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TB Questions and Answers - Section 3c

Containment Dilution By Irradiation with Ultra Violet Lamps


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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