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Ductless enclosures require filtration efficiency testing to validate performance.
Independent testing, conducted by a consultant and the University of Kansas,
concluded the tested filtration efficiency for acetone, ethanol, isopropyl alcohol,
toluene and hydrochloric acid was excellent. Filtration capacity is defined as a
percentage of the chemical mass adsorbed compared to the total carbon filter weight.
Utilizing analytical instrumentation, the organic vapor filter and acid vapor filter were
both independently tested for filtration efficiency. The solvents and acids listed below
were evaporated at both low and high evaporation rates. Low evaporation rates are
typical in ductless enclosures in order to maximize useful carbon filter life. Both
ethanol and acetone were specifically tested at low evaporation rates of 14ppm and
22ppm, respectively, to simulate real laboratory conditions of chemicals with low
filter capacities. High evaporation rates of 100-462ppm were used for most of the
organic solvents and mineral acid to accelerate the testing process of chemicals with
higher filtration capacity and determine filter saturation and chemical breakthrough.
The testing was designed to assess the filtration efficiency of the filters. As suggested
by carbon manufacturers, carbon filters usually have a 30 percent to 40 percent
filtration capacity of theoretical values for organic chemicals with higher carbon
affinity. The test results show a filtration efficiency of 33-39 percent for chemicals
with higher affinity for organic vapor carbon and directly in line with the 30-40
percent as suggested by carbon manufacturers. Since ethanol has very low filter
capacity, it is not alarming that the filtration efficiency is 17-19 percent; the test
results prove the practical matter of using low quantities of ethanol or any other
chemical with very lower filter capacity. The mineral acid filtration efficiency of
hydrochloric acid approached 83 percent of theoretical value and is attributed to the
chemisorption process of the treated acid filters. To conclude, the filtration efficiency
test data and charts indicate the ductless enclosure filtration was in line with carbon
manufacturer expectations and will provide a safe working environment for
controlled environments.
Exposure Evaporation No. of
3' Paramount
Chemical Mass
Detected Saturation
Filtration Capacity
Filtration
Chemical
Limit
Rate
Filters Carbon Filter Mass
Adsorbed
Breakthrough Concentration Tested Theoretical Efficiency
Acetone
250 ppm
22 ppm
4
13500 grams
153 grams
1-2 ppm
1.1%
2.8%
39%
Ethanol or
1000 ppm
14 ppm
4
13500 grams
32 grams
6-9 ppm
0.3%
1.6%
19%
Ethyl Alcohol
1000 ppm
206 ppm
4
13500 grams
148 grams
6-9 ppm
1.1%
6.3%
17%
Isopropyl Alcohol
400 ppm
462 ppm
4
13500 grams
824 grams
8-11 ppm
6.1%
17.7%
34%
Toluene
100 ppm
155 ppm
4
13500 grams
1317 grams
0.5-1 ppm
9.8%
29.7%
33%
37% Hydrochloric
5 ppm
100 ppm
4
18000 grams
2529 grams
0.5-1 ppm
14.1%
17.0%
83%
Acid
of treated carbon
