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Q: Are
ultraviolet (UV) lamps effective in eliminating TB
bacteria from the air?
A: According
to the Center for Disease Control (CDC), UV lamps installed
in the exhaust ducts from the rooms of patients with
infectious tuberculosis were shown to prevent infection
of guinea pigs, which are highly susceptible to tuberculosis.
The CDC also states that the efficacy of UV irradiation
in clinical settings has not been demonstrated, but there
is a theoretical and experiential basis for believing
they are effective.
Q:
I've also heard that UV lamps cause skin cancer and
cataracts. Is this true?
A: This seems
to be a controversial issue but according to the CDC, "the
potential for serious adverse effects of short and long-term
exposure to germicidal UV has been identified as a major
concern". The CDC also states that with proper installation
and maintenance, the risk of short term exposure is low.
Q:
Where are the UV lamps installed?
A: There
are four basic ways in which UV lamps can be installed.
They are as follows:
a. Ceiling
fixture - upper air irradiation
b. Wall fixtures
- upper air irradiation
c. Air re-circulating
duct
d. Portable
air cleaner
Q:
Is there anything that can be done to safeguard patients
and personnel from the potentially adverse
effects of UV?
A: Ceiling
and wall fixtures can be installed with shields that
deflect the UV radiation up and to the sides of the fixture
while shielding those underneath from exposure. UV lamps
in return ducts or portable air purifiers do not pose
very much of threat as they are usually completely enclosed
within their respective systems.
Q:
How does upper air irradiation work?
A: Upper
air irradiation relies on consistent vertical mixing
between upper and lower air. Proper air mixing can be
enhanced with mechanically induced air currents within
the space being treated. This can help to deliver the
TB laden droplet nuclei to within close proximity of
the UV lamp
Q:
How does UV radiation within a duct or air cleaner
differ from upper air disinfection?
A: By placing
the UV lamps in an air handling system, the contaminated
air can be passed directly over the UV lamps and treated
with a higher, more intense dose of UV.
Q:
What factors effect the ability of UV lamps to disinfect
the air?
A: High humidity,
intensity of radiation, dust borne organisms in the air
or attached to the lamps, and ceiling height, are considered
to be the most important conditions effecting UV irradiation.
Q:
How does humidity effect the performance of UV?
A: The CDC
states that "UV lamps are less effective in areas
with high relative humidity". The germicidal effectiveness
of UV decreases sharply at a relative humidity above
65 - 70%.
Q:
How does the distance of the contaminant from the
UV lamp effect the ability of the lamp to disinfect
the air?
A: There
is a direct correlation between the distance of the contaminant
from the lamp and the intensity with which it is irradiated.
The higher the intensity with which it is irradiated.
The higher the intensity of radiation, the more effective
the air disinfection capability of the lamp.
Q: How
does dust in the air or on the lamp effect the ability
of the UV lamp to disinfect the air?
A: Certain
large dust particles in the air may shield the
TB bacteria from the UV radiation. Sometimes bacteria
can attach itself to these particles and be shielded.
Also, dust on the UV lamp itself can greatly reduce the
intensity of the radiation given off by the lamp.
Q:
How high should my ceiling be to install ceiling
or wall mounted UV fixtures?
A: The California
Department of Health Services recommends a minimum of
a nine foot ceiling in order to achieve maximum effectiveness.
-End of Section
3c-
Next- Section
3d
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