The Use of UV Lights for Disinfection
Last month there was an incident at ASU in which a lab worker was burned by ultraviolet (UV) light in a laminar flow hood. Although that
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CDC UV-Light Testing Protocol Ultraviolet (UV) lamps are not recommended in BSCs nor are they necessary. If installed, UV lamps must be cleaned weekly to remove any dust and dirt that may block the germicidal effectiveness of the ultraviolet light. The lamps should be checked weekly with a UV meter to ensure that the appropriate intensity of UV light is being emitted. (BMBL 5th Edition, page 306). The surface on the bulb should be cleansed with 70% ethanol prior to performing this test. Five minutes after the lamp has been turned on, the sensor of the UV meter is placed in the center of the work surface. The radiation output should not be less than 40 microwatts per square centimeter at a wavelength of 254 nanometers (nm) (BMBL 5th edition, page 310, Section J). Testing equipment must be appropriately maintained and calibrated. |
situation involved issues of training and failure to follow proper work practices, it does bring up the question of using UV light in labs.
UV light bulbs are found in laminar flow hoods such as biological safety cabinets (BSC) and clean benches, in aquatic animal tanks, and occasionally as whole-room installations for decontamination. UV inactivation doses have been determined for a variety of organisms and are commonly included on disinfection reference charts for disinfecting/sterilizing vegetative organisms, some spore-forming bacteria, and viruses. Because of its mechanism of germicidal action, UV is particularly useful in Polymerase Chain Reaction (PCR) work.
There are some severe limitations to using UV radiation for decontamination. First, there is the risk of overexposure to workers. Second, UV does not penetrate well, so any dirt or organic material will prevent killing of microorganisms. Although UV can disinfect an empty BSC, it will only disinfect the outer surface of any material such as such as pipets or pipet tips stored in the BSC. Third, the germicidal effectiveness of a UV bulb diminishes with time. Lastly, there is evidence that UV radiation can damage plastics and rubber-based materials left in the BSC when the UV is being used.
Guidance from national regulatory agencies warns against the use of UV lights. The Centers for Disease Control (CDC) and the National Institutes of Health (NIH) in the Biosafety in Microbiological and Biomedical Laboratories (BMBL, 5th edition) state that UV lamps are not recommended in BSCs nor are they necessary (page 306). The National Sanitation Foundation in its Standard 49, which gives performance criteria for testing BSCs, notes that UV lighting is not recommended in class II BSCs (NSF 49 Section 5.25.2).
If UV is desired as a disinfectant, it must be used in careful combination with other cleaning and chemical disinfectant methods. Its use and hazards must be documented in the laboratory’s specific standard operating procedures (SOPs) and included in training for each lab worker. The method of cleaning the UV bulb and testing its effectiveness must be in the SOP. Appropriate personal protective equipment (PPE) must be determined, provided by the PI, and always used.
Background
UV radiation is a form of non-ionizing radiation characterized by wavelength and frequency. UV-C (110-280 nm) is used for disinfection purposes. The mechanism of germicidal action involves chemical reactions facilitated by the UV radiation, so disinfecting effectiveness varies with the composition of the target organism as well as physical conditions.
Physical variables affecting the germicidal effects of UV radiation include temperature, humidity, and air movement. Additionally, the cleanliness of the UV light bulb, its age and history of use will impact the effectiveness of sterilization. In dynamic air flow, such as in a BSC, particles or microorganisms do not stay close enough to the UV source for a sufficient period of time to be inactivated. The presence of any dust or organic matter will also impede the penetration of UV radiation.
Biological effects on humans of over-exposure to UV radiation generally occur to the skin and eyes. Erythema, or reddening of the skin like sunburn, is the most common symptom. Chronic exposure to UV radiation might accelerate the skin aging process and increase the risk of developing skin cancer. (UV-C is classified as a probable human carcinogen.) Increased eye exposure to UV-C may cause photokeratitis (burn of the cornea) or conjunctivitis (inflammation of the eye surface). These rarely result in permanent eye damage, though they may hasten the development of cataracts.
Overexposure from UV lights mounted in a BSC can occur in 13-24 minutes at eye level while seated at the BSC and in less than one minute at hand level at the cabinet face, according to studies by Boettrich, Meechan and others. Even at the center of the room, the permissible exposure limit may be reached in 30 minutes. Photo-sensitive individuals may suffer biological effects in less time.
Good work practices with UV lights includes the use of personal protective equipment (PPE). UV-rated goggles and appropriate gloves appear to reduce UV exposure. Tyvek arm shields, coveralls, and lab coats provide partial protection against UV radiation (Meechan).
Administrative controls are also necessary. BSC and clean benches should NEVER be used while the UV light is on. Due to the short time for UV overexposure to occur, it is recommended that neither laboratory nor maintenance /custodial personnel work in a room where UV lights are on. Minimize the storage of material within the BSC to reduce damage by UV radiation and to allow the UV light to reach the surfaces of the BSC for disinfection. Keep the sash of the BSC closed when using the UV light. Use of a UV light for more than an hour or overnight is not necessary nor desirable. (Maximum kill of spore-forming bacteria occurs in approximately 15 minutes if the bulb is working correctly.) Ask the manufacturer to interlock the UV light with the sash or add a timer to the UV light to enhance safety without loss of disinfection potential.
Note: Thanks to Jyl Burgener, Applied Biosafety 2006; Meechan and Wilson, Applied Biosafety 2006.
For more information about ultraviolet light bulbs, please contact Chris Carlson , Associate Biosafety Officer , at 480.965.1344.
