cage CO 2 concentration was monitored at each cage decay location. Solenoid valves and 
Viewdac computer software were used to control from that cage location each sample was 
drawn. Concentrations were monitored from the beginning of injection until stabilization had 
been reached. Stabilization was defined as the point when two consecutive readings at all three 
decay sampling points were constant. Once stabilization had been reached, data collection from 
the decay sampling points were stopped. At this time constant injection sampling began. 
Constant injection data were recorded for 20 seconds at both the front and back locations of the 
cage with a 73.8 second pause between readings. The constant injection method samples were 
taken at various locations depending on cage orientation (see figures 4.05 to 4.07). 
Once constant injection data had been taken, the decay method began. Soon after starting the 
decay method, the tracer gas flow was stopped. All decay samples were taken sequentially from 
one of three zones. Sequential data collection sequences for the decay method were randomly 
chosen from one of the six possible sequences that could be formed with three numbers. 
Series Set Six and Seven 
In results sets six and seven, tests was conducted with the filter lid on but it was sealed with putty 
around the lip edges so all airflow through the cage had to pass through the filter in the top, or it 
