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Effectiveness of Germicidal UV Radiation for
Reducing Fungal Contamination within Air-Handler Units
This is a summary of
research completed on the fungi growing on insulation within
air-handling units (AHUs) in an office building and levels of
airborne fungi within the AHUs measured before the use of
germicidal UV lights and again after 4 months of operation.
Fungal contamination in
air-handling units is a problem in many buildings with central
heating, ventilation and air conditioning systems and is a
potential source of contamination for occupied spaces.
Control of fungi in indoor environments has traditionally
focused on source control or air cleaning as methods of
removal. UV irradiation, used to disinfect indoor
environments in hospitals and other healthcare facilities has
various effects on fungi. This investigation was undertaken
to determine the effectiveness of germicidal UV radiation on
reducing fungal contamination within AHUs.
The test facility was a
286,000 square foot building in Tulsa, Oklahoma and was
originally constructed in the 1920’s and completely remodeled
in 1976. Each of the floors of the 4-story facility is
equipped with four primary AHUs and two perimeter units. When
the study was undertaken in 1996, acoustical insulation within
many of the AHUs exhibited abundant mold growth, as did the
drain pans. Preliminary air and insulation samples were
collected to develop the sampling protocol.
Two floors were selected
for investigation; no UV lamps had been installed in these
units. The floors were designated the study floor and the
control floor. In May 1997, air samples and insulation
samples were collected from the eight AHUs. UV lamps were
installed on both floors – each AHU being retrofitted with 10
lamps, installed downstream of the coils. Output of the lamps
was 158 microwatts per square centimeter at 1 meter or 10
microwatts per square centimeter for every 2.54 centimeters of
tube length.
UV lamps on the control
floor were not operated and on the study floor were operated
24/7 throughout the summer and early fall months – while the
AHUs were in the air conditioning mode. Sampling was done
using paired-stage Anderson (N-6) samplers with malt extract
agar for viable fungi and paired Burkard personal samplers for
total spores. Two-minute Anderson and 5-minute Burkard
samples were collected approximately 40 centimeters downstream
of the cooling coils. Pieces of the insulation, approximately
60 square centimeters, were cut from the ductwork directly
opposite the cooling coils. Dominant fungi found within the
AHUs for both air and insulation included Penicillium
corylophyllum, Aspergillus versicolor and a strain of an
unidentified Cladosporium species.
In May, before the UV
lights were initiated, mean concentrations of the total fungi
isolated from the insulation on the two floors were similar in
type and quantity (see table 1), while the total concentration
of viable fungi in the AHUs on the study floor and control
floor in the fall were significantly different.
While this study
indicated that concentrations of fungi were significantly
lower when UV lamps were in use, the study did not show what
stages of fungal growth were most susceptible, nor did it
show whether there was a reduction in spore viability. Also,
the study was not able to show if all of the fungi obtained
fro the AHUs were susceptible to UV light. Asthana and
Tuveson (2) showed that germicidal effects were highly
selective for certain species.
In summary, this study
indicates that germicidal UV irradiation may be an effective
approach for reducing fungal contamination with AHUs. The
use of germicidal UV lamps in AHUs resulted in significantly
lower levels of fungal contamination in insulation lining of
the study floor as opposed to the control floor (see Table
1). Also, there were significantly lower levels of viable and
total airborne fungi than in the study floor units than in the
control floor units when samples were taken during the periods
(see Tables 2 & 3).
Table 1.
Mean
concentrations of fungi isolated from insulation samples in
AHUs before and
after
installation of germicidal UV lamps
|
Fungal taxon isolated |
Concn
(103 CFU/cm2) |
|
Study
floora |
Control
floor |
|
Mayb |
September |
Mayb |
September |
Acremonium
|
|
0.65 (0.65) |
5.81 (5.81) |
23.81 (23.68) |
|
Aspergillus versicolor |
64.87 (38.56)c |
0.96 (0.56)d |
87.58 (32.95) |
1,765.46 (1,702.1)d |
|
Cladosporium (unknown) |
135.28 (50.38) |
8.42 (5.22)d |
22.68 (10.19) |
95.31 (37.74)d |
|
Cladosporium cladosporioides |
0.26 (0.26) |
5.04 (5.04) |
0.65 (0.39) |
228.59 (226.92) |
|
Cladosporium (other) |
|
0.13 (0.13) |
|
1.72 (1.60) |
|
Curvularia |
|
0.05 (0.05) |
|
|
|
Hyalodendron |
4.65 (3.84) |
13.95 (13.95) |
83.96 (83.10) |
109.66 (72.09) |
|
Penicillium |
8.16 (4.35) |
1.05 (0.63) |
9.27 (8.11) |
16.0 (15.59) |
|
Sporothrix |
0.01 (0.01) |
|
|
|
|
Nonsporulating colonies |
0.04 (0.04) |
|
1.94 (1.94) |
|
|
Total |
213.27 (82.53) |
30.51 (24.85) d |
211.89 (10.80) |
2,240.55 (1,622.4) d |
a
UV lamps were used only on the study floor
b
May concentrations were measured before the UV lamps were
turned on
c
Mean (standard error).
d
The concentrations on the control floor and the study floor
were significantly different after the use of germicidal UV
lamps (P < 0.05).
Table
2.
Mean
concentrations of viable airborne fungi during disturbance
sampling within AHUs before and
after
installation of germicidal UV lamps
|
Fungal
taxon isolated |
Concn
(102 CFU/m3) |
|
Study
floora |
Control
floor |
|
Mayb |
September |
Mayb |
September |
Acremonium
|
0.11 (0.10)c |
|
0.16 (0.10) |
0.10 (0.10) |
|
Alternaria |
0.02 (0.01) |
0.01 (0.01) |
0.02 (0.01) |
|
|
Aspergillus |
3.08 (2.58) |
0.91 (0.48)d |
1.89 (0.27) |
7.46 (3.37)d |
|
Cladosporium |
15.64 (8.83) |
1.28 (0.5)d |
14.75 (9.25) |
11.87 (1.99) d |
|
Epicoccum |
|
|
|
0.04 (0.04) |
|
Humicola |
|
|
0.01 (0.01) |
|
|
Hyalodendron |
0.07 (0.03) |
|
0.02 (0.02) |
|
|
Penicillium |
2.18 (0.28) |
0.68 (0.28) d |
5.39 (2.36) |
220.05 (63.06) d |
|
Sporothrix |
0.11 (0.11) |
|
|
|
|
Yeast |
0.10 (0.03) |
0.05 (0.02) |
0.06 (0.03) |
|
|
Nonsporulating |
0.33 (0.09) |
0.06 (0.02) |
0.25 (0.03) |
|
|
Total |
21.65 (11.27) |
2.98 (1.06) d |
22.55 (11.1) |
239.52 (58.55) d |
a
UV
lamps were used only on the study floor
b
May
concentrations were measured before the UV lamps were turned
on
c
Mean (standard error).
d
Concentrations on the control floor and the study floor were
significantly different after the
use
of germicidal UV lamps (P < 0.05).
Table
3.
Concentrations of total airborne fungal spores during
disturbance sampling within AHUs
before
and after installation of germicidal UV lamps
|
Fungal
taxon isolated |
Concn
(103 spores/m3) |
|
Study
floora |
Control
floor |
|
Mayb |
September |
Mayb |
September |
Alternaria
|
0.04 (0.03) c |
|
|
|
|
Cladosporium |
29.54 (8.75) |
5.43 (3.35) d |
19.00 (14.16) d |
68.42 (30.91) d |
|
Penicillium-Aspergillus |
27.49 (20.92) |
6.69 (2.09) d |
5.63 (2.55) |
186.56 (52.51) d |
|
Ascospores |
0.01 (0.01) |
0.01 (0.01) |
0.03 (0.01) |
|
|
Basidiospores |
0.12 (0.06) |
0.04 (0.02) |
0.05 (0.03) |
0.06 (0.04) |
|
Smuts |
0.03 (0.01) |
|
0.01 (0.01) |
0.04 (0.02) |
|
Other |
0.70 (0.25) |
0.24 (0.06) |
0.47 (0.2) |
1.46 (1.09) |
|
Total |
57.92 (25.09) |
12.41 (4.47) d |
25.19 (16.73) |
255.54 (82.27) d |
a
UV
lamps were used only on the study floor
b
May
concentrations were measured before the UV lamps were turned
on
c
Mean (standard error).
d
Concentrations on the control floor and the study floor were
significantly different after
the
use of germicidal UV lamps (P < 0.05). |