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Ventilation Design Handbook on Animal Research Facilities Using Static Microisolators 
Series Set Base 
Carbon dioxide (at least 99.8 percent pure, bone dry) was injected into the cage near the bedding 
at a rate of 1 L/min through two diffuser stones spaced 0.08m (3.15”) apart. The injection rates 
were calibrated using a digital flow meter (Humonics 650 Digital Flowmeter). The injection rate 
was monitored continuously with a Gilmont (model 1260) calibrated flowmeter with an accuracy 
of +/- 2 percent. The CO 2 was injected at locations that allowed enough distance to mix well with 
the cage air before it was sampled at the cage exhaust area. The injection locations were also 
determined with smoke tests and are presented in figures 4.05 to 4.07. 
Air was sampled from two sampling tubes at different locations in the cage to determine CO 2 
content of air exhausting from and air entering into the cage as discussed above. The cage 
airflow was allowed to stabilize for ten minutes before samples were drawn. Sampling rate was 1 
L/min at each location but samples were not drawn from both locations at the same time: a two 
minute minimum stabilization time was allowed between sampling the front and back locations 
of the cage. Consequently, at all sampling times, 1 L/min of CO 2 was injected into the cage and 1 
L/min of air / CO 2 mixture was removed from the cage by the sampling system. Sampling air was 
drawn from the cage with a SKC Airchek Sampler pump and the flow rate was checked against 
the Gilmont (model 1260) flowmeter prior to and during the experiment. Sampling was taken 
through tubes with five uniformly distributed holes to obtain an average CO 2 concentration over 
a distance since the concentration varies with location, figure 4.18. CO 2 concentration also varied 
slightly over time so the samples were drawn for five minutes into a gas sampling bag (Tedlar, 
polyvinyl fluoride), then the concentration in the bag was measured to determine the average 
concentration over the five sampling locations and over the five minute period. Three bags of gas 
samples were taken at the air exiting location and one at the entering air conditions. The same 
sampling procedure was used as for the exhaust air. CO 2 levels in the gas sampling bags were 
measured with a Beckman LB2 carbon dioxide infrared gas analyzer (Beckman Instruments, 
Inc.). The analyzer calibration was compared to two certified gases (0.55 percent and 1.58 
percent CO 2 ) prior to each use. Before the bags were used again they were emptied using a 
vacuum pump to remove any accumulated CO 2 . The tubing system going into the analyzer was 
checked for leaks before any concentration readings were taken. The analyzer was calibrated by 
first adjusting the instrument zero dial to match the lower concentration and then by adjusting the 
gain to match the higher concentration. 
To monitor the possibility of CO 2 buildup in the test room, a CO 2 analyzer (Fuji Electric model 
ZFP5YA31) was periodically turned on and background CO 2 concentrations were taken. 
Series Sets One and Two 
The same injection/sampling procedures as followed in series set base were maintained for series 
set one, but for series set two, that considered SF6 as the tracer gas, the procedures were 
somewhat different. 
